[The development of an antimony electrode with a built-in thermocouple and a temperature-compensated pH meter for the determination of intramyocardial pH during open-heart surgery].

Myocardial acidosis as reflected in pH measured by a glass (G) electrode during ischemic arrest may adversely affect postoperative cardiac function. However, (G) is slow in response and fragile. We report the development of an antimony electrode (Sb) and a pH meter based on our investigation and the results of their clinical application. As a biological material, CPD blood was chosen and subjected to a series of experiments determine its pH by (Sb) and (G). There was a small (within 0.1), but statistically significant difference in pH between (Sb) and (G). To simulate myocardial cooling during operation, CPD blood was cooled and its pH measured by (Sb) and (G). (Sb) showed significantly different behaviour from (G), i,e, the pH tended to fall with the falling temperature, whereas with (G) it tended to rise as had been previously known. The thermodynamic property of (Sb) was checked in appropriate buffer solutions by varying their temperatures. There was an almost linear correlation between EMF by (Sb) and the temperature of the buffer solutions (1 mV/1 degree C, or 0.017 pH/1 degree C). Accordingly, a pH meter incorporating an electronic circuit compensating for the temperature-depending EMF and a (Sb) with a built-in-thermocouple were constructed. Utilizing the new apparatus, CPD blood was again tested and it was proved that the new electrode and the pH meter worked in similar manner to (G). The new apparatus was applied to a series of measurement of intramyocardial pH during open-heart surgery and the results compared with that previously obtained by (G). There were no significant differences either between control pH or rate of its fall in the initial 10 minutes. following aortic cross-clamping and the administration of the cardioplegic solution. It is concluded that although (Sb) is not as accurate as (G), it is a reasonable alternative for the determination of the intramyocardial pH during open-heart surgery.