Effects of positive end-expiratory pressure on liver function and splanchnic microcirculation

Introduction

The effects of positive end-expiratory pressure (PEEP) on liver function and blood flow in experimental and clinical studies revealed non-uniform results. In this clinical study, we investigated the effects of PEEP on liver function (indocyanine green plasma disappearance rate [ICG-PDR]) and splanchnic microcirculation as estimated by regional PCO₂ (PRCO₂) using gastric tonometry.

Methods

With approval by our local ethics committee and written consent, we studied 14 patients after elective coronary bypass surgery using extracorporal circulation (13 males, one female; age 48–74, mean 63 ± 7 years). All patients underwent extended hemodynamic monitoring by a pulmonary artery catheter for clinical indication. ICG-PDR and gastric mucosal PRCO₂ were assessed on ICU admission (PEEP 5 mbar), 2 hours after increasing PEEP to 10 mbar and again after 2 hours at PEEP 5 mbar. In addition, the cardiac index, central venous pressure (CVP) and left atrial pressure (LAP) were measured. All patients were on pressure-controlled ventilation and the inspiratory peak pressure was adapted to maintain PaCO₂ constant. Vasoactive drugs, blood pressure, minute volume and sedation were kept constant.

Results

The cardiac index significantly increased during the study. However, there was a trend for ICG-PDR to change between the different time points (P = 0.05). However, the difference between regional and arterial PCO₂ (PCO2-gap) significantly increased following PEEP5 (1) and remained higher at PEEP5 (2) than at PEEP5 (1) (Table 1).

Table 1

Conclusion

Increasing PEEP from 5 to 10 mbar was accompanied with a trend towards a decrease in liver function and blood flow (ICG-PDR). The changes in PCO₂-gap were within the physiological range and of no clinical relevance. An increase in PEEP from 5 to 10 mbar can be applied without compromising liver blood flow and function and splanchnic microcirculation.