Review question/objective
The objective is to identify the effectiveness of cerebral oximetry monitoring in reducing the incidence of perioperative stroke in patients undergoing coronary artery bypass.
Background
Anesthesia providers have long been concerned with maintaining appropriate hemodynamics in the anesthetized patient, but more recently, the focus has shifted from arbitrary hemodynamic values (e.g. minimum blood pressure or heart rate) to tissue perfusion (i.e. the delivery of blood to various body organs and tissues). Many of the measures of tissue perfusion are indirect and non-specific (e.g. pulse oximetry measures hemoglobin oxygen saturation of blood going to the organ, but not the amount of oxygen actually being used), so these measures cannot truly address the clinical goal of adequate organ perfusion.
While rapid medical advances in cardiac surgery are being made, the demographics of the cardiovascular surgical population are shifting. Patients undergoing procedures are now older, with an increasing number of comorbidities, including pre-existing cerebrovascular disease, and impaired autoregulation. These patients in particular are at an increased risk of stroke during coronary artery bypass grafting (CABG).1-3 Coronary artery bypass graft surgery is a procedure which bypasses the diseased coronary arteries of the heart, therefore optimizing blood flow to the heart itself.
Proper hemodynamic management of the coronary artery bypass patient is necessary, not only to ensure a successful procedure, but also for improving the postoperative quality of life of the patient. Complications occur frequently, due to the complexity of the procedure and coexisting patient comorbidities. A major cause of morbidity in the postoperative period after cardiac revascularization surgery is neurological injury,1 and the most common neurologic complication associated with the procedure is stroke. Neurologic deficits related to intraoperative events can be reversible or permanent and occur at a high frequency (nearly 60% of cases). Stroke occurs less frequently (in an estimated 2-9% of all cases) but because of the severity of morbidity, it remains a substantial clinical concern.4 Goldman et al. found that with a decrease in perioperative stroke comes decreased costs, shorter length of stay, and improved patient outcomes.5
Stroke, defined as brain, spinal cord or retinal cell death attributable to ischemia, is of particular concern in light of the rising number of older surgical patients, especially those with pre-existing cerebral vascular disease.3 The criterion for determining perioperative clinical stroke is an acute focal neurologic deficit persisting greater than 24 hours and confirmed by brain computed tomography imaging.1-3 Hypoperfusion, a physiologic element that is thought to play a major role in the etiology of perioperative stroke, can be detected by cerebral oximetry through preservation of regional brain oxygen saturation values (rSO2) at baseline, thus reducing the occurrence and periods of hypoperfusion intraoperatively.5 Hypoperfusion, a pronounced decrease in middle cerebral artery flow velocity, in conjunction with low rSO2, is associated with neurologic injury.6
Cerebral oximetry is a simple device that allows for the monitoring of rSO2,7 and can assist clinicians in correcting cerebral deoxygenation in moments, with the goal of improving clinical outcomes. Interventions that may be utilized to maintain cerebral oxygen saturation include: verification of proper cerebral oximeter placement, optimization of cerebral oxygen delivery through adjustment of FiO2 or PaCO2, or a reduction of the cerebral metabolic rate of oxygen consumption (CMRO2) by increasing anesthetic depth.1 While not a relatively new piece of medical equipment, Jobsis brought about cerebral oximetry in 1970, but its potential impact was misunderstood due to the lack of data concerning cerebral tissue oxygenation.7 Until further research was published concerning regional cerebral oxygenation, the use of cerebral oximetry was scarce.8 Presently, the use of cerebral oximetry continues to increase with findings presented through expanding research.
An early-randomized controlled trial conducted by Murkin was performed to determine if the use of cerebral oximetry during coronary artery bypass surgery directly correlates with improved clinical outcomes, specifically a decrease in postoperative stroke and decreased length of stay (LOS). Though a small sample size was utilized, applicable findings include: maintenance of rSO2 greater than 75% of the patient's baseline directly corresponding to a decreased length of stay from 10-22 days to seven days following coronary artery bypass surgery.8 Murkin also describes cerebral oximetry as being useful in early detection of cerebral ischemia, ultimately decreasing serious clinical outcomes often seen after coronary artery bypass.8
Cerebral oximetry, unlike pulse oximeters, does not require pulsatile blood flow, which allows for its utilization during cardiopulmonary bypass.1 Additionally, cerebral oximetry monitoring measures primarily venous blood within the brain because it cannot distinguish between arterial and venous blood. The widely accepted calculated arteriovenous saturation (i.e. "70% jugular bulb venous saturation and 30% arterial saturation"7[p1015]) is used to evaluate the precision of cerebral oximeters,7,9 thus providing practitioners with data regarding the adequacy of cerebral oxygen supply and demand.1 This valuable information, in turn, results in early identification and neuroprotective intervention of the hypoperfused brain.3 Furthermore, according to Edmonds, the use of cerebral oximetry shows lower incidences of stroke.6
The impact of cerebral oximetry has been widely studied in cardiac surgery, and while there are studies looking at a variety of variables and outcome measures, there is currently no systematic review looking at stroke in the coronary artery bypass patient population. A search of Cochrane Library of Systematic Reviews, JBI Database of Systematic Reviews and Implementation Reports, and MEDLINE was performed, and no systematic review was found pertaining to cerebral oximetry monitoring during coronary artery bypass grafting and perioperative incidence of stroke. The initial search has revealed several high-level evidence studies regarding this topic, which indicates investigation of the proposed research may be of benefit.
Inclusion criteria
Types of participants
This review will consider studies that include human subjects, aged 18 years and older, undergoing coronary artery bypass surgery; therefore patients 17 years and younger will be excluded from this study. Our exclusion of pediatric patients is due to the variability in cardiac pathology presentation and the various etiologies of cardiac complications in children, which are not similar to those in the adult cardiac population.
Types of intervention(s)/phenomena of interest
This review will consider studies that evaluate cerebral oximetry monitoring in comparison to absence of cerebral oximetry monitoring. When cerebral oximetry was utilized in intervention groups, desaturation guidelines were individually established to guide treatment. Desaturation was defined differently between studies; however, regardless of varying guidelines, steps were taken to correct saturations back to established baselines set by the individual study.
Types of outcomes
This review will consider studies that include the following outcome measures: the incidence of perioperative stroke (i.e. from the surgical period to end of hospitalization), defined as brain, spinal cord, or retinal cell death attributable to ischemia, based on neuropathological, neuroimaging and/or clinical evidence of injury.
Types of studies
The quantitative component of the review will consider experimental study designs including randomized controlled trials, non-randomized controlled trials, prospective and retrospective cohort studies and case control studies to ensure high level evidence is available for inclusion.
Search strategy
The search strategy aims to find both published and unpublished studies. A three-step search strategy will be utilized in this review. An initial limited search of MEDLINE and CINAHL will be undertaken followed by an analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. A second search using all identified keywords and index terms will then be undertaken across all included databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies. Studies published in English or English translation will be considered for inclusion in this review. Studies published between 2000 and 2015 will be considered for inclusion in this review to ensure the most recent interventions are provided. Additionally, little information exists before 2002 regarding cerebral oximetry monitoring specifically during coronary artery bypass surgery.
The databases to be searched include:
EMBASE, MEDLINE, Cochrane, Wiley Online Library, CINAHL, Elsevier Science Direct
The search for unpublished studies will include:
Google Scholar, New York Academy of Medicine Grey Literature Report, MedNar, ProQuest, ClinicalTrials.gov
Initial keywords to be used will be:
Cerebral oximetry, coronary artery bypass, perioperative stroke, stroke
Assessment of methodological quality
Papers selected for retrieval will be assessed by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) (Appendix I). Any disagreements that arise between the reviewers will be resolved through discussion.
Data extraction
Data will be extracted from papers included in the review using the standardized data extraction tool from JBI-MAStARI (Appendix II). The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives.
Data synthesis
Quantitative data will, where possible be pooled in statistical meta-analysis using JBI-MAStARI. All results will be subject to double data entry. Effect sizes expressed as odds ratio (for categorical data) and weighted mean differences (for continuous data) and their 95% confidence intervals will be calculated for analysis. Heterogeneity will be assessed statistically using the standard Chi-square and also explored using subgroup analyses based on the different study designs included in this review. Where statistical pooling is not possible the findings will be presented in narrative form including tables and figures to aid in data presentation where appropriate.
Conflicts of interest
The authors have no conflicts of interest to declare.
Acknowledgements
None
References