Relationship of common hemodynamic and respiratory target parameters with brain tissue oxygen tension in the absence of hypoxemia or hypotension after cardiac arrest: A post-hoc analysis of an experimental study using a pig model

Brain tissue oxygen tension (PbtO(2))-guided care, a therapeutic strategy to treat or prevent cerebral hypoxia through modifying determinants of cerebral oxygen delivery, including arterial oxygen tension (PaO(2)), end-tidal carbon dioxide (ETCO(2)), and mean arterial pressure (MAP), has recently been introduced. Studies have reported that cerebral hypoxia occurs after cardiac arrest in the absence of hypoxemia or hypotension. To obtain preliminary information on the degree to which PbtO(2) is responsive to changes in the common target variables for PbtO(2)-guided care in conditions without hypoxemia or hypotension, we investigated the relationships between the common target variables for PbtO(2)-guided care and PbtO(2) using data from an experimental study in which the animals did not experience hypoxemia or hypotension after resuscitation. We retrospectively analyzed 170 sets of MAP, ETCO(2), PaO(2), PbtO(2), and cerebral microcirculation parameters obtained during the 60-min post-resuscitation period in 10 pigs resuscitated from ventricular fibrillation cardiac arrest. PbtO(2) and cerebral microcirculation parameters were measured on parietal cortices exposed through burr holes. Multiple linear mixed effect models were used to test the independent effects of each variable on PbtO(2). Despite the absence of arterial hypoxemia or hypotension, seven (70%) animals experienced cerebral hypoxia (defined as PbtO(2) <20 mmHg). Linear mixed effect models revealed that neither MAP nor ETCO(2) were related to PbtO(2). PaO(2) had a significant linear relationship with PbtO(2) after adjusting for significant covariates (P = 0.030), but it could explain only 17.5% of the total PbtO(2) variance (semi-partial R(2) = 0.175; 95% confidence interval, 0.086–0.282). In conclusion, MAP and ETCO(2) were not significantly related to PbtO(2) in animals without hypoxemia or hypotension during the early post-resuscitation period. PaO(2) had a significant linear association with PbtO(2), but its ability to explain PbtO(2) variance was small.