Résumé : Introduction: Therapeutic hypothermia (TH) can improve neurological outcome after cardiac arrest (CA); little is known about how cooling actually affects brain dynamics after resuscitation from CA.Hypothesis: The aim of this study was to investigate the effects of TH on brain microcirculation and metabolism after CA.Methods: 10 anesthetized, invasively monitored and mechanically ventilated domestic pigs were randomized into two groups (n=5): normothermia (NT, 39.5 +/- 1.0 [degrees]C) and therapeutic hypothermia (TH, 34.0 +/- 1.0[degrees]C). After 3 min of untreated ventricular fibrillation, cardiopulmonary resuscitation (CPR) was started and continued for 3 min before defibrillation. Hypothermia was induced at the start of CPR using IV infusion of 30 mL/kg cold saline for 60 min, trans-nasal evaporative cooling (Rhinochill, Benechill Inc, USA) and surface cooling with ice packs. Cooling was maintained for 6 hours, followed by controlled rewarming to baseline temperature. Intraparenchymal probes were used to measure brain temperature (Licox CC1.SB, Integra, NeuroSciences Ltd., Hamphsire, UK) and the lactate-pyruvate ratio (LPR, microdialysis CMA20, CMA, Sweden) hourly. After left craniectomy, the microvascular network of the frontal cortex was evaluated using Sidestream Dark-Field videomicroscopy (Microscan, MicroVision Medical, Netherlands) at baseline (T0), 1 hour after cooling induction (T1), at the end of hypothermia (T2) and after rewarming (T3). The proportion of perfused cerebral small vessels (PPV) was calculated using standard formulas.Results: Time to return of spontaneous circulation was similar in both groups (7 [6-22] mins for NT and 9 [6-21] mins for TH). Microvascular perfusion was significantly decreased after CA, but was better preserved in the TH than in the NT group (PPV: T0 87 +/- 3 vs 86 +/- 2, T1 37 +/- 13 vs 29 +/- 3, T2 36 +/- 15 vs 24 +/- 7, T3 58 +/- 7 vs 17 +/- 3 - p<0.01). The LPR was higher in the NT than in the TH group throughout the study period (T0 14.1 +/- 3.6 vs 13.4 +/- 2.6, T1 27.4 +/- 9.7 vs 21.7 +/- 4.4, T2 43.7 +/- 20.4 vs 35.4 +/- 9.4, T3 110.4 +/- 57.3 vs 62.8 +/- 12.6, p<0.05).Conclusions: The cerebral microcirculation was significantly altered after resuscitated CA; TH attenuated these microvascular alterations and had a protective effect on brain metabolism.