Obstructive sleep apnoea – debunking the myths
OBSTRUCTIVE SLEEP APNOEA – DEBUNKING THE MYTHS: ANAESTHESIA
JA Loadsman
Royal Prince Alfred Hospital, Camperdown, NSW
Issues to consider:
- Obesity or OSA? Which causes the perioperative problems?
- Is the perioperative risk of OSA (per se) given the prevalence, especially in elderly, really all that bad?
- Do standard definitions of OSA severity apply perioperatively?
- Suitability of OSA sufferers for outpatient surgery/anaesthesia?
Myth: “60-90% of persons with OSA are obese” (Benumof, 2004)
OSA and obesity are not the same thing. Approximately 41% of people with obstructive sleep apnoea (OSA) are obese, rising to 58% for moderate or worse OSA (Young, 2005). Additionally, the association between obesity and OSA is weaker in Polynesian, Asian and African(-American) populations, the latter being 2-2.5 times more likely than Caucasians to have severe OSA independent of BMI and other confounders (Young, 2002). While there is certainly an association between OSA and obesity, it is important to separate obesity and OSA in terms of their impact on anaesthetic risk. Is OSA, per se, a significant anaesthetic risk factor? Morbid obesity certainly causes problems with airway management etc but OSA, by itself, probably does so much less commonly.
Myth: A diagnosis of OSA infers considerable anaesthetic risk.
“…disastrous respiratory outcomes during the perioperative management of patients with OSA are a major problem for the anesthesia community” (Benumof, 2004) . Dire warnings like this are not uncommon in the literature. It appears to be a fairly gross exaggeration. 1 in 5 adults has OSA (using standard definitions). 1 in 15 adults has at least moderate OSA. The prevalence is 2-4 times higher again in elderly subjects, 80% and 49% of people over 70 years of age having apnoea/hypopnoea indices (AHI) greater than 5 and 15/hour respectively in one large study. Most of these patients are undiagnosed and remain so throughout their surgical admissions. If the risk of perioperative morbidity and mortality associated with OSA, defined according to standard criteria, was significant, we would be killing people all the time! Fortunately that is not the case. What this probably means is that other factors play a significant role in perioperative problems associated with OSA, morbid obesity in particular.
Myth: OSA severity using standard definitions is a useful determinant of perioperative risk.
A patient with an AHI of 31/hour will probably be labelled as “severe” using standard sleep medicine criteria. These criteria are fairly arbitrary and based on the likelihood of long-term development of hypertension. A patient with an AHI of 29 will probably be labelled moderate, although other factors and clinical impressions will usually also be considered. Is the former patient at significantly greater risk of perioperative morbidity or mortality than the latter? Obviously not. In the absence of a better definition of perioperative risk however, sleep medicine-defined severity classifications are nevertheless used as major determinants even in the most recent practice guidelines (American Society of Anesthesiologists Task Force, 2005).
Myth: “The typical patient with OSA should be treated as an inpatient” (Benumof, 2004).
Various authorities (AASM, 2003; Benumof, 2004) have stated that only patients with mild OSA are suitable for outpatient surgery. The American Society of Anesthesiologists has recently provided more practical advice regarding this issue (ASA Task Force, 2005; Joshi, 2006) but even these practice guidelines are, in some respects, illogical for reasons given above. The benefit of sleeping in a room at the end of a normal hospital ward, with no monitoring apart from hourly or second hourly observations, over sleeping at home is doubtful. For any particular benefit to be afforded by hospitalisation in these circumstances the environment would need to be a high dependency area at least and this is unlikely for the vast majority of cases. There is also some retrospective evidence that a diagnosis of OSA is, on its own, not an independent risk factor for unanticipated hospital admission after scheduled outpatient surgery (Sabers, 2003).
Time of Presentation
Saturday 13 May 2006 - 1530-1700
References
1. Benumof JL. Obesity, sleep apnea, the airway and anesthesia. Current Opinion in Anaesthesiology 2004; 17(1):21-30.
2. Young T. Peppard PE. Taheri S. Excess weight and sleep-disordered breathing. Journal of Applied Physiology 2005; 99(4):1592-9.
3. Young T. Peppard PE. Gottlieb DJ. Epidemiology of obstructive sleep apnea: a population health perspective. American Journal of Respiratory & Critical Care Medicine 2002; 165(9):1217-39.
4. American Society of Anesthesiologists taskforce report. Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea 2005. http://www.asahq.org/publicationsAndServices/sleepapnea103105.pdf
5. American Association of Sleep Medicine Clinical Practice Review Committee report. Upper Airway Management of the Adult Patient with Obstructive Sleep Apnea in the Perioperative Period – Avoiding Complications. Sleep 2003; 26(8):1060-5.
6. Joshi GP. Are patients with obstructive sleep apnea suitable for ambulatory surgery? http://www.asahq.org/Newsletters/2006/01-06/joshi01_06.html
7. Sabers C. Plevak DJ. Schroeder DR. Warner DO. The diagnosis of obstructive sleep apnea as a risk factor for unanticipated admissions in outpatient surgery. Anesthesia & Analgesia 2003; 96(5):1328-35.
