Haemodynamic effects of cold versus warm fluid bolus in healthy volunteers: A randomised crossover trial

Objective: To test the hypothesis that changes in cardiac index and mean arterial pressure (MAP) during and after a fluid bolus (FB) are altered by fluid temperature. Design: Randomised, controlled, crossover trial. Setting: Research laboratory at Swedish teaching hospital. Participants: Twenty-one healthy adult volunteers. Interventions: Subjects were randomly allocated to 500 mL of Ringer’s acetate at room temperature (22°C; cold) or body temperature (38°C; warm). Main outcome measures: For 2 hours after starting the FB, we measured cardiac index, MAP, systolic blood pressure, diastolic blood pressure and pulse rate (PR) continuously. We recorded temperature and O ₂ saturation every 5 minutes during infusion and every 15 minutes thereafter. In a second session, volunteers crossed over. Results: During the first 15 minutes, mean cardiac index increased more with warm FB (0.09 L/min/m ² [95% CI, 0.06– 0.11] v 0.03 L/min/m ² [95% CI, 0.01–0.06]; P < 0.001). This effect was mediated by a significant difference in mean PR (+0.80 beats/min [95% CI, 0.47–1.13] v –1.33 beats/ min [95% CI, –1.66 to –1.01]; P < 0.010). In contrast, MAP increased more with cold FB (4.02 mmHg [95% CI, 3.63–4.41] v 0.60 mmHg [95% CI, 0.26–0.95]; P < 0.001). Cardiac index and MAP returned to baseline after a median of 45.3 min (interquartile range [IQR], 10.7–60.7 min) and 27.7 min (IQR, 5.3–105.0 min), respectively, after cold FB, and by 15.8 min (IQR, 3.8–64.3 min) and 22.7 min (IQR, 3.3–105.0 min), respectively, after warm FB. Conclusion: Intravenous FB at body temperature leads to a greater increase in cardiac index compared with room temperature, while the reverse applies to MAP. These findings imply that in healthy volunteers, when a room temperature FB is given, the temperature of the fluid rather than its volume accounts for most of the MAP increase.