Evaluation of near-infrared spectroscopy in patients with acute coronary syndrome undergoing on and off-pump coronary artery bypass graft surgery

Thesis (M. Tech. (Clinical technology)) - Central University of technology, Free State, 2012

The objective of this study was to investigate whether intra-operative regional cerebral tissue oxygen saturation (NIRS) and hemodynamic monitoring in patients with Acute Coronary syndrome (ACS) during coronary bypass graft surgery (CABG on-pump vs. off-pump) can predict clinical outcomes and complications. Data from 60 CABG patients (30 on-pump and 30 off-pump) were analyzed. The regional cerebral tissue oxygen saturation was monitored by using near-infrared spectroscopy (NIRS). The sensors were positioned in the middle of the patient's forehead and the cables were connected to the sensors and to the INVOS 5100C® Oximeter. According to NIRS values obtained, patients were subdivided into two groups. Patients in Group 1 had absolute NIRS values more than 50 or less than a 20% drop from the baseline value. Patients in Group 2 had absolute NIRS values of less than 50 or a drop of more than 20% from the baseline value. The lowest value recorded during the procedure was recorded for this purpose, irrespective of the time this value was obtained. Intra-operative hemodynamic monitoring was captured by a computer software program (Supplier Datex Ohmeda, South Africa). In order to describe surgical outcomes several parameters were analysed and compared. This included a Pre- and Post-operative Mini-Mental state examination that was performed to identify neurological outcomes or impairment. The NIRS values and trends in relation to renal function (U&E and creatinine, urine output, and urine electrolytes), as well as clinical outcomes were analyzed post-operatively for the different groups. Clinical outcomes were described using the Society of Thoracic Surgeons Database (STS database) data fields, and specifically the recording of complications. The overall clinical outcomes were analysed between the on-pump and off-pump groups as well as the NIRS results between the two groups. In order to elucidate the predictive role of NIRS the patients were divided into groups with either impaired /reduced NIRS values or acceptable NIRS values according to published results where a reduction of more than 20% from baseline or absolute values of less than 50 were associated with inferior outcomes. Finally, the predictive value of NIRS was evaluated within the on- and then the off-pump groups. In this analysis the outcomes of patients with reduced NIRS values was compared to those of patients with acceptable NIRS values. The study demonstrated that by far the majority of patients with reduced cerebral flow/oxygen delivery as reflected in cerebral NIRS, had on-pump CABG procedures (84% fell in risk group 2). It also showed that a NIRS reduction of more than 20 % from baseline and values of less than 50, has an impact on post–operative renal function. Monitoring of cerebral oximetry intra-operatively by using near-infrared spectroscopy during cardiac surgery (especially in on-pump cardiac surgery patients) allows the perfusionist and anaesthesiologist to detect cerebral desaturation and to intervene as necessary. This study also showed a tendency towards less renal function impairment in patients with absolute NIRS values > 50 or where there was < 20% drop from baseline. It is probably important to consider studying the time spend below 50 or a drop of more than 20% from baseline NIRS values, or the “area under the curve” as a specific factor contributing to the increased risk for post-operative complications applied on an increased study population. The study supports the routine use of NIRS as a non-invasive trend monitor of cerebral saturation and certainly initiated interventions by both anaesthetic and perfusion staff which contributed to excellent clinical outcomes in this research study.