Continuous measurement of blood pH with an indwelling arterial glass electrode.

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Abstract
The pH sensitive cell consists of a glass electrode and a silver/silver chloride reference electrode, both lying in the lumen of a modified Cournand intra-arterial needle. Blood flows through the needle and out of a side arm; in animals the blood is returned to the circulation. Since the lumen of the needle is partially occluded by the electrode a high velocity of blood flow is achieved in the annular space between the electrode and the wall of the needle, despite a low over-all flow rate. In vitro, the 90% response time to a change in pH was 0.5 sec. at a flow rate of 2 ml/min. through the needle; at higher flow rates the 90% response time was about 40 msec. Changes in chloride concentration and blood pressure, likely to be encountered in physiological or pathological conditions, do not affect the electrode in vitro. In vivo, experiments showed that changes in blood pH, recorded by the electrode system, agreed well with changes in the pH of samples taken at the same time.