The effect of ambient temperature on cold saline during simulated infusion to induce therapeutic hypothermia

BACKGROUND: This study was done to determine the effect of ambient temperature on cold saline during simulated infusion to induce therapeutic hypothermia. The study hypothesis was that cold saline would warm rapidly during simulated infusion and that an insulating SIGG neoprene pouch would slow the process. METHODS: Paired 1-l bags of normal saline [with or without an insulating SIGG neoprene pouch (NEO+ and NEO- respectively)] were refrigerated together for at least 24h. With an ambient room temperature (RT) between 32 and 34 degrees C, the fluid was allowed to flow unrestricted through standard tubing connected to a 20-guage angiocath while the line reservoir temperature was monitored every 30s. The order of the bags was pre-determined and alternated for each session. During 5 sessions, ten 1-l bags were included (5 NEO+ and 5 NEO-). The data were analyzed descriptively using Stata SE v8.1 for Macintosh. RESULTS: The average ambient RT during the experimental sessions was 32.6 degrees C (StDev: 0.8 degrees C). The relative humidity was a constant 16%. The average low saline temperature at the beginning of infusion was 6.2 degrees C (StDev: 2.7 degrees C). The average rate of infusion was 48.2cm(3)/min (StDev: 3.7cm(3)/min). The average rise in saline temperature during the first 15min of the infusion was 2.9 degrees C (StDev: 1.2 degrees C). The average high saline temperature reached near the end of the infusion was 13.4 degrees C (StDev: 4.1 degrees C). The average temperature change during infusion was 7.2 degrees C (StDev: 3.5 degrees C). The baseline data for the NEO+ and NEO- samples were not statistically different. The average temperature change over the first 15min for the NEO+ group was 2.0 degrees C (95% CI: 1.4 degrees C and 2.5 degrees C) and for the NEO- group it was 3.9 degrees C (95% CI: 2.6 degrees C and 5.1 degrees C). The average change over the entire infusion for the NEO+ group was 4.3 degrees C (95% CI: 3.1 degrees C and 5.5 degrees C) and for the NEO- group it was 10.2 degrees C (95% CI: 7.4 degrees C and 12.9 degrees C). CONCLUSIONS: During simulated infusion to induce therapeutic hypothermia, cold saline begins to warm toward ambient temperature but the rate is not rapid. An insulating SIGG neoprene pouch slows the rate of warming