Steady-state and time-dependent thermodynamic modeling of the effect of intravenous infusion of warm and cold fluids.
BACKGROUND
Hypothermia results in vital sign lability, coagulopathy, wound infections, and other sequelae. Normothermia can be restored by several modalities, including passive blanket heating, warm forced-air devices, and active fluid warming (AFW). In AFW, intravenously administered fluids are heated to 40 to 45 °C to minimize net thermal losses and to raise body temperature. Clinical studies have demonstrated the efficacy of AFW as part of a strategy encompassing several methods, but the isolated contribution of AFW to warming has not been theoretically examined in detail.


METHODS
A calorimetric model is derived to determine the functional dependence of warming on patient weight, hypothermia severity, infusion temperature, and volume infused. A second heat transfer model is derived to describe the time-dependent temperature changes of the periphery and core after warmed-fluid infusion.


RESULTS
There is an inverse linear relationship between the patient's initial temperature and the amount of warming achieved with a given volume. In contrast, as the temperature of the infusion approaches the desired final temperature, the volume required for a fixed temperature change increases nonlinearly. For weight-based boluses, the temperature change scales appropriately with patient mass. Infusion of 2 L of room-temperature crystalloid results in a decrease in body temperature of approximately one-third degree Celsius in the average normothermic adult. For the heat transfer model, previously reported rates of temperature drop and recovery after the intravenous infusion of cold fluids are qualitatively reproduced with a blood mixing time of approximately 15 minutes.


CONCLUSIONS
Our calculations reveal that AFW has a larger measurable beneficial effect for patients with more severe hypothermia, but true rewarming of the patient with AFW alone would require prohibitively large fluid volumes (more than 10 L of 40 °C fluid) or dangerously hot fluid (20 mL/kg of 80 °C fluid for a 1 °C increase). The major beneficial effect of AFW is the prevention of further net heat loss.
Division of Pediatric Surgery, Children's Hospital Los Angeles, Los Angeles, California 90027, USA.
Erik R
ER
Barthel
James R
JR
Pierce
D000222:Adaptation, Physiological; D000328:Adult; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D003080:Cold Temperature; D005260:Female; D005440:Fluid Therapy / Q000379:methods; D006358:Hot Temperature / Q000627:therapeutic use*; D006801:Humans; D007035:Hypothermia / Q000209:etiology / Q000401:mortality* / Q000503:physiopathology / Q000628:therapy*; D007262:Infusions, Intravenous; D015601:Injury Severity Score; D008297:Male; D008962:Models, Theoretical; D012151:Resuscitation / Q000379:methods; D017694:Rewarming / Q000379:methods*; D018570:Risk Assessment; D015996:Survival Rate; D013816:Thermodynamics; D013997:Time Factors; D014947:Wounds and Injuries / Q000150:complications / Q000628:therapy