Cerebral Oximetry: FORE-SIGHT versus Hindsight
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Editor’s Note:
I have used BIS monitoring forever, and have always found it a very valuable tool. So recently I get an email from a guy named Eric Sughrue, and some stuff about the FORE-SIGHT cerebral oximeter. At first I wasn’t that interested, but he was exceptionally polite, professional, and kinda like a tic on a blood hound. Surprisingly persistent… but not in an unpleasant way.
It wasn’t until he mentioned that the director of clinical education coming to assist institutions on the learning curve- was none other than a perfusionist and friend of mine that I had done contract work with, in Hawaii back in the mid 90’s.
Well that guy is not only an excellent perfusionist, but he was also AMSECT president at one time, and remains a very big name in our industry.
I have always admired George Galbraith, CCP, and his dry sense of humor- and exceptionally keen analytic approach to problem solving- be it Perfusion, politics, or social agendas.
So anyway- back to the FORE-SIGHT monitor…
Below is a brief look at some key points during heart surgery- the numbers you might see- and a CASMED clinical specialist (Kelly Cullerton, Clinical Specialist, Midwest Region) taking the time to give her perspective and interpretations of what the values indicate or why the numbers have changed.
Contact Information
CAS Medical Systems, Inc.
44 East Industrial Road
Branford, CT 06405
Direct: (203) 745-7293
A Brief Dialogue on FB Today: 4/29/2014
OP CABG @ incision:
The cerebral oxygen saturation (StO2) acceptable range is between 60-90%, with an intervention threshold at <60%. This reflects a mixed venous to arterial capacity (70%/30%) in the microvasculature of the frontal lobe.
Cerebral tissue oxygen saturation reflects regional cerebral metabolism and the balance of cerebral oxygen supply and demand. Cerebral oxygen delivery is contingent on two variables: arterial oxygen content and cardiac output (the latter is affected by afterload, contractility and preload).
At time of incision (medial sternotomy), the cerebral oxygen readings were: 70/73 (L brain; R brain). This reflects an acceptable range for both L and R brain at time of sternotomy and exposure of the heart.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
@ Sternotomy
The StO2 readings at time of sternotomy were 74/80 (L brain/R brain). This reflects a continued stable range for both L and R StO2 readings, despite exposure of the heart.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
@ LIMA Dissection
At time of harvesting of the LIMA (Left internal mammary artery; also known as the LITA, or Left internal thoracic artery). The StO2 readings were 70/73 (L to R). This is a slight decrease from readings noted at the previous event. This can be due to manipulation and displacement that may occur with harvesting this artery.
It should be noted that the readings are still within the acceptable range of 60-90%.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
@ SVG to Diag- Off Pump
At time of SVG to Diag, the patient was hypoventilated to allow for distal access. During hypoventilation, the body’s carbon dioxide levels increase. Carbon dioxide (at 35 and above) is a potent mediator of cerebral vascular tone. Therefore, the cerebral flow increased, which then produced an increase in the StO2. The readings were 93/95 (L/R brain). These values are above the acceptable range due to manipulation of the ventilation status of the patient.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
Lima > LAD Anastamosis
At time of graphing of the LIMA to the LAD, the patient was hypoventilated to allow for vascular access. By hypoventilation, the patient’s carbon dioxide levels were increased, which allowed for greater cerebral blood flow. This supported cerebral perfusion during a time where flow and perfusion to the cerebral tissue could be decreased due to the surgical procedure of attaching the LIMA to the LAD.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
Reverse Trendelenberg- LIMA
The patient was placed in the reverse trendelenberg position to allow for access and positionality of the patient. The patient’s lower extremities are leveled lower than the head, and the patient is elevated on inclined plane. The reverse trendelenberg position compromises the circulation of blood. A considerable volume of blood is pooled towards the lower extremities, which results in reduced cardiac output.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
@ Sternal Closure
At time of closing, the patient’s StO2 readings were 90/93 (L/R). Once again, this is at the top of the acceptable range, with the R cerebral readings 3% above. This could be due to intermittent hypoventilation during the surgical procedure and it’s effect on CO2. The StO2 readings were stable and consistent between 70’s-90’s during the procedure.
Procedure considerations to note that can affect the cerebral perfusion and oxygenation are: use of adenosine or esmolol to slow the rate and contractility, which will decrease flow and therefore perfusion; circumflexion of the heart, which will impede the emptying of blood from the head; and exposure of the heart. At time of this position change, the patient’s StO2 readings were 86/89 (L/R). Therefore, despite the potential effects of the position change were tolerated well by the patient.
Analysis: Kelly Cullerton, Clinical Specialist, Midwest Region
Nice Job Kelly-
Very cogent- and your assessments make sense and are clinically sound in my opinion.
Frank 🙂
