Effect of heparinization of catheters on pulmonary artery oximetry

A clinical study was performed in two phases to determine whether pulmonary artery oximeter catheters that were impregnated or bonded with heparin would affect the accuracy of measurements of in vivo mixed venous oxygen saturation (SO₂). In phase 1, 40 patients were catheterized with either a heparin-impregnated or a plain pulmonary artery catheter. Blood was sampled at random times to correlate in vivo with in vitro SO₂ measurements. In phase 2, 16 patients who were not receiving systemic heparin therapy or aspirin and who had no coagulopathies were catheterized with either a heparin-bonded or a plain pulmonary artery catheter in a blinded order. In phase 1, a total of 364 blood samples were obtained from 40 patients. Linear regression analysis of the pooled data demonstrated y=0.98x–0.01,r=0.93,P<0.001, andn=141 with heparin-impregnated catheters; and y=0.87x+8.0,r=0.81,P<0.001, andn=223 with plain catheters. The mean difference (in vivo minus in vitro) revealed a similar error (–1.3±0.4 versus –1.4±0.4, respectively, mean±SE). The 95% confidence limits of an individual value (±8.1 versus ±12.3) suggested slightly greater accuracy with heparin-impregnated catheters. In phase 2, a total of 134 blood samples were obtained from 16 patients. Linear regression analysis showed nearly equal performance with heparin-bonded and plain catheters (r=0.97 versusr=0.98, respectively) with similar slopes (1.0 versus 1.1, respectively) but different intercepts (–0.6 versus –8.4, respectively). Analysis of the mean difference revealed a measurement error of 0.4±0.3 versus –1.3±0.3 with similar 95% confidence limits of individual values (±5.0 versus ±4.8, respectively). These differences do not appear clinically important. These data suggest that heparinization only minimally enhanced accuracy with a pulmonary artery oximetry system, which accurately measured SO₂ to within 3 to 4% of true values.