ObjectivesControversy exists regarding the ideal injectate temperature for measuring cardiac output. Iced temperature injectate gives a higher signal/noise ratio and less variability in the measured cardiac output. Thus, less volume and fewer measurements are required. Advocates of room temperature injectate have suggested that iced temperature injectate may perturb cardiodynamics. This concern has remained largely untested. To help resolve this controversy, we examined the effects of 5 mL iced injectate (0 degree C to 4 degrees C) infusions on cardiodynamics.DesignProspective, randomized, controlled study.SettingA critical care research laboratory.SubjectsFive domestic pigs, weighing between 20 to 25 kg.InterventionsUnder barbiturate anesthesia, pigs underwent placement of a) a thermodilution catheter in the right internal jugular vein; b) a right carotid artery catheter for mean arterial pressure; and c) sonomicrometry crystals for dynamic measurements of left ventricular dimensions. Calculations were made of end-systolic and end-diastolic left ventricular volume and ejection fraction. Six cardiac output measurements were performed in each pig. Data were obtained at baseline (just before iced temperature injectate infusion) and every 3 secs for 9 secs.Measurements and Main ResultsThe only significant effect seen with iced temperature injectate infusion was a small, transient decrease in heart rate (minus 5.9 plus minus 1.1 beats/min from a baseline heart rate of 144.8 plus minus 20.6 beats/min). Indices of preload, contractile function, and dynamic cardiac geometry were unaffected.ConclusionsIced temperature injectate used in clinically relevant volumes causes transient negative chronotropic effects, but reservations regarding other perturbations of cardiodynamics are unfounded. Thus, the use of iced temperature injectate for cardiac output determination is still a viable alternative to room temperature injectate use, especially when a larger signal/noise ratio is required.(Crit Care Med 1996; 24:495-500)