Hepatic and abdominal carbon dioxide measurements detect and distinguish hepatic artery occlusion and portal vein occlusion in pigs.

Hepatic artery (HA) occlusion and portal vein (PV) occlusion are the most common vascular complications after liver transplantation with an impact on mortality and retransplantation rates. The detection of severe hypoperfusion may be delayed with currently available diagnostic tools. Hypoperfusion and anaerobically produced lactic acid lead to increases in tissue carbon dioxide. We investigated whether the continuous assessment of the intrahepatic and intra-abdominal partial pressure of carbon dioxide (PCO(2) ) could be used to detect and distinguish HA and PV occlusions in real time. In 13 pigs, the HA and the PV were fully occluded (n = 7) or gradually occluded (n = 6). PCO(2) was monitored intrahepatically and between loops of small intestine. The hepatic and intestinal metabolism was assessed with microdialysis and PV as well as hepatic vein blood samples, and the results were compared to clinical parameters for the systemic circulation and blood gas analysis. Total HA occlusion led to significant increases in hepatic PCO(2) and lactate, and this was accompanied by significant decreases in the partial pressure of oxygen and glucose. PV occlusion induced a significant increase in intestinal PCO(2) (but not hepatic PCO(2) ) along with significant increases in intestinal lactate and glycerol. Gradual HA occlusion and PV occlusion caused steady hepatic and intestinal PCO(2) increases, respectively. Systemic clinical parameters such as the blood pressure, heart rate, and cardiac output were affected only by PV occlusion. In conclusion, even gradual HA occlusion affects liver metabolism and can be reliably identified with hepatic PCO(2) measurements. Intestinal PCO(2) increases only during PV occlusion. A combination of hepatic and intestinal PCO(2) measurements can reliably diagnose the affected vessel and depict the severity of the occlusion, and this may emerge as a potential real-time clinical monitoring tool for the postoperative course of liver transplantation and enable early interventions.

Perioperative detection of myocardial ischaemia/reperfusion with a novel tissue CO2 monitoring technology.

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.

Early detection of cardiac ischemia using a conductometric pCO(2) sensor: real-time drift correction and parameterization.

For detection of cardiac ischemia based on regional pCO(2) measurement, sensor drift becomes a problem when monitoring over several hours. A real-time drift correction algorithm was developed based on utilization of the time-derivative to distinguish between physiological responses and the drift, customized by measurements from a myocardial infarction porcine model (6 pigs, 23 sensors). IscAlert conductometric pCO(2) sensors were placed in the myocardial regions supplied by the left anterior descending coronary artery (LAD) and the left circumflex artery (LCX) while the LAD artery was fully occluded for 1, 3, 5 and 15 min leading to ischemia in the LAD-dependent region. The measured pCO(2), the drift-corrected pCO(2) (DeltapCO(2)) and its time-derivative (TDpCO(2)) were compared with respect to detection ability. Baseline stability in the DeltapCO(2) led to earlier, more accurate detection. The TDpCO(2) featured the earliest sensitivity, but with a lower specificity. Combining DeltapCO(2) and TDpCO(2) enables increased accuracy. Suggestions are given for the utilization of the parameters for an automated early warning and alarming system. In conclusion, early detection of cardiac ischemia is feasible using the conductometric pCO(2) sensor together with parameterization methods.