Association of physical examination with pulmonary artery catheter parameters in acute lung injury

Abstract

Objective: To correlate physical examination findings, central venous pressure, fluid output, and central venous oxygen saturation with pulmonary artery catheter parameters.

Design: Retrospective study.

Setting: Data from the multicenter Fluid and Catheter Treatment Trial of the National Institutes of Health Acute Respiratory Distress Syndrome Network.

Patients: Five hundred thirteen patients with acute lung injury randomized to treatment with a pulmonary artery catheter.

Interventions: Correlation of physical examination findings (capillary refill time >2 secs, knee mottling, or cool extremities), central venous pressure, fluid output, and central venous oxygen saturation with parameters from a pulmonary artery catheter.

Measurements: We determined association of baseline physical examination findings and on-study parameters of central venous pressure and central venous oxygen saturation with cardiac index <2.5 L/min/m2 and mixed venous oxygen saturation <60%. We determined correlation of baseline central venous oxygen saturation and mixed venous oxygen saturation and predictive value of a low central venous oxygen saturation for a low mixed venous oxygen saturation.

Measurements and main results: Prevalence of cardiac index <2.5 and mixed venous oxygen saturation <60% was 8.1% and 15.5%, respectively. Baseline presence of all three physical examination findings had low sensitivity (12% and 8%), high specificity (98% and 99%), low positive predictive value (40% and 56%), but high negative predictive value (93% and 86%) for cardiac index <2.5 and mixed venous oxygen saturation <60%, respectively. Central venous oxygen saturation <70% predicted a mixed venous oxygen saturation <60% with a sensitivity 84%,specificity 70%, positive predictive value 31%, and negative predictive value of 96%. Low cardiac index correlated with cool extremities, high central venous pressure, and low 24-hr fluid output; and low mixed venous oxygen saturation correlated with knee mottling and high central venous pressure, but these correlations were not found to be clinically useful.

Conclusions: In this subset of patients with acute lung injury, there is a high prior probability that cardiac index and mixed venous oxygen saturation are normal and physical examination findings of ineffective circulation are not useful for predicting low cardiac index or mixed venous oxygen saturation. Central venous oxygen saturation <70% does not accurately predict mixed venous oxygen saturation <60%, but a central venous oxygen saturation >or=70% may be useful to exclude mixed venous oxygen saturation <60%.

Figure 1

Mixed venous oxygen saturation (SvO₂) correlated with central venous oxygen saturation (ScvO₂) in 218 patients with acute lung injury at baseline. Analysis by median regression: Spearman's ρ = 0.64 (p < .0001), SvO₂ = 0.71*ScvO₂ + 18.5 (95% confidence interval for intercept [7.4, 22.5] and slope [0.64, 0.87]). The dashed lines are 95% confidence limits for the regression line. The predicted SvO₂ for an ScvO₂ of 70% is SvO₂ = 68% (95% confidence limits, 52%–83%).

Figure 2

Mixed venous oxygen saturation (SvO₂) correlated with central venous oxygen saturation (ScvO₂) in 107 patients with acute lung injury and severe sepsis at baseline. Analysis by median regression: Spearman's ρ = 0.63 (p < .0001), SvO₂ = 0.72*ScvO₂ + 17.5 (95% confidence interval for intercept [4.5, 24.4] and slope [0.65, 0.91]). The dashed lines are 95% confidence limits for the regression line.

Figure 3

Cardiac index (CI) plotted against mixed venous oxygen saturation (SvO₂) in 335 patients with acute lung injury at baseline. Analysis by median regression: SvO₂ = 2.07*CI + 60.4 (95% confidence interval for intercept [54.9, 62.5] and slope [1.65, 3.56]); Spearman's ρ = 0.34 (p < .0001). The dashed lines are 95% confidence limits for the regression line. For the correlation of CI and ScvO₂, Spearman's ρ = .30, p < .0001 (data not shown).