Comparison of venous hemoglobin saturation measurements obtained by in vivo oximetry and calculated from blood gas analysis in critically ill dogs

Objective To compare in vivo central venous hemoglobin saturation measurement (ScvO2) using a fiber optic catheter with saturation calculated from blood gas analysis in critically ill dogs. Design Prospective observational study. Setting University veterinary teaching hospital intensive care unit. Animals A convenience sample of 20 dogs with severe illness. Interventions Dogs were instrumented with either a central venous catheter with an integrated fiber optic cable or a conventional catheter with a fiber optic probe inserted through its distal port. Baseline saturation was measured with the fiber optic system (FSO2), then monitored continuously. Central venous blood was collected for analysis and FSO2 was recorded by the principal investigator (PI) or nursing staff participating in data collection (staff) at baseline and at 1, 2, 3, and 6 hours. Hemoglobin oxygen saturation (SO2) values calculated using human Bohr coefficients were taken directly from the analyzer (GPSO2), and were also calculated using temperature‐correction and canine Bohr coefficients (RSO2). Measurements and Main Results Ninety‐seven paired measurements from 20 dogs were analyzed. FSO2 obtained by the PI (n = 41) had better agreement with both GPSO2 (concordance correlation coefficient ρc = 0.926 vs 0.5562) and RSO2 (ρc = 0.75 for PI vs 0.54) than did staff (n = 56). RSO2 values were always smaller than GPSO2. FSO2 ‐ GPSO2 differences were smaller when measurements were collected by the PI versus Staff (mean difference 0.21 vs −6.6, respectively, P