The influence of basic ventilation strategies and anesthetic techniques on cerebral oxygenation in the beach chair position: study protocol

BACKGROUND: Beach chair positioning during general anesthesia is associated with a high incidence of cerebral desaturation; poor neurological outcome is a growing concern. There are no published data pertaining to changes in cerebral oxygenation seen with increases in the inspired oxygen fraction or end-tidal carbon dioxide in patients anesthetized in the beach chair position. Furthermore, the effect anesthetic agents have has not been thoroughly investigated in this context. We plan to test the hypothesis that changes in inspired oxygen fraction or end-tidal carbon dioxide correlate to a significant change in regional cerebral oxygenation in anesthetized patients in beach chair position. We will also compare the effects that inhaled and intravenous anesthetics have on this process. METHODS/DESIGN: This is a prospective within-group study of patients undergoing shoulder arthroscopy in the beach chair position which incorporates a randomized comparison between two anesthetics, approved by the Institutional Review Board of the University of Michigan, Ann Arbor. The primary outcome measure is the change in regional cerebral oxygenation due to sequential changes in oxygenation and ventilation. A sample size of 48 will have greater than 80% power to detect an absolute 4-5% difference in regional cerebral oxygenation caused by changes in ventilation strategy. The secondary outcome is the effect of anesthetic choice on cerebral desaturation in the beach chair position or response to changes in ventilation strategy. Fifty-four patients will be recruited, allowing for drop out, targeting 24 patients in each group randomized to an anesthetic. Regional cerebral oxygenation will be measured using the INVOS 5100C monitor (Covidien, Boulder, CO). Following induction of anesthesia, intubation and positioning, inspired oxygen fraction and minute ventilation will be sequentially adjusted. At each set point, regional cerebral oxygenation will be recorded and venous blood gas analysis performed. The overall statistical analysis will use a repeated measures analysis of variance with Tukey’s HSD procedure for post hoc contrasts. DISCUSSION: If simple maneuvers of ventilation or anesthetic technique can prevent cerebral hypoxia, patient outcome may be improved. This is the first study to investigate the effects of ventilation strategies on cerebral oxygenation in patients anesthetized in beach chair position. TRIAL REGISTRATION: NCT01535274