Abstract 109: Lower Ventilation Rates Improve Brain Tissue Oxygenation and Perfusion During Hemorrhagic Shock
Background: Recent studies showed that arterial blood pressure during hemorrhagic shock is made worse with hyperventilation and improved with a ventilation rate of 6 breaths/min.
Objective: To compare the effect of three ventilation strategies on brain tissue PO2 (PbrO2) and perfusion in an animal model of hemorrhagic shock.
Methods: Swine (mean weight 52.4 ± 3.3 kg) were randomly allocated to receive one of three ventilation strategies after hemorrhage: 12 breaths/min (N=7), 6 breaths/min (N=6), or ventilation rate adjusted to maintain a target end-tidal CO2 (ETCO2) = 40 mm Hg. Sufficient blood was removed to maintain a target mean arterial pressure (MAP) = 35 ± 5 mm Hg during a 40 min period. Three LICOX probes (Integra Neurosciences) and a tissue perfusion probe (Integra Neurosciences) were placed in the cerebral cortex, and output was recorded continuously. During the baseline period, ventilation rate was 12/min for all groups. Tidal volume was adjusted to maintain ETCO2 = 40 mm Hg during the baseline period and remained unchanged thereafter. FIO2= 1 and arterial hemoglobin oxygen saturation was 100% for all animals at all times . Immediately after hemorrhage and achieving the target MAP, ventilation rate was changed according to group assignment. Measurements were compared using Mann-Whitney U; p < .025 is significant (with Bonferroni correction).
Results: Mean (= SD) MAP, ETCO2, PbrO2, and brain tissue perfusion measurements at baseline and after 40 min of shock are given in the table⇓ below: