Success of recruitment maneuvers during pneumoperitoneum is dependent on the intraabdominal pressure

Introduction

Intraabdominal hypertension is a condition affecting respiratory mechanics in many situations such as laparoscopy or morbid obesity. We investigated the effects of different intra-abdominal pressures (IAP) at different positive end-expiratory pressure (PEEP) levels on nonlinear respiratory mechanics and the effects on hemodynamics and oxygenation in a rat model. The application of a pneumoperitoneum served as a model for elevated IAP.

Methods

A helium pneumoperitoneum was established in 20 anesthetized female Wistar rats that were randomly allocated to one of four PEEP levels (0, 3, 6 and 9 mbar). IAP of 9, 12, 15 and 18 mbar was instilled in a random sequence in each rat, followed by respiratory mechanics measurement and blood gas analysis. From the low flow maneuvers' pressure–volume loops, the lower inflection point and the mathematical turning point within the expiratory limb were detected and compared with the IAP applied during the measurement. For investigation of the lung's intratidal compliance, 10 consecutive breaths before and after low flow maneuvers were analyzed. Intratidal nonlinear compliance was calculated using a modified SLICE method [1].

Results

A higher IAP led to a decreased steepness of quasistatic pressure–volume loops resulting in a right shift of the expiratory lower inflection point. The pressure at the mathematical turning point of the expiratory limb correlated well with the IAP (r = 0.97, P < 0.001). Intratidal compliance decreased with increasing IAP before and after the low flow maneuvers. After execution of the low flow maneuvers the compliance increased. Relative compliance gain caused by the low flow maneuvers was dependent on PEEP, IAP and slice (all P < 0.001). The peak inspiratory pressure increased with increasing IAP and was significantly smaller after recruitment maneuvers (P < 0.001). The peak inspiratory pressure was dependent on PEEP and IAP (P < 0.001). PaO₂ was dependent on PEEP (P = 0.008) but not on IAP (P = 0.153). Arterial pressure was not dependent on PEEP (P = 0.068) or IAP (P = 0.292).

Conclusion

Intraabdominal hypertension alters respiratory mechanics. IAP has no effect on oxygenation as long as PEEP is applied. The examination of nonlinearity holds important information for the evaluation of respiratory mechanics. The success of recruitment maneuvers on healthy lungs depends strongly on the IAP.