Abdominal pressure volume determinants

The abdominal pressure–volume relation can be described by a linear relation giving an elastance (E) and a pressure at zero volume (P_V0). The goal of this study was to measure this relation in a large group of patients with different characteristics looking for the factors that influence and explain this relation. It is believed that obese persons have higher abdominal pressures and it is unclear whether muscle relaxation lowers it.

A large group of 70 patients, ASA class I or II, between 21 and 75 years old and scheduled for laparoscopic surgery were included in this study with approval from the hospital ethical committee.

Anaesthesia was induced with propofol 200 mg, sufentanil 20 μg, and sevoflurane 1.5 Mac in 50% O₂/N₂O. Some patients were fully muscle relaxed with nimbex 20 mg while others not. Patients were asked to empty the bladder before surgery. The stomach was emptied by suction through a gastric tube. An Olympus insufflator UHI-3 was initialised and the abdomen was inflated with a stepwise flow to 7, 10, 13 and 16 mmHg. When the pressure was reached, flow was stopped and the actual pressure and volume measured giving four data points. E and P_V0 were calculated by fitting to a linear relation. The following recorded determinants were evaluated by regression analysis for their effect: age, length, weight, BMI, sex, gravidity and muscle relaxation.

P_V0 increases significantly with body weight and decreases significantly with muscle relaxation.

Table 1