Obstructive Sleep Apnea: Preoperative Assessment
Section snippets
Prevalence
OSA is the most prevalent breathing disturbance during sleep,9 with an incidence in the general population estimated in the range of 1 in 4 men and 1 in 10 women.10 Moderately severe OSA was present in twice as many men (11.4%) than women (4.7%).11, 12 Aside from male gender predominance, OSA is more prevalent in obese patients; there is a 7 in 10 risk of OSA in patients presenting for bariatric surgery.13
A significant proportion of patients with OSA are undiagnosed before surgery.14 It is
Diagnosis of OSA
The diagnosis of OSA is established by an overnight sleep study or polysomnography. The apnea hypopnea index (AHI) is the number of abnormal respiratory events per hour of sleep. Classically, the accepted minimal clinical diagnostic criteria for OSA are an AHI of 10 plus symptoms of excessive daytime sleepiness (American Academy of Sleep Medicine Task Force 1999). The United States Medicare guidelines diagnose OSA with an AHI of 15, or an AHI of 5 with 2 comorbidities. Canadian Thoracic Society
Comorbidities and predisposing factors associated with OSA
OSA is associated with several comorbidities (Table 1): cardiovascular disease,18 including acute myocardial infarction,19 heart failure,20 arrhythmias,21 hypertension,22 cerebrovascular disease,23 metabolic syndrome,24 obesity, and gastroesophageal reflux.25
Certain patient profiles (male, >50 years old, neck circumference >40 cm), endocrine disorders (Cushing disease, hypothyroidism), connective tissue disorders (Marfan syndrome), lifestyle habits (alcohol, smoking), and anatomic abnormalities
Practical screening of patients with suspected OSA in the preoperative clinic
A large number of surgical patients with OSA are undiagnosed when they present for surgery and anesthesia. Polysomnographic diagnosis of OSA is prohibitive as it is costly and resource-intensive. Therefore, anesthesiologists are in need of a practical preoperative screening tool to identify patients more likely to have true OSA. For safety reasons, the screening tool should have a high degree of sensitivity, at the expense of lower specificity.
In a preoperative survey of elective surgeries, 24%
Nocturnal oximetry and home sleep testing
Nocturnal oximetry may be a sensitive and specific tool to detect OSA in surgical patients. The authors' recent research found that there was a strong correlation between oxygen desaturation index (ODI) from nocturnal oximetry and the AHI from polysomnography.37 ODI greater than 5, ODI greater than 15, and ODI greater than 30 were sensitive and specific predictors for surgical patients with AHI greater than 5, AHI greater than 15, or AHI greater than 30, respectively. The sensitivity was found
Evaluation of patients with suspected OSA in the preoperative clinic
A patient is at high risk of OSA if 2 items or more score positive on the STOP questionnaire, or 3 items or more score positive on the STOP-Bang questionnaire (see Box 1, Fig. 1). Urgent or emergent surgery should not be delayed for the detailed evaluation of suspected OSA. Based on recent research, expert opinion, and the collation of various departmental protocols on OSA, a flow diagram for the suggested preoperative evaluation of a suspected OSA patient is outlined in Fig. 1.
If the high-risk
Evaluation of patients with known OSA in the preoperative clinic
In patients who are known to have OSA, the severity of the sleep disorder may be assessed from the patient history or from previous polysomnography results (see Fig. 1). Long-standing OSA may have systemic complications, which should be ascertained. These complications include hypoxemia, hypercarbia, polycythemia, and cor pulmonale. A simple screening tool in the preoperative clinic may be pulse oximetry. In the authors' opinion, an oxygen saturation value of less than 94% in room air in the
Preoperative PAP therapy
Conventional PAP therapy acts as an airway stent and is the primary treatment of patients with OSA. There are several kinds of PAP devices: continuous PAP, autotitrating PAP, and bilevel PAP. PAP therapy has been shown to alleviate undesirable symptoms of OSA.39 PAP has the potential to reduce cardiac rhythm abnormalities,40 stabilize variability of blood pressure,41 and improve the hemodynamic profile.42 One week of PAP treatment has been shown to improve pharyngeal collapsibility and increase
OSA and difficult airways
Upper airway abnormalities, which predispose to OSA, share a similar etiologic pathway with difficult airways: mask ventilation and tracheal intubation. Snoring and OSA were found to be independent risk factors for difficult or impossible mask ventilation.45 In a retrospective matched case-control study of 253 patients, difficult intubations was found to occur 8 times as often in the patients with OSA versus the control group (21.9% vs 2.6%, P<.05). OSA therefore is a risk factor for difficult
Planning for local, regional, or general anesthesia
The use of local and regional blocks (neuroaxial or peripheral nerve blocks) as a sole anesthetic without sedation may potentially be beneficial to the patient with OSA as it circumvents the issue of upper airway patency in the perioperative period. Based on expert opinion and consensus by consultants, ASA guidelines recommend regional anesthesia rather than general anesthesia for peripheral surgery.33 The ASA guidelines, however, remain equivocal regarding whether combined regional and general
Planning for postoperative analgesia
Optimal intraoperative management encompasses knowledge of the problems associated with OSA, and taking measures to minimize the aggravating effects of anesthesia. Patients with OSA are sensitive to the respiratory depressant effects of anesthetic drugs, in particular opioid analgesic agents. This sensitivity is largely a result of the propensity of airway collapse, sleep deprivation, and blunting of the physiologic response to hypercarbia and hypoxia. Therefore avoidance or minimization of the
Planning for ambulatory surgery
Controversy exists as to whether patients with OSA should be treated on an ambulatory basis. ASA guidelines highlighted that superficial surgeries or minor orthopedic surgery using local or regional techniques and lithotripsy may be performed on an ambulatory basis.33 Considerations include the types of surgeries, the comorbidities, patient age, status (treated vs untreated) and severity of OSA, use of postoperative opioids, type of anesthesia, and the level of home care.33
Based on expert
Planning for inpatient surgery
Depending on the severity of the OSA, the extent of the surgery, and the type of anesthetics administered, and postoperative analgesics required, the patient may shift to the higher end of the risk continuum, increasing the need for step-down care (see Fig. 2). The anesthesiologist should ensure that a postoperative monitored bed is available for a patient with a high AHI undergoing major surgery or airway surgery. A monitored bed refers to an environment with continuous oximetry with the
Summary
In the perioperative setting, OSA is underappreciated, with a high proportion of patients being undiagnosed. Patients with OSA have a plethora of comorbid conditions, and may be associated with less favorable postoperative outcomes. Surgical patients with OSA are vulnerable to the aggravating effects of sedation and opioid analgesia. Adverse outcomes such as episodic sleep-related desaturations and cardiorespiratory arrest may result in extreme cases.
The patient with OSA poses special
Acknowledgments
The authors wish to thank Dr Terence Davidson (San Diego Health Care System University of California, San Diego, CA, USA), Dr Janet Van Vlymen (Kingston General Hospital, Kingston, ON, Canada), Dr Stephen Cohen (Beth Israel Daeconess Medical Center, Boston, MA, USA), Dr Norman Bolden (MetroHealth Medical Center, Cleveland, OH, USA), Dr Michael Bishop (University of California, San Diego, San Diego, CA, USA), and Dr Gregory Bryson (The Ottawa Hospital, Ottawa, ON, Canada) for sharing with us
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