Anesthetic Management of Patient with Obstructive Sleep Apnea
Safe anesthetic management of patients at risk for or who carry a diagnosis of obstructive sleep apnea (OSA) is imperative to guiding this subset of patients through the perioperative period. OSA carries perioperative risk both due to the direct respiratory effects of the disease, comorbidities of patients with OSA, as well as the associated long-term sequelae of patients with untreated or severe OSA. There is a relatively low number of studies examining best practices in anesthesia regarding patients with OSA, so much of the literature and recommendations focus on small studies and expert opinion.
OSA is a disorder where upper airway tissue collapses into the upper airway during sleep, causing periods of apnea or hypopnea that often requires the patient (unbeknownst to them) to wake briefly to catch their breath. It is a quite common disorder, with up to 15-30% of males and 10-15% of females in North America carrying the diagnosis. Risk factors include male gender, obesity, smoking, craniofacial abnormalities, and older age.
The first step for an anesthesia provider in the pre-operative period is to ascertain whether a patient carries a diagnosis of OSA, and if they do not, if they have risk factors for the disorder. If the patient carries an OSA diagnosis and has therefore had a sleep study (which is the gold standard for diagnosis), then the results of that study should be read by the anesthesia provider. Severity of OSA is classified by the apnea-hypopnea index (AHI), which is a scale based on the number of apneic or hypopneic episodes per hour of sleep. Less than 5 events indicates no OSA, 5-15 events is mild, 15-30 is moderate, and greater than 30 is severe. The more severe the disease, the more at risk a patient is both for perioperative morbidity, as well as long-term sequelae of the disease. If a patient is not diagnosed with OSA, there are a number of assessments that can be used to indicate risk. The best combination of sensitivity and specificity is the STOP-BANG questionnaire, which includes a variety of questions (snoring, daytime sleepiness, observed awakenings sleep partner, etc.). There are seven total questions, and a confirmatory answer to three or more questions indicates a high risk of OSA.
The most important aspect of an anesthesia provider’s pre-operative assessment and perioperative plan is being aware of the risks factors associated with long-standing or untreated OSA; these include hypertension, coronary artery disease, heart failure, arrythmias, and stroke. Patients with OSA and pulmonary disease are also at particular risk for pulmonary hypertension. As a result, in a patient with OSA, functional status is an essential part of the preoperative evaluation, and cardiac catheterization or transthoracic echocardiography may be indicated prior to surgery as well.
Once a pre-operative assessment is complete, OSA patients have a higher risk of a number of intraoperative difficulties. OSA patients are often obese, and as a result can be difficult intravenous access, high aspiration risk, and can have difficult airways, with a particularly high risk of being difficult to mask ventilate. As a result, avoiding general anesthesia using regional techniques can and should be used when possible. However, even mild to moderate amounts of sedation can be risky in OSA patients, as they by definition have airways that obstruct quite easily. When general anesthesia is required, an RSI may be indicated depending on the patient’s weight and comorbidities, and in other circumstances an awake fiberoptic intubation may be the safest approach.
Post-operatively, hypoventilation is the most important concern for OSA patients. Patients with OSA tend to be sensitive to narcotics, and as stated above, obstruct their airways easily. This combination can be devastating if high doses of narcotics are used, so this should be avoided during surgery and afterwards. In addition, moderate to severe OSA patients are not good candidates for same day surgery, and should be monitored in a hospital setting postoperatively until the effects of anesthesia have completely worn off. The use of CPAP in OSA patients post-operatively has been studied without clear conclusions, but positive pressure ventilation techniques should, at the least, be readily available to post-operative providers.
References:
Chung et al. Society of Anesthesia and Sleep Medicine Guidelines on Preoperative Screening and Assessment of Adult Patients With Obstructive Sleep Apnea. Anesth Analg. 2016 Aug;123(2):452-73. doi: 10.1213/ANE.0000000000001416.
Okoronkwo U. Ogan, M.D.; David J. Plevak, M.D. Anesthesia Safety Always an Issue with Obstructive Sleep Apnea. APSF Newsletter. Volume 12, No. 2, 1997.