Background:
Near-infrared spectroscopy-based cerebral oximetry is commonly used to monitor brain oxygenation during cardiovascular operations. Decreases in oximetry readings can suggest decreased cortical perfusion and impending ischemia by a variety of mechanisms. A recent study shows that avoiding low intraoperative cerebral oximetry values decrease mortality and major organ morbidity in patients undergoing coronary artery bypass grafting (CABG). We report the case of intraoperative cerebral oxygen desaturation with simultaneous decreased left internal mammary arterial flow in the setting of left sternal retraction.
Case description:
A 60-year-old woman, 59 inches tall, with diabetes mellitus, hypertension, and coronary artery disease was scheduled for three-vessel coronary artery bypass grafting, including a graft from the left internal mammary artery (LIMA) to left anterior descending (LAD) artery. Pre-operative workup was notable for 60-79% stenosis of the right carotid artery, from which the patient was asymptomatic. In addition to standard ASA monitors, Fore-Sight Cerebral Oximetry, with bilateral sensors, was applied. A catheter was placed in the left radial artery for invasive blood pressure monitoring. General endotracheal anesthesia was induced uneventfully and maintained with a combination of inhaled sevoflurane and intravenous sufentanil infusion and rocuronium boluses. The chest and sternum were opened, a Rultract skyhook was used for retraction of the left chest, and the surgeon began to dissect the LIMA. Blood pressure was maintained with administration of phenylephrine as needed. Cerebral oximetry readings remained close to their baseline of 75%. The surgeon then reported a lack of arterial blood flow through the LIMA; simultaneously, bilateral cerebral oxygen saturation readings began to drop quickly with a nadir of about 40%. Throughout this time, the arterial blood pressure reading remained steady. The retractor was removed, arterial blood flow returned to the LIMA, and the cerebral oxygen saturation readings returned to their baseline values.
Discussion:
In this case, bilateral cerebral oxygen desaturation occurred simultaneously with decreased LIMA flow, suggesting compromised perfusion affecting a number of vessels. Improvement in both cerebral oximetry readings and LIMA flow seemed to improve with removal of the left-sided sternal retractor. In this patient with relatively short height, the retractor may have compressed the left common carotid and subclavian arteries, or the patient may have had an anomalous more proximal origin of the LIMA, decreasing left-sided cerebral and LIMA perfusion. In the setting of right carotid stenosis, the parallel decrease in right-sided cerebral oxygen would suggest a dependency on collateral perfusion via the Circle of Willis. Alternatively, simultaneous systemic hypotension may have led to decreased global cerebral and internal mammary arterial perfusion; treatment with phenylephrine may have been enough to maintain peripheral radial arterial perfusion and thus a pressure waveform, but not sufficient to improve cerebral and internal mammary perfusion. Overall, cerebral oximetry monitoring during cardiac operations can offer valuable information regarding possible insults to end-organ perfusion, thereby heightening patient safety during these procedures.
References:
Hensley FA, et.al. A Practical Approach to Cardiac Anesthesia, 4th ed.
Mjrkin JM, et.al. AnesthAnalg 2007; 104 (1):51-58.
Vretzakis G, et.al. J Thorac Dis. 2014 Mar; 6(Suppl 1): S60–S69.
