Dosing Heat: Expected Core Temperature Change with Warmed or Cooled Intravenous Fluids

Abstract

Emergent modification of a patient's body temperature is crucial in certain disease or injury states. Advanced targeted temperature management techniques such as central venous catheter devices are not universally available, however, virtually all medical centers have access to intravenous fluids. This study approximates the change in body temperature for a given volume of room temperature, chilled, or heated isotonic crystalloid bolus. Using thermodynamic principles, a mathematical model was created to approximate change in body core temperature in response to a given volume and temperature of intravenous fluid. The model assumes rapid fluid infusion and the previously published specific heat capacity of the human body of 3.47 J/kg · °C. Values were calculated under conditions of varying body temperatures from profound hypothermia to hyperthermia (18°C-45°C). Various crystalloid temperatures representing iced, room temperature, and warmed (4°C, 20°C, 42°C) were used in the calculations. Each 30 mL/kg dose of 20°C crystalloid is expected to cool a hyperthermic (38°C-45°C) patient by 0.6°C-0.9°C. Each 30 mL/kg dose of 4°C crystalloid is expected to cool a hyperthermic (38°C-45°C) patient by 1.2°C-1.4°C. Each dose of 42°C crystalloid is expected to warm a hypothermic patient by 0.2°C-0.8°C. Using the results in this study, clinicians may roughly estimate the effect of temperature management with varying doses of intravenous fluids and thus assess the benefits of this technique. Risk should be evaluated based on inevitable coadministered volume and electrolytes. Individuals with volume-sensitive conditions such as heart, liver, or kidney failure deserve particular attention. Based on a mathematical model, typical expected core temperature change is about 0.2°C-1.4°C per 30 mL/kg crystalloid bolus, depending on patient and fluid temperature.