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.