Feasibility Study of Isoxic/Normocapnic End-tidal Gas Control to Decrease Incidence of Postoperative Delirium (POD) During Anesthetic Management

A. Background and Rationale:

Although respiratory end-tidal gas control is a fundamental principle of anesthetic management, the range of end-tidal (ET) O2 and CO2 typically seen during the conduct of anesthesia can significantly deviate from the awake baseline state, but has not been considered as a potential contributor to POD in previous investigations. Periods of both hypocapnia during mechanical ventilation and hypercapnia during the reestablishment of spontaneous ventilation are common. The use of 100% oxygen during anesthesia induction and emergence and maintenance of anesthesia with O2 concentrations of 50% are typical. The effects of these alterations in respiratory gases have significant effects on cerebral blood flow and oxygenation, which may be implicated in cognitive dysfunction. The investigators plan to examine the effects of controlled alterations in ET O2 and CO2 during anaesthesia and surgery on the incidence of POD.

B. Hypothesis and Study Objectives:

The investigators advance the hypothesis that ET respiratory gas control is a critical management consideration during anaesthesia; a much more important consideration than previously thought. Older patients appear to be at greater risk of 'intracranial steal' of regional CBF with alterations in CO2 and O2. The investigators previous study confirms an association between CO2 management and POD. Prior MR imaging suggests that a combination of hyperoxia and hypocapnia may be particularly worrisome, a very common situation during anesthesia. The investigators suggest that anesthetic management may be optimized for cerebral health by attempting to maintain respiratory gases at or near the patient baseline values to stabilize CBF during the conduct of anesthesia. An exception occurs during neurosurgical procedures where deliberate alterations to lower ET CO2 may be required. The marked CBF fluctuations as seen with controlled ET gas manipulation in our prior work imply that such CBF changes can occur under anesthesia where similar changes in ET gases routinely occur. The investigators propose that such large alterations in CBF and oxygenation may be a contributing factor to the development of POD in susceptible individuals. Here is proposed a feasibility trial of rigorous maintenance of ET gases at a patient's own baseline to study if such management has an influence on the incidence of POD.

C. Methodology: Summarize study location (facility), eligibility criteria, details regarding recruitment, consent, and randomization, interventions(s), covariates, data sources as applicable.