Cerebral regional oxygen saturation evaluated by near-infrared spectroscopy during cardiac surgery under cardiopulmonary bypass: an observational study

Abstract

Introduction. Near-infrared spectroscopy (NIRS) is a non-invasive method of cerebral monitoring, offering real-time survey of the regional cerebral oxygen saturation (rSO2). The growing popularity of NIRS monitoring in cardiac surgery is supported by promising results regarding outcome, and as a monitoring of cerebral autoregulation and tissue oxygenation. Normal rSO2 values, before anaesthesia, range from 60% to 80%, and from 55-60% for cardiac surgery patients. Cerebral desaturation is considered pathological when rSO2 values decrease more than 20% from baseline. Cardiac output, hemoglobin concentration, PaCO2, inspired oxygen concentration and hemoglobin saturation primarily affect rSO2. The aim of this retrospective study was to evaluate the occurrence of cerebral oxygen desaturation in our cardiac surgery population scheduled for cardiac bypass and/or valvular replacement. Methods. After Ethical Committee approval, we reviewed 117 patient records scheduled for coronary artery grafting (CABG) and/or valvular replacement under cardiopulmonary bypass (CPB) within a 17 months period. Nonpulsatile pump flow rate of 2.0-2.5 L/min/m2, membrane oxygenator and 27-μm arterial line filter was used during CPB. Perfusion pressure was maintained above 60 mm Hg. The whole procedure was realised under hypothermia at 28°C with α- Stat pH management. A standardized anaesthesia protocol consisted of target-controlled infusion of Remifentanil/Propofol. During CPB, blood pressure targets, transfusion of packed red blood cells, and the rate of rewarming were based on institutional standard clinical practice. rSO2 values were recorded by NIRS (INVOS® ) at the following time points during procedure: intubation, sternotomy, cannulation, on CPB, cooling, aortic clamping, cardioplegia, warming, declamping, off CPB, and sternum closure. Statistical analysis included Student's T and Fisher test. Data are presented as mean ± standard deviation (SD); p<0.05 was considered significant. Results. Patients included 86 male and 31 female, aged 67.26 ± 13.17, ASA III score. Abnormal rSO2 values under 20% from baseline were found in 34 patients (29,1%) during surgery. Of these patients, 47% presented desaturation at warming, and 35.4% at unclamping. rSO2 varied between 19.3% and 22.5% at all the others time points excepted intubation, sternotomy, and start of cooling (3.2%, 12.9% and 9.6% respectively). Secondary comparison, between the group presenting desaturation (n=34) and the other group (n=83) did not provide significant differences regarding, baseline Hemoglobin concentration (13.56 ± 1.72 vs 13.41 ± 1.92, p=0.69), history of HBP (23/27, 85.19% vs 58/63, 92.06%, p=0.44), duration of CPB (143.50 ± 39.88 vs 149.53 ± 57.99, p=0.52) and aortic cross clamping (101.47 ± 31.82 vs 104.18 ± 39.59, p=0.72). Conclusion. Cerebral regional oxygen desaturation was observed in 29% of patients mainly during hypothermia, warming and non-pulsatile CPB. No evident causes can be provided by the present study.