The influence of positioning on spectroscopic measurements of brain oxygenation

This study was designed to evaluate the influence of body position during neurosurgical and cerebrovascular operations on regional cerebral oxygen saturation (rSO(2)). Awake volunteers (group I; n = 14), anesthetized patients (group II; n = 48) undergoing lumbar discectomy, and 12 patients undergoing carotid endarterectomy (group III) with internal carotid artery (ICA) stenosis were studied. Anesthesia in the patient groups was performed with sevoflurane (1.1 Vol% insp.) in N2O2/O-2 mixture (FiO(2) 0.4) rSO(2) was monitored with a INVOS 4100 cerebral oxymeter (Somanetics Corporation, Troy, MI). Measurements were done in all groups in supine position with head turned to the right and left side. Furthermore, in groups I and II, rSO(2) was measured in right lateral, left lateral, prone, or sitting position. In each position the parameters were registered at three times (1, 3, and 5 min after taking up the position). In the healthy volunteers, the mean rSO(2) values of both hemispheres were 71.3 +/- 5.0%. No significant changes of rSO(2) were found interhemispherical and upon turning the head to both sides or positioning to the prone and both lateral positions. After assuming the sitting position, the decrease of rSO(2) was not significant. In group II, rSO(2) decreased significantly in the sitting position. In group III, baseline readings for rSO(2) obtained from the side of ICA stenosis were significantly lower, compared to the contralateral side. After turning the head to the ipsilateral side, this difference diminished. In contrast, turning the head toward the contralateral side, the rSO(2) difference remained nearly constant, both values decreasing constantly throughout the observation period. In conclusion, after different positioning maneuvers awake and under anesthesia, alterations of rSO(2) can be registrated by near-infrared spectroscopy (NIRS).