Chapter 14 Perioperative monitoring in obstructive sleep apnea hypopnea syndrome
Obstructive sleep apnea hypopnea syndrome (OSAHS) is a prevalent condition resulting from a decrease in upper airway size and patency during sleep. Apneas, hypopneas and episodes of airflow limitation occur during sleep resulting in physiological changes including reductions in oxygen saturation and arousals from sleep. Arousals lead to cessation of the respiratory event, only to be followed by repetitive airflow obstructions and arousals. The arousals cause sleep fragmentation, and secondary daytime symptoms including non-restorative sleep, excessive daytime somnolence, memory loss and other psychometric changes. Arousals also lead to a rise in sympathetic tone, with secondary changes in blood pressure, pulse and cardiac output. In addition to the nocturnal and daytime symptoms, obstructive sleep apnea may contribute to significant complications including hypertension, cardiac arrhythmias, myocardial infarction, and stroke.
Safe perioperative management of patients with obstructive sleep apnea requires special attention to preoperative, intraoperative and postoperative care. These patients are more likely to have hypertension, esophageal and laryngopharyngeal reflux disease, coronary artery disease and obesity. Operative treatment of these patients requires special care due to these co-morbidities.
In addition, anatomical features (retrognathia, micrognathia, macroglossia, tonsil and uvula hypertrophy, nasal obstruction, abnormal epiglottis position, anterior positioning of the larynx, elongation of the airway) and alterations in arousal responses may lead to difficulty with ventilation and intubation. Airway narrowing may predispose to increased risk of complications including intraoperative airway obstruction, postoperative airway obstruction, myocardial infarction, stroke and cardiac arrhythmia. These patients are also prone to complications associated with reducing their arousal response. Anesthetic agents, narcotic analgesics, and sedative hypnotics reduce arousals responses and may lengthen respiratory events, hypoxemia and hypercarbia during sleep thus leading to postoperative airway obstruction, myocardial infarction, stroke, cardiac arrhythmia and sudden death. Obesity may also contribute to deep vein thrombosis and pulmonary emboli. There is growing evidence that sleep apnea is a risk factor for anesthetic morbidity and mortality. These risks are present when undergoing upper airway surgery or any surgical procedure. The care of these patients requires vigilance before, during and after surgery in order to minimize risks associated with their underlying diseases. This chapter discusses these potential complications along with avoidance strategies.
The surgeon must select an operating room with personnel and equipment adequate for an elective and controlled management of the patient’s airway. Preoperative preparation is intended to improve a patient’s medical status and reduce the risk of complications. The literature is insufficient to offer guidance regarding which patients can be safely managed as an outpatient as opposed to an inpatient basis or the appropriate time for discharge from the surgical facility.1
Upper airway surgery in sleep apnea patients can temporarily worsen the sleep apnea and lead to serious and potentially fatal complications, including acute upper airway obstruction, hypoxemia, hypercarbia, myocardial infarction, cardiac arrhythmias, stroke and death. Prevention of these complications requires early detection of pending airway problems. Postoperative monitoring is performed in order to detect and prevent potential complications. While there are insufficient published data, it is assumed that patients with more severe sleep apnea are at greater risk for perioperative complications.
The determination to perform surgery as an outpatient, in an outpatient surgery center with ambulance transfer to a hospital facility, admit for a short extended recovery room stay, admit to a 23-hour unit, regular hospital room or an intensive care unit should be made with consideration of associated co-morbidities, severity of apnea, sites of airway narrowing, type of anesthesia, length of time for anesthesia, need for postoperative narcotic agents, and type of surgery being performed. This determination should be made preoperatively.1 Confusing the matter is the use of the term ‘outpatient’ by some organizations to refer to all surgical stays less than 24 hours and by other organizations to label any stay after midnight as ‘inpatient.’ In a recent report of the American Society of Anesthesiologists,1 consultants were surveyed using a non-validated scoring system about opinions regarding outpatient surgery in patients with OSAS. This survey suggested that a patient with mild sleep apnea undergoing uvulopalatopharyngoplasty (UPPP) or nasal surgery was not at increased risk, while a patient with moderate sleep apnea undergoing UPPP was at increased risk of complications.1
Care should be taken in selecting patients for outpatient procedures. It is my opinion that most patients with mild or moderate sleep apnea undergoing nasal surgery only may safely be treated as an outpatient, while those with severe sleep apnea may require some observation before discharge. Similarly, most patients with mild OSAHS undergoing UPPP or other pharyngeal airway surgeries should at least be observed for several hours prior to discharge, while those with moderate or severe OSAHS should stay as an inpatient or for a longer observation period. The importance of the postoperative observation period is to document the presence or absence of sleep apnea and oxygen desaturation in the patient while sleeping without supplemental oxygen. The need for postoperative monitoring depends upon the procedure performed and associated co-morbid conditions. The quality of the hospital nursing care and skill of the anesthesiologist also have an impact on the level and type of postoperative monitoring. Some facilities can perform continuous pulse oximetry in the extended recovery unit or regular nursing unit, while others require an intensive care unit to administer this same level of care.
The literature is insufficient to evaluate the effects of different anesthetic techniques on surgical outcomes after surgery for OSAS. Since airway reconstructive surgery for sleep apnea causes blood to enter the airway, it would be safest to perform these surgeries under general anesthesia, in order to control and protect the airway. When a patient with OSAS is undergoing non-airway related surgery, then a local anesthesia, or monitored anesthesia care (MAC) would be preferred. If the patient is to undergo any sedation during a non-airway surgery, then oximetry and CO2 monitoring should be used. General anesthesia with a secure airway is preferred if the patient is going to require moderate or deep sedation.
There is an alteration of sleep architecture and frequently sleep deprivation prior to and after surgery, including sleep deprivation due to anxiety about the surgery.2,3 Once surgery is done and these factors are gone, however, the patient is more likely to enter deeper levels of sleep and may be predisposed to more severe sleep apnea.4 It would therefore seem to be beneficial to improve sleep quality as much as possible before and after surgery. When possible, a patient should be asked to use CPAP for several weeks prior to and after surgery and to bring their machine into the hospital for perioperative use. While the majority of patients are undergoing surgery because they cannot tolerate CPAP, even moderate use of CPAP preoperatively may be beneficial.
Use of narcotics, sedative hypnotics and anxiolytic agents should be avoided prior to surgery in a patient with OSAS. These agents have been reported to lead to sudden death, even in the preoperative holding area.5 These drugs suppress respiration, blunt the arousal response and may lead to life-threatening hypoxemia. Benzodiazepine agonists affect upper airway muscle tone and worsen sleep apnea.6 Flurazepam has been shown to increase the Apnea Index7 and triazolam increased the arousal threshold to airway obstruction, apnea and hypopnea duration and oxygen desaturation.8 If a sleep apnea patient requires sedation or an anxiolytic, this necessitates require continuous pulse oximetry, and possibly supplemental oxygen.
Obesity is common in patients with sleep disordered breath-ing, leading to an increased risk of gastroesophageal reflux9,10 which is caused by increased intra-abdominal fat, intra-abdominal pressure and higher incidence of hiatal hernia. Ninety percent of obese patients have greater than 25 ml of gastric fluid prior to surgery, a pH under 2.5 and will be at increased risk of aspiration during induction of anesthesia11 or upon extubation. In order to reduce these risks, obese patients should receive an H2 blocker, proton pump inhibitor or esophageal motility stimulant prior to surgery.12
A consultation with the primary physician, cardiologist, anesthesiologist or other specialist should be considered in patients with complicated co-morbid conditions, or in patients with multiple co-morbidities. For example, a patient with hypertension requiring three antihypertensive agents may require a consultation for medical clearance. A patient with poorly controlled diabetes may benefit from a preoperative clearance. The selection of an internist, cardiologist or anesthesiologist may be based on availability or expertise of the consultant. The purpose of the preoperative clearance is to optimize control of the co-morbidities prior to surgery and to reduce the risk of surgical complications.
Patients with OSAS are at increased risk of hypertension due to an increased sympathetic drive.13,14 Undiagnosed hypertension is common in the sleep apnea patient. Blood pressure screening should be done at the time of initial evaluation or after initial diagnoses of OSAS. If blood pressure is elevated, these patients should be referred for treatment. Blood pressure should again be checked at a preoperative visit to be sure that hypertension is well controlled.
As the head of the surgical team, it is the responsibility of the surgeon to advise the anesthesia team about any potential difficulty with the airway. While it should be assumed that all OSAS patients may be more difficult to ventilate or intubate, there will be some with macroglossia, retrognathia or micrognathia who are going to be particularly challenging. In these patients, the surgeon may wish to have difficult airway instruments in the operating room, a tracheostomy set available or to be ready to assist with a fiberoptic intubation. I have found that patients are typically more difficult to intubate or ventilate if they have Friedman palate/tongue position IV or if the larynx is not visible with a mirror on indirect laryngoscopy.
Prior to surgery, an anti-reflux agent and anti-sialogogue should be administered to reduce the risk of aspiration and reduce saliva production.12 It is important to maintain continuous control of the airway by the anesthesiologist. In order to ventilate the patient, the anesthetized patient will require positive pressure breathing by mask, head and neck extension, jaw protrusion, and insertion of a properly sized oral airway or long nasal airway in order to keep the tongue from falling posteriorly. A two-person ventilation approach may be needed, one for jaw positioning and mask seal and the other for ventilation.15 A 3–5 minute period of ventilation is used to increase oxyhemoglobin saturation and reduce the rate of desaturation, prior to intubation.
A variety of methods are available to maintain ventilation in a difficult airway (Table 14.1). The simplest approach is to insert a long nasopharyngeal airway that extends inferior to the base of tongue. A laryngeal mask airway (LMA) is another excellent way to stabilize the airway and allow ventilation.16,17 The LMA is inserted blindly, and keeps the base of tongue and epiglottis from collapsing posteriorly. Other options require additional equipment and expertise such as use of a rigid ventilating bronchoscope, an esophageal–tracheal combitube, or the placement of a 14 gauge angiocath into the cricothyroid membrane followed by transtracheal jet ventilation.
|Long nasopharyngeal airways|
|Laryngeal mask airway|
|Rigid ventilating bronchoscope|
|Intratracheal jet stylet|
|Transtracheal jet ventilation|
The sleep apnea patient can be a challenge to intubate due to the combination of skeletal deficiency, a long airway, excessive oropharyngeal and hypopharyngeal soft tissue, and a relatively anterior larynx. If easily ventilated, then short-acting paralyzing agents such as succinylcholine may be used. Oral intubation may not be feasible if the larynx cannot be visualized. Alternative methods (Table 14.2) are available for difficult intubations. The safest approach is an awake oral or nasal intubation as the patient continues breathing. A more comfortable approach for the patient is a planned awake transnasal fiberoptic intubation performed with the patient in a sitting or semi-sitting position. Another simple option is the use of a light wand (lighted stilet) inserted into the endotracheal tube, with transcutaneous guidance into the trachea, in a darkened room. If the patient is ventilated through an LMA, then the easiest intubation approach is through the LMA. One of the newest approaches is the use of a video laryngoscope, which has a small video camera on the end, allowing the anesthesiologist to visualize the larynx on a screen. As a result, the endotracheal tube can be guided through the vocal cords, by visualizing the video screen.
|Intubation through laryngeal mask airway (LMA)|
|Blind nasal intubation|
A patient may also require a planned temporary or skinned lined tracheostomy. Planned tracheostomy should be considered in those with severe sleep apnea and failure of CPAP, those with life-threatening cardiac arrhythmias or severe oxygen desaturation,18 or in those with a failed intubation at a prior surgery. Temporary tracheostomy should also be considered if significant postoperative edema is expected. An emergency tracheostomy or cricothyrotomy may be needed if a patient cannot be ventilated or intubated.
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