Anesthetic Equipment Made Easy® S Ahanatha Pillai
INDEX
Page numbers followed by f indicate figures.
A
Absorber type of 208
Adam's
pressure 29f
valve 29f, 121
Adjustable airway pressure limiting valve 33
Adjustable pressure limiting valve 45, 46f, 47, 60, 66
Air
brake 58
ventilation, expired 254
Airway
artificial 244
Berman's 246, 250
Brook's 255, 255f
Guedel's 246, 247, 249f
Hewitt's 246, 250
mechanism of 246f
nasopharyngeal 251
obstruction 245
oropharyngeal 245
parts of 247f
Phillips 246, 250
pressure release valve 204
Resuci 254, 255f
Safar's 254
sizes of 248
tube 257, 266
with widely flared end 251
types of 245
Aladin cassette vaporizer 166, 167
Allen key 43f
Aluminium float, made of 127
Alveolar
cleft 287f
plateau 285
Ambu bag 64
American National Standard Institute 33, 61
Anesthesia
clinical 295
depth of 277
exhausted sodalime in 286f
gas machine 27
machine 27, 28
checking 63
equipment 64
system 63
gas supply and suction 63
monitors 64
power supply 63
scavenging 64
two bag test 64
ventilator 64
color coding of cylinders in 77f
components of 30
essential components 33, 34f
history of 28
modern 29, 32f
modern pressure reducing valve of 119
pressure reducing valve used in 42
various components of 1
worktop of 48
spinal 301
techniques of regional anesthesia 301
workstation 32f, 104
Anesthetic
breathing system 33, 173, 174
classification 175
closed system 176
criteria for 177
modern classification 176
non-rebreathing system 176, 177
open system 175
rebreathing system 176
semi-closed system 176
semi-open system 175
gas
cylinders 77
mixture of 174
mixture 48, 57
vapor concentration 61
waste gas scavenging system 58f
Antinociceptive drugs 313
Anti-spill 159, 164, 169
funnel filling device 170f
Antistatic
black rubber 211
rubber
tyres 34
wheels 59
Applied physics 1
Arterial
blood pressure 61
oxygen saturation 289
pressure 289
pulse waveform 277f
Arteriole 274
Atomic weight 2
Atomizer vaporizer 154
Automatic thermocompensating valve 149
Avogadro's
constant 3
hypothesis 3, 3f
hypothesis specific weight 4
Ayre's t-piece system 178, 191, 192, 192f
B
Back bar 33, 42
Back pressure, compensated flow meter 138, 139f
Baffles 153
in plenum 154f
Bag mount 180
Bag valve mask 64
face mask 66
nonrebreathing unidirectional valve 66
self-inflating bag 66
unidirectional inlet valve 66
Bain's breathing system 178, 187, 189f
Bain's system 186
parallel 190f
with block assembly 190f
Baralyme 197
Barotrauma 41
Beer's law 275
Bend test 72, 73
Bernoulli's principle 22, 22f, 23f
Bimetallic strip valve 157, 158f
Bivona fome cuff 235
Blades of turbine 131
Bleed valve 180
Bobbin 127, 130
annular orifice around 129f
flow of gas around 128
shaped 130
used in flow meters 130f
Bodok seal 33, 36f, 37, 38f, 8284
Boiling point 6, 145, 146
Bougie used for aiding difficult intubation 244f
Bourdon gauge 37, 39
Boyle's
anesthesia machine, safety features in 59
apparatus 28
F machine 132f
law 17, 17f, 18f
machine 29, 30f, 31f, 36
back bar of 43
two primitive versions of 29
type of 46
Brachial plexus block 301
Breathing
bag 206
circuit type of 46
resistance to 206
system 44, 48
configuration to 193
resistance in 184
respiratory requirements 183
Broken inner tube, test for identifying 191
Bronchial cuff 237, 238
Bronchospasm, expiratory obstruction 287f
Bronchospirometry 236
Broolle's indicator, modified 310
Bubble through device 154
Bullnose
type of valve 88
valves different varieties of 88f
Bupivacaine 310
C
Calcium hydroxide 196
Calorie 5
Capillary tube 310
Capnography 197, 199, 273, 280, 281f
components 280
end-tidal CO2 monitoring 281
factors that decrease EtCO2 284
infrared analyzer 280
interpretation of values 283
mainstream CO2 analyzer 282
normal capnogram 284
principle of 280
sidestream CO2 analyzer 282
uses 281
Carbon 70
Carbon dioxide 15
Carbon dioxide absorption 195, 196
Carbon steel alloy
advantages 71
features of ideal cylinders 71
high 70
low 70
Cardiorespiratory status assessment 278
Cardiorespiratory system, noninvasive monitor for 273
Carinal hook 237f
Carlen's double lumen tube 236, 237f
Carlen's double lumen tube, modified 238
Catheter mount 215f
Catheter mount and connectors 214
Cauda
equina 308f
epidural 307
Ceiling
mounted pendants, types of 106f
outlets, types of 106
reel outlets different types of 106
pipeline supply
advantages of
asepsis 93
economical 94
efficient 94
psychological effects 94
reliable and safe 94
saves space 94
Central reducing valve 101
Central vacuum
suction 107
unit 108f
Cesarean sections 313
Channeling 201
Charles’ law 20f, 20
Chloroform 145, 173
Choledochscope 224
Chondrodendron tomentosum 295
Chromium 71
Circle absorber 204f, 205f
essential components of 202
methods to check the integrity of 207
with double canister 209f
Circle system 201
advantages of 202
Circuit breakers 61
Circular facemasks 212f
Circulation monitoring 288
Coaxial systems 187
Cobb's suction union 241, 242f
Cole's tube 238, 239f
Collar index 103
Color coding 77
Combined spinal epidural
anesthesia 312
needle 312, 313
technique of 313
Common gas outlet 47, 174
Compressed medical air 108
Connell meter 133, 137, 138f
Continuous breathing system pressure 61
Continuous epidural 311, 314f
analgesia 311
infusion pumps for 313
technique 311
Continuous positive airway pressure, amount of 193
Control panels, modern 100
Copper kettle
for ether vaporization 145
vaporizer 160
Corrugated
breathing hoses 173, 180, 204, 206f
tube 178
Cowl 151
for directing gas surface of liquid 153
Coxeter bobbin 133
flow meter 136f
Cuff different, types of 229, 230
Cuff
pressure 230
volume 272
Cyclopropane 6
Cyclopropane 79
Cylinder 59
A- and B-type 76
cautions and rules to be strictly followed with 86
cracking 87
decanting or filling of 89
engraved on the shoulder of 79
indicates the status of 87
key 80
label on body of nitrous oxide 78
outlet valves 80
oxygen and nitrous oxide 76
parts of 74
shoulder of 74
steel-carbon fibers 75
pressure 56, 113
size 79
spanner 36f, 81
structure 199
transfilling of 97f
with bullnose valve 96f
with protective cover 72f
Cylindrical with a head and tail 130
Cyprane inhaler 148, 149f
Cytotoxic drugs intrathecally 304
D
Dalton's law
application of 14
partial pressures of 13
Datex-ohmeda 166
Defibrillation, principle of 291
Defibrillator 290
paddles on the chest wall 292f
unit with ECG monitor and recorder 291f
Deflated cuff 260
Depolarising block 296f, 296, 298
Desflurane 44, 145, 165, 167
Desflurane filling system 166, 169, 170
Diaphragm
elastometal 117
large 116
rubber 117
small 116
Dicrotic notch 273f
Digital nerve block 301
Disc with rod 130
Dogliotti's technique 307
Double burst stimulation 295, 299, 300
Double needle double interspace method 312
Double-canister absorbers 208
Dropper type 156
Dural cuff 308f
Durren's sign 310
E
Easy-fil 168, 169, 170
filling system 171f
Electrical
cardioversion 291
stimulation 296
stimulations, types of 295
Electrocardiogram monitor 285
Electronic
device 54
mechanisms 49
Elwyn tubes 233
Emergency oxygen flush 30f, 33, 43, 46, 47, 47f, 48, 61
Endobronchial tube
green and Gordon's 237
reinforced or armoured 233f
Endotracheal
connectors 239
tube 66, 224, 227, 258, 282
double lumen 236
for laser surgeries 235
for special purposes 231
indications for 227
size of 230
used to connect 239
End-tidal carbon dioxide monitoring 281
End-tidal CO2 287
Enflurane 164, 167
Entonox 85, 86
Epidural anesthesia 307
equipment for 301
technique of 307
Epidural catheter 308, 309f, 310
with sterile dressings 311f
Epidural needle 307, 309f, 313f
Epidural set 309f
Epidural space 308f, 313f
anteroposterior diameter of 313
methods for identifying 310
Epiglottis 222, 253
Epispinal 301
Ether 6, 9, 142, 145
inhaler model of 173f
Ethyl
chloride 145
violet 197
Ethylene oxide 79
Evaporation, process of 142
F
Facemask 178, 182, 209, 214
latex-free mask 212
pediatric masks 212
Rendell-Baker-Soucek mask, for neonates 213
Fentanyl 313
Fiber-optic intubating
bronchoscope 224
parts of 225
principle and design 224, 225f
laryngoscope 225f
Fick's law 14
Field block 301
Filling ratio 91
critical pressure 91
critical temperature 91
practical significance 92
Filling systems 169
Filum fermin de interna 302, 308f
Fine-graduated polyvinyl catheter 311
Fish mouth valve 68f
Fixed orifice 127
dry type 133
dry type flow meter 134
variable pressure difference type 126
wet type 133
with variable pressure difference 133
Fixed outlet pressure, type of 120
Fixing the breathing system 47
Flattening test 72, 73
Flexi-tip laryngoscope 221f
Flow control valve 56
Flow meter 43, 60, 123, 127
bank 44f, 131, 132f
classification of 126
in anesthesia machine 125
principles and types 123
safe arrangement of 140f
Flow-splitting device 150, 151f
Flow test 207
Fluorescent plate 132
Fluotec mark 2 162
characteristics 162
limitation 162
Fluotec mark 3 163
characteristics 163
vaporizer 45f
Flush valve 35f, 80, 86
Foregger flow meter 134, 135f
Forrester spray 26
Fresh gas flow 192
Funnel filling 169
G
Gamma ray sterilized 311
Gas 4, 6, 7
bubbles 145
chemical symbol of 78
cylinders labels of 79f
delivery 57
diffusion of 14f
flow 123
inlet 173
pattern in circle-breathing system 203f
laws 16
conversion 20
diffusion 21
filling ratio 18
practical applications 17
specific volume 16
vapor and gas 16
manifold and control panel 94
mixture 44
power outlet 56
specific feeding connectors 60
supplies 35, 57
withdrawal line 111
Gay-Lussac's law 21
Genitofemoral nerve, femoral branch of 301
Globular surface, liquid gas interface 144
Goldman
halothane vaporizer 45f
vaporizer 161
molecular weight 3
Granule
from braking 198
size 198
Grease 86
Guedel type airway 259
Gum elastic bougie 243
Gwathmey machine 28
H
Halothane 6, 27, 44, 145, 164, 167, 170
Hanging drop 310
Heat 4
boiling points of 6, 7
critical
pressure 6
temperature of various gases 6
energy in calories 146
specific 5, 146
unit of heat 5
Heidbrink flow meter 137f
Heidbrink's expiratory valve 179
Heidbrink's spring-loaded valve 181
Heidbrink's valve 185
Heidbrinks meter 133, 137
Helium 21
Hollow square tubular structures 34
Hospital for oxygen 112
Hot climate 92
Howland lock 220
Howland lock 221f
Huber point 309f
Hydraulic
flow meters 133
force 116
sight feed meter 135
Hydraulic test 72, 73
Hypotension, onset of 310
Hypovolemia 279
indicate 280
state 278
Hypoxic
drive 26
guard device 51f
I
Iliohypogastric nerve 301
Ilioinguinal nerve 301
Impact test 72, 73
Indicators and alarms 100
Infiltration block 301
Inflatable rim 211
Inflation tube 258
Infraglottic airway 244
Infrared absorption spectrometry 280, 282
Infusion pumps 314f
Inguinal herniorrhaphy 301
Inhalational anesthetic agents 142, 174
Injector device 154
Inspiratory capacity 200
Inspiratory down stroke 284f, 285
Inspired oxygen concentration 61
Intergranular space 197
Interlock system 169
Interspinous ligament 304
Intrathecal block 301
Intrathecal injection 304
Intubating bronchoscope, single use flexible 226
Intubation
position of head and neck for 219
technique of
advantages 226
disadvantages 226
Iron 70
Isoflurane 27, 44, 145, 164, 167, 170
J
Jackson Rees, modification of Ayre's t-piece 178, 194f
Jaw thrus, maneuver of 246f
Joule-Kelvin, principle of 8
Joule-Thomson's, effect of 8
Junker bottle for insufflation technique 173
K
Keyed filling 169
adapters 171f
Knob of oxygen flow meter 60
Kuhn bag 193
L
Lack's system 178, 186
Lambert's law 275
Laminar and turbulent flow 124f
Laminar flow 124
pressure difference 185f
Laryngeal mask airway 257
accessories to 268
adverse effects 262
classic and the parts 257f
contraindications 261
different size of 258
directions for removal 259
flexible 262, 263f
indication 259, 271
intubating 264
method of inserting 260f
method of using 258, 270
modified versions of 262
precautions 261
proseal 266
proseal anatomical relations of 268f
proseal and parts of 267f
proseal with introducer and deflator 268f
short tube 263
sizes and specifications 261, 262
standard 257
supreme 269, 270f, 271
technique of using 265
unique 263, 263f
Laryngeal reflexes 271
Laryngeal spray 26
Laryngectomy tube 239
Laryngoscope 217
Laryngoscope
Bullard fiberoptic 222, 223f
endotracheal tubes and airways 217
Patil-syracuse 222, 223f
polio 222, 222f
traditional screw type 218
types of 219
position of 220
Laryngoscopy, technique of 218, 223
Laryngospasm 253
Laser-flex tube 235, 236f
Latex
allergy 253
rubber armoured tubes 232
rubber tube 232
Law of volumes 20
Leak test 207
Ligamentum flavum 304, 310
Like's spring-loaded syringe 310
Limb
expiratory 191
inspiratory 191
Link 25 safety device 53f
Liquid 4
and gas 2, 2f
anesthetic agents, volatility of 145
drops 9
ether 147
gas interface methods 143, 144f
increasing the surface area of 153
O2 89
oxygen 109, 112
precautions for 112
withdrawal line 111
Local anesthetic
eutectic mixture of 301
injection of 308f
Lumbar
dural puncture 304
epidural 301, 307
puncture position of 303
region 313
Lung anesthesia 238, 238f
M
Macintosh's
blade, curved blade 220f
indicator 310
laryngoscope 217
needle 310
spray 25f
spring-loaded needle 310
Magill's
breathing system 29f, 173, 178, 179, 183
components of 179f, 181, 182f
components of 180
connector 214, 215f, 240
flow in 85f
endotracheal tube 228, 240f
forceps 267
intubating forceps 244, 245f
red rubber endotracheal tube 228f
suction union 241, 242f
Magnetic field, unit of measurement of 57
Mainstream analyzer adapter 283f
Malignant hyperthermia 286
Mallinckrodt laser 235
Manganese 70
Manifold room 94
bulk gas cylinders 99
control panel 96
gas manifold and control panel 94
oxygen pipeline 95
partial automatic system 97
safety precautions in a manifold room 99
Mapleson's
A configuration 179, 186
B system 186, 187f, 200f
C system 187f
classification 178, 178f
D system 186, 188
E system 191
F system 192
Mask and inflation line 257
Master switch 56, 61
Matter
compound 1
element 1
molecular movement 1
molecule 1
Maximal current 293
McCoy laryngoscope 220
tip of 221
McKesson meter 138, 138f
Medical air, tank for supplying 110
Medical compressed air 109
Medical gas
cylinders 70
pipeline system 93
Metal
ball electrodes 294f
bellows 157, 158f
connector 240
ring 83
spiral reinforced tubes 232
tube 137f
Methyl orange 197
Microbacterial filter 311
Miller straight blade
laryngoscope 218, 220f
pediatric laryngoscope 217
Minimum contact gauge 97, 98f, 100
Mixed spinal nerve 308f
Moisture content 196
Molecular weight 2
Molecules 2, 124, 142
number of 3
solid of 2f
Molybdenum 71
Monitors multiparameter 273
Monoatomic 21
Murphy’ safety eye 229f, 230, 234
N
Nasal tube plain 234f
Nasopharyngeal airway 244
assessing size 253
different types of 252
Necrosis of nasal mucosa 253
Needle beside needle single interspace method 312
Needle valve 125
flow meter of 126f
Negative intrapleural pressure, transmission of 310
Negative pressure sign 310
Neonates and infants, anatomical differences of 219
Nerve block 301
Neuromuscular block
during anesthesia 294
monitoring 293
types of 295
Nitrogen in atmospheric air 15f
Nitrous oxide 49, 132
Nitrous oxide 90
cylinders assessing the contents of 40
round knob for 133f
Nondepolarising blocks 296, 296f
Noninvasive airway management device 257
Noninvasive blood pressure 273
Nonkinkable tubes 232
Noseworthy connector 241, 241f
Nylon
heads 87f
reinforced 117
O
Oblique expiratory upstroke 285
Odom's indicator 310
Oil-free air compressors 110f
Opioids 313
Oral airways different 247
Orifice 124
fixed pressure difference type 126
type 135
wet type 135
dry type 136
Oropharyngeal airway 244
Outlet points from ceiling 104
Outlet pressure type 120
Outlet valve 79
construction of 88
Oxford tubes 233, 234f
connectors for 235f
Oxygen 27, 70
bottling unit 89
cylinder 32f, 90
dissolved in blood, amount of 273
failure alarm 48
checking the anesthetic machine 54
fail-safe system 49
features of an ideal device 48
limitations 50
link 25 52
minimum ratio gas system 51
prevent hypoxic gas mixtures 49
principle of 50f
safety devices 49
three pressure’ systems 55
flow meter 132
problems related to the position of 141
safety of positioning 140f
flush valve 56
manifold in manifold room 95f
Oxygen pipeline 95
pressure failure alarm 56
reservoir bag 68f
saturation 275
continuous monitoring of 278
in hemoglobin 273
supply failure alarm 61
Oxy-hemoglobin levels 274
P
Paddles placement of 293
Partial pressure of
gases in air 13f
oxygen 15f
Perfusion bar, purpose of 279
Perfusion indicator 277, 279
Peripheral nerve 301
different types of 297f
stimulator 294, 294f, 295
Peripheral perfusion 289, 290
Peripheral pulse 289
Pethick test 191
Pharyngeal cavity 258
Phenolphthalein 197
Photoplethysmography 276
Physics 123
Pilot balloon 258
Pin index 86
safety system 33, 38, 59, 84
Pin valve 60, 125
and flow of gas 128f
Piped medical gas and vacuum 93
Pipelines and isolation valves 102
Pipes end in wall outlet units 102
Piping up to flow meter 56
Plastic
armoured tubes 232
catheter mount 214, 215f
endotracheal tubes 228
hammer 87f
Plateau, expiratory 285
Plenum 150, 161
Plethysmograph 276, 278, 279
Plexus block 301
Poikilothermic 4
Polycarbonate 66, 211
facemasks with flap rim 211f
mask 210
transparent mask 211
Polysulfone 258
Poppet valve 117
Position oxygen flow meter 60
Postanesthetic care unit 102
Postdural puncture headache 305
Postspinal headache 305, 310
Post-tetanic count 295, 299f
Potassium hydroxide 196
Power failure indicator 61
Poynting effect 21
Pressure 12, 12f
atmospheric pressure 15
critical 6
difference 127, 129
gauge 33, 38, 56, 59
for oxygen and nitrous oxide cylinders 39f
in oxygen cylinder and in nitrous oxide cylinder 40f
practical significance of 40f
types of 134
limiting valve 68f
partial pressure 13
reducing valve 41, 56, 59, 113, 114, 122f
mechanism of 117
simple design of 115f
two-stage 121f
types of 120
regulator 41, 59, 113
basic principle 114
benefits of 113
release valve 42, 43, 119, 120f
relief device 56, 60
relief valve 60, 202
sensors 100
switches 97
system
high 56
intermediate 56
low 56
Pressurizing effect 172
Proximal end of the catheter 311
Pulmonary embolus 287f
Pulsatile blood flow in the arterioles 275
Pulse oximeter 273, 273f, 279
features 275
finger probe of 275
fingertip 274
functional saturation 275
functioning of 276
important information 278
measure 289
working principle 274
Pulse plethysmography 289
Pulse rate 273
Pulse waveform 273, 276, 279
Pumping effect 172
Q
Quick-fil 169, 170
Quinke point 305
R
Radial pulse 289
Rebreathing system 194, 199
advantages 195
functioning 194
principle 194
Reducing valves, type of 116
Regulator
multistage 121
two stage 121
Reserve bank reducing valve 101
Reserve power 61, 173
Reservoir bag 178, 180
purpose of 183
Resistance signs, loss of 310
Respiration 273
Respiratory cycle 184f
Resuscitator bag
child size 67f
infant size 67f
self-inflating 64, 65f
three sizes of 69f
Rigid material, reservoir of 58
Ring Adair tubes 233
Robert Shaw double lumen tube 238f, 238
Rotameter 127, 129, 133
Rotameters 43
Rotor 131f
Rowbotham's connector 240, 240f
flow in 185f
Running bank reducing valve 101
Ryle's tube, size of 272
S
Sacral epidural 301
Safety devices 57
Saturated vapor pressure 8f, 146
Scavenging system 57
collecting system 57
disposal system 58
receiving system 58
transfer system 58
Schimmelbusch mask 147, 148f, 173
Schrader
self-sealing valves 103, 104
type self-sealing valves 103f
valve socket 103
Screw threaded
hose connections 104f
noninterchangeable 37, 104
Segmental epidural 307
Select-A-tec mounting 168, 168f
Semi-closed breathing system 179
Sevoflurane 27, 44, 145, 167, 170
cassettes 168
decomposition 199
Sheila Anderson laryngoscope 217
Shuttle valve 97
Silica 196
traces of 196
Silicon 70
masks 210
rubber flap brim 66
Single needle single interspace method 312
Slave control valve for N2O 51
Slender glass tube fixed 134
Sniffing position 218
Sodalime 196, 197, 208
canister 203, 204f
caution about 198
clinical indicators of exhausted 198
composition 196
exhaustion of 202
granules 197f
indicators 197
methods to find out exhaustion of 199
Sodium carbonate 196
Sodium hydroxide 196
Soft silicon round facemasks 213f
Solid drawn cylinders 71
Spill valve 204f
Spinal analgesia 302
equipment for 301
ideal sitting position for 303
positioning for 304
positioning for right lateral 304
positioning for sitting position 304
Spinal column, sagittal section 302
Spinal needle 304
different types of tip of 306
disposable with transparent and lock 306f
parts of 305
structures passed through 305f
tip of 305
Splitting ratio 170
Stainless steel shell, inner 111
Steel-carbon fiber cylinder 75f
Sterile disposable sets 311
Stout metal plates 122f
Strict formula of composition 71
Striking point 27
Stylet 242
types of 243f
Subarachnoid block 301, 302
Subarachnoid central neural block 302
Subcutaneous tissue 304
Submaximal 293
Succinylcholine 295
Sufentanil 313
Sulfur 70
Superheater 111
Supramaximal 293
Supraspinous ligament 304
Suxamethonium chloride 295
Switches 100
Swivel mount
for endotracheal connectors 243
with suction port 242
Swivel pendant 106, 107f
Syringe infusion pump 314f, 315
T
Tec 4 164
Tec 4, characteristics 164
Tec 5 164
Tec 6 165
Tec 7 166
Tec 7, vaporizer 167
Temperature
and pressure, standard conditions of 7
compensated vaporizers 161
compensation 156
critical 6
gas flowing of 157
liquid of 157
near the boiling point 156
Tensile test 72, 73
Terminal outlets 102
Tetanic stimulation 295, 298
Thermal capacity 146
Thermal conductivity 146
Thoracic epidural 301, 307
Throat soreness 262
Tracheobronchial stimulation 299
Transient dysarthria 262
Trichloroethylene 148
Trilene 145, 199
vaporizer 157
Tube
fluid pathway 123
from incisors, length of 231
Tuohy needle 311
Turbulent flow 124, 185f
U
Unequal pressures, points of 123
Unidirectional valves 204
Universal F
breathing system 210f
circuit 209
Upstroke, expiratory 284f, 285
Urine output 290
Urine production 289
V
Vacuum-insulated evaporator 110, 111f
Valve
expiratory 173, 178
modern adiabatic compression 118
modern advantages 118
modern dangers 118
modern main features 118
nonrebreathing 150
Vapor 145
Vapor and gases 7
adiabatic compression 12
evaporation of liquid in a closed container 8
explanation of latent heat of vaporization 9
fall of temperature of evaporating liquid 11
latent heat of
condensation 11
crystallization 11
liquefaction 11
melting 11
vaporization 8
sublimation 10
Vapor, formation of 10
Vapor, pressure 145
Vaporization 7, 8f
factors modifying the rate of 157
latent heat of 146
means to enhance 143
methods to improve the rate of 150
Vaporizer 44, 142, 145, 158
backpressure compensation 158
bubble through 155f
classification of 147
draw over 147
dropper type 157f
EMO 148
flow compensation 158
flow-over 150
fully calibrated 158
injector type 156f
inside circuit 30f
interlock system in 169f
mounting device 56
safety features in 172
stable 159
temperature compensation 158
Venous blood 16
Ventilation
adequacy of 274
controlled 188
spontaneous 188
Ventimask 24
Venting gas 42
Ventricular fibrillation, treatment of 291
Venturi device
construction of 24
ventimask working with 25f
Vernier effect 125
Versatile inventions 273
Video laryngoscopes 223, 224f
Vital organs perfusion of 289
Vital parameters 27
Volatile anesthetic agents 44
concentration of 174
Volatile anesthetic liquid 142
W
Wall mounting suction unit 109f
Wall outlet
for vacuum 108
of pipeline 102
series of 105
units, two types of 105f
Wall-Rail mounted designs 57
Water
depression meter 134
jacket method 73
manometer 134
sight feed meter 133, 135, 136f
vapor condensation of 9f
Waterproof plasters 311
Waveform
interpretation of 277
pulse oximeter of 277f
Wet flow meters 136f
Wick-in-jar 161
Wicks 153
Wood's metal 82
Wooden hammer 87f
Workstations
fail-safe valve, safety features in 62
flow meter, safety features in 62
hypoxia preventing devices, safety features in 62
oxygen analyzer, safety features in 63
oxygen failure protection device 62
pipeline wall outlets, safety features in 62
pressure sensor shut-off valve 62
safety features in 61
scavenging system, safety features in 63
vaporizers, safety features in 63
ventilators, safety features in 63
X
Xenon 21
Xomed laser 235
Xylocaine 301, 310
ampule 304
fixed proportions of 301
heavy spinal ampule 304
Y
Yoke 37, 59
assembly and A-type cylinders 80f
for oxygen 85f
hanger assembly 56
of anesthetic machine 82
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Chapter Notes

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Applied Physicschapter 1

 
INTRODUCTION
The applied physics discussed in this chapter is related to the fundamental principles of functioning of various components of an anesthesia machine. The relevant applications in the working of the equipment and their practical significance are discussed in appropriate places.
 
MATTER
 
Element
It is a substance that has the smallest particle known as atom. Atom is the smallest part to which an element can be subdivided that retains the properties of the substance. Atom cannot be further divided by ordinary means. Examples: hydrogen, helium, oxygen, carbon, chlorine.
 
Compound
It is composed of two or more elements, united chemically. This forms a substance with different properties from that of those individual elements composing it. Example: ether is a compound of carbon, hydrogen and oxygen. Nitrous oxide is a compound of nitrogen and oxygen. So, a compound can be divided into molecules without losing its identity.
 
Molecule
A molecule is the smallest particle of a substance which still possesses the distinctive properties of the substance. For example, oxygen does not exist as a single atom. It combines with another oxygen atom to form oxygen molecule (O2). The oxygen gas that we know consists of molecules of oxygen. If oxygen atom combines with atoms of other elements a new compound will be formed. For example, (C2H5)2O is ether— two ethyl groups with one atom of oxygen—(C2H5) O (C2H5). It is a compound of one atom of oxygen with 4 atoms of carbon and 10 atoms of hydrogen. If a molecule is subdivided, it loses its properties.
 
Molecular Movement
  • All substances, solids, liquids, or gases are composed of molecules. These molecules are in a state of incessant motion. The ability of the molecules to alter their position varies according to its state, solids, liquids or gases.
  • In a solid state, as the density is very high the molecules cannot alter their relative positions, and merely oscillate about a fixed point. The relative volume of the solid is small (Fig. 1.1).2
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Fig. 1.1: The molecule in a solid, liquid and gas. • Solid: The molecule does not change the position, but oscillates about a fixed point in all directions; • Liquid: The molecule constantly changes position and moves slowly a short distance within the container; • Gas: The molecules are in violent movement, change their position faster and to a greater distance within the container
  • The molecules in a liquid are mobile and gradually shift their position throughout the whole liquid as the density is relatively less. The free path of a molecule in the liquid, however, is very short before it collides with its neighbours (Fig. 1.1).
  • In the gaseous state the molecules have a much greater degree of mobility, and travel longer distances before colliding with others (Fig. 1.1).
  • The relative status of molecules in solid, liquid and gases is shown in Figure 1.2.
  • Owing to the mobility of its molecules, a liquid or gas has no fixed shape like solid and so assume the shape of the container.
  • All gases and many liquids mix readily with their fellows.
 
Atomic Weight
  • Atomic weight of oxygen is used as the basis on which atomic weight of other elements are determined.
  • Atomic weight of oxygen is 16.
  • Hydrogen is 16 times lighter than oxygen, so the atomic weight is 1.
  • Carbon atom has 3/4th of the weight of oxygen, so the atomic weight is 12.
 
Molecular Weight
  • The molecular weight of a substance is the sum of the atomic weights of the elements of which it is composed.
zoom view
Fig. 1.2: The molecule of a solid, liquid and gas and their relative movements. In solid, the molecules are compact, the volume is small. Do not change position but oscillate in its place; • In liquids the molecules are loose and the volume is relatively bigger. Molecules move very slowly throughout the liquid; • In gases the molecules are very loose, volume is very large. They move very fast and travel long distance within the container
  • 3Oxygen with formula O2 has a molecular weight of 32.
  • Ether (C2H5)2 O has molecular weight of 74 (12 × 4 + 1 × 10 + 16).
  • Nitrous oxide N2O has molecular weight of 44.
    This explains that 74 g of ether contains the same number of molecules as in 44 g of nitrous oxide.
 
Gram Molecular Weight
The term ‘mole’ is used to refer to what was known earlier as ‘gram molecular weight’. One ‘mole’ of a substance is the molecular weight of the substance expressed in grams. So, one ‘mole’ of all substances contain the same number of molecules. The number of molecules per ‘mole’ is known as ‘Avogadro's constant’.
It is defined that the mass of one mole of a substance, expressed in grams, is equal to the mean relative molecular mass of the substance. For example, the mean relative molecular mass of natural water is about 18.015, therefore, one mole of water has a mass of about 18.015 grams.
 
AVOGADRO'S HYPOTHESIS
Equal volumes of all gases under the same condition of temperature and pressure contain the same number of molecules.
  • It is shown that a ‘mole’ (gram molecular weight) of any gas at the same temperature and pressure occupies the same volume.
  • At 0°C temperature and 760 mm Hg pressure (normal temperature and pressure or NTP) this volume is 22.4 L.
Figure 1.3 explains Avogadro's hypothesis and shows how equal volumes of two different gases O2 and H2 under the same temperature and pressure have same number of molecules.
 
Density
The density of a gas is usually expressed as the weight of 1 L of gas in gram.
  • The weight of 22.4 L of the gas is the gram molecule of the gas.
  • So the weight of 1 L of a gas = molecular weight/22.4 g.
  • Molecular weight of ether is 74.
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Fig. 1.3: Avogadro's hypothesis. • Equal volumes of oxygen and hydrogen under same temperature and pressure have same number of molecules
  • 4So, the weight of 1 L of ether vapor = 74/22.4 = 3.31 g/L.
  • Similarly, the density of nitrous oxide = 44/22.4 = 1.96 g/L.
For practical purposes, air contains 1 volume of oxygen and 4 volumes of nitrogen. (20% + 80%)
At normal temperature and pressure (NTP),
  • The weight of 1/5 L of oxygen
=
32/22.4 × 1/5 g
= 0.29 g
  • The weight of 4/5 L of nitrogen
=
28/22.4 × 4/5 g
= 1.0 g
  • So, the weight of 1 L of air
=
0.29 g + 1.0 g
= 1.29 g
  • Therefore, the density of air is
=
1.29 g/L
The density of a gas is expressed in relation to the density of air which is given the value of 1.
  • Thus, the relative density (specific gravity) of nitrous oxide is 1½, ether vapor is 2½. (Ether vapor settles on the floor because it is 2½ times heavier than air).
  • Though the term ‘density’ is used popularly to denote the weight of a given volume of gas, the proper scientific term is ‘specific weight’.
 
Specific Weight
Weight per unit volume.
Liquids: The ratio of the specific weight of the liquid at any given temperature to that of water at 4°C.
Gases: The ratio of specific weight of the gas to that of air; both given at NTP (0°C and 760 mm Hg).
 
HEAT
Heat is an energy that can be given to a substance or abstracted from it.
Heat and temperature are different.
Temperature is the thermal status of a substance which determines whether it will give heat or receive heat from another substance when brought in contact with it.
Always heat is transferred from a substance of higher temperature to a substance of lower temperature. This difference in temperature between the two is known as temperature gradient. Heat may be transferred by three means conduction, convection and radiation.
Practical application:
  • When a blood bag is removed from store, it may have the temperature of 10°C. It has to be warmed to room temperature before transfusion. When the room temperature is 20°C, there is a good gradient of 10°C for heat from the atmosphere to be rapidly transferred to the blood bag. If the bag is covered with a towel or some such material, it will insulate the bag and prevent the transfer of heat from atmosphere and cause delay in warming.
  • In situations where body's thermoregulation fails—as in deep plane of anesthesia the patient becomes ‘poikilothermic’. Hence, the patient suffers hypothermia. The body temperature would continue to fall till it becomes equal to ambient temperature of the operating room (around 23°C). To prevent the loss of body heat to the atmosphere, he is well covered with thick insulating covers. A radiant heater will be placed at a suitable distance to transfer heat and raise the body temperature.5
 
Unit of Heat
 
Calorie
  • It is defined as the quantity of heat required to raise the temperature of 1 g of water by 1°C.
  • This is the unit of measuring heat (cal).
Example: The heat required to raise the temperature of 1 L (1000 g or mL) of water from 18°C to 37°C.
1 g of water
raised 1°C
1 cal
1000 g of water
raised 1°C
1000 cal
1000 g of water
raised 19°C
19000 cal
= 19 kcal
The larger heat unit kilocalorie (kcal) is usually used to express the caloric value of food.
 
Specific Heat
The specific heat of a substance is the number of calories required to raise the temperature of 1 g of the substance (ideally it is 1 cm3 of the substance) by 1°C.
  • Since the temperature of 1 g of water is raised by 1°C by 1 calorie, the specific heat of water is 1.
  • The specific heat of ether is 0.5 cal/g (Considering 1 cm3 of the liquid).
  • But the specific heat of ether vapor is 0.0016 (Considering 1 cm3 of the vapor).
 
Critical Temperature
Critical temperature of a gas:
Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase. The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.
For example water can exist only as water vapor above 374°C. Hence, the critical temperature of water is 374°C.
The critical temperature of a gas is the temperature to which it must be cooled before it can be liquefied by the pressure:
It is defined as the temperature above which a liquid cannot continue to be in that state.
In other words, above this temperature gases cannot be liquefied (Compressed into liquid).
Still more simple explanation is; the temperature to which the gas to be brought before it can be liquefied by pressure.
  • The lower the temperature, the more the latent heat is needed to vaporize the liquid.
  • The higher the temperature, the less the latent heat is required until a critical temperature is reached.
  • At the critical temperature of the liquid the latent heat of vaporization is zero.
  • Above this temperature the liquid changes spontaneously into vapor without heat being required for the change.
  • Above this temperature the substance cannot exist in the liquid state.6
 
Critical Temperature of Various Gases
  • Air
– 141°C
  • N2
– 147°C
  • O2
– 119°C
  • N2O
– 36.5°C
The critical temperature should not be confused with the boiling points of the liquid gases.
It may be recalled that boiling point is the temperature in which the vapor pressure of the gas equals the atmospheric pressure.
 
Boiling Points of Various Gases
  • Air
– 194°C
  • N2
– 196°C
  • O2
– 183°C
  • N2O
– 88°C
Practical application:
If a gas is to be liquefied for storing in cylinders, it must be brought below the critical temperature. Otherwise liquefaction is not possible. Critical temperature of N2O is 36.5°C. So above this temperature, the N2O in the cylinder may be in gaseous form—not liquid. In hot climates, it is unsafe to expose the cylinders to direct sun as the whole liquid nitrous oxide is converted into gas and dangerous pressure inside the cylinder may be caused.
At this point of discussion, it is necessary to know about critical pressure of gases.
 
Critical Pressure
The critical pressure of a gas is the minimum pressure required to liquefy the gas at its critical temperature.
Example: Critical pressure of N2O is 71.6 atm.
Cyclopropane has a critical temperature of 125°C. But at room temperature of 20°C the pressure required to liquefy cyclopropane is only 5 atm pressure (75 psi). Hence, the gas was supplied in light aluminum alloy cylinders.
(1 atm pressure is = 760 mm Hg = 14.7 psi = 33.9 ft of H2O—1.3 kg/cm2)
Critical temperatures and critical pressures of various gases have been tabulated below.
  Gas
Critical temperature
Critical pressure
Boiling point
  • O2
118°C
50 atm
182°C
  • N2
140°C
75 atm
195°C
  • N2O
36.5°C
71.6 atm
89°C
  • CO2
31°C
72.9 atm
78°C
  • Ethylene
13°C
51.5 atm
104°C
  • Cyclopropane
125°C
54 atm
33°C
The critical temperature should not be confused with the boiling point of the liquid.
Critical temperature
Boiling point
  • Water
374°C
100°C
  • Ether
194°C
34.6°C
  • N2O
36.5°C
88°C
  • Halothane
296°C
50°C
7Example:
Water boils at 100°C and becomes water vapor and when the temperature falls the vapor condenses into water. But above 374°C water vapor cannot become water again even if pressure is applied to liquefy the vapor.
This means that these substances cannot exist in liquid state above their critical temperature.
The liquid that is being converted into gaseous form (vapor) also has the same phenomenon. Ideally the liquid must be at a temperature near its boiling point.
 
Boiling Point
Boiling point of a liquid is the temperature at which the vapor pressure is equal to the atmospheric pressure.
Example:
Commercially, O2 is prepared by fractional distillation of liquid air using the difference in the boiling points of O2 (–183°C) and N2 (–196°C).
 
Standard Conditions of Temperature and Pressure
The volume of a gas is often corrected to that it could occupy at ‘standard temperature and pressure’ (STP)—the volume it occupies at 760 mm Hg and 0°C.
 
VAPOR AND GASES
Vapor is the gaseous state of a substance which at room temperature and pressure is a liquid.
Example: Ether vapor, Water vapor, etc.
Gas is a substance, which is in gaseous state at room temperature and liquefaction at this temperature is not possible as the room temperature is very much above the critical temperature of the gas.
Example: Oxygen and nitrogen.
 
Vaporization
  • The molecules of a liquid are in constant motion, but there is a strong mutual attraction of the closely packed molecules (cohesion). Some of the molecules on the surface of the liquid move vertically with sufficient speed to overcome the force of cohesion with which their neighbors tend to pull them back into the liquid.
  • The molecules escape into the surrounding atmosphere, where it is called the vapor of the liquid. This process is named as ‘vaporization’ or evaporation (Fig. 1.4).
  • In the process of evaporation, there is an expenditure of energy by the molecule to overcome the force of cohesion or mutual attraction of the molecules. This expenditure of energy causes drop in the temperature of the liquid.
  • This loss of energy is termed as the latent heat of vaporization and is derived from the liquid itself and also from the surrounding structures—the container and the air around it.
  • Hence, the temperature of the liquid falls initially followed by that of the container.8
zoom view
Fig. 1.4: Vaporization and saturated vapor. • Molecules from the liquid surface escape into the atmosphere to form vapor; • The escaped molecules in a closed container reach a point where no further molecules can escape (Saturated vapor); • If some molecules escape at this point equal number of molecules re-enter the liquid; These molecules exerting pressure on the wall of container is saturated vapor pressure
  • If the liquid is heated and the temperature is raised the movement of molecules becomes more violent and more number of molecules escape out into the atmosphere above the liquid and the rate of vaporization increases.
  • Conversely when the temperature of the liquid falls, there will be corresponding decrease of the vapor above the liquid.
 
Evaporation of Liquid in a Closed Container
  • When the liquid is in a closed container the molecules escape out of the liquid in the same way.
  • But after certain period of time, when the concentration of vapor above the liquid (the number of molecules in the space) becomes constant—a certain value for the given temperature-evaporation stops. This is the point of equilibrium when there will be a fixed number of molecules above the liquid.
  • Even at state of equilibrium, the molecules do escape into the space above the liquid but equal number of molecules will re-enter into the liquid to maintain equilibrium. This point where the number of molecules in the space becomes constant is called saturated vapor for that temperature. At this time, the pressure exerted on the walls of the container is known as the saturated vapor pressure for the temperature (Fig. 1.4).
 
Latent Heat of Vaporization
The latent heat of vaporization of a liquid is the amount of heat in calories required to convert 1 g of the liquid at its boiling point into its vapor without altering the temperature of the liquid (heat is to be supplied).
 
The Joule–Kelvin Principle or Joule–Thomson's Effect
If a compressed gas expands against atmospheric pressure or a lower pressure, it will become cooler (because the gas has done some amount of work) equivalent to the product of reduction in pressure and change of volume.9
This is explained as follows: When the gas is released, the molecules recede from each other and lose kinetic energy because they move against forces of mutual attraction (cohesion). Thus they lose speed (recall the definition of pressure). This loss of speed is manifested as fall of temperature. This phenomenon is called Joule-Thomson's effect. (Nomenclature: Prof. W Thomson became Lord Kelvin later).
 
Explanation of Latent Heat of Vaporization
 
Ether and N2O
When ether evaporates from the Boyle bottle vaporizer (glass bottle), initially the latent heat of vaporization is derived from the liquid ether itself. As the liquid becomes cooler, then the latent heat is derived from the bottle and the bottle becomes cooler. Later on, the heat is derived from the surrounding atmosphere so that the water vapor in the atmosphere condenses on the surface of the bottle as dues.
Similarly, when a cylinder of N2O in the anesthetic machine is opened for use, gaseous nitrous oxide escapes out of the cylinder. This causes a reduction in the pressure of the gas (vapor) above the liquid in the cylinder. To compensate this and to raise the pressure, the liquid N2O starts evaporating. As molecules leave the liquid, the latent heat of vaporization is derived from the liquid and the temperature of the liquid drops rapidly. After sometime the latent heat of vaporization is derived from the cylinder and it gets cooled. In course of time the surrounding atmospheric air gets cooled and consequently the water vapor in the atmospheric air gets condensed on the cylinder as due. If carefully watched this condensation of water vapor is confined more to the level of liquid N2O inside the cylinder. In cold countries the level of condensation is seen on the surface as white snow (Fig. 1.5).
zoom view
Fig. 1.5: Condensation of water vapor on N2O cylinder in use. • The latent heat of vaporization is derived from the cylinder and it is cooled rapidly; • Surrounding atmospheric air also gets cooled; • Water vapor from the air gets condensed on the surface of cylinder; • When the ambient temperature is very low it forms snow on the surface; • The snow settles up to the level of liquid N2O in the cylinder
10As vapor is defined as the gaseous form of a substance it is essential to remember the following points.
  • Liquids can be converted into gaseous form (vapor). That process is known as Vaporization.
  • Usually, the solids melt into liquids and then vaporize into gas form. Example: ice, water, water vapor. Both the processes need heat energy—‘latent heat’.
  • When the reverse process happens, the vapor condenses into liquid and then the liquid is changed to solid, heat energy (latent heat) is released. Example: water vapor, water, ice.
  • Some substances can be converted from solid state into gaseous state without passing through liquid state. That process is known as sublimation. Example: camphor, naphthalene.
  • Therefore, as it is known that heat can either be given to a substance or abstracted from it, taking water as example, there can be; latent heat of melting, latent heat of vaporization which need heat to be supplied and latent heat of condensation, latent heat of crystallization, latent heat of fusion (solid) which release heat.
  • When a solid sublime into a vapor, latent heat of sublimation to be supplied to it.
  • The latent heat of vaporization, latent heat of condensation and latent heat of sublimation are schematically represented in Figure 1.6.
 
Sublimation
  • Sublimation is the direct change from solid to vapor without going through the liquid stage.
  • Solids can also lose molecules (particles) from their surface to form a vapor. In this case we call the effect as sublimation rather than evaporation. The reverse phenomenon is also possible.
  • In most cases, at ordinary temperatures, the saturated vapor pressures of solids range from low to very, very, very low.
  • This is because the forces of attraction among molecules in many solids are too high to allow much loss of particles from the surface.
  • However, there are some which do easily form vapors. For example, naphthalene (‘mothballs’) and camphor have quite a strong smell.
    zoom view
    Fig. 1.6: Latent heat of vaporization, condensation, sublimation. • The latent heat of vaporization being used in vaporization and being released in condensation; • Similarly latent heat of sublimation used in formation of vapor is released in the reverse process
    11Molecules must be breaking away from the surface as a vapor, otherwise the smell would not emanate from it.
  • Another fairly common example is solid carbon dioxide—dry ice. This never forms a liquid at atmospheric pressure and always converts directly from solid to vapor. That is why it is known as dry ice.
 
Latent Heat of Condensation
The latent heat of condensation is defined as the heat released when one mole of the substance condenses.
  • The condensation is the opposite process of evaporation.
  • If the vapor condenses to a liquid on a surface, then the vapor's latent energy absorbed during evaporation is released.
  • Hence, latent heat of condensation is energy released when water vapor condenses to form liquid droplets.
 
Latent Heat of Crystallization
It is the amount of heat given out or liberated when 1 g of the substance is changed from the liquid to the solid state without alteration of the temperature.
For water it is about 585 calories at room temperature.
 
Latent Heat of Melting (Latent Heat of Liquefaction)
For converting solid into its liquid state, latent heat of liquefaction is supplied.
It is the amount of heat energy required in calories to convert 1 g of solid into its liquid form without altering its temperature.
It is amount of heat that must be supplied to the substance to change into its liquid form without change of temperature. For water it is the same; about 585 calories.
Examples:
  • About 580 calories are required to convert 1 g of water into vapor without changing the temperature.
  • So also, 580 calories are liberated when 1 g of water gets condensed (Latent heat of condensation)
  • Water has the highest latent heat of vaporization than any other liquid.
  • Latent heat of vaporization of ether is 63 calories.
 
Fall of Temperature of Evaporating Liquid
In vaporizing volatile anesthetic agents:
  • When a gas flows over the surface of a liquid, the vapor of the liquid is carried away and is replaced by fresh vapor. This continuous process of vaporization is accompanied by corresponding loss of heat; as the ‘latent heat of vaporization’ is being derived from the liquid. So when a volatile anesthetic is used in a vaporizer, as time passes, the temperature of the liquid falls and there will be progressive reduction in vaporization unless heat is supplied.
  • When the liquid becomes very cold, the heat may be derived from the surrounding structures or air. The water vapor in the air around the container gets condensed on the surface of the container.
  • To prevent this phenomenon and to make the vaporization constant, various temperature compensation devices are used (Discussed in Chapter 7 on vaporizers).12
 
Adiabatic Compression
The process of sudden release of gases and instant recompression without allowing the time for dissipation of the heat of compression is known as Adiabatic compression. Adiabatic means—without the loss of heat to the outside.
 
Practical Significance
When a cylinder of oxygen in the yoke of the anesthetic machine is opened, the gas under pressure (2000 lb/sq inch) is released quickly; it gets cooled as latent heat of vaporization is used. But the released gas is instantly recompressed into the pressure reducing valve where enormous amount of latent heat of compression is released and there is no time for dissipating it. This heat is sufficient enough to ignite a combustible material like oil if present resulting in a disaster of fires or explosion. That is why ‘Danger—Use No Oil’ sign is used wherever compressed gases are used, especially oxygen cylinder.
 
PRESSURE
Pressure is defined as force per unit area.
By definition, pressure is = force × area. It may be expressed as lbs/sq. inch or kg/cm2, kPa.
  • Pressure of a gas is a measure of the molecular bombardment on each unit area of the wall of its container. The closer the molecules the greater the number which strikes each unit area, and therefore the greater pressure exerted.
  • Except at – 273°C (absolute zero) all gases exert pressure. Such pressure is due to the force exerted by molecules as they bombard the walls of the space of container in which they are confined. This happens because the molecules are in rapid constant motion, at the temperatures usually existing (Fig. 1.7).
zoom view
Fig. 1.7: Pressure exerted by the bombardment of molecules on the walls of a closed container
  • 13The standard unit for pressure is the Pascal (Pa), which is a Newton per square meter.
  • The SI unit of pressure (the Newton per square meter) is called after the seventeenth-century philosopher and scientist Blaise Pascal as Pascal (Pa)
  • A pressure of 1 Pa is too small, hence everyday pressures are often stated in kilopascals (1 kPa = 1000 Pa).
 
Partial Pressure
  • When gases associate as mixture, the pressure of each gas is entirely independent.
  • The total pressure exerted by a mixture of gases equals the arithmetic sum of individual pressures exerted by each of the constituent of the mixture.
  • It was discussed earlier that under the same conditions of temperature and pressure, equal volumes of all gases contain same number of molecules (Avogadro's hypothesis).
  • Air contains 80% nitrogen and 20% oxygen. So in a container of air 20% (1/5) volume is occupied by oxygen and 80% (4/5) volume is occupied by nitrogen.
  • Therefore, oxygen exerts 1/5th of the total pressure and nitrogen exerts 4/5th of the total pressure. This is known as ‘partial pressure’ of the gas in a mixture (Figs 1.8A to C).
  • In a mixture of gases, each gas will exert the same pressure which it exerts if it occupies the container alone.
Dalton's law of partial pressures states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases. (John Dalton in 1801).
This is explained as follows:
  • In a mixture of gases, the pressure exerted by each gas is called its partial pressure the total pressure exerted equals the arithmetic sum of individual pressures exerted by each of the constituent of the mixture.
zoom view
Figs 1.8A to C: Partial pressure of gases in Air. • Chamber A contains 4 molecule of nitrogen and exerts a pressure of 4 units; • Chamber B contains 1 molecule of oxygen and exerts a pressure of 1 unit; • The contents A and B are transferred to chamber C; • Chamber C has total of 5 molecules and exerts pressure of 5 units
  • 14In such a mixture, each gas exerts the same proportion of the total pressure as its volume of total volume.
  • Thus, in a mixture of 25% cyclopropane, 25% O2 and 50% helium, having a total pressure of 800 mm Hg. Partial pressures of O2 = 200 mm Hg; cyclopropane = 200 mm Hg and helium = 400 mm Hg.
 
Fick's Law
This law states that the rate of diffusion of gas is proportional to the gradient of concentration. When the concentration gradient is high the rate of diffusion is fast.
Application of Dalton's Law and Fick's Law partial pressure in the diffusion of gases
  • If a gas exists on either side of a diffusible membrane, the direction of its diffusion is determined by the differences in its partial pressure it exerts on either side of the membrane—(not by the difference in its amount).
  • The gas diffuses from the side of higher partial pressure to the side of lower partial pressure till the equilibrium of partial pressure is reached.
  • The difference in the partial pressure is the pressure gradient that drives the gas across the membrane (diffusion).
  • This is the mechanism by which the diffusion of O2 and CO2 occurs across alveolar capillary membrane in the lung as well as in the tissue level (Fig. 1.9).
  • In the alveoli the percentage of oxygen is 14. Therefore, the partial pressure of this gas is 14% of 760 mm = 100 mm Hg.
zoom view
Fig. 1.9: Diffusion of gases aided by gradient in partial pressure
  • 15The tension of oxygen (partial pressure) in the capillaries of the lungs is approximately 40 mm Hg. There is a pressure gradient of 60 mm Hg.
  • The oxygen from alveoli diffuses rapidly to the venous blood and this raises the tension of arterial blood leaving the alveoli to 95 mm Hg.
 
Atmospheric Pressure
It is the pressure exerted by the column of air in the atmosphere on earth which can lift a mercury column of 760 mm in a vacuum tube.
One atmospheric pressure is 760 mm Hg
  • It is equivalent to 1 kg/cm2 or 14.7 (15) lbs/sq inch or 1030 cm of H2O or 1 bar or 100 kPa or 1000 millibar.
  • Atmospheric pressure at sea level will support a column of mercury to 760 mm height.
  • Hence, 760 mm Hg is referred to as one atmospheric pressure.
  • The partial pressure of oxygen in air is 21% of 760 mm Hg= 160 mm Hg.
  • The exact partial pressures of atmospheric air are illustrated in Figure 1.10.
  • The total is 752 mm Hg as the remaining 8 mm Hg is constituted by carbon dioxide and other trace gases.
Atmospheric pressure in high altitude
  • At heights above sea level the weight of the overlying air is less. The molecules are less closely packed so that they exert less pressure.
  • At 6000 feet above sea level the atmospheric pressure is 600 mm Hg; hence partial pressure of oxygen is 126 mm Hg.
  • At 10,000 feet, the pressure sufficient to support a column of mercury is only 520 mm Hg.
Interesting aspects of partial pressures, atmospheric pressure and breathing in high altitude
  • Carbon dioxide is excreted from the bloodstream into the alveoli and the partial pressure it exerts in the alveoli remains practically constant at 40 mm Hg.
  • Another gas inevitably present in the alveoli is water vapor. Since the body temperature remains is constant, the partial pressure of water vapor in the alveoli remains constant at 47 mm Hg.
  • Therefore, these two gases exert a combined pressure of about 90 mm Hg under all conditions.
zoom view
Fig. 1.10: The partial pressures of oxygen and nitrogen in atmospheric air
  • 16Hence, at sea level the pressure of other gases (nitrogen and oxygen) in the lungs is 760 – 90 = 670 mm Hg.
  • The percentage of oxygen in atmospheric air is unaffected by altitude and remains constant at 21.
  • The percentage of oxygen in the alveolar gas is only 15%.
  • At sea level, the partial pressure of oxygen in alveolar air is 15% of (760 – 90 = 670 mm Hg) = 100 mm Hg.
  • At 6000 feet (1800 m) atmospheric pressure is 610 mm Hg and the partial pressure of oxygen in alveoli is 15% = 78 mm Hg. If the venous oxygen tension is 40 mm Hg, there is still a pressure difference (gradient) 78 – 40 = 38 mm Hg for adequate oxygenation of the blood.
  • At 14000 feet (4200 m) the atmospheric pressure is 540 mm Hg. Partial pressure of carbon dioxide and water vapor remain constant in the alveoli as 90 mm Hg. So, combined pressure of nitrogen and oxygen is 540–90 = 450 mm Hg. Therefore, the pressure of oxygen in the alveoli is 15% of 360–54 mm Hg. Now the gradient of pressure between the alveoli and venous blood is reduced to 14 mm Hg. Oxygenation of blood resulting from this is sufficient to support life, though it leaves many of the body functions considerably impaired. Saturation of oxygen in hemoglobin will be about 80%.
  • At 30000 feet (9100 m) the atmospheric pressure is 225 mm Hg. Alveolar oxygen pressure would be 15% of (225–90) = 20 mm Hg. This pressure is less than the tension of oxygen in the venous blood. Diffusion of oxygen occurs in reverse direction into the alveoli.
  • It has been shown in experiments simulating conditions of 40000 feet, had shown that the alveolar oxygen pressure was 15 mm Hg and after a few breaths the pressure fell to 6 mm Hg, consciousness was lost. (reverse diffusion and sever hypoxia).
  • At 50000 feet the total atmospheric pressure is only 90 mm Hg. So, in theory, the alveolar space is filled with CO2 and water vapor only.
 
GAS LAWS
 
Vapor and Gas
  • Vapor is the gaseous state of a substance which at room temperature and pressure is a liquid. Example: water vapor, halothane vapor.
  • More scientifically, the vapor is gaseous state of the substance above its ‘critical temperature’ as above the ‘critical temperature’ it could not be liquefied.
  • Gas is a substance which at room temperature exists only in the gaseous state. Example: oxygen.
  • Liquefaction of such a gas is impossible at the room temperature since it is much above the critical temperature of the gas. Example: Critical temperature of oxygen –118°C.
 
Specific Volume
The volume which 1 g of any substance, solid, liquid or gas, occupies under a given conditions of temperature and pressure is known as its Specific Volume.
  • Gaseous substance always occupies the whole of the container in which it is held.17
  • Thus, the molecule of the gas thin out to suit the size of the container.
  • The specific volume is inversely proportional to the density.
Specific Volume = 1/density
  • When a given weight of a gas is allowed to expand, its specific volume increases.
  • There are fewer molecules in a cm3 and so less number of molecules bombard on unit are of the walls. Therefore, the pressure falls. Thus, the pressure is inversely proportional to the increase in the specific volume.
 
Boyle's Law (1662)
When the temperature is kept constant, the pressure of a gas is inversely proportional to the specific volume.
Pressure ∝ 1/Specific Volume
Since the density of a gas is inversely proportional to its specific volume, it can be defined as;
When the temperature is kept constant, the pressure of a gas is directly proportional to the density.
PressureDensity
The Boyle's Law is explained in Figure 1.11.
 
Practical Applications
If the O2 cylinder is full, pressure is 120 (137) atm (2000 lbs/sq inch or 150 kg/sq cm). If the contents are reduced to half, in the process of use, the pressure is also reduced to half. The specific volume is doubled. The pressure gauge will be showing half of the original pressure—say 1000 lbs/sq inch. So if the total content of the cylinder is known in measures of liters then, by looking at the pressure gauge one can calculate the amount of gas remaining in the cylinder (Fig. 1.12).
Pressure gauge is rarely used for N2O, cyclopropane, CO2 or any liquefied gases.
The cylinders when full contain a small amount of gaseous N2O above the liquid N2O at room temperature and the saturated vapor pressure is 51 atm. This continues to be the same although with the fall of temperature of the cylinder; the saturated vapor pressure may be a little reduced, depending upon the temperature of the cylinder. But with the cylinder at 21°C, the pressure is always at 51 atm, which shows that there is some liquid in the cylinder, but gives no idea of how much liquid.
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Fig. 1.11: Boyle's Law explained. • The pressure is inversely proportional to the volume; • As the pressure applied is increased the volume gets reduced
18
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Fig. 1.12: Application of Boyle's Law in oxygen cylinder
When the last drop of liquid is vaporized the vapor pressure is still 51 atm. After that the vapor pressure falls rapidly (depending upon the flow rate) to zero. So, the pressure gauge does not serve any useful purpose in such cylinders of liquefied gases. In the modern anesthetic machines there are pressure gauges fitted and they indicate the pipeline pressure as 60 psi (4 bar).
But if the cylinder is used it serve to know whether all the liquid has been used up and the cylinder nearing to be empty (Fig. 1.13).
  • The amount of N2O remaining in the cylinder can be ascertained only by weight.
  • The weight of empty cylinder is seen stamped on it, i.e. Tare weight.
  • The difference in weight is converted into the amount of liters of gas present in the cylinder.
  • 455 L of N2O weighs 850 g (1 L = 1.87 g).
 
Filling Ratio
The degree of filling of a nitrous oxide cylinder is expressed as the mass of nitrous oxide in a cylinder divided by the mass of water that the cylinder could hold. Normally, a cylinder of nitrous oxide is filled to a ratio of 0.67.
This should not be confused with the volume of liquid nitrous oxide in a cylinder. A full cylinder of nitrous oxide at room temperature is filled to the point at which approximately 90% of the interior of the cylinder is occupied by the liquid, the remaining 10% being occupied by gaseous nitrous oxide.
Simply, filling ratio is the weight of the fluid in the cylinder divided by the weight of the water required to fill it.
  • Usually, nitrous oxide cylinders are filled from a pipeline containing liquid nitrous oxide under a pressure well above the saturation pressure of the temperature in the room.19
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Fig. 1.13: Pressure gauge in N2O cylinder. • The gauge shows full pressure until it is nearing exhaustion
  • The cylinders are filled with a little gas above the liquid N2O. When the specific volume is 1.5 cm3/g the cylinder is said to be full.
  • The cylinder can be filled beyond this stage to when the cylinder is full of liquid.
  • As the liquid is virtually incompressible, even an addition of even a minute amount of gas will result in enormous increase in pressure.
  • Since the density of water is 1, the ratio is;
Weight of N2O in the cylinder/weight of water the cylinder could hold
A 455 L cylinder has an internal volume of 1.3 L (1300 mL)
The volume of water it can hold is 46 oz or 1300 mL
= 1300 g
The volume of liquid N2O in ‘full’ cylinder is 30 oz
= 850 g
Therefore the filling ratio
= 30/46 or 850/1300 = 0.65
This gives the average density of the contents and the figure is known as the ‘filling ratio’.
  • N2O cylinders are normally filled to a ratio of 0.67.
  • This is suitable for temperate and tropical climates (0.75 is acceptable for temperate climates).
 
How this Filling Ratio is Practically Very Important?
The filling ratio of 0.65 corresponds to specific volume of 1.5.
This cylinder;
At 20°C
has a pressure of
51 atm
At 40°C
has a pressure of
90 atm
At 60°C
has a pressure of
160 atm (2400 lbs/sq inch)
This is possible in tropics and the pressure is similar to a full oxygen cylinder at the same temperature.
The filling ratio of 0.77 corresponds to specific volume of 1.3.
This cylinder;
At 20°C
has a pressure of
51 atm
At 40°C
has a pressure of
125 atm
At 60°C
has a pressure of
190 atm (2850 lbs/sq inch)
20This is almost closer to the testing pressure of the cylinder.
When the cylinder is completely filled with liquid N2O;
At 20°C, it may have a pressure of 51 atm or a little more.
But, if warmed as described above, will cross the test pressure to reach dangerous values.
 
Charles's Law (Law of Volumes)
Charles's law describes how gases tend to expand when heated. A modern statement of Charles's law is—When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be directly related.
If the pressure remains constant the volume of a gas is directly proportional to its absolute temperature (Kelvin temperature).
Figure 1.14 explains Charles’ Law.
Absolute temperature is the temperature of an object on a scale where 0 is taken as absolute zero. Absolute temperature scale is Kelvin. Absolute zero is the lowest temperature at which the system is in a state of lowest possible (minimum) energy. No electronic device can operate at this temperature.
Common temperatures in the absolute scale are:
  • 0°C (freezing point of water)
= 273.15 K
  • 25°C (room temperature)
= 298.15 K
  • 100°C (boiling point of water)
= 373.15 K
  • 0 K (absolute zero)
= – 273.15°C
To convert from the Celsius scale into the absolute temperature, add 273.15 and change °C to K. To get a temperature on the absolute scale to the Celsius scale, subtract 273.15 and change K to °C.
 
Conversion
Kelvin to Celsius: K = C + 273
Celsius to Kelvin: C = K – 273
zoom view
Fig. 1.14: Charles’ Law
21Note:
  • The pressure applied on the gas is constant, but temperature is increased from 23°C = 300 K to 327°C = 600 K.
  • Therefore, when the K (Absolute temperature) 300 K is doubled as 600 K the volume of the gas is doubled.
  • If the temperature remains constant, the volume of the gas varies inversely with its pressure. (Therefore halving the pressure doubles its volume and doubling its pressure halves its volume.)
  • The volume decreases by 1/273 for every degree it is cooled below 0°C and increases by 1/273 for every degree it is heated above 0°C.
  • In this absolute scale of temperature is used (Kelvin temperature).
  • 0° Absolute is equivalent to –273°C.
  • 273 Absolute is equivalent to 0°C.
  • Absolute temperature is mentioned as K (after Lord Kelvin).
 
Gay-Lussac's Law
If the volume remains constant, the pressure of a gas is directly proportional to its absolute temperature.
If the volume is kept constant, for each degree Celsius (°C) rise in temperature, the pressure of the gas raises by 1/273 of its pressure at 0°C.
 
Diffusion
Gaseous molecules tend to distribute themselves evenly in any given space.
  • When two different gases are allowed to mix in a container, there is a rapid intermingling of molecules among the two gases and both the gases are uniformly distributed in the container.
Example: In the alveoli the inspired air diffuses readily into the residual air.
  • Liquids also have the same process of diffusion of intermingling of molecules, but at an extremely slow rate.
    Example: In spinal anesthesia diffusion of local analgesic is so slow that the upward spread is not a common problem by diffusion. There are other factors that cause the spread.
This happens with all gases and vapors whether it is monoatomic, diatomic, triatomic or multiatomic.
Example:
Monoatomic
Diatomic
Triatomic
Multiatomic
Helium (He)
O2, N2
O3
C3H6 (Cyclopropane)
Xenon (Xe)
H2
N2O
C2H4 (Ethylene)
 
POYNTING EFFECT
  • This is also known as ‘overpressure effect’
  • The critical temperature and critical pressure of one gas may be affected by its admixture with another gas.
  • When a cylinder is partially filled with liquid nitrous oxide is inverted and further filled with oxygen from a high pressure source, an unexpected phenomenon occurs. The oxygen gets dissolved in liquid nitrous oxide and subsequently nitrous oxide liquid evaporates and mixes with oxygen.22
  • At one point of time the cylinder contains a mixture of nitrous oxide and oxygen in gaseous form at a pressure of 2000 psi (137 atm) at room temperature.
  • In this process, the critical temperature of nitrous oxide 36.5°C changes to a pseudocritical temperature of–6°C.
  • This effect of modifying the critical pressure of one gas by mixing with other gas is called “Poynting effect”.
  • Entonox is a 50: 50 mixture of nitrous oxide and oxygen in gaseous form used in obstetrics analgesia.
 
Bernoulli's Principle (1738)
Daniel Bernoulli (1700–1782) in 1738 demonstrated that when a fluid passes through a tube of varying cross sectional areas (diameter) the pressure is least where the velocity (speed) is greatest. This is Bernoulli's Effect.
Bernoulli's theorem, or Bernoulli's Law states that when a fluid is passing through a tube of varying cross sectional areas, the velocity is highest in the narrowest portion and the pressure is lowest; whereas in the widest portion the velocity is low and the pressure is high.
Simply, when a fluid passes through a tube of varying diameters, the pressure is low at the point of maximum velocity.
Figures 1.15 and 1.16 explain the Bernoulli's principle.
The diameter of a tube is smoothly reduced to half to form a constriction and the again it is widened to the original diameter smoothly. When fluid is allowed to flow through this tube of varying diameters the speed is greatest in the area of constriction which can be measured by connecting a narrow tube vertically perpendicular to the tube where fluid flows. The pressure is highest in the proximal end lowest in the constriction and again raises to a higher level that is a little lower than that at the proximal end.
It is necessary to recall that Pressure = Force ÷ Area (Force acting on unit of surface area). In low velocity more molecules bombard the walls of the tube to exert pressure. In high velocity the time available for such bombardment is minimal and so exerts minimal pressure.
The pressure drop seen in the constriction is due to the temporary conversion of pressure energy into increased kinetic energy.
When the velocity (speed) of the flow is increased, the pressure drops further and may become negative (subatmospheric).
zoom view
Fig. 1.15: Bernoulli's principle. • Fast moving fluid exerts low pressure and slow moving fluid exerts high pressure; • The velocity is highest and the pressure is lowest in the constriction of the tube; • Shown by attaching a narrow vertical tube where fluid level is seen as pressure
23
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Fig. 1.16: Bernoulli's principle. • When air is the driving fluid the tubes are dipped in a container of water—water level being sucked show the pressure. • In the narrow portion of the tube ‘B’ the driving fluid has highest velocity and the pressure is lowest at that point. So the water level is sucked higher
zoom view
Fig. 1.17: Subatmospheric pressure caused by Bernoulli's principle. • The very high velocity of fluid at the very narrow tube causes drop in pressure; • The velocity is so high that the drop of pressure becomes subatmospheric; • The subatmospheric pressure causes entrainment of air bubbles through the side tube
Similarly if the constriction of the tube is made narrower, naturally the velocity increases and the same effect of developing subatmospheric pressure are caused (Fig. 1.17).
 
Venturi
In 1797—about 60 years later, Giovanni Battista Venturi (1746–1822) an Italian physicist developed an appliance known as Ventury based on Bernoulli's principle. With suitable flow in the cone shaped ‘venturi tube’ subatmospheric pressure can be easily produced.
Where the cross sectional area of the tube (Main driving fluid) is very much reduced like a ‘Jet’ and allowed become larger by gradual widening, or called ‘swaying’, there is a negative pressure created at the point of maximum narrowing. If a side port is attached at this point (Entrainment port), this will allow suctioning of fluid (Entraining fluid) connected to the entrainment port. This device is known as ‘Venturi device’ or ‘Jet’ (Fig. 1.18).
The device is actually known as ‘Injector’ where the smooth constriction of the venturi tube is replaced with a nozzle through which fluid is injected at great velocity. This is known as ‘driving fluid’. Subatmospheric pressure created around the nozzle.24
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Fig. 1.18: Construction of Venturi device or Jet
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Fig. 1.19: Venturi device. • Input is driving fluid; • The constriction is replaced with a jet; • Suction is entrainment port; • The tube widens very smoothly; • The special funnel shaped downstream tube is called ‘diffuser’
A tube that is known as ‘entrainment port’ is connected to the main tube near nozzle that can allow the desired fluid—‘entrained fluid’ (Gas or liquid) in to the main stream by suction effect (Fig. 1.19).
In a properly designed ventury device the driving gas may entrain as much as twenty times it own volume.
The appliances based on this device:
  • Venturi suction
  • Oxygen therapy mask—Ventimask (Fig. 1.20)
  • Jet ventilator
  • Macintosh laryngeal spray (Fig. 1.21).
 
Ventimask
  • The ‘Ventimask’ works on this ‘Venturi Principle’
  • It gives a predetermined concentration of oxygen to the patient and it can be set as needed.25
zoom view
Fig. 1.20: Ventimask working with Venturi device. • Used for oxygen therapy with regulated percentage of oxygen; • Very large volume of air is entrained to maintain the percentage; • In addition the flow rate of oxygen controls the percentage; • Color coded ventury adapters for desired percentage of oxygen and the flow rate of oxygen needed are shown; • Oxygen tubing is attached to the adapter
zoom view
Fig. 1.21: Macintosh spray working on ventury principle
  • It is used for guarded, calculated percentage of oxygen in air delivered to the patients who maintain their ventilation by the hypoxic drive and not by CO2 drive. e.g. patients with COPD.26
  • If 100% O2 is administered to them, it abolishes this hypoxic drive, they become apneic and PaCO2 rises rapidly to make them unconscious, (CO2 Narcosis)
  • The actual oxygen concentration is determined by varying the size of the entrainment port.
  • Gas passes out of the holes of mask mostly due to high fresh gas flow rate. Thus rebreathing is practically eliminated and there is no increase in dead space.
 
Laryngeal Spray: (Macintosh)
 
Forrester Spray
  • Works on Venturi principle
  • Container can hold only 4 mL of 4% xylocaine solution.
  • Restricts the dose to 160 mg: this prevents accidental overdose
  • Malleable sprout is used for spraying the nasal cavity, oropharynx, larynx and laryngeal inlet for topical analgesia.
FURTHER READING
  1. Jerry A Dorsch, Susan E Dorsch. Understanding anesthesia equipment, 5th edn. Lippincott Willaims & Wilkins,  Philadelphia; 2008.
  1. John TB Moyle, Andrew Davey. Ward's anaesthetic equipment, 4th edn. WB Saunders Company Limited,  Philadelphia; 1998.
  1. Atkinson RS, Rushman GB, Davies NJH, Lee's synopsis of anaesthesia, 11th edn. Butterworth-Heinemann Limited  London; 1993.
  1. Sir Robert Macintosh, William W Mushin, Epstein HG. Physics for the anaesthetist, 4th edn. Blackwell Scientific Publications,  Oxford; 1963.