Reversing Cerebral Oxygen Desaturations Greater That 10% of Baseline Values Using NIRS in the ICU

Background and Rationale: Cerebral desaturation has previously been shown to be associated with significant morbidity in cardiac surgery postoperatively. As such, previously reported efforts have been aimed at treating intraoperative desaturation events, with early evidence suggesting that this may reduce the incidence of these adverse events. Our previous study, NIRS ICU (B2011:110) has demonstrated that significant cerebral oxygen desaturation [measured using near infrared spectroscopy (NIRS) derived cerebral oximetry] frequently occurs in the intensive care unit (ICU) within the first 24 hours following cardiac surgery. To date, no studies have addressed the early postoperative period (i.e. in the ICU) with respect to treating (and/or preventing) these desaturation events.

Specific Aims and Experimental Design: The specific aim of this pilot prospective interventional trial is to determine the feasibility/efficacy of treating cerebral oxygen desaturation in the ICU following cardiac surgery. Two groups of patients will be studied. Both groups will have cerebral saturation measured continuously both intraoperatively and postoperatively. The control group however, will have these measurements blinded to the intraoperative and postoperative caregivers. The interventional group will have the cerebral oximetry measurements available to the intraoperative and postoperative care team allowing them to intervene when a desaturation event occurs. If a cerebral desaturation occurs, defined as a decline in saturation of 10% from the patient's preoperative baseline, then a previously utilized interventional algorithm, normal cerebral oxygen saturation (NORMOSAT) (B2012:005), will be instituted to reverse the decrease in cerebral saturation, ideally preventing it from becoming a clinically meaningful desaturation (previously defined by others as saturation decline of 25% from the baseline). The algorithm used addresses many of the known causes of desaturation, including low arterial oxygen content (both saturation and hemoglobin) and cardiac output influences on cerebral blood flow. As such, if a desaturation occurs, the patient will first have the partial pressure of oxygen (PaO2) increased by increasing the inspired oxygen content. The partial pressure of carbon dioxide (PaCO2) will also be normalized by adjusting the ventilator settings. The cardiac output will be optimized and the blood pressure will be increased with standard ICU protocols to administer phenylephrine. If remaining low, the patients will be transfused to standard of care hemoglobin levels.

In this pilot trial, a convenience sample of 50 consecutive consenting patients undergoing cardiac surgery employing cardiopulmonary bypass (CPB) will be studied. After obtaining consent, bilateral cerebral oximetry sensors will be placed on the forehead of patients prior to the induction of anesthesia. Baseline (breathing room air) regional cerebral saturation will be recorded. Following this, induction of anesthesia will occur and continuous NIRS measurements will be collected during the surgical procedure with continued monitoring occurring for the first 24 hours (or until discharge) within the ICU. In the control group, conventional anesthesia and ICU standards of care will be carried out throughout the study period. In the interventional group, an algorithm based on the modification of previously defined important physiologic variables will be initiated to reverse the desaturation (beginning when the saturation drops at least 10% from the baseline) that occurs in the operating room (OR) and ICU.