Biphasic response after brain death induction:: Prominent part of catecholamines release in this phenomenon

Background: The physiopathology of hemodynamic instability that occurs after brain death remains unknown. The aim of this study was to examine the initial response to brain death induction. Methods: After anesthesia and monitoring, 16 pigs were randomized into a control group (C, n = 8) and a brain death group (BD, n = 8). We inflated a subdural catheter balloon to induce brain death. We analyzed hemodynamic and plasmatic biochemical data for 180 minutes after brain death induction. Energetic compounds were measured. We expressed the results in comparison with the C group. Results: The C group remained stable. One minute after brain death, the Cushing reflex appeared, with a hyperdynamic response to plasma catecholamines levels increasing (norepinephrine and epinephrine, 3.1-fold, p = 0.02, and 3.8-fold, p = 0.07, respectively). After a return to baseline, we recorded a second hyperdynamic profile 120 minutes later. At this time, a second peak of catecholamines appeared (6.3-fold, p = 0.04, and 9.1-fold, p = 0.02, concerning norepinephrine and epinephrine). At the same time, we observed brief myocardial lactate production (+175%, p < 0.01), with a rise of troponine I (+64%, p = 0.03). The energetic index was similar in both groups: 0.85 (+/-0.02) in the C group vs 0.87 (+/-0.02) in the ED group. Conclusions: In this model, biphasic plasmatic catecholamine release appears to primarily explain the physiopathology of the hemodynamic response to brain death induction.