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A novel fiber optic transducer has been developed for continuous monitoring of physiological pH. In the current embodiment, the miniature transducer was evaluated for intracutaneous pH monitoring within the conjunctiva! mucosal membrane in anesthetized juvenile pigs. A vasodilator was administered percutaneous prior to insertion of the transducer to minimize localized ischemic reactions. During the 5-6 hour trials the data from the fiber optic transducer was compared to an in dwelling electrochemical pH micro-electrode in close proximity. The test subject's vascular pH was manipulated via a pressure-cycled respirator. Through a combination of adjustments made to the BPM(breaths per minute), PIP(peek inspiratory pressure), and Fi02(% oxygen in respiratory mix), arterial pH levels were made to change by as much as 0.5 pH units over a range of 7.2 to 7.7 pH without significant detriment to the test subject. A skeletal muscle relaxant was administered frequently in addition to the anesthesia to limit ventilator compromise. Arterial blood gases were monitored through conventional blood gas analysis equipment. Additionally, arterial and venous pressure and wave form, EKG and expired C02 were continuously monitored to follow the test subjects physiologic state. In one representative trial run, the mean(±SD) difference between the fiber optic transducer and the electrochemical pH micro-electrode measurements was no greater than 0.080±0.050 pH units. Further, there was a strong interrelation between the tissue pH and the arterial pH measurements. In vitro stability tests showed that in buffered saline at pH=7.4 and 37°C, the transducer presented no greater than 0.048 pH unit drift in approximately six(6) hours. Stability tests in porcine blood under the same conditions indicated a drift of no greater than 0.015 pH units in approximately six(6) hours. One unique feature of this approach throughout the study was that the test units were freeze-dried and gamma sterilized for storage and subsequently reconstituted and calibrated immediately prior to use. This obviates the problems normally associated with wet storage of devices such as these.
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