[Continuous pH registration in the coronary sinus in vivo in ischemic and normoxic lactic acidosis using an ion sensitive field effect transistor catheter]. / Kontinuierliche pH-Registrierungen im Koronarsinus in vivo bei ischämischer und normoxischer Laktazidose mittels eines ISFET-Katheters.

A new catheter with an Ion Sensitive Field Effect Transistor (ISFET) for continuous measurements of blood pH in vivo was employed. In canine heart preparations (n = 15), two catheters were positioned in the coronary sinus and in the abdominal aorta, respectively. A close agreement between pH-measurements with the pH-ISFET-sensor and the corresponding pH-determinations on blood samples by conventional means (r = 0.97; pH-range 7.15-7.50) was found. The ISFET-sensor revealed a sensitivity of 50-55 mV/pH, a long-term drift rate of 1-2 mV/h, as well as a response time shorter than 100 ms. The ISFET-sensor was sensitive for the detection of respiratory and metabolic acidosis and alkalosis (hypo-, hyperventilation, myocardial ischemia, intracoronary infusion of 0.3-M lactic acid). There was a close correlation between the changes of coronary venous pH and lactate concentrations during myocardial ischemia (r = 0.83; n = 9). During ischemic acidosis there was a drastic reduction of left ventricular dp/dtmax, whereas contractility changes during normoxic lactacidosis were moderate. The pH-decrease (pH = 7.1) was identical in both interventions. The observed data suggest that the newly developed ISFET-pH-catheter is working precisely and enables respiratory and metabolic control of the whole organism as well as of individual organs.

Intravascular pH-ISFET, a method of the future.

Since blood pH reflects the metabolic state as well as the functioning of the respiratory and circulatory systems, it appears to be one of the vital parameters that should be continuously monitored. The point to point measurement of pH by sampling has limitations, since results are available after some time only. A continuous pH signal is necessary in rapidly changing situations such as often occur during intensive treatment. The application of ion-selective field-effect transistor (ISFET) technology to intravascular pH measurement seemed attractive since these devices offer a short response time, are suitable to miniaturization and fabrication in large quantities, and have a low output impedance. The system was tested in dog experiments. Two to four pH-ISFET catheters were tested simultaneously in each dog. Arterial samples for blood-gas analysis with a Radiometer ABL2 system were taken during periods in which plasma-pH was stable. Clinical trials were performed in patients who were admitted to the intensive care unit after coronary artery bypass grafting. Testing the pH-ISFET system in dogs (N = 12) and comparing it with ABL2 measured samples (n = 132 with a pH range of 6.72-7.86), resulted in a delta pH (ISFET-ABL2) of 0.016 +/- 0.024 pH with a maximum deviation of 0.06. The clinical trials proved that the system is well-suited for monitoring intravascular pH in critically ill patients.