Non-invasive conjunctival PCO2 and PO2 monitoring during hyper- and hypoventilation

In order to evaluate potential applications of non-invasive fiberoptic conjunctival carbon dioxide (Pcj,CO2) and polarographic oxygen (Pcj,O2) sensors, we studied the effects of graded hyper- and hypoventilation on Pcj,CO2 and Pcj,O2 values in dogs. Pcj,CO2 values correlated well with Pa,CO2 (r = 0.95, n = 114); the mean Pcj,CO2--Pa,CO2 gradient was 4 +/- 3 (S.D.) Torr. Both hyper- and hypoventilation resulted in decreased Pcj,O2 values, whereas decreased Pa,O2 was observed only during hypoventilation; thus, the Pcj,O2/Pa,O2 index decreased during hyperventilation but was maintained during hypoventilation. Because both cerebral and conjunctival capillary beds vasoconstrict during hyperventilation, this methodology may assist in the non-invasive monitoring of cerebral oxygenation during cerebral resuscitation and surgery. Non-invasive Pcj,CO2 monitoring, which reflects Pa,CO2 during changes in ventilation, may be used to simplify ventilator management and weaning, as well as guide appropriate timing of arterial blood gas analysis in hemodynamically stable patients.