Jugular bulb oxygen saturation and the pyruvate lactate ratio are good signals for cerebral metabolism and oxygenation during hypothermia with altered target ventilation

Background The effect of deliberate hypothermia and hypocapnia on brain protection during neurosurgical procedures has been studied for many years, but in this study, the combination of deliberate hypothermia and hypocapnia was analyzed to detect their effects on cerebral oxygenation by the assessment of SjvO2 and cerebral metabolism by the measurement of both jugular bulb lactate and pyruvate. Patients and methods Sixty patients scheduled for excision of supratentorial space-occupying lesions were randomly allocated into two groups. In group I, hypocapnia was induced combined with hypothermia, and in group II, normocapnia was maintained combined with hypothermia. Hypothermia was induced using a water blanket under the patient controlling the tympanic membrane temperature at 35°C. Jugular bulb venous and arterial blood gas analyses were performed before the induction of hypothermia ± hypocapnia (baseline), and then every 20 min till closure of the dura. The arterio-jugular venous oxygen content difference (AJDO2) and the cerebral oxygen extraction ratio (COER) were calculated. Jugular bulb lactate and pyruvate levels were measured before the induction of hypothermia ± hypocapnia (baseline) and then every 30 min till closure of the dura. Results There was a significant increase in pjH and significant decreases in both PjCO2 and SjvO2 in the hypocapnic group after the induction of hypocapnia. SjvO2 reached 80.32 ± 4.59% in the normocapnic group, whereas it reached 75.3 ± 4.02% in the hypocapnic group. AJDO2 and COER started to decrease after induced hypothermia in both groups compared with readings before induced hypothermia, but the hypocapnic group had a significantly higher AJDO2 and COER than the normocapnic group during the period of induced hypothermia (AJDO2 reached 3.98 ± 0.47 ml/dl and COER reached 25.93 ± 4.13% in comparison with the hypocapnic group, where AJDO2 reached 4.58 ± 0.51 ml/dl and COER reached 31.96 ± 4.01%).Jugular bulb lactate and pyruvate levels were signifi cantly higher during hypocapnia than during normocapnia. Conclusion Cerebral oxygenation and metabolism were better during hypothermia combined with normocapnia as refl ected by relative ↑↑SjvO2 and ↓↓AJDO2 and COER as well as ↓↓jugular bulb lactate and pyruvate.