Breathing movements of the chest and upper abdomen in mechanically ventilated paralyzed patients

Abstract

Assessment of breathing on clinical examination requires visualization of "chest" wall movement. However, in mechanically ventilated paralyzed patients, chest expansion is smaller than that of the abdomen. The aim of this study was to determine chest and upper abdominal movements in mechanically ventilated patients under general anesthesia. The subjects were 68 patients scheduled for general anesthesia. Chest and upper abdominal wall movements were measured using laser light at tidal volumes (VT) of 6, 10, and 15 mL/kg. The subjects were divided into the Lean group [body mass index (BMI) < 18.5 kg/m2], Normal group (BMI 18.5-24.9 kg/m2), and Obese group (BMI ≥ 25 kg/m2), and the relationships between chest and upper abdominal wall excursions and BMI at each VT were investigated. At VT of 10 mL/kg in all subjects, chest and upper abdominal wall excursions were 4.4 and 9.4 mm, respectively. The same pattern (upper abdominal wall excursions were twice as much as those of the chest wall) was noted in all groups and all VTs. Upper abdominal wall excursions were significantly larger than those of the chest wall in mechanically ventilated paralyzed patients, regardless of BMI. Assessment of breathing by clinical examination should avoid emphasis on "chest" wall movement alone, and instead include upper abdominal wall movement.