APNEIC DESATURATION TIME IN PATIENTS WITH MILD-T0-MODERATE OBESITY

Abstract

S411 INTRODUCTION: This study was undertaken to define the effects of mild to moderate obesity on the time required for arterial desaturation during anesthetic-induced apnea. METHODS: A cross-section observational study was conducted in 60 ASA I-II adult patients scheduled for elective surgery under general anaesthesia. The principal study variable was Tm_DESAT, the time required for a 5 percentage point decrease in arterial oxygen saturation during apnea. The apneic state was induced with intravenous Thiopental and Succinylcholine following three minutes of preoxygenation with 100% O2. Arterial saturation (SpO2) was measured noninvasively at the right index finger with a Nellcor pulse-oximeter. Tm_DESAT was recorded in seconds and analysed for correlation with measured body weight and several derived morphometric indices which correct body weight for the effects of height. These included: (1) weight as a percent of ideal weight; (1) weight as a percent of frame-adjusted ideal weight; and (3) body mass index (BMI). Obesity was graded according to BMI on the scale of Garrow1, where BMI <or=to 24.9 is grade 0 (non-obese), BMI 25-29.9 is grade I (mild), and BMI 30-40 is grade II (moderate). RESULTS: Tm_DESAT varied over a 22-fold range and was inversely related to each of the measures of body mass studied (Figure 1A). Correlation coefficients for the relation to Tm_DESAT were similar for all derived morphometric indicies, and none correlated significantly better than uncorrected body weight (Tm_DESAT=638-5.23*WT; R=0.73; P< 0.01). Tm_DESAT was shorter in moderately obese (grade II) and mildly obese (grade I) patients than in non-obese subjects (Figure 1B; P<0.01 and P<0.02 respectively). Moderately obese subjects also desaturated more quickly than those with mild obesity. (P<0.01)Figure 1CONCLUSION: Mild-to-moderate obesity has a significant negative impact on the time course arterial desaturation during anesthetic induced apnea. Desaturation time is inversely related to body mass for patients in this weight range.