THE EFFECTS OF INCREASED ABDOMINAL PRESSURE ON LUNG AND CHEST-WALL MECHANICS DURING LAPAROSCOPIC SURGERY

We tested the hypothesis that increases in pressure in the abdomen (P-ab) exerted by CO2 insufflation during laparoscopy would increase elastance (E) and resistance (R) of both the lungs and chest wall. We measured airway flow and airway and esophageal pressures of 12 anesthetized/paralyzed tracheally intubated patients during mechanical ventilation at 10-30/min and tidal volume of 250-800 mL. From these measurements, we used discrete Fourier transformation to calculate E and R of the lungs and chest wall. Measurements were made at 0, 15, and 25 mm Hg P-ab in the 15 degrees head-down (Trendelenburg) posture and at 0 and 15 mm Hg P-ab in the 10 degrees head-up (reverse Trendelenburg) posture. Lung and chest wall Es and Rs while head-down increased at P-ab = 15 mm Hg, and both Es increased further at P(a)b = 25 mm Hg (P < 0.05). Both Es and Rs also increased while head-up at P-ab = 15 mm Hg (P < 0.05), but increases in lung E and R were less than while head-down (P < 0.05). The increases in lung E and R at P-ab = 15 mm Hg in either posture were positively correlated to body weight or body mass index, whereas the increases in chest wall E and R were negatively correlated to the same factors (P < 0.05). Lung and chest wall mechanical impedances increase with increasing P-ab; the increases depend on body configuration and are greater while head-down. These changes should be considered in patients where increases in impedance may be critical, such as in obese patients and those with pulmonary disease.