The relationship of conjunctival and arterial blood gas oxygen measurements

Conjunctival oxymetry (Cjo2) measures peripheral tissue oxygen at the conjunctival level. Cjo2 changes can indicate pulmonary or circulatory conditions leading to shock. Literature review does not define ‘normal’ Cjo2/ABG Pao2 ratios. We designed a study to measure these ratios. Twenty-two healthy patients undergoing cardiac catheterization had simultaneous Pcjo2 and Pao2 measurements completed. The range of conjunctival oxygen measurements was from 34 to 68 mmHg with a mean of 50.5 mmHg. The Pao2 readings ranged from 65 to 93 mmHg with a mean of 77.1 mmHg. The average Pcjo2Pao2 ratio was 0.656 with a range of 0.47–0.93. Thus the Pcjo2 is on average 66% of the arterial blood gas Pao2. This ratio of 0.66 can serve as a base for further clinical studies in which Pcjo2 is looked at in patients with pulmonary or circulatory illnesses or injuries.