Can a Cold (4°C) IV Fluid Bolus to Induce Therapeutic Hypothermia Really Deliver 4°C to Children?

Abstract

Induced therapeutic hypothermia after pediatric cardiac arrest is under investigation. Animal and adult data suggest that rapid achievement of temperatures (T) <34°C may improve outcomes. Cold intravenous fluids (IVF) rapidly induce hypothermia in adults. We sought to evaluate the actual T of IVF entering a pediatric simulated model when a 4°C 30 mL/kg normal saline bolus was infused at standard rates. At ambient T 25°C, T probes were placed in 4°C 1 L normal saline bags (T_bag) and at distal tip infusion tubing at simulated patient entry (T_in). Simultaneous T_bag and T_in were recorded every 15 seconds during infusion. About 30 mL/kg was infused by pressure bag over 30 minutes for 10 kg (300 mL at 10 mL/min), 25 kg (750 mL at 25 mL/min), and 65 kg (2000 mL at 67 mL/min) patients. Tests were run in duplicate. For 10 kg, T_bag was 6.4°C±1.1°C and T_in was 17°C±0.9°C. For 25 kg, T_bag was 7°C±1.4°C and T_in was 12°C±1.2°C. For 65 kg, T_bag was 5.8°C±1.6°C and T_in was 8.6°C±1.7°C. T_bag<T_in for all three simulated patient sizes (p<0.01). ΔT (10.6°C±1.8°C) was largest for 10 kg and smallest for 65 kg (2.8°C±1.7°C) simulated patients (p<0.01), confirming that ΔT is infusion rate dependent. Using simulations of cold IVF boluses to induce therapeutic hypothermia, we found that infusion rates and techniques influence T gradient from fluid bag to patient entry. We speculate that alternative techniques may be needed if 4°C IVF boluses are used to induce therapeutic hypothermia in small children.