Cerebral Oximetry and Perioperative Outcome in Non-Cardiac Surgery

There have been a number of studies that have examined a link between intraoperative decreases in rSO2 and adverse perioperative outcome3-7. These studies, the vast majority of which have been in the setting of cardiac surgery, suggest that decreases in rSO2 (as detected by near-infrared spectroscopy) may be related to both adverse neurologic and non-neurologic sequelae. Interestingly, and importantly, the studies examining cerebral desaturation in non-cardiac surgical patients (such as those undergoing major abdominal surgery, carotid endarterectomy, liver transplantation, and pulmonary resection) have also uncovered a link between cerebral desaturation and non-neurologic outcomes3,7-12. These small studies have reported preliminary correlates between decreases in rSO2 and various postoperative complications and prolonged length of stay. These studies have also shown that the changes in rSO2 are not correlated with changes in traditional hemodynamic parameters (mean arterial pressure (MAP) and heart rate).

All of these studies suffer from similar flaws, however. They are typically small in size, have varying definitions of what constitutes a cerebral desaturation event, and have incompletely, or poorly defined complications. Also lacking is a mechanistic explanation for the cerebral desaturations as peripheral oxygen saturation typically remains near normal.

As a result, two natural questions arise in relation to this prior research. First, are these cerebral desaturations causative of the adverse outcomes (including non-neurologic complications), and second if these desaturations were treated (i.e. if cerebral oxygenation was normalized) would outcome be improved (i.e. or are cerebral desaturations merely an epiphenomenon)? Numerous studies have demonstrated the poor correlation of traditional hemodynamic parameters (such as blood pressure and heart rate) to cardiac output and oxygen delivery13-17. Historically in the fields of anesthesiology and critical care, we have focused our monitoring and resuscitation targets on perfusion pressures rather than organ flows. Neglecting the fact that organs require flow as well as pressure has led to an over-reliance on normal vascular pressures (such as arterial, central venous, and pulmonary capillary wedge pressures) as a surrogate for adequate organ flow18.

It is entirely possible that monitoring cerebral oxygenation and discovering a link between desaturation and non-neurologic outcomes may show that the brain is an index organ for tissue perfusion monitoring. That is to say, since the perfusion of major organs are typically not monitored during anesthesia, cerebral oximetry is an excellent means to monitor global decreases in tissue oxygen delivery. Consistent with this hypothesis, in the largest cerebral oximetry trial to date, Murkin and colleagues discovered that the incidence and magnitude of cerebral desaturations was related to major non-neurologic organ morbidity19.

The investigators will also be collecting blood samples preoperatively and at 24 hours postoperatively to determine if a panel of inflammatory biomarkers has the ability to predict postoperative complications.

Primary Objective: to determine the incidence and severity of cerebral desaturation in high-risk patients undergoing major vascular and abdominal surgery

Secondary Objectives:

1. To determine the factors associated with the occurrence of cerebral desaturation
2. To determine the relationship between desaturation and adverse perioperative outcome
3. To determine if the levels of a panel of inflammatory biomarkers is related to cerebral desaturation and postoperative complications.

Study design: prospective observational study Population: 200 consecutive high-risk patients undergoing non-cardiac surgery. High-risk patients will be defined as age> 65 undergoing major non-cardiac surgery including abdominal aortic aneurysm repair, major hepatic resection, colonic resection, pancreatoduodenectomy, or esophagectomy.

Methods: In addition to standard CAS monitors, all patients will undergo pulse contour cardiac output monitoring and cerebral oxygen saturation monitoring. The anesthetic technique will be at the discretion of the attending anesthesiologist. During the procedure, the attending anesthesiologist will be blinded to the rSO2 data.

As with previous studies conducted at our institution, cardiorespiratory variables (such as heart rate, systolic, diastolic and mean arterial blood pressures, peripheral and cerebral oxygen saturation, end tidal CO2 tension, end tidal anesthetic gas concentration, and cardiac index) will be sampled at a frequency of 60Hz. Data will be acquired from the Philips Intellivue® Monitor (Philips Healthcare, Andover, MA), FloTrac/Vigileo® minimally invasive CO monitor (Edwards Lifesciences, Orange County, CA), and the ForeSight® Cerebral Oximiter (CasMED, Brantford CT) and processed with TrendFace Solo® software (IExcellence Software, Germany). Arterial blood gas sampling will occur every 20 minutes. Other intraoperative variables collected will include case duration, blood loss, total narcotic dose, total benzodiazepine dose, use and dose of vasopressors, and use of neuraxial local anesthetics.

The definition of a cerebral desaturation differs between previously performed studies. Some have used an absolute decrease below 55%, variably defined decreases from the patients 'baseline' (either breathing room air or 100% oxygen), the time below a specific cerebral saturation threshold, or area under a specific cerebral saturation threshold (this measurement takes into account the duration and magnitude of a desaturation)3,5,21,22. Based on the intraoperative data collected, The investigators will examine all of the currently utilized definitions of cerebral desaturation and then construct receiver operating characteristic curves to determine which parameter has then highest predictive ability to link cerebral desaturation with perioperative outcome.

In consultation with our Biostatistical Consulting Unit the investigators calculated our sample size using previously reported incidences of cerebral desaturation, which range from 15-26% and accepted a margin of error of 5%. Based on a conservative estimate of the incidence (15%), The investigators would need a total of 195 patients to determine the incidence of cerebral desaturations with a 5% margin of error (see figure 1). The investigators will include 5 additional patients in our study due to our previous experience of a 1% rate of data loss during acquisition of rSO2 data (related to technical failures). The Lan and DeMets alpha spending function will be utilized to determine if the trial can be stopped early.

As secondary outcomes, the investigators will attempt to correlate decreases in rSO2 with a composite of well defined perioperative complications such as death, myocardial infarction, cerebrovascular accident, acute kidney injury (defined by the AKIN criteria, table 223), delirium (as defined by the CAM-ICU method, figure 324), postoperative infections, and the need for mechanical ventilation >24 hours in the first 28 postoperative days.

Based on the results of this study the investigators will be able to determine, with the aid of multivariate logistical regression analysis and the calculation of odds ratios, which definition of cerebral desaturation is mostly closely linked with the aforementioned outcome measures.