Spontaneous breathing during airway pressure release ventilation in experimental lung injury: effects on hepatic blood flow

Objective: Positive pressure ventilation can affect systemic haemodynamics and regional blood flow distribution with negative effects on hepatic blood flow. We hypothesized that spontaneous breathing (SB) with airway pressure release ventilation (APRV) provides better systemic and hepatic blood flow than APRV without SB. Design: Animal study with a randomized cross-over design. Setting: Animal laboratory of Bonn University Hospital. Subjects: Twelve pigs with oleic-acid-induced lung injury. Intervention: APRV with or without SB in random order. Without SB, either the upper airway pressure limit or the ventilator rate was increased to maintain constant pH and PaCO2. Measurements and results: Systemic haemodynamics were determined by double-indicator dilution, organ blood flow by coloured microspheres. Systemic blood flow was best during APRV with SB. During APRV with SB blood flow (ml g(-1) min(-1)) was 0.91 +/- 0.26 (hepatic arterial), 0.29 +/- 0.05 (stomach), 0.64 +/- 0.08 (duodenum), 0.62 +/- 0.10 (jejunum), 0.53 +/- 0.07 (ileum), 0.53 +/- 0.07 (colon), 0.46 +/- 0.09 (pancreas) and 3.59 +/- 0.55 (spleen). During APRV without SB applying high P-aw it decreased to 0.13 +/- 0.01 (stomach), 0.37 +/- 0.03 (duodenum), 0.29 +/- 0.03 (jejunum), 0.31 +/- 0.05 (ileum), 0.32 +/- 0.03 (colon) and 0.23 +/- 0.04 (pancreas) p < 0.01, respectively. During APRV without SB applying same P-aw limits it decreased to 0.18 +/- 0.03 (stomach, p < 0.01), 0.47 +/- 0.06 (duodenum, p < 0.05), 0.38 +/- 0.05 (jejunum, p < 0.01), 0.36 +/- 0.03 (ileum, p < 0.05), 0.39 +/- 0.05 (colon, p < 0.05), and 0.27 +/- 0.04 (pancreas, p < 0.01). Arterial liver blood flow did not change significantly when SB was abolished (0.55 +/- 0.11 and 0.63 +/- 0.11, respectively). Conclusions: Maintaining SB during APRV was associated with better systemic and pre-portal organ blood flow. Improvement in hepatic arterial blood flow was not significant.