Arterial Line Insertion and Pressure Monitoring
Arterial catheters are used commonly in critical care patients to obtain blood, measure the blood pressure directly and estimate the cardiac output. As this is an invasive procedure, caution should be exercised and complications should be avoided.
Indications
- Blood pressure monitoring in hypotension, hypertensive episodes, major surgeries and guiding vasoactive medication therapy
- Frequent blood gas or laboratory measurements in sick patients
- Monitoring cardiac output by softwares like LiDCO (lithium dilution cardiac output).
Insertion
Identify the palpable artery. Radial artery is the most commonly used. The collateral flow can be checked by occluding the ulnar artery. The arm is immobilized and area is aseptically cleaned and prepared. Local anesthetic can be used to numb the area. Ultrasound can also be used for locating the artery. Various techniques are used depending on the user experience and include separate-guidewire, integral guidewire, direct puncture or the seldinger technique.
Contraindications and Complications
Coagulopathy and use of thrombolytic agents are relative contraindications.Complications include:
- Hematoma and bleeding
- Pain and bruising
- Thrombosis and embolism
- Infection
Pressure Monitoring
Arterial pressure monitoring remains the gold standard of blood pressure measurement (Fig. 1.1). It correlates well with indirect measurements in healthy patients, but not so much in sick patients or patients with calcified arteries, arrhythmias or certain medications. The arterial trace accuracy depends on a number of factors though including proper calibration, position of the transducer and also the damping coefficient and resonant frequency of the system.
Golden Tips
- Use of ultrasound can increase the success rate and reduce time taken for catheterization
- Local anesthetic usage reduces pain without reducing the chance of success
- Arterial catheters should not be replaced routinely unless there are signs of infection or catheter failure.
Central Line Insertion and Pressure Monitoring
Central venous catheter placement is common in the ICU settings. It is an invasive procedure with higher rate of infections and more serious complications compared to the arterial line.
Indications
- Administration of medications such as vasoactive medications, parenteral nutrition, chemotherapy, concentrated electrolytes like potassium
- Renal replacement therapy (hemodialysis/hemofiltration) and plasmapheresis
- Hemodynamic monitoring in the form of central venous pressure, central venous oxygen saturations and insertion of pulmonary artery catheter
- Transvenous pacing and stent placement
- Poor venous access.
Contraindications
- Coagulopathy
- Local infection
- Bleeding diasthesis
- Already indwelling catheter presence are all relative contraindications.
Method
The common sites of insertion are internal jugular, subclavian and femoral veins. The catheter can be placed percutaneously or surgically. They can also be tunnelled or non-tunnelled. They come in various sizes and number of lumens. Another type is the peripherally inserted central catheter (PiCC) that is generally inserted in the basilic/cephalic vein and ends in the right atrium/superior vena cava. This device has lower complication rate and better patient satisfaction. The device to be inserted should be selected carefully based on the need of the particular patient and the need reviewed daily.
The common sites for cannulation include jugular vein, subclavian vein and femoral vein. There is little difference in the mechanical or infective complications with jugular or subclavian vein with subclavian access having higher mechanical complications while jugular vein access having higher infective complications. If a patient has respiratory compromise, jugular route is preferred and subclavian site is generally avoided in coagulopathy. Femoral site may have higher infection risk compared to jugular or subclavian route, more so with increased BMI. After consent, monitoring and sterile prepping of the site, the patient should be positioned such that the vein is prominent (head down for jugular vein if tolerated by patient). Ultrasound may be used here if available in a sterile fashion. Seldinger technique is generally used for cannulation. Local anesthetic is used to numb the skin and extra sedation/analgesics given as appropriate. Vein is then cannulated to get the blood back following which the guidewire is inserted. Needle is then removed, skin nicked with a blade and dilated using the dilator. The catheter is then inserted over the guidewire and guidewire removed. The catheter is then secured to the skin after all the ports have been aspirated and flushed. A sterile transparent dressing is applied and the position checked with a chest X-ray in cases of subclavian and jugular routes.
Complications
- Hematoma and bleeding
- Arterial puncture
- Arrythmias due to guidewire stimulating the heart
- Pneumothorax/hemothorax
- Injury to nerves, thoracic duct, other structures around the area
- Loss of guidewire into the vein.
Golden Tips
- Jugular and subclavian routes can be used unless specific contraindications exist. Femoral route may have higher infection rates
- The need for central venous access should be reviewed daily.
Pulse Oximetry
Pulse oximetry has become a vital part of monitoring in the recent years. This is a non-invasive method of estimating the arterial hemoglobin concentration while avoiding the requirements of arterial puncture and blood gas machine for calculation of dissolved oxygen in the blood.
Concepts
Photoplethysmography is used to calculate the oxygenation of hemoglobin using the Beer–Lambert law. Two different wavelengths are used to differentiate between deoxyhemoglobin and oxyhemoglobin. Deoxyhemoglobin absorbs light in the red band (600–750 nm), while oxyhemoglobin in the infrared (850–1000 nm). The relative absorbance is used to calculate the oxyhemoglobin saturation in percentage. The diodes in the probe emit at 660 and 940 nm and the probe is placed on the fingers or earlobes. This data is collected during pulsatile and non-pulsatile flow and then the noise is eliminated based on this. The pulse oximeter can also display the heart rate based on the pulsatile flow. The values are accurate from 70–100% range.
Uses
Any situation where there is a risk of variation in the saturations or chances of deterioration over time. This may include:
- Intensive care units, where the saturations can be followed instead of repeated arterial blood gas measurements
- Emergency departments for use in sick patients
- Intra- and peri-operatively to monitor the oxygenation of patients
- Sleep and exercise laboratories, conscious sedations, labor suites.It has the benefit of providing the hemoglobin saturation rather than the dissolved oxygen content. As 98% of the oxygen is attached to hemoglobin, it offers a better indicator of oxygenation.
Limitations
- Poor perfusion may result in artifacts
- Motion artifacts, ambient light and electromagnetic radiations can all interfere with the readings
- Skin pigmentation, nail polish and some dyes like methylene blue can also cause low oximetry readings
- Does not measure the CO2 and hence ventilation status of the patient.
- There is a delay of several seconds which may be significant in neonates/pediatric patients
- Large decrease in dissolved oxygen will still not be detected with pulse oximetry as the dissociation curve only changes around 70 mm Hg.
Golden Tips
- Pulse oximetry gives the hemoglobin saturations compared to dissolved oxygen content from arterial gases
- It is a cheap, continuous and non-invasive method of monitoring patients status.
End-tidal Carbon Dioxide Measurement
Carbon dioxide monitoring or capnography/capnometry is a noninvasive way of monitoring the partial pressure of CO2 in expired gases. This can be represented in the form of a number, change in color or a waveform (Fig. 1.2). Capnography can be used for a variety of clinical indications as discussed below and have become a standard part of monitoring in anesthesia and critical care.
Concepts
End tidal carbon dioxide measurement can be done by sidestream or mainstream systems. The measurement is done with qualitative methods or quantitative methods. Quantitative methods give the waveform (capnography) or a number (capnometry); while qualitative methods report a range by change in color by use of treated litmus paper. These are useful when confirmation of endotracheal tube placement is warranted. Capnography uses infrared waves for the measurements. This is absorbed by CO2 in the breath and is displayed in the form of a wave or number.
The capnograph has various phases depending on the cycle of respiration. The first phase (with CO2 close to 0) is the expiration where the dead space is being cleared. The ascending phase is when the alveolar gases start reaching the capnograph monitor.
The next phase is the plateau phase of alveolar expiration which peaks towards the end (end-tidal CO2) of the tidal breath. The number may be represented on the monitor and the final phase is the inspiratory phase where fresh air is breathed in. The end-tidal CO2 may be very close to the arterial CO2 (PaCO2) in healthy patients, but can be below the PaCO2 in diseased states like COPD, pulmonary embolism, pneumonia, etc.
Uses
- Correlation with PaCO2 in health patients
- Verifying placement of endotracheal tube
- Titration and determination of ventilation adequacy
- Useful in transport of patients
- Diagnosing cardiac output drop (if the end-tidal CO2 reduces suddenly)
- Calculation of respiratory rate and monitoring of sedated patients.
Limitations
- Cannot help in diagnosing the cause of ventilation problem
- There may be delay in getting the measurements in side-stream analysers while the mainstream analyzers may be bulky
- They should not be relied completely to represent PaCO2 unless the patient is healthy with normal lung function.
Golden Tips
- End-tidal CO2 monitoring may be qualitative or quantitative
- The capnograph can give a lot of information about the patient including presence of airway disease, adequacy of ventilation, respiratory rate, limited information on perfusion and metabolism and response to treatment
- It should be used in all patients with airway device in situ
Intracranial Pressure Monitoring
Neurological insult in the form of trauma, stroke, tumors and metabolic derangements can lead to increase in the intracranial pressure. Recognition and early treatment with the use of intracranial monitoring devices can be important in treating and reversing these conditions.
Concepts
The normal intracranial pressure is <15 mm Hg. As the intracranial compartment has a fixed volume, any change in any of its contents—blood, brain matter and cerebrospinal fluid will cause a rise in the intracranial pressure and affect organ perfusion and blood supply (Monro-Kellie doctrine). The cerebral perfusion pressure is important and is calculated from the intracranial pressure measurement.
CPP = MAP – ICP (Cerebral perfusion pressure = Mean arterial pressure – Intracranial pressure).
Cerebral perfusion pressure of more than 70 mm Hg is considered adequate and hence the mean arterial pressure is manipulated to keep the CPP at a reasonable level. ICP monitoring is hence useful in this calculation. Intracranial pressure can be measured by various devices and should be kept if possible below 20 mm Hg.
Devices
The use of ICP monitoring is to help the clinicians make adjustments to maintain the CPP. This can improve the patient outcome especially in trauma patients. CT scans are the preliminary diagnostic tools for such neurological insult and can demonstrate mass lesions, midline shifts and herniation of brain matter or hydrocephalus. This can point towards increased ICP, but cannot measure the actual value. Also ICP can be raised with normal CT scans too. Thus other types of devices are used for more direct measurement of ICP. These can be intraventricular, intraparenchymal, subarachnoid and epidural devices.
Intraventricular
Intraventricular monitors measure the pressure directly from the ventricles and are most reliable. They also have the benefit of draining the CSF to relieve the pressure, hence they have therapeutic role. Infections can occur and there is small chance of hemorrhage. They cannot be placed if the ventricles are small.
Intraparenchymal
Intraparenchymal monitors have a small transducer at their tip and are directly left in the brain parenchyma through a small drill (bolt). They are easy to place, 8have lower risk of infection and bleeding, but cannot be used to drain the CSF. They are useful when the ventricles are small.
Subarachnoid
Subarachnoid monitors are placed through the skull into the dura and the dura then perforated for communication with the transducer. They have low infection or hemorrhage rates, but can be unreliable and inaccurate.
Epidural
Epidural monitors are placed on the dura without piercing the dura. They can be unreliable too, but are more useful in patients with bleeding diasthesis.
Waves generated from the monitors can give an idea of the advanced pathology (Figs 1.4A to C). Pathological A waves are marked elevations in the ICP to 100 mm Hg lasting minutes to hours, B waves can be transient due to vasospasm and C waves are smaller changes related to respiration and cardiac activity.
Non-invasive methods for ICP estimation are also used in the form of transorbital sonography, transcranial Doppler, tympanic membrane displacement, intraocular pressure monitoring, tissue resonance analysis, etc.
Golden Tips
- ICP monitors are invasive monitors with increased chances of infection, hence should be placed in appropriately indicated situations
- Intraventricular drains have benefit of draining CSF to reduce pressure.
FIGURES 1.4A TO C: Intracranial pressure waves: (A) A waves (Plateau waves); (B) B waves; (C) C waves
Pulmonary Artery Catheter Placement
Flow directed pulmonary artery catheter has been the gold standard for cardiac output monitoring and estimation of right sided pressures for years. This technique has now slowly waned to give way to new non-invasive or semi-invasive methods of cardiac output monitoring like LiDCO and PiCCO.
Concepts
Hemodynamic data obtained from the correct placement of the pulmonary artery catheter (Fig. 1.5). This can give direct measurements of pressures from the right atrium, right ventricle, pulmonary artery and the pulmonary artery 10wedge. Thermodilution technique may be used to estimate the cardiac output quite accurately and based on these measurements; data can be derived for pulmonary vascular and peripheral vascular resistance to guide vasoactive therapy. Blood gases obtained can give the mixed venous oxygen saturations for guiding fluid therapy too. This advantage of the catheters has not been shown to improve morbidity or mortality in various studies and the risks involved because of the invasive nature has made them less favorable compared to other techniques in many situations.
Placement of Catheter
The PA catheter is inserted in an aseptic technique through the introducer; which is a central venous line usually placed in the jugular or subclavian veins. The catheter is connected to the transducer to check the trace during insertion. Once the catheter is in the right atrium, the balloon at the tip of the catheter is inflated and the flow of blood should direct the catheter towards the pulmonary artery via the right ventricle. The waveform should continuously guide the operator about the position of the catheter (Fig. 1.6). Once the catheter is in the pulmonary artery branch, the balloon wedges and stops flow through the arteriole, hence equilibrating the pressure with the left atrium. This gives the 11estimation of the left heart pressures. Caution should be exercised in insertion and withdrawal of these catheters as serious complications can result including pulmonary artery rupture.
Complications and Precautions
All the complications associated with central line placement can occur while placing the introducer.
During floatation of the PA catheter:
- Atrial and ventricular tachycardia needing urgent intervention
- Vascular injury including pulmonary artery rupture
- Knotting of the catheter
- Misplacement
- Infection
- Valvular rupture/avulsion
- Pulmonary infarction
- Thrombus and embolism (including air embolism)
- Data interpretation and calibration issues.
Golden Tips
- Pulmonary artery catheters are slowly falling out of favor due to poor evidence of benefit and increased risk to the patients
- PA catheters provide direct measurement of a wide variety of hemodynamic parameters and may be useful if used appropriately
Intercostal Drain Insertion
Intercostal drain or tube thoracostomy is performed to drain air or fluid from the pleural space and rarely to introduce medications for chemotherapy or pleurodesis.
Indications and Contraindications
Indications
- Pneumothorax (spontaneous, iatrogenic, traumatic, tension or bronchopleural fistula)
- Hemothorax (trauma, postoperative, malignant)
- Pleural effusion (infection, empyema, malignant, chyle, parapneumonic effusions)
- Others: Pleurodesis, instillation of chemotherapeutic agents.
Contraindications/Cautions
- Coagulation abnormalities
- Anticoagulation
- Transudative effusions like cardiac failure, hepatic or renal failure.
Intracostal Drain Placement
Appropriate patient selection is important. If there is previous history of difficult placement, repeated infections (leading to fibrosis) or history of malignancy, caution should be exercised and ultrasound or CT-guidance obtained. Care must be taken with very large effusions where sudden removal of fluid can cause pulmonary edema. Appropriate size tube should be selected. Small tubes for simple pneumothorax and transudative effusions may be appropriate, but larger tubes are needed for empyema, blood, infected and exudative effusions. Similarly bronchopleural fistulas may need bigger tubes. Seldinger technique can be used depending on the indication and user experience.
Procedure should be explained to the patient, area prepared aseptically and local anesthetic used to reduce discomfort. The 4/5th intercostal space in the anterior/mid axillary line is preferred due to safety (safe triangle) (Fig. 1.7). Ultrasound can be helpful in deciding the site of insertion and depth. Patients arms can be placed above the head for better access. Skin incision is made parallel to intercostal space and subcutaneous tissue and muscles are dissected bluntly with forceps. The insertion should preferably be just above the rib to avoid the neurovascular bundle. Once close to the pleura, the forceps or clamp is used to go through the pleura after checking with a finger. The finger is sweeped to clear the space and check the lung for adhesions and other structures. The tube is then held with clamp/forceps and introduced through the tract and directed appropriately. For pneumothorax, the tube is directed anteriorly, while for hemothorax posteriorly. All the drainage holes should be 13within the pleural space to avoid leaks and subcutaneous emphysema. Once the tube is in place, this should be connected to the closed seal system and sutured securely to the skin. Many different types of seals are available (Fig. 1.8). For better drainage, suction can be applied too (0 to −40 cm H2O).
Chest X-ray is obtained to confirm the location and also the assess lung expansion. Seldinger technique is used in selected patients and is similar to placing the central line. Caution should be exercised as the initial needle insertion can cause lung and vascular injury.
Complications
- Bleeding
- Lung parenchymal injury
- Subcutaneous emphysema
- Injury to the neurovascular bundle
- Pain
- Expansion pulmonary edema with rapid drainage
- Malposition (do not remove till a new tube in place)
- Infection.
Golden Tips
- Use ultrasound or CT scan if small effusion or possibility of difficult insertion
- Use pain relief in the form of systemic painkillers and local anesthetic
- Do not use trocar with sharp tip for insertion as it can result in parenchymal injury
- Malposition is common and new tube should be inserted prior to removal of malpositioned tube
- Limit the drainage to 1–1.5 L initially to reduce the chances of pulmonary edema.
Suggested Reading
- American Society of Anesthesiologists Task Force on Central Venous Access (03/2012). Practice guidelies for central venous access: a report by the American Society of Anesthesiologists task force on central venous access. Anesthesiology (Philadelphia) (0003-3022), 116(3), p 539.
- BTS guidelines for the insertion of a chest drain. Laws D, Neville E, Duffy J, on behalf of the British Thoracic Society Pleural disease group (Subgroup of the British Thoracic Society Standards of Care Committee). Thorax 2003; 58(suppl II): ii53–ii59.
- Fishman R. Cerebrospinal fluid in diseases of the nervous system. WB Saunders. Philadelphia 1980.
- Jubran A. Pulse oximetry. Intensive Care Med. 2004;30:2017–20.
- Shah MR, Hasselblad V, Stevenson LW, et al. Impact of the pulmonary artery catheter in critically ill patients: meta-analysis of randomized clinical trials. JAMA. 2005; 294:1664.
- Swan HJ, Ganz W, Forrester J, et al. Catheterization of the heart in man with use of a flow directed balloon-tipped catheter. N Engl J Med. 1970;283:447.
- Tegtmeyer K, Brady G, Lai S, et al. Placement of an arterial line. http://content.nejm.org/cgi/video/354/15/e13 (Accessed on Feb 10, 2014).
- www.capnography.com; Maintained by Dr Bhavani Shankar Kodali, MD. Accessed on Feb 11, 2014.