In reply: Obstructive sleep apnea (January 2016)

IN REPLY: We thank Dr. Keller for his thorough reading of our article.¹

Regarding the predictive value of neck circumference for obstructive sleep apnea, (OSA), neck circumference is one of many tools to screen for OSA. If neck circumference greater than 38 cm is applied without other predictors (such as the presence of snoring, daytime sleepiness, or elevated body mass index), it provides only a 58% sensitivity and 79% specificity.² It is less an issue of inches vs collar size vs centimeters than of combining circumference with other parameters (as in the STOP-BANG questionnaire) before proceeding with a sleep study. The senior author of our article (G.R.) uses 38 cm.

With respect to home vs sleep lab monitoring, the question was beyond the scope of the paper and outside our expertise, as we are both general internists. The home venue recommendations in this instance were taken directly from the American Academy of Sleep Medicine.³ We would rely on consultation with a sleep specialist before ordering home monitoring to determine the potential success of non-CPAP interventions for OSA.

As for Parkinson disease as an exception to OSA and hypertension, we wrote in the paper, “Untreated OSA is associated with a number of conditions.”¹ Yes, resistant hypertension is prominent in today’s epidemic of obesity, diabetes, and OSA, but not everyone with coronary artery disease, atrial fibrillation, or heart failure—as in persons with Parkinson disease—has hypertension. The associated conditions in our paper are more typical of a general medical practice, but we agree that Parkinson disease is associated with OSA. Patients with hypertension and OSA are more prevalent because the clinical risk factors for OSA and hypertension are common to both conditions.⁴

In adults, apnea is considered present when the airflow drops by 90% or more from the pre-event baseline. Hypopnea in adults is present when the airflow drops by 30% or more of the pre-event baseline for 10 or more seconds in association with either 3% or greater arterial oxygen desaturation or an electroencephalographic arousal.⁵ Studies have shown that episodes of hypopnea with 2% oxygen desaturation are associated with an increased prevalence of metabolic impairment.⁶ A higher degree of desaturation, ie, more than 4%, was associated with increased prevalence of self-reported cardiovascular disease.⁷ But the significance of episodes of hypopnea without arterial desaturation is not well known to us and was beyond the scope of our article.

Our article was primarily focused on screening for OSA in ambulatory clinical practice and was not intended as a comprehensive review of screening in different settings of patient care. As to the importance of recognizing OSA in patients undergoing elective surgery under general anesthesia, we agree that screening is important to reduce the risk of postoperative adverse respiratory events in patients with a high pretest probability of OSA. In a recent study by Seet et al,⁸ patients with high STOP-BANG questionnaire scores (≥ 3) had higher rates of intraoperative and early postoperative adverse events than those with low scores (< 3). The risk of adverse events correlated with higher scores, and patients with a STOP-BANG score of 5 or more had a five times greater risk of unexpected intraoperative and early postoperative adverse events, whereas those with a STOP-BANG score of 3 or more had a one in four chance of an adverse event. We recommend polysomnography for patients with a STOP-BANG score of 5 or more before elective surgery.

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