What is the recommended protocol for active core rewarming with intravenous (IV) fluid in a patient with hypothermia?

Active Core Rewarming with Intravenous Fluids for Hypothermia

For active core rewarming with IV fluids in hypothermia, administer warmed isotonic crystalloid (normal saline or Ringer's lactate) at 40-45°C, with volumes ranging from 500 mL to 30 mL/kg, but recognize that IV fluids alone primarily prevent further heat loss rather than achieve true rewarming, and must be combined with other active rewarming methods. 1

IV Fluid Protocol Specifications

Fluid Selection and Temperature

• Use warmed isotonic crystalloid solutions (0.9% saline or Ringer's lactate) heated to 40-45°C 1
• Administer volumes of 500 mL to 30 mL/kg safely without significant adverse cardiopulmonary effects 1
• Nine case series demonstrate that cooling can be initiated safely with IV ice-cold fluids in post-cardiac arrest patients, and the same safety profile applies to warmed fluids 1

Critical Limitation to Understand

• IV fluid warming alone will NOT achieve true rewarming - it primarily prevents further net heat loss 2
• True rewarming with IV fluids alone would require prohibitively large volumes (>10 L of 40°C fluid) or dangerously hot temperatures 2
• IV fluids must be combined with other active rewarming methods such as forced-air warming blankets, heated humidified oxygen, or extracorporeal techniques 1

Temperature Monitoring Requirements

Core Temperature Measurement

• Use esophageal thermometer, bladder catheter (in nonanuric patients), or pulmonary artery catheter for accurate core temperature monitoring 1
• Axillary and oral temperatures are inadequate during active temperature manipulation 1
• Monitor core temperature every 5 minutes during active rewarming 3
• Consider secondary temperature source, especially with closed feedback cooling systems 1

Rewarming Targets

• Target minimum core temperature of 36°C before considering the patient stable 3, 4
• Cease rewarming at 37°C - temperatures above this threshold are associated with poor outcomes and increased mortality 3, 4

Severity-Based Treatment Algorithm

Mild Hypothermia (32-35°C)

• Remove wet clothing immediately 1, 5
• Move to warm environment and apply warm blankets 1, 5
• Passive rewarming may be sufficient if patient is shivering 1
• Consider warmed IV fluids if IV access established 5

Moderate Hypothermia (28-32°C)

• Initiate active external rewarming with forced-air warming blankets (e.g., Bair Hugger) 3, 5
• Administer warmed IV fluids at 40-45°C 1, 5
• Provide heated humidified oxygen 3, 5
• Continue all Level 1 interventions (passive warming) 1, 5

Severe Hypothermia (<28-30°C)

• Continue all moderate hypothermia interventions 5
• Consider active core rewarming methods including peritoneal lavage with warmed fluids, extracorporeal blood warming, or cardiopulmonary bypass 1, 6
• Handle patient gently to avoid triggering ventricular fibrillation 3, 5
• Extracorporeal venovenous rewarming may be most appropriate when rapid correction of hypothermia-related coagulopathy and arrhythmia is necessary 6

Critical Complications to Monitor

During Rewarming

• Cardiac arrhythmias - particularly with unintended temperature drops below target 1
• Coagulopathy - hypothermia impairs coagulation; control any ongoing bleeding before decreasing temperature further 1
• Hyperglycemia - especially with temperature drops below target 1
• Rewarming shock - monitor continuously 5
• Increased infection risk - pneumonia and sepsis likelihood increases with prolonged hypothermia 1

Fluid-Related Concerns

• Although theoretical concern exists for pulmonary edema with rapid fluid loading, case series demonstrate safety 1
• One case series showed deterioration in oxygenation after ROSC was not significantly affected by infusion of cold fluids (3427 mL ± 210 mL) 1
• Infusion of 2 L of room-temperature crystalloid results in approximately 0.3°C decrease in normothermic adults 2

Common Pitfalls and Caveats

Avoid These Errors

• Do not rely on IV fluids as sole rewarming method - they prevent heat loss but don't achieve true rewarming 2
• Do not use axillary or oral temperatures for monitoring during active rewarming 1
• Do not actively rewarm post-cardiac arrest patients who spontaneously develop mild hypothermia (32°C) during first 48 hours after ROSC 1
• Do not exceed 37°C target temperature - higher temperatures worsen outcomes 3, 4

Prevention is Key

• Hypothermia is often overlooked during initial resuscitation 1
• Emphasis should be on prevention first, treatment second - it becomes increasingly difficult to rewarm once significant heat is lost 1
• Early organized prehospital hypothermia protocols reduce incidence from 19% to 3% 1

Prehospital Considerations

• Two randomized controlled trials and multiple case series indicate warmed IV saline can be initiated safely in the prehospital setting 1
• All intravenous fluids must be reliably warmed before infusion in the prehospital environment 7