Changes in Prefrontal Cortical Oxygenation During Tilt Table Orthostatic Hypotension in Subarachnoid Haemorrhage Patients

Cerebral vasospasm and delayed cerebral ischaemia in patients with subarachnoid haemorrhage (SAH) are more likely to occur within the first two weeks of bleeding. Thus, conventional management involves absolute rest for two weeks. Recently, studies have reported on the possibility of early mobilisation after SAH; however, its safety has not been sufficiently evaluated. The present study investigates the relationship between cerebral cortex oxygenation and orthostatic hypotension in SAH patients using near-infrared spectroscopy (NIRS). Four SAH patients were laid supine for 5 min before performing a head-up tilt (HUT) to 30°, 45°, and 60° every 5 min using a tilt table bed. Arterial blood pressure was measured before and immediately after HUT. We evaluated O2Hb levels of the left and right prefrontal cortex (PFC) in 11 of 12 times that could be performed without stopping due to orthostatic hypotension. We analysed O2Hb levels at up to 60 s at 10-s intervals after HUT 60 s before mobilisation. We found that O2Hb levels decreased after the first (30°) HUT, but increased after HUT at 45° and 60°. Over a 60-s period, no statistically significant difference was observed. Arterial blood pressure fell by 6% on average across all the 12 tests. These results reveal that HUT orthostatic arterial hypotension caused an instantaneous decrease in oxygenation, but it returned to the baseline shortly thereafter. It is important to monitor the degree of orthostatic hypotension in patients after SAH. Gradual mobilisation may minimise the decrease in arterial blood pressure and maintain oxygenation of the cerebral cortex.