Effects of moderate and severe arterial hypotension on intracerebral perfusion and brain tissue oxygenation in piglets

Background: Hypotension is common in anaesthetised children, and its impact on cerebral oxygenation is unknown. The goal of the present study was to investigate the effects of moderate systemic arterial hypotension (mHT) and severe hypotension (sHT) on cerebral perfusion and brain tissue oxygenation in piglets. Methods: Twenty-seven anaesthetised piglets were randomly allocated to a control group, mHT group, or sHT group. Cerebral monitoring comprised a tissue oxygen partial pressure (PtO 2) and laser Doppler (LD) perfusion probe advanced into the brain tissue, and a near-infrared spectroscopy sensor placed over the skin measuring regional oxygen saturation (rSO2). Arterial hypotension was induced by blood withdrawal and i.v. nitroprusside infusion [target MAP: 35–38 (mHT) and 27–30 (sHT) mm Hg]. Data were analysed at baseline, and every 20 min during and after treatment. Results: Compared with control, PtO 2 decreased equally with mHT and sHT [mean (SD) after 60 min: control: 17.1 (6.4); mHT: 6.4 (3.6); sHT: 7.2 (4.3) mm Hg]. No differences between groups were detected for rSO2 and LD during treatment. However, in the sHT group, rSO2 increased after restoring normotension [from 49.3 (9.5) to 58.9 (8.9)% Post60]. sHT was associated with an increase in blood lactate [from 1.5 (0.4) to 2.4 (0.9) mmol L−1], and a decrease in bicarbonate [28 (2.4) to 25.8 (2.6) mmol L−1] and base excess [4.7 (1.9) to 2.0 (2.7) mmol L−1] between baseline and 60 min after the start of the experiment. Conclusions: Induction of mHT and sHT by hypovolaemia and nitroprusside infusion caused alterations in brain tissue oxygenation in a piglet model, but without detectable changes in brain tissue perfusion and regional oxygen saturation.