Effects of controlled hypotension induced by sodium nitroprusside on regional cerebral blood flow and oxygenation in pigs

To investigate the effects of controlled hypotension induced by sodium nitroprusside on regional cerebral blood flow and oxygenation in pigs.

Six healthy female Landrace pigs (aged 4~6 months, weighing 22~25 kg) were included in this study. Sodium nitroprusside was used for controlled hypotension under sevoflurane anesthesia (20%, 30% and 50% lower than the baseline of mean arterial pressure or mean arterial pressure (MAP), corresponding to mild, moderate and severe hypotension, respectively). Oxygen to see (O2C), a monitoring instrument, was used to measure regional cerebral blood flow (rCBF) and regional cerebral oxygen saturation (rSO₂). rCBF, rSO₂, regional cerebral haemoglobin (rHb), heart rate (HR), peripheral oxygen saturation (SpO₂) and incidence of cerebral hypoxia events were recorded under different MAP.

rCBF was significantly correlated with MAP (r=0.793) and also obviously correlated with rSO₂ (r=0.843) in the whole hypotension process. rSO₂ had a linear correlation with rHb, MAP and rCBF (R²=0.853, P<0.05), respectively. And the order of their linear correlation with rSO₂ is rHb>MAP>rCBF. During mild hypotension, rCBF and rSO₂ were increased by 7.4% (P<0.05) and 2.5% (P<0.05), respectively compared with the baseline, and the increase of rCBF was more remarkable. During moderate hypotension, compared with the baseline, rCBF was decreased by 0.9% (P>0.05), while rSO₂ was decreased by 5.8% (P<0.05). During severe hypotension, rCBF and rSO₂ were decreased by 7.6% (P<0.05) and 12.1% (P<0.05) respectively, and there was no cerebral hypoxia event during mild to severe hypotension. From 5 to 15 min after drug withdrawal, both rCBF and rSO₂ were increased by 8.4% and 3.7%, respectively when compared with the baseline (both P<0.05).

Controlled hypotension with sodium nitroprusside is beneficial to maintain cerebral perfusion and cerebral oxygenation, but mild hypotension can cause an increase in cerebral blood flow, which is disadvantageous to patients with increased intracranial pressure.