ObjectivesTo characterize the decreases in pulmonary artery temperature that coincide with the inflation cycle of pneumatic calf compression stockings and to examine their effects on the thermodilution measurement of cardiac output.DesignThree-part observational study.SettingUniversity hospital surgical intensive care unit.PatientsPostoperative patients with indwelling pulmonary artery catheters.InterventionThermodilution cardiac output measurements with and without pneumatic calf compression.Measurements and Main ResultsPhase 1 (n = 18) examined the effects of pneumatic compression on pulmonary artery temperature. There was no effect on pulmonary artery temperature (device off, 37.468 +/- 0.008[degree sign]C; device on, 37.458 +/- 0.014[degree sign]C), but the difference between the maximum and minimum pulmonary artery temperatures was increased (off, 0.031 +/- 0.006[degree sign]C; on, 0.055 +/- 0.012[degree sign]C [p < .001]). Phase 2 (n = 12) found that the mean thermodilution cardiac output with 10 mL of cold (0-5[degree sign]C) injectate was unchanged by pneumatic compression (off, 7.00 +/- 2.28 L/min; on, 6.89 +/- 2.22 L/min). However, when the compression devices were operating, the variability between the individual measurements was increased, as reflected by larger coefficients of variation (off, 3.19 +/- 1.96; on, 8.72 +/- 6.56 [p < .02]). Similar results were obtained during phase 3 (n = 5), when cardiac output was measured with room temperature Injectate.ConclusionsIntermittent pneumatic calf compression increased lower limb venous return, causing acute but transient decreases in pulmonary artery blood temperature. This did not affect the accuracy of thermodilution cardiac output measurements that were made using 10 mL of either cold or room temperature injectate. (Crit Care Med 1999; 27:1096-1099)