Objectives: Detection of perioperative myocardial ischaemia in cardiac surgery remains challenging, as current clinical bedside monitoring is insufficient in making proper diagnoses in real-time. Cellular metabolism gets altered during ischaemia and tissue PCO2 is produced in the course of buffering anaerobic lactic acidosis. Myocardial tissue PCO2 has been suggested as a parameter of ischaemia, but PCO2 measurement devices for routine clinical usage are lacking. Study aims were to (i) evaluate the diagnostic potential of PCO2 in early detection of localized myocardial metabolic changes, (ii) compare PCO2 obtained by novel conductometric PCO2 sensors (IscAlert) with fibre-optical sensors (Neurotrend), and (iii) investigate the relationship between myocardial PCO2, PO2 and parameters of energy consumption during regional myocardial ischaemia/reperfusion.
Methods: In nine pigs, IscAlert sensors, Neurotrend sensors and microdialysis catheters were placed in the myocardium in the supply region of the left anterior descending (LAD) or circumflex (CX) coronary artery. LAD was occluded for 1, 3, 5 and 15 min, with 30 min of reperfusion between occlusion intervals. PCO2, PO2 and pH were measured continuously, microdialysis samples were obtained intermittently. The generation rate of CO2 (time-derivative of PCO2, TDPCO2) was calculated.
Results: Myocardial ischaemia was confirmed by PO2 and pH decline, accompanied by lactate and lactate/pyruvate ratio increase. PCO2 measured by IscAlert increased significantly (P<0.01) during all occlusions and the increase was related to duration of ischaemia. PCO2 normalized during reperfusion. No significant changes were observed in CX region, indicating high regional sensitivity and specificity. Similar results were found with fibre-optically measured PCO2 and maximum PCO2 values during each interval correlated well with PCO2 values measured by IscAlert (R=0.93±0.05, P<0.001). Maximum TDPCO2 depicted beginning of anoxia and diminishing metabolism during anaerobic conditions.
Conclusions: IscAlert sensors enable reliable and continuous detection of myocardial ischaemia by measuring myocardial PCO2. A combination of PCO2 and TDPCO2 seems promising in revealing information about substrate supply and cellular homeostasis during ischaemic events.