Yearbook of Anesthesiology-4 Raminder Sehgal, Anjan Trikha, Baljit Singh
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Anesthetic Management of Patients with Obstructive Sleep ApneaCHAPTER 1

Rashid M Khan,
Saba Khan,
Naresh Kaul
 
INTRODUCTION
Obstructive sleep apnea (OSA) is a breathing disorder that is characterized by periodic cycles of apnea and hypopnea during sleep. It is caused by depression of the pharyngeal muscle tone leading to partial or complete collapse of the pharyngeal structures thereby causing airway obstruction.1
Definition of hypopnea and apnea is when airflow is reduced by >50% and 100% respectively that lasts for >10 seconds leading to oxygen desaturation of >4%.2 This repetitive upper airway obstruction usually results in oxygen desaturation and arousal from sleep. A constellation of symptoms resulting in sleepiness during daytime, loss of memory, feeling tired despite having slept, impaired concentration, fatigue and morning headaches are labeled as ‘OSA syndrome’.
 
EPIDEMIOLOGY
Western data suggests that the incidence of OSA is 25% in males and 10% in females, respectively for mild OSA,3,4 while it is 11% and 5% in males and females, respectively for moderate OSA.5,6 In India, nearly 19.5% of urban men between 35–65 years have OSA.7 Nearly similar findings were observed by others8 who reported the prevalence of OSA in Indian male as 19.7% and female as 7.4%. A relatively recent data from New Delhi reported the prevalence rate of OSA as 9.3%. Incidence of OSA was 13.4% in males and 4% in females.9 These data suggest that the incidence of OSA in Indian population is quite identical to that reported in the west.
 
PATHOPHYSIOLOGY
Collapse of the pharyngeal airway is mainly responsible for apnea during sleep or anesthesia. Chances of this collapse are maximum during rapid eye movement of natural sleep. It is in this state of sleep that a decrease tone occurs2 in the pharyngeal dilator muscles (genioglossus and geniohyoideus). In obese patients, increased adipose tissue in the neck and pharyngeal tissues narrows the airway. This predisposes the airway to close during sleep. In non-obese patients, hypertrophy of the tonsils or craniofacial skeletal abnormalities (for example Down's, Treacher-Collins and Pierre-Robin syndrome) may lead to airway narrowing and sleep apnea.
During awaken state, neural control mechanisms generate sufficient pharyngeal dilator muscle tone in OSA patients to overcome the collapse of relatively smaller upper airway. This prevents apneic spells during awake state. However, sleep and anesthesia substantially attenuate pharyngeal dilator muscle activity. OSA generally develops by this combination of altered anatomical structure and neural compensatory mechanisms.
It appears that genetic constitution of OSA patient also has a role to play. This disorder is seen more commonly in patients with a family history of OSA. Smoking has also been implicated in the development of OSA. The causative factor lies in chemical irritants present in smoke that produce inflammation of the soft tissue in the upper airway. This inflammation promotes fluid retention that leads to narrowing of the upper airway and subsequent symptoms of OSA.
Temporary periods of OSA are not unknown. This may be observed in individuals who suffer from upper respiratory infection that results in the congestion of the nose, along with swelling of the throat, or enlarged tonsils. During acute infection, the Epstein-Barr virus has also been incriminated to produce symptoms of OSA by increasing the size of lymphoid tissue with resultant narrowing of airway. The obstructive sleep apnea may also be observed in patients suffering from severe infectious mononucleosis. Individuals who consume alcohol or drugs such as heroin and other narcotics may also suffer from temporary spells of OSA syndrome. Both drugs (heroin, narcotics) and alcohol may produce relaxation of body tone and suppress wakefulness that could interfere with normal arousal from sleep mechanisms during this temporary period of OSA.
 
Effect of OSA on Other Body Systems
Sleep apneic spells results in deprivation of sleep and periods of hypoxemia that may be responsible for numerous health risks such as cardiovascular disease, hypertension,10 stroke,11 diabetes, clinical depression,12 weight gain and obesity. After periods of prolonged and neglected OSA, patients may develop congestive heart failure or cor pulmonale as a result of chronically increased pulmonary vascular resistance.
 
PREANESTHETIC EVALUATION
Interestingly, such as hypertension, a high proportion of patients coming for elective surgery remain undiagnosed of their OSA status.13 When subjected for screening, 24% of patients coming for surgical procedures were found to be at high-risk of OSA. The 81% of these patients remained undiagnosed previously.14,15
It is this high incidence of undiagnosed OSA with all its deleterious anesthetic implications, which makes it necessary for us to screen our patients for OSA3 as a part of routine preoperative evaluation. Some of the important screening methods are:
 
The STOP-BANG Assessment Method
The STOP-BANG assessment method is a readily adoptable questionnaire that should be included in routine preoperative evaluation to identify unrecognized OSA.16
The STOP-BANG model consists of eight items that would consume less than 5 min time by the assessor:
S How loudly do you Snore? Is it loud enough to be heard across closed doors?
T Is it common for you to feel Tired or fatigued during the daytime?
O Has it been Observed by anyone that you stop breathing during sleep?
P Is there a history of high blood Pressure, with or without treatment?
B Patient having Body mass index (BMI) >35 kg/m2
A Age >50 years
N Neck circumference >40 cm
G Male Gender
Of these 8 items, patients who are positive for up to 2 items may be at low risk. Those having 3-4 items are at intermediate risk and 5-8 items at high risk of OSA.17
STOP-BANG questionnaire is useful in planning safe anesthesia and surgery:18
  • Patients with score of 0-2 on STOP-BANG face no risk of OSA. They do not require any special care during routine anesthesia and surgery.
  • Patients with STOP-BANG score of 3-4 may undergo surgery and anesthesia without any further testing. However, one needs to take precautions during the perioperative period (discussed under risk reduction strategy).
  • For patients with co-morbid diseases) and with STOP-BANG score between 5-8 posted for major elective surgery, a fresh re-evaluation is necessary by the sleep physician. On occasions, it may become necessary to postpone elective surgical procedures to allow adequate evaluation and optimization of severe OSA.
 
Epworth Sleepiness Score
Epworth Sleepiness Score:19 This is another widely used assessment scale for screening OSA patients. In this, a list of eight social circumstances during which there is increased likelihood that the person will fall asleep is rated on a four-point scale (0 = would never dose, 1 = Slight chance of dosing, 3 = Moderate chance of dosing, 3 = High chance of dosing). The eight social circumstances are:
  1. Sitting and reading
  2. Watching TV
  3. Sitting, inactive in public places such as theater or meetings
  4. As a passenger in a car for an hour without a break
  5. Lying down to rest in afternoon when circumstances permit
  6. Sitting and talking to someone4
  7. Sitting quietly after lunch without alcohol
  8. In a car, while stopped for a few minutes in traffic.
A score less than 10 is normal, score greater than 12 signify sleep disorder while a maximum score of 24 is definite OSA.
 
Muller's Maneuver
This is technically easy, inexpensive and widely used test to identify the location of upper airway obstruction and severity of the disease. However, a recent review of literature on this subject has questioned its creditability.20
In this maneuver, the patient is asked to inhale with his mouth close and nostril plugged except for a flexible fiberscope in hypopharynx. The person viewing via the fiberscope witnesses the area of collapse and identifies weakened sections of the airway. A positive test result means that the site of upper airway obstruction is below the level of soft palate. The anesthetist can use this information in deciding whether the patient shall benefit from a nasopharyngeal or oropharyngeal airway, if airway obstruction is encountered during facemask ventilation.
 
Polysomnography
An overnight polysomnography or sleep study is an essential requirement for confirming the diagnosis of OSA. Polysomnography is a time consuming study. It may need upto 30-60 min set-up time before sleep and about 30 min time in the morning for detaching the electrodes, leads and ancillary equipment. All this mandates that the staff responsible for the study be available for at least ten hours overnight to perform and monitor this test. Another four hours may be needed to analyze the results. Thus this test should not be taken casually as it requires significant equipment and personnel resources. The study results give us the apnea hypopnea index (AHI). The AHI is defined as the mean of abnormal breathing events per hour of sleep. The AHI is used to confirm the presence of OSA. The diagnostic criteria for establishing OSA by the American Academy of Sleep Medicine for OSA requires either an AHI ≥15, or AHI 5–15 but with symptoms. These symptoms may include sleepiness during daytime, observed obstruction during sleep or loud snoring.21 On the other hand, diagnosis of OSA is made by the Canadian Thoracic Society when polysomnography shows AHI ≥5, plus daytime sleepiness or at least two other symptoms of OSA (e.g. gasping or choking during sleep, intermittent awakenings, poor quality sleep, daytime fatigue).22 Severity of OSA is graded as mild, moderate or severe when the AHI is between 5-15, 15-30 or more than 30, respectively.
 
Identifying Comorbidities
In addition to the above eight items and sleep apnea testing where available, one should also look for signs and symptoms associated with the development of systemic complications of OSA, such as hypoxemia, hypercarbia, polycythemia and cor pulmonale. It is essential that one attempts to identify other comorbid conditions in these patients, such as morbid obesity, poorly or uncontrolled5 hypertension, dysrrhythmias, metabolic syndrome, cerebrovascular disease, and congestive cardiac failure. OSA may be seen in 78% of patients with morbid obesity.18 In addition to obesity, there are numerous other factors that predispose to OSA. These may be patients with anatomical abnormalities, such as craniofacial deformities, macroglossia, and retrognathia. All of these abnormalities result in mechanical reduction in patient's airway diameter. Endocrine diseases are also associated with OSA, such as Cushing disease and hypothyroidism. One should be suspicious of OSA in patient with connective tissue diseases such as Marfan syndrome. The OSA is more likely in male patients, those above 50 years, or who have neck circumference >40 cm, and are smokers or consume alcohol.23
 
Miscellaneous Tests
One can perform a simple bedside test using pulse oximetry in the preanesthetic clinic to predict postoperative complications in patients with OSA. Patients showing oxygen saturation of ≤94% on room air without any known cause suggests prolonged duration of severe OSA. These patients are often associated with adverse postoperative outcome.24
Some other tests that can be done during preanesthetic assessment may include: awake indirect laryngoscopy, radiographic cephalography, and arterial blood gas analysis. Advance tests such as dynamic MRIs and CTs are also useful imaging aids in the diagnosis of patients with OSA.
Some of these patients may be receiving positive airway pressure (PAP) support with devices such as continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), or the more advanced machines such as the automatically adjusting positive airway pressure (APAP) machines. Detailed history of this should be elicited during preanesthetic assessment. One may have to refer these patients for reassessment by a sleep medicine physician for revision of PAP strategy. It is important to note the current PAP therapy settings of these patients. It is advisable that patients receiving routine PAP therapy for moderate or severe OSA continue to use it perioperatively.25 Generally, the pressure requirements range from 5–20 cm H2O, depending on the severity of the obstruction.
 
ASSESSING THE PERIOPERATIVE RISK AS PER GRADE AND SEVERITY OF OSA
The American Association of Anesthesiologists Obstructive Sleep Apnea Guideline26 under the supervision of Benumof developed the following scoring system to estimate the perioperative risk in patients with OSA. It takes into consideration the following points:
  • Sleep apnea severity based on AHI or clinical indicators, if sleep study is not available: none = 0; 1 = mild OSA; 2 = moderate OSA; 3 = severe OSA. Subtract a point, if the patient has been on CPAP or bilevel positive airway pressure (BiPAP) prior to surgery and shall continue to do so during the postoperative period. On the other hand, patient with mild or moderate OSA with PaCO2 >50 mm Hg should have a point added to his/her score6
  • Nature of surgical procedure and anesthesia: 0 = superficial surgery under local or peripheral nerve block anesthesia without sedation; 1 = superficial surgery with moderate sedation or general anesthesia or peripheral surgery under central neural block (with no more than moderate sedation); 2 = peripheral surgery with general anesthesia or airway surgery with moderate sedation; 3 = major surgery under general anesthesia or airway surgery under general anesthesia
  • Postoperative opioids requirement: 0 = none; 1 = low dose oral opioids; 2 = moderate dose oral opioid; 3 = high-dose oral opioids or parenteral or neuraxial opioids.
To calculate the perioperative risk, look at the total score that includes sum of A + B + C. This total score may range from 0-9. Patients with cumulative score of 4 or greater carry increased risk of perioperative complications from OSA.
This scoring system also helps to decide suitable candidate for ambulatory surgery. Patients having overall score 5 or more should not be considered for ambulatory surgery.
 
SURGERY AND OTHER MEASURES ADVOCATED FOR HELPING PATIENTS WITH OSA
Today we have devices that help to advance the mandible. These devices are found to be useful for mild OSA. These devices help to position the mandible forward, displacing the tongue away from the posterior pharyngeal wall with resultant opening of the collapsed airway. Uvulopalatopharyngoplasty, a much advocated technique in the past to alleviate symptoms of OSA is no longer performed. Patients who have had this procedure previously should still be considered to have OSA and remain at risk of perioperative complications. Preoperative weight loss should be strongly recommended especially when the patient is obese.
 
ANESTHETIC TECHNIQUE
By adhering to the following simple stepwise strategies one can deliver safe anesthetic to these patients with OSA.
 
Premedication
Sedative premedication should be avoided, psychological counseling to be encouraged.27 Alpha-2 agonists (dexmedetomidine) should be considered as pain adjuvant in these patients. They not only reduce anesthetic requirement but also help to avoid or reduce need for opioid.28
Patients with OSA are known to have hypotonia of the lower esophageal sphincter. This results in gastresophageal reflux disease29 with possibility of silent regurgitation and aspiration. It is therefore advisable to take necessary steps to reduce the risk of gastric acid aspiration. This may include using proton pump inhibitors and antacids in the preoperative period. Rapid sequence induction and cricoid pressure is often indicated. However, remember that application of cricoid pressure may make mask ventilation and tracheal intubation difficult.7
 
Perioperative Monitoring
Monitoring modalities are determined by known medical conditions. Besides the routine monitoring, if the patient with sleep apnea has morbid obesity, an intra-arterial catheter may be helpful, if noninvasive blood pressure monitoring is unreliable or not possible for technical reasons. Transesophageal echocardiography may be useful in selected patients with sleep apnea because it can provide insight into heart function and pulmonary artery pressures.
 
Airway Management
Difficult mask ventilation should always be anticipated.30 Mask ventilation may require two anesthesia providers using two or three-handed bilateral jaw thrust and mask seal. Remember that difficult tracheal intubation is eight times more common in patients with OSA.5 This necessitates the presence of skilled airway management person and alternative equipment for these patients.
The patient should be preoxygenated employing 100% oxygen with CPAP of 10 cm H2O for 3–5 min. Maintain head-up tilt of 25-degree or a ramped position (ramp from scapula to head to achieve an anatomical position where a horizontal plane between the sternal notch and the external auditory meatus is established especially, if patient is obese) during preoxygenation. This has been reported to achieve higher end-tidal concentrations of oxygen31,32 and favors tracheal intubation.
The OSA is a known risk factor for difficult intubation.31 Development of airway obstruction is always possible in these patients, and the necessity for emergency airway management, even during the initial phases of establishing a secure airway, must be kept in mind. One should be prepared for difficult tracheal intubation. A difficult airway cart with oro- and nasopharyngeal airways, fiberoptic bronchoscope, laryngeal mask airway, intubating stylets and bougies, and a tracheostomy kit should be arranged and kept nearby. Careful dosing of medications, especially sedatives and analgesic agents, is essential. It is prudent to have an assistant who is versatile in airway management techniques.
 
Induction and Maintenance of Anesthesia
The OSA patients are unduly sensitive to volatile agents, intravenous induction agents, anxiolytics and opioids. Adopt incremental use of these agents rather than use of bolus dose. Titrate inhaled anesthetic using end-tidal concentrations (0.7–1.3 minimum alveolar concentration values) and propofol based total intravenous anesthesia using bispectral index monitoring to prevent intraoperative awareness with recall.
These patients are sensitive to the respiratory depressant effects of sedative drugs. It is therefore essential to have a complete washout of volatile agents prior to extubation. Propofol, remifentanil and desflurane should be preferred because of their short duration of action, if available. Sevoflurane is another safe alternative.
Preference should be given to the use of non-steroidal anti-inflammatory drugs, cyclo-oxygenase-2 inhibitors, tramadol, paracetamol, and adjuvants such8 as pregabalin and gabapentin intraoperatively. They are helpful in reducing intra- and postoperative opioid requirements. It has observed that the OSA patients receiving opioids intraoperatively were 12–14 times more susceptible to oxygen desaturation postoperatively.33
Finally, it should be remembered that the OSA patients may have down-regulation of alpha- and beta-receptors and may not respond appropriately or as expected to vasoactive substances.
Be judicious in the use of muscle relaxants intraoperatively as even minor degree of residual neuromuscular blockade can increase postoperative morbidity. At the conclusion of surgery, the dose of neostigmine should be titrated to the degree of residual neuromuscular blockade as judged by the peripheral nerve stimulator. It is more appropriate to monitor the adductor pollicis for train-of-four (TOF) ratio as against orbicularis muscles of the forehead. Monitoring the later has more than 5-fold higher risk of postoperative residual paralysis than those who had monitoring of the former.34
 
Tracheal Extubation
Great caution needs to be exercised during tracheal extubation of these patients. Adverse respiratory events are more commonly observed in patients receiving muscle relaxant with an intermediate duration of activity.35 In the post-extubation period, even minor degree of residual neuromuscular blockade can lead to increased risks of aspiration and other adverse events such as airway obstruction, hypoventilation, and hypoxemia. A greater incidence of re-intubation is also noted in such patients.36 Patients should be extubated only when TOF ratio is more than 0.9 and the patient is fully conscious. Following tracheal extubation, patient should be nursed in a semi-upright or lateral position.
 
Local and Regional Anesthesia Techniques
These are preferred in patients with OSA as they avoid airway instrumentation and the postoperative analgesic requirement is reduced.25 Capnography should be used for monitoring ventilation in OSA patients undergoing monitored anesthetic care for their surgical procedures. Some of the OSA patients are receiving PAP therapy at home. Such patients may require the use of their PAP devices while undergoing surgical procedures under mild-to-moderate sedation.37
 
Postoperative Analgesia
A multimodal approach to analgesia should be employed to restrict the use of opioids postoperatively. Opioid sparing agents such as alpha-2 agonists (clonidine, dexmedetomidine), NSAIDs, and other modalities (e.g. ice, transcutaneous electrical nerve stimulation) should be considered in conjunction with other techniques of analgesia such as wound infiltration, peripheral nerve block catheters and infusions via epidural catheters with local anesthetic agents alone. In case postoperative, parenteral opioids are unavoidable, one should strongly consider patient controlled analgesia. If this postoperative analgesia modality is selected, care should be taken that there is no basal infusion and9 per hour dose is limited. This may help reduce the total amount of opioid used. One should remember that OSA patients might have an upregulation of the central opioid receptors secondary to recurrent hypoxemia. This up regulation makes them more susceptible to the respiratory depressant effects of opioids. In addition, supplemental oxygen should be provided to OSA patients, if they are receiving parenteral opioids.38 In addition, the Anesthesia Patient Safety Foundation advises that ventilation of OSA patients should be monitored for the early detection of hypoventilation, if they are receiving supplemental oxygen.39
 
Postoperative Period
The postoperative phase is equally vulnerable period for patients with OSA. Patients in the recovery room (RR) are prone to adverse respiratory events such as: (1) apneic spells ≥10 seconds, (2) respiratory rate <8 breaths/min, (3) poor correlation between pain and sedation, or (4) oxygen desaturation <90% off and on.
Keeping these in mind, it is advisable to extend RR observation of OSA patients with continuous pulse oximetry for extra 30-60 minutes in a quiet undisturbed environment after having met the modified Aldrete or any other criteria for discharge.40,41
Several advances have been made in the postoperative monitoring modalities. Today we have multiple parameters monitoring equipment that can keep a continuous track of patient's cardiorespiratory parameters. These monitors are programmed to analyze trends as per prefed algorithms. Adopting this technology will certainly improve early detection of at-risk patients in the recovery phase. In addition, these sophisticated monitors shall help in reducing the frequency of false alarms as well as providing a safe postoperative period for the patients.39,42
OSA patients require continued vigilance once they are discharged from the RR. Patients with severe OSA should not be transferred to the ward but should be nursed in high dependency unit for the first 24 hours. Moderately severe OSA patients who need opioids for pain relief may be managed in a regular surgical ward provided, it has the facility for continuous oximetry. Patients with mild OSA require routine ward care in the postoperative period.18 It is essential to continue PAP therapy postoperatively in patients who have been using it at home.
Lastly, one should remember that when supplemental oxygen is delivered to these patient in the postoperative period, it makes them more susceptible to longer periods of apneic spells. In addition, it may interfere in detecting atelectasis, hypoventilation by pulse oximetry and even short spells of apnea. If necessary, close monitoring is advocated and this aspect should be kept in mind.
 
DAYCARE (AMBULATORY) SURGERY AND OSA PATIENT
OSA patients having well optimized co-comorbid conditions and who comply with their PAP therapy may be considered for ambulatory surgery. However, patients using PAP devices should be advised to continue with their PAP therapy even during daytime naps in the days following surgery. Patients with severe OSA having poorly optimized co-morbid conditions should not be considered for ambulatory surgery.43,44 All OSA patients can be discharged home after daycare10 surgery at the discretion of the attending physician and must be escorted home by a reliable adult.
 
OSA IN PEDIATRIC PATIENTS
The etiopathogenesis of OSA is somewhat different in pediatric population. In this age group, enlarged adenoids or tonsils are the most common cause of OSA. One should therefore be vigilant for encountering these patients during ENT list.
Preanesthetic assessment should include questioning of parents about a history of snoring and breathing pattern in their child. Snoring tends to be continuous and parents often note that their child breathes through an open mouth. In this population, hypopnea is more frequent than apnea. These children may show aggression, irritability, loss of concentration in studies, and letharginess due to sleep disruption.
Confirmation of OSA diagnosis often rests on the findings of overnight pulse oximetry. This is not only cheaper but an easier alternative to polysomnography.
It should be always remembered that children with OSA have a diminished ventilatory response to CO2. This mandates extravigilance in the postoperative period. Like adults, these children also have a heightened sensitivity to opioids. It is recommended that children under two years of age be monitored overnight in intensive care or high dependency unit postoperatively, and that all children under three years should be admitted to the ward. Only children over three years old could be considered for discharge on the day of surgery. It is advisable that these children avoid supine position in the first few postoperative days.

KEY POINTS

  • Prevalence of obstructive sleep apnea (OSA) in Indian males is 19.7% and in females, it is 7.4%
  • Collapse of the pharyngeal airway results in apnea during sleep or anesthesia
  • OSA results in numerous health risks such as hypertension, congestive heart failure, cor pulmonale, stroke, diabetes, clinical depression, weight gain and obesity
  • High incidence (81%) of unrecognized OSA, mandates that all patients are adequately screened in the preanesthetic clinic
  • Regional anesthetic techniques should be preferred, where applicable
  • If general anesthesia is unavoidable, rapid and clear-headed recovery with early return of the patient's protective airway reflexes should be ensured
  • Postoperatively, avoid opioids, employ a multimodal postoperative analgesia and consider using continuous positive airway pressure (CPAP).
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