Morbidly obese patients (MOP) [body mass index (BMI) > 40-kg/ m2] undergo multiple tests to determine etiology of low partial pressure of arterial oxygen (PaO2) and/or high partial pressure of carbon dioxide (PaCO2) without regard to their BMI. This study was done to examine the correlation between increasing BMI and arterial blood gases on room air (ABG-ra) in MOP.
MOP [n=76] who were evaluated for bariatric surgery were enrolled in the study. Data gathered included demographics, ABG-ra in sitting position, pulmonary function tests (FEV1: Forced Expiratory Volume in 1 second, Forced Vital Capacity, FEV1/FVC, and Expiratory Reserve Volume (ERV), Maximum voluntary ventilation (MVV). The Spearman correlation coefficient was computed in order to determine the degree of correlation between each of PaCO2, PaO2, FEV1, FVC and BMI.
VariablesBMI: 40- 50 kg/m2BMI: >50–60kg/m2BMI: >60 kg/m2n412114Mean age (years)39.7633.8941.64M:F3:384:171:13FEV1(L)2.742.702.21FVC (L)3.273.302.78FEV1/FVC83.4877.7178.92TLC (L)4.774.934.75Expiratory reserve volume (L).52.46.41PaO2 mm Hg94.2889.1582.97PaCO2 mm Hg38.3040.9443.93pH7.417.407.39
There was a significant correlation between BMI and PaCO2 (, r=0.43; p< 0.0001). There was a significant correlation between BMI and PaO2 (r=-0.27; p<0.02). There was a significant correlation between BMI and FVC and FEV1 (FVC: r = −0.24; p<0.04, and FEV1: r = −0.26; p<0.03).
Decrease in FEV1 and FVC with increasing BMI reflects the restrictive ventilatory defect seen in MO patients. Increasing BMI may affect PaO2 and PaCO2 significantly and this should be taken into consideration before performing multitude of tests to determine the etiology of hypoxia & hypercarbia in MO patients. MO patients with no retention of PaCO2 may start retaining PaCO2 with further increase in their BMI and may represent onset of obesity hypoventilation syndrome.
A. Chiang, None.