How much gas is required for initial insufflation at laparoscopy?

Objective To determine how much gas is required for initial insufflation of the abdomen at laparoscopy. Design A prospective observational study. Setting Specialized minimal access gynaecological operating theatre in a di strict general hospital. Subjects 43 female patients undergoing laparoscopy. Interventions In 30 patients, changes in the vertical depth of the pneumope ritoneum at the umbilicus were measured when the volume and pressure of the insufflated CO2 was changed. The depth was also measured in response to ch anges in the downward force applied to the umbilicus with insertion of the primary cannula. Non-invasive monitoring of respiratory and circulatory par ameters was carried out on a further 13 patients during these procedures an d with variation in head-down tilt. Main outcome measures The vertical depth of the pneumoperitoneum, and cardi ovascular and respiratory parameters. Results When a downward force of 3 kg force is applied at the umbilicus, th e mean vertical depth of the pneumoperitoneum is only 0.6 cm (the range inc ludes zero) when the intra-abdominal pressure is 10 mmHg (approximately equ ivalent to insufflation of 31 CO2). This increases to 5.6 cm (range 4-8) wh en the intra-abdominal pressure is raised to 25 mmHg. The mean volume of CO 2 required to achieve a pressure of 25 mmHg is 5.581 (range 3.7-11.1). The maximum respiratory effects of the 25-mmHg intra-abdominal pressure (with t he patient flat) are no greater than the effect of the Trendelenburg positi on with an intra-abdominal pressure of 15 mmHg. No adverse circulatory effe cts are demonstrated. Conclusions This 25-mmHg pressure-limited method produces a greater splinti ng of the abdominal wall and a deeper gas bubble than the traditional volum e-limited pneumoperitoneum of 2-31, which should lead to a reduced risk of injury.