Adult Renal Near Infrared Spectroscopy and Oxygen Delivery During CPB: Correlations to Prevent Acute Kidney Injury

Abstract

A major complication associated with cardiopulmonary bypass (CPB) is acute kidney injury (AKI), with around 30% of patients experiencing some sort of renal insult (31). Kidney performance is strongly linked to cardiac performance, so perfusionists can play a major role in implementing strategies to reduce the incidence of AKI. The use of Near Infrared Spectroscopy (NIRS) has been validated for the use of cerebral oximetry for both pediatric and adult patients, unlike somatic monitoring where only pediatric randomized control trials have proven to be successful. Since the distance from sensor to organ for adults is greater than 1.4 centimeters, there are not any studies to correlate perfusion parameters to adult renal oximetry. The primary goal of this pilot study was to correlate renal oximetry values to pre-established perfusion outcome markers that are routinely measured during CPB. In this way, renal NIRS may be used as a real time trending device to help prevent AKI. The INVOS™ system was used for both cerebral and renal NIRS monitoring. Renal oximetry pads were placed between the 11th-12th intercostal spaces and the most accurate baseline rSO2 (regional oxygen saturation) level was obtained before sedating the patients. Baseline variables obtained were: age, weight, height, body surface area, history of diabetes, ejection fraction, creatinine, hemoglobin, hematocrit, cerebral oximetry, renal oximetry, and lactate values. Operative variables obtained were: hemoglobin, mean arterial pressure, pump flow, cardiac index, cerebral oximetry, renal oximetry, lactate, temperature, venous oxygen saturation, and oxygen delivery. A multivariable statistical analysis model was used to correlate the data. The results showed the strongest statistical correlations of renal oximetry with hemoglobin (p<0.01, p=0.01), cardiac index (p<0.0001, p<0.01), and oxygen delivery (p<0.0001, p<0.0001). The higher these variables were, the higher the renal oximetry values and vice versa. The changes in oxygen delivery were correlated to the changes in renal oximetry values. Specifically as the DO2 increases 1.15 mL/min1/m2 (p<0.01), the percent change in the left renal oximetry increases 1%. As for the right renal, when the DO2 increases 0.94 mL/min1/m2 (p<0.01), the percent change in the right oximetry increases 1%. A renal oximetry value with a decrease of more than 20% from pre-operative baseline is associated with a significantly lower DO2 than renal oximetry values without a decrease more than 20% from pre-operative (p=0.01). The DO2 difference was calculated at 21.97 ml/min1/m2. There is a direct correlation between oxygen delivery values and renal oximetry saturation values. In conclusion, this pilot observational study has shown the INVOS™ system to be a valuable real-time trending device for renal oximetry saturation values with perfusion parameters to help prevent or reduce acute kidney injuries for cardiopulmonary bypass patients.