2002 Use of Overnight Oximetry in the Diagnostic Process of Obstructive Sleep Apnea
Dr K STang, Tuen Mun Hospital
Abstract Obstructive sleep apnea (OSA) is common in both Western and local
populations. It is associated with traffic accidents, hypertension and other
CVS risk factors. Early diagnosis and treatment of OSA is therefore
desirable. The standard diagnostic polysomnography study (PSG) is labor
intensive and expensive. Portable oximeters are widely available and many
physicians use overnight oximetry to screen for OSA. In fact, many
studies have been done to assess the role of overnight oximetry in diagnosis
of OSA. The results have been conflicting. Heterogeneity in study samples,
design and analytical methods probably explain these seemingly
inconsistent results. A systematic review of these studies is presented.
Some fairly consistent trends can then be appreciated.
This is followed by a study on 54 Chinese patients presented to Tuen Mun
Hospital with suspected OSA. All have overnight oximetry tracing
compatible with OSA and PSG subsequently performed. Information on
Epworth Sleepiness Score (ESS), Neck Circumference (Ne), Body Weight
(BW) and Waist Circumference (We) were collected. The digital output of
the oximeter was analyzed to obtain total time of SpO2 less than 90%
(CT90), number of desaturation below 90% per hour (fall<90), average
saturation and lowest saturation. We found that the investigated clinical
parameters (ESS, NC, BW, We) cannot be used to predict AHI reliably
(r=0.335). Among the oximetric parameters, AHI and fall<90 was noted to
be highly correlated (r = 0.822). In addition, the regression equation of
AHI=7.357+1.184(fall<90) gives a reasonably accurate estimate of AHI.
