Haemodynamic changes and vasopressin release are not consistently associated with carbon dioxide pneumoperitoneum in humans

Background: Conflicting haemodynamic changes, suggested to be caused by vasopressin release, have been reported during carbon dioxide (CO ₂) pneumoperitoneum. However, peritoneal stimulations including open surgery cause both a systemic vasopressor response and a vasopressin release, which are suppressed by opiate administration. Also, a decreased venous return of blood to the heart causes vasopressin release. Furthermore, previous haemodynamic assessments of laparoscopic surgery have been conducted using various anaesthetic regimens, which are likely to have caused various haemodynamic effects. We hypothesised that intraoperative haemodynamic and/or humoral changes would not be observed in association with laparoscopic surgery provided that, (a) normovolaemia is continuously maintained using transoesophageal echocardiographic (TEE) assessment, and (b) adequate depth of general anaesthesia is continuously maintained by bispectral index (BIS) monitoring and high plasma level opiate administration. Methods: Twenty ASA 1 women undergoing laparoscopic surgery received 10 ml · kg ^-1 lactated Ringer's solution and thereafter were randomly allocated to receive intraoperatively either 8 ng · ml ^-1 or 4 ng · ml ^-1 plasma remifentanil concentrations while BIS was maintained at 50±5 by isoflurane alteration. The group receiving 4 ng · ml ^-1 remifentanil was used as control. Expired CO ₂ was maintained within a 32-38 kPa range throughout the investigation. Complete TEE haemodynamic investigation was performed before pneumoperitoneum (PP) (T1), and during PP horizontal (T2), with a head-up tilt (T3), with a head-down tilt (T4), horizontal (T5), and PP released (T6). Plasma vasopressin, epinephrine and norepinephrine levels were measured at T1, T3, and T6. ANOVA, Student's t-test and Mann-Whitney U-test were used for statistical analysis. Results: Haemodynamic indices and humoral values did not change significantly within and between remifentanil groups throughout the investigation (all P<0.05). Conclusion: Continuous adequate depth of anaesthesia and normovolaemia may have prevented both a humoral and a haemodynamic response, initiated in the peritoneum by the contact with CO ₂ in previous investigations.