A miniaturized fiberoptic PCO2 probe permits direct measurement of tissue PCO2 on nonkeratinized tissue surfaces without the heating effects produced by transcutaneous PCO2 sensors. This study of anesthetized dogs compared PCO2 measured at the palpebral conjunctiva (PcjCO2) with PaCO2 and mixed venous (PVCO2) measurements during normovolemic normotension and hypovolemic hypotension. During the control period, the average PcjCO2 was 3 +/- 1 (SEM) torr greater than PaCO2 (r = 0.98) when the latter ranged from 20 to 80 torr. There was a close association (r = 0.94) between PcjCO2 and PaCO2 when the cardiac index (CI) was greater than 2.0 L/min X m2. However, as CI decreased below this value, PcjCO2 and PaCO2 were less well correlated (r = 0.69). PcjCO2 was closely associated with PVCO2 at all stages of the experiment, both above (r = 0.95) and below (r = 0.82) a CI of 2 L/min X m2. Fiberoptic conjunctival PCO2 monitoring seems promising as a noninvasive measure of physiologic status.

Animals↗

PubMed1985

Continuous monitoring of tissue pH with a fiberoptic conjunctival sensor.

To assess the relationship between conjunctival pH (pHcj), arterial pH (pHa), and cardiorespiratory variables during normal and low-flow conditions, hemorrhagic hypotension was induced in eight dogs. Conjunctival pH became significantly less than control values after a hemorrhage volume of 15 mL/kg (P less than .05); mean arterial pressure (MAP) did not fall until blood loss was 20 mL/kg. There was poor correlation between pHcj and pHa, cardiac index (CI), or MAP. There was a high degree of correlation, however, between pHcj-pHa difference (delta pH) and MAP (r = -0.886), CI (r = -0.846), and tissue oxygen extraction ratio (r = .896). The results of these experiments indicate that pHcj is a sensitive monitor of peripheral tissue perfusion, and that the degree of physiologic compromise associated with hemorrhage can be determined by analysis of the difference between arterial and conjunctival pH.

Animals↗