• 
• 

Three Part Question

Does [the use of Cerebral Oximetry] in [Cardiac Surgeries] carry [the clinical significance and financial relevance which is generally attributed to it]

Clinical Scenario

You are a final year medical student visiting US for a Month long clinical rotation in the department of cardiothoracic surgery. During the Grand Rounds the attending surgeon makes a statement that the use of cerebral oximetry is not clinically significant and puts an extra burden on the patient’s medical bills. He tells you that there is not much evidence regarding effectiveness of Cerebral Oximetry (Transcranial Near-Infrared Spectroscopy-NIRS to monitor ScO2) for Cardiac Surgery and about its potential applications, overall clinical value and whether to keep using it or not. You take the issue at hand to check the literature yourself and reach a conclusion.

Search Strategy

The medical archives including Pubmed, Embase, index copernicus and index medicus were searched to find out suitable articles already published and written on the relevant subject considering Cerebral Oximetry Use for Cardiac Surgery. Different papers were looked upon and each had an argument, scientific evidence and background.
We structured a best evidence topic in cardiothoracic surgery according to the given protocol. The question addressed was Does the use of Cerebral Oximetry in Cardiac Surgeries carry the clinical significance and financial relevance which is generally attributed to it

300 papers were found using the reported search. From these 5 papers were identified. That provided the best evidence to answer the question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that The effectiveness and reliability of intraoperative cerebral oxygen saturation (ScO2) monitoring in terms of critical neurological outcomes after cardiac surgery is NOT demonstrated by these studies. A strong association was found with a less duration of hospital stay but cerebral oximetry poorly predicts postoperative neurological dysfunction. This can rightly be concluded from this study that NIRS Cerebral Oximetry does not carry the clinical significance and relevance which is generally attributed to it and is not cost effective.

Key Words: Transcranial Near-Infrared Spectroscopy; Neurological outcome; Cerebral Oximetry

Search Outcome

300 papers were found using the reported search. From these 5 papers were identified. That provided the best evidence to answer the question. These are presented in table 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Murkin 2007 England	Two-Hundred Coronary artery bypass patients were randomized into two group, with one group n=100 received intraoperative cerebral regional oxygen saturation (rSO2) monitoring with active display and treatment intervention protocol whereas the other control group n=100 did not.	Randomised Prospective study	Patients in the control group stayed longer in the Intensive care unit (P 0.029) and had significantly more mortality compared to the intervention group	There was a significant inverse correlation between RSO2 and duration of postoperative hospitalization in patients. However, the incidence of major adverse complications was same between the two groups	By monitoring cerebral rSO2 in coronary artery bypass patients adverse effects like profound cerebral desaturation and significant major organ dysfunction can be avoided, however the overall incidence of adverse effects remain the same whether RS02 monitoring is done or not.
Reents et al 2002 Germany	Forty-seven patients undergoing Coronary Bypass surgery underwent preoperative and postoperative neuropsychological evaluation. Patients were classified into two groups based on the presence or absence of post op cognitive dysfunction	Prospective Observational Study3	Sixteen patients (34%) showed postoperative cognitive dysfunction. Cerebral oxygen saturation values less than 40% occurred in 17, whereas a decrease of more than 25% occurred in 37 patients.	The duration and extent below the two cutoff ScO2 values was similar in patients with and without cognitive dysfunction.	INVOS 4100 device is not predictive for postoperative cognitive performance in patients undergoing coronary artery bypass grafting.
Hong et al 2007 South Korea	One-hundred patients undergoing elective VHS, underwent neurocognitive evaluation one day before and 7 days after surgery. The incidence and duration of decrease in RSO2 values was recorded	Prospective Observational Study	Twenty-three patients (23%) demonstrated POCD.	No significant difference was observed in either the incidence or duration of decrease in RSO2 values between patients with or without POCD. However longer postoperative hospitalization was associated with cerebral desaturation.	Cerebral oximetry cannot predict POCD, however cerebral desaturation can be used as an index for systemic perfusion.
Fischer et al 2011 USA	Thirty Patients underwent aortic arch surgery and regional oxygen saturation was recorded. adverse outcome, extubation time, intensive care unit length of stay, and hospital length of stay data were collected and compared with the integrals of regional oxygen saturation	Prospective Observational Study	There were 30 major and 29 minor complications identified. Sixteen (53.3%) patients had at least 1 major complication.	Logistic regression showed statistically significant associations between low oxygen saturation and severe adverse outcome. Incidence for regional oxygen saturation. threshold of 60% had an extended hospital stay of 4 days leading to an additional cost of $8300.00.	Our findings lend evidence to support the association of decreased perioperative cerebral oxygenation values with poor outcomes after aortic arch surgery.
Samra et al 2000 USA	Ninety-nine patients undergoing 100 CEAs, were studied to find the association between cerebral desaturation and poor neurological outcome.	Prospective Observational Study	The mean decrease in rSO2 after carotid occlusion in the neurologic symptoms was significantly greater (P = 0.0002) than in the no neurologic symptoms group	A 20% decrease in rSO2 reading from the preclamp baseline, as a predictor of neurologic compromise, resulted in a positive predictive value of 33.3% and a negative predictive value of 97.4%.	Cerebral oximetry performs poorly when it comes to positive predictive value in detecting patients with poor neurological outcome.

Comment(s)

Stroke, CNS Ischemia and a wide range of neurological outcomes may result as part of an open heart surgery. The embolic phenomena and regional cerebral microcirculation imbalance as a result of Cardiac surgery may be the cause of CNS defects and leads to increase hospital stay. An invasive technique can be used to find ScO2 by placing probe in the internal jugular vein but the non-invasive NIRS technique carries its advantage. Cerebral hemispheres oxygenation is vital for the neurological functioning. Murkin found that though cerebral oxygen monitoring can reduce the incidence of cerebral desaturation and major organ dysfunction but the overall, incidence of adverse effects remain the same whether you do cerebral oxygen monitoring or not. Moreover Reents also found that cerebral oximetry cannot decrease the incidence of postoperative cognitive dysfunction, something that is generally attributed to it. Hong and his team found that cerebral oximetry can be used as an index of system oxygen perfusion which is associated with poor post-op outcomes and amounts to increased duration of hospitalization post-op. Hence it can be argued that there are cheaper alternatives to measure systemic oxygen perfusion than cerebral oximetry, hence new studies need to be done to find out if cerebral oximetry does carry any mortality benefit for the patient and is cost-effective. A study done by Fisher and his team found out that incidence for regional oxygen saturation threshold of 60% had an extended hospital stay of 4 days leading to an additional cost of $8300.00. These adverse outcomes are due to systemic oxygen desaturation, and not due to post-op neurological dysfunction. Another study done by Samra, found that cerebral oxygen monitoring has a poor positive predictive value when it comes to identifying patients with poor neurological outcome.

Clinical Bottom Line

The effectiveness and reliability of intraoperative ScO2 monitoring in terms of critical neurological outcomes after cardiac surgery is demonstrated by these studies. A strong association was found with a less duration of hospital stay and decrease neurologic Injury with the use of Cerebral Oximetry. This can rightly be concluded from this study that NIRS Cerebral Oximetry does not carry the clinical significance and relevance which is generally attributed to it.

References

1. Murkin et al Monitoring Brain Oxygen Saturation During Coronary Bypass Surgery: A Randomized, Prospective Study International Anesthesia Research society 104 (1): 51-58. 2007.
2. Reents et al CEREBRAL OXYGEN SATURATION AND EARLY POSTOPERATIVE COGNITIVE FUNCTION Ann Thorac Surg 2002;74:109–14.
3. Hong et al Prediction of cognitive dysfunction and patients’ outcome following valvular heart surgery and the role of cerebral oximetry European Journal of Cardio-thoracic Surgery Europeon J of Cardio-Thoracic Surgery 33 (2008) 560—565.
4. Fischer et al Noninvasive cerebral oxygenation may predict outcome in patients undergoing aortic arch surgery The Journal of Thoracic and Cardiovascular Surgery 2011 Mar;141(3):815-21.
5. Samra et al Evaluation of a cerebral oximeter as a monitor of cerebral ischemia during carotid endarterectomy Anesthesiology 2000 Oct;93(4):96470.