Original Article

Monitoring the Conjunctiva for Carbon Dioxide and Oxygen Tensions and pH During Cardiopulmonary Bypass

^* Department of Pediatrics, David Geffen School of Medicine at UCLA, Mattel Children’s Hospital UCLA, Los Angeles, California
^† Department of Ophthalmology, Los Angeles Biomedical Institute at Harbor-UCLA Medical Center, Los Angeles, California
^¶ Department of Anesthesiology, Los Angeles Biomedical Institute at Harbor-UCLA Medical Center, Los Angeles, California
^‡ UCLA Brain Injury Research Center, Division of Neurosurgery, Los Angeles, California
^§ Jules Stein Eye Institute, Los Angeles, California

Address correspondence to: Irwin K. Weiss, MD, Division of Pediatric Critical Care Medicine, Mattel Children’s Hospital/Ronald Reagan UCLA Medical Center, Los Angeles, CA 90095-1752. E-mail: iweiss@mednet.ucla.edu

Received: 2 November 2010
Accepted: 21 January 2011

Abstract

The purpose of this study was to measure, for the first time, multiple physiologic parameters of perfusion (pH, PCO₂, PO₂, and temperature) from the conjunctiva of adult patients during cardiopulmonary bypass while undergoing cardiothoracic surgery. Ten patients who underwent either intracardiac valve repair, atrial septal defect repair, or coronary artery bypass graft surgery had placement of a sensor which directly measured pH, PCO₂, PO₂, and temperature from the conjunctiva. Data were stratified into seven phases (0–5 minutes prior to bypass; 0–5, 6–10, and 11–15 minutes after initiation of bypass; 0–5 minutes prior to conclusion of bypass; and 0–5 and 6–10 minutes after bypass) and analyzed using a mixed model analysis. The change in conjunctival pH over the course of measurement was not statistically significant (p = .56). The PCO₂ level followed a quadratic pattern, decreasing from a mean pre-bypass level of 37.7 mmHg at baseline prior to the initiation of cardiopulmonary bypass to a nadir of 33.2 mmHg, then increasing to a high of 39.4 mmHg at 6–10 minutes post bypass (p < .01). The PO₂ declined from a mean pre-bypass level of 79.5 mmHg to 31.3 mmHg by 6–10 minutes post bypass and even post-bypass, it never returned to baseline values (p < .01). Temperature followed a pattern similar to PCO₂ by returning to baseline levels as the patient was re-warmed following bypass (p < .01). There was no evidence of any eye injury or inflammation following the removal of the sensor. In the subjects studied, the conjunctival sensor yielded reproducible measurements during the various phases of cardiopulmonary bypass without ocular injury. Further study is necessary to determine the role of conjunctival measurements in critical settings.