Pulse pressure variation as a tool to detect hypovolaemia during pneumoperitoneum

Background: Pulse pressure variation (Delta PP) and systolic pressure variation (SPV) induced by mechanical ventilation have been proposed to detect hypovolaemia and guide fluid therapy. During laparoscopic surgery, chest compliance is decreased by pneumoperitoneum. This may affect the value of SPV and Delta PP as indicators of intravascular volume status. Thereby, we investigated the effects of pneumoperitoneum and hypovolaemia on SPV and Delta PP. Methods: We measured Delta PP, SPV and the inspiratory (Delta up) and expiratory (Delta down) components of SPV, at baseline, during pneumoperitoneum, during pneumoperitoneum and hypovolaemia and after the return to baseline conditions, in 11 mechanically ventilated rabbits. Pneumoperitoneum was induced by inflating the abdomen with carbon dioxide, and hypovolaemia was induced by controlled haemorrhage. Results: Pneumoperitoneum induced an increase in SPV from 8.5 +/- 1.6 to 13.3 +/- 2.6 mmHg (+56%, P < 0.05) as a result of an increase in Delta up from 2.0 +/- 1.0 to 6.7 +/- 2.1 mmHg (+236%, P < 0.05), but no significant change in Delta down, nor in Delta PP. Haemorrhage induced a significant (P < 0.05) increase in SPV from 13.3 +/- 2.6 to 19.9 +/- 3.7 mmHg (+50%), in Delta down from 6.6 +/- 3.3 to 14.0 +/- 4.9 mmHg (+112%) and in Delta PP from 11.1 +/- 4.8 to 24.9 +/- 9.8% (+124%) but no change in Delta up. All parameters returned to baseline values after blood re-infusion and abdominal deflation. Conclusions: SPV is modified by haemorrhage but it is also influenced by pneumoperitoneum. In contrast, Delta PP is modified by haemorrhage but not by pneumoperitoneum. These findings suggest that Delta PP should be used preferentially instead of SPV to detect hypovolaemia and guide fluid therapy during laparoscopic surgery.