Authors: Girish P. Joshi, M.B.B.S., M.D., FFARCSI
ASA Monitor 07 2017, Vol.81, 16-18.
Girish P. Joshi, M.B.B.S., M.D., FFARCSI, is Professor of Anesthesiology and Pain Management, University of Texas Southwestern Medical Center, Dallas.
Sleep-disordered breathing (SDB) includes obstructive sleep apnea (OSA), central sleep apnea and obesity hypoventilation syndrome.OSA is an increasingly common disease1,2 of particular concern to anesthesiologists as it is associated with increased perioperative complications.3 It is estimated that the prevalence of OSA in the United States is on a rise probably because of the aging population and increase in obesity. However, another possibility could be related to the liberalization of OSA definition (i.e., use of a lower threshold for defining hypopnea).2 The apnea-hypopnea index (AHI), which comprises the number of apneic and hypopneic events per hour, is used to diagnose and determine the severity of OSA. OSA is common in patients with heart failure, atrial fibrillation, diabetes mellitus and chronic obstructive pulmonary disease. Therefore, it is suggested that OSA should be considered as a spectrum of diseases characterized by a severity spectrum akin to systemic blood pressure or cholesterol levels, rather than a diagnosis with rigid AHI cutoff.2 Nevertheless, it appears that moderate to severe OSA, defined as an AHI of >15, appears to be clinically relevant. Therefore, individuals with mild OSA (AHI <15) and at low risk for comorbidities could be treated conservatively.2
Several systematic reviews have found increased post-operative complications in OSA patients.3,4 However, one of the major limitations of these studies is that the definitions of complications are varied. Also, some studies used desaturation to assess the complication rate, but its clinical significance is questionable, as desaturation without a need for an intervention may not have any clinical consequence, similar to hypoxemia that occurs in this patient population during sleep. Therefore, any study that does not assess need for interventions such as non-invasive ventilation, tracheal intubation and mechanical ventilation, and transfer to intensive care unit should not be considered clinically relevant.
So how do we prevent perioperative complications in OSA patients? The first step is to screen all patients who would receive sedation/analgesia or anesthesia. It is well recognized that almost 70 percent of patients with OSA are oblivious to their ailment. Although there are several screening tools, the STOP-BANG questionnaire is the most commonly utilized.4 –6 Identifying OSA patients prior to surgery heightens the index of suspicion and prompts implementation of risk-modification strategies.
It is clear that intraoperative anesthetic care influences not only the immediate postoperative outcome (e.g., delayed emergence) but also increases postoperative morbidity (e.g., postoperative pulmonary complications). The drugs commonly used during sedation/analgesia and anesthesia (i.e., sedative-hypnotics, opioids and muscle relaxants) reduce upper-airway muscle tone, ventilatory response to hypoxia and hypercarbia, and may worsen or even induce OSA.1 Because these drugs inhibit arousal responses that protect against asphyxia, OSA patients are at a risk of life-threatening apnea. In addition, the residual effects of these drugs might cause pharyngeal dysfunction and respiratory-swallowing discoordination7 as well as delayed gastric emptying,8 which may increase postoperative aspiration risk.9,10 Also, post-operative hypoventilation, which is common in obese and OSA patients, can result in reanesthetization and associated cardiorespiratory complications.11
Routine use of premedication with midazolam should be avoided, particularly in OSA patients who are older and morbidly obese and those with significant comorbidities.12,13 In addition, when possible, local/regional anesthesia should be preferred, as it avoids the residual effects of anesthetic drugs. If general anesthesia is deemed necessary, shorter-acting drugs, with rapid metabolism and elimination, should be used at the lowest possible dose (i.e., avoid deep anesthesia). In fact, this approach should be taken for all patients, not just OSA patients. In recent years, nitrous oxide has been commonly avoided despite its several benefits, including rapid elimination.14 Recent evidence from large, randomized, controlled trials confirm that the reasons given to avoid nitrous oxide (e.g., increase in nausea and vomiting) are not valid in current clinical practice in which routine antiemetic prophylaxis has become a standard of care.15 Therefore, nitrous oxide should be used in most cases, as it allows reduction in inhaled anesthetic and opioid requirements resulting in lower risk of residual effects of these drugs. Overall, there is no convincing reason to routinely avoid nitrous oxide. Postoperative pulmonary complications associated with residual muscle paralysis (train-of-four ratio <0.9) are well described.16 Therefore, muscle relaxants should be used sparingly and deep paralysis should be avoided unless absolutely necessary. In addition, appropriate reversal of neuromuscular blockade is of critical importance. This requires proper monitoring of neuromuscular function.16
Most important, it is critical to limit or avoid opioids during both the intraoperative and postoperative period because they are the biggest culprits in inducing complications in this patient population. Therefore, it is necessary to use non-opioid analgesics such as local/regional analgesia, acetaminophen and non-steroidal anti-inflammatory drugs whenever possible.17 Several questions still need to be answered. For example, is there a dose relation between opioid use and OSA-related complications? Is simply avoiding opioids an answer for preventing OSA-related perioperative complications? How do other factors that might influence OSA in the immediate postoperative period, such as surgical stress-induced sleep pattern disturbances, influence outcome?
“So how do we prevent perioperative complications in OSA patients? The first step is to screen all patients who would receive sedation/analgesia or anesthesia. It is well recognized that almost 70 percent of patients with OSA are oblivious to their ailment.”
At the end of surgery, it is important that tracheal extubation is performed when the patient is completely awake (i.e., appropriately responding to verbal command). In the immediate postoperative period, patients should be maintained in head-up position when possible. Also, they should be closely monitored for respiratory depression and apneic events as well as pain and sedation mismatch. Occurrence of such events suggests that the patient has a high likelihood of complications after discharge from the recovery room. Patients experiencing persistent hypoxemia may benefit from positive airway pressure (PAP) therapy, and should be considered. However, PAP therapy may not be tolerated. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) administers warmed humidified nasal O2 at a rate of up to 70 L/min.18 It is increasingly used in the postoperative period as it provides a low-level positive airway pressure, which keeps the upper airway open and improves oxygenation. Patients experiencing obstructive events or hypoventilation combined with severe hypoxemia should be monitored after discharge from the recovery room (e.g., oximetry, capnography, minute ventilation, respiratory rate), particularly if they are to receive parenteral opioids.
In summary, patients with moderate to severe OSA with inadequately treated comorbid conditions are at a greater risk of complications. Increased awareness of the presence of OSA should modify perioperative care. Use of procedure-specific clinical pathways that include perioperative risk stratification and risk modification strategies should reduce perioperative complications in this patient population.
SASM Is Growing
The Society of Anesthesia and Sleep Medicine (SASM) is a relatively new but rapidly growing group of anesthesiologists, sleep physicians, scientists and other health care professionals. The mission of SASM is to advance standards of care for clinical problems shared by anesthesiology and sleep medicine, including perioperative management of patients with SDB, and to promote interdisciplinary communication, education and research in matters common to anesthesia and sleep.
The objectives of SASM are to:
- ■ Encourage the cross-fertilization of ideas between anesthesiology and sleep medicine.
- ■ Promote clinical and epidemiological studies determining the associations between SDB and perioperative risk.
- ■ Examine methods of minimizing perioperative risk of upper-airway obstruction or ventilatory insufficiency in predisposed individuals.
- ■ Explore the use of non-invasive positive airway pressure therapies to prevent and treat perioperative upper-airway obstruction or hypoventilation.
- ■ Stimulate research examining the relationships in respiratory, neurophysiological, neuropsychological and neuropharmacological function between anesthesia and sleep.
SASM consists of motivated members interested in advancing the science of sleep and SDB and their interactions with anesthesia as well as improving clinical outcomes in patients with SDB subjected to sedation/analgesia and anesthesia. The collaborative efforts of the members should give rise to unlimited opportunities in perioperative care of patients with SDB. The SASM annual meeting is held every year just prior to the ASA annual meeting. Details regarding membership and the meeting are available on the SASM website at www.sasmhq.org. Finally, as SASM President, I personally invite you to attend the SASM meeting in Boston.
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