Intraoperative oxygen concentration and neurocognition after cardiac surgery: study protocol for a randomized controlled trial

Postoperative cognitive dysfunction (POCD) is a common complication of cardiac surgery. Studies have identified potentially injurious roles for cardiopulmonary bypass (CPB) and subsequent reperfusion injury. Cognitive dysfunction has also been linked to the deleterious effects of hyperoxia following ischemia-reperfusion injuries in several disease states, but there has been surprisingly little study into the role of hyperoxia in reperfusion injury after CPB. The potential for tightly regulated intraoperative normoxia to ameliorate the neurocognitive decline following cardiac surgery has not been investigated in a prospective manner. We hypothesize that the use of a protocolized management strategy aimed towards maintenance of an intraoperative normoxic level of oxygen, as opposed to hyperoxia, will reduce the incidence of POCD in older patients undergoing cardiac surgery.

One hundred patients aged 65 years and older undergoing non-emergency coronary artery bypass grafting surgery on cardiopulmonary bypass will be enrolled in this prospective, randomized, controlled trial. Subjects will be randomized to receive a fraction of inspired oxygen of either 35% or 100% while under general anesthesia throughout the intraoperative period. The primary outcome measure will be the incidence of POCD in the acute postoperative phase and up to 6 months. The assessment of neurocognition will be undertaken by trained personnel, blinded to study group, with the telephone Montreal Cognitive Assessment (t-MoCA) tool. Secondary outcome measures will include assessment of delirium using the Confusion Assessment Method (CAM and CAM-ICU), as well as time to extubation, days of mechanical ventilation, length of ICU and hospital stay and mortality at 6 months. With the aim of later identifying mechanistic aspects of the effect of oxygen tension, blood, urine, and atrial tissue specimens will be taken at various time points during the perioperative period and later analyzed.

This trial will be one of the first randomized controlled studies to prospectively assess the relationship between intraoperative oxygen levels and postoperative neurocognition in cardiac surgery. It addresses a promising biological avenue of intervention in this vulnerable aging population.

ClinicalTrials.gov Identifier: NCT02591589, registered February 13, 2015.