Background: Systemic-blood flow, cerebral-blood flow, and spinal cord blood flow can be affected by mechanical ventilation. We investigated the effect of spontaneous breathing on cerebral and spinal blood flow during airway pressure release ventilation (APRV) with and without spontaneous breathing.
Methods: Twelve pigs with oleic-acid-induced lung injury were ventilated with APRV with or without spontaneous breathing in random order. Without spontaneous breathing, either the upper airway pressure limit of mechanical ventilation or the ventilator rate was increased to maintain pH and PaCO2 constant. Systemic hemodynamic parameters were determined by the double indicator dilution method, cerebral and spinal cord blood flow was measured with colored microspheres.
Results: As compared with APRV without spontaneous breathing and high tidal volume (V(T)) spontaneous breathing during APRV showed higher systemic blood flow and perfusion of the basal ganglia, frontal lobe, hippocampus, brain stem, temporal lobe, thalamus (all P<0.001), cerebellum, spinal cord (all P<0.01), and the central cortical region (P<0.05). During APRV without spontaneous breathing and low V(T) blood flow was lower in the basal ganglia, frontal lobe, hippocampus (all P<0.01), and temporal lobe (P<0.05) whereas perfusion of the thalamus, central cortical region, brain stem, cerebellum, and spinal cord were not different compared with APRV with spontaneous breathing.
Conclusions: In parallel with higher systemic blood flow regional cerebral and spinal cord blood flow were also higher when spontaneous breathing was maintained during APRV. The higher regional blood flow by maintaining spontaneous breathing was more pronounced when compared with full ventilatory support using high V(T).