Novel use of new parameters in nirs cerebral oximetry in cabg surgery to display changes in brain perfusion

Abstract

Introduction The use of near-infrared spectroscopy (NIRS) to monitor continuous rSO2 values for the brain is well established (1,2). However the separation of oxygenated & deoxygenated components of NIRS is novel. We report a case of these parameters in CABG surgery. Methods A 68 year old diabetic male underwent CABG. Anaesthesia was induced with etomidate, fentanyl and rocuronium and maintained with air oxygen and isoflurane to a sedation index of 30. The surgery proceeded uneventfully. Some new observations were noted: The effect of increased CMRO2 and rising PSI: At 1042 the effect of increased EEG activity and MAP (85mmHg) leads to a rise in the Sedline PSI which increases delta O2HBi as the oxygen requirements of cerebral activity increase. Autoregulation in vivo. Venous (IVC) and aortic cannulation take place uneventfully cardiopulmonary bypass is commenced at 1052. Effect of CPB, hemodilution and non pulsatile flow: As flow switches from pulsatile to non pulsatile flow and CPB starts, there is an immediate reaction in the delta cHbi values. Haemodilution takes place as pump prime enters the circulation, so the haematocrit falls. O3 values fall but we see a large decrease in delta cHbi because of a reduction in delta O2Hbi as clear pump prime is being administered. Then as oxygenated blood from the CPB pump enters the circulation the delta cHbi recovers as oxygenated blood returns to the head. Note the marked reduction in cHbi and delta O2Hbi values that remains throughout subsequently, and which never recovers. This is the effect of non pulsatile blood flow and the effect it has on cerebral autoregulatory capacity. At this point the MAP is 78. Results: Discussion Principles of NIRS: As oxygenation in cerebral tissue changes, the wavelengths of light absorbed by tissue also change, forming the basis for measurement of regional cerebral oxygen saturation, rSO2. With these indices, we can display information about the changes in the underlying components calculating rSO2 values. δO2Hb is an index representing changes in the oxyhemoglobin component of rSO2. δHHb is an index representing changes in the deoxyhemoglobin component of rSO2. These indices provide visibility into changes in underlying oxyhemoglobin and deoxyhemoglobin components of rSO2. The relative contribution of each component to a patient's overall rSO2 was observed and the use of these additional monitoring indices may allow earlier detection of changes in the blood supply to the brain such as during commencement of cardiopulmonary bypass and the effects of raised CMRO2 and its effects on flow, and hence allow earlier corrective intervention. This may be of value in preventing impending cerebral injury in those patients who may be susceptible.