Conjunctival and mixed-venous oximeters as early warning devices of cardiopulmonary compromise

Abstract

To evaluate potential clinical applications of conjunctival (PcjO2) and mixed venous (SvO2) oximeters in the care of surgical patients, we compared continuous measurements of PcjO2 and SvO2 to conventional invasive hemodynamic and oxygen transport variables during normoxia, hyperoxia, hypoxia, hemorrhagic shock, and resuscitation in dogs. During the normoxic control periods, PcjO2 averaged 76% of the arterial oxygen tension (PaO2). During hyperoxia and hypoxia, PcjO2 correlated well with PaO2 values (r = 0.88) but not with mixed venous oxygen tension (PvO2), whereas the SvO2 correlated well with PvO2 (r = 0.88) but not with PaO2 values. Controlled hemorrhage produced significant, progressive decreases in PcjO2, SvO2, cardiac output, and oxygen delivery (P less than 0.01), whereas PaO2 values remained constant throughout this period (FIO2 = 40%). There were no significant differences between the decreases in PcjO2 and SvO2 at 15, 30, and 45 ml/kg blood loss. Reinfusion of the shed blood resulted in a rapid, significant increase in PcjO2, SvO2, cardiac output, and oxygen delivery (P less than 0.01); the PaO2 remained constant. During hemorrhage and resuscitation, both PcjO2 and SvO2 tracked cardiac output; the weighted mean correlation coefficient, rw, was 0.90 for both PcjO2 versus cardiac output and SvO2 versus cardiac output. The correlation coefficient for PcjO2 versus SvO2 during hemorrhage and resuscitation was 0.72. One dog died unexpectedly during hemorrhage. In the 29 min period immediately prior to death, PcjO2 remained at 9 torr and SvO2 at 10%; the simultaneously measured PaO2 was 133 torr. Both oximeters had in vivo stabilization and 90% response times of less than 2 min. We conclude that both oximetry systems are potentially useful in high-risk surgical patients to provide better cardiorespiratory surveillance and to signal the need for more intensive assessment of hemodynamic stability. This approach may lead to reduced costs from unnecessary invasive procedures as well as reduced morbidity secondary to earlier warning of cardiorespiratory compromise.