What are the implications of hypothermia (abnormally low body temperature) post cardiac arrest?

From the Guidelines

Targeted temperature management (TTM) is recommended for comatose adult patients after cardiac arrest, with a constant temperature between 32-36°C for at least 24 hours, as it has been shown to improve neurological outcomes and reduce morbidity and mortality 1.

Key Considerations

• The optimal duration for mild induced hypothermia and TTM is unknown, but it is currently most commonly used for 24 hours, with some studies suggesting no difference in mortality or poor neurological outcome with 24 h compared to 72 h of hypothermia 1.
• The term targeted temperature management or temperature control is now preferred over the previous term therapeutic hypothermia, and it is recommended to maintain a constant, target temperature between 32 and 36 °C for those patients in whom temperature control is used 1.
• Whether certain subpopulations of cardiac arrest patients may benefit from lower (32–34 °C) or higher (36 °C) temperatures remains unknown, and further research may help elucidate this 1.

Implementation

• Begin cooling as soon as possible after ROSC, with a target temperature reached within 4-6 hours, using external cooling devices (cooling blankets, ice packs) or internal methods (cold saline infusion, intravascular cooling catheters) 1.
• Monitor core temperature continuously via esophageal, bladder, or central venous temperature probes, and provide sedation (propofol 5-50 mcg/kg/min or midazolam 0.02-0.1 mg/kg/hr) and neuromuscular blockade (cisatracurium 0.15 mg/kg bolus followed by 1-2 mcg/kg/min infusion) to prevent shivering 1.
• After the maintenance period, rewarm slowly at 0.25-0.5°C per hour to avoid rebound hyperthermia, and maintain normothermia (36.5-37.5°C) for at least 72 hours after ROSC 1.

Special Considerations

• For hypothermic patients in cardiac arrest, continue resuscitative efforts until the patient is evaluated by advanced care providers, and use passive warming in the out-of-hospital setting until active warming is available 1.
• Avoid rough movement, and transport the victim to a hospital as soon as possible, removing wet clothes and insulating or shielding the victim from wind, heat, or cold, and ventilating with warm, humidified oxygen if possible 1.

From the Research

Hypothermia Post Arrest

• Therapeutic hypothermia (TH) has been shown to improve neurological outcome and survival after witnessed cardiac arrest (CA) that is due to ventricular fibrillation 2.
• Experimental studies have emphasized the importance of initiating cooling soon after the return of spontaneous circulation (ROSC) or even during cardiopulmonary resuscitation (CPR) 2.
• Clinical studies have shown that pre-hospital induction of hypothermia is feasible and has no major adverse events-even when used intra-arrest-and may provide some additional benefits compared to delayed in-hospital cooling 2.

Treatment Methods

• Various methods (both non-invasive and invasive) are available to achieve and maintain the target temperature; however, only some of these methods-which include cold fluids, ice packs, iced pads and helmet and trans-nasal cooling- are easily deployed in the pre-hospital setting 2.
• Conventional rewarming methods and continuous, prolonged CPR can lead to successful outcomes in patients with hypothermia in cardiac arrest when extracorporeal life support (ECLS) is not available 3.
• Active external and minimally invasive rewarming techniques (e.g. chemical, electrical or forced air heating packs, blankets and warm parenteral fluids) can be used for hypothermic patients with a core body temperature ≥ 28 °C without cardiac instability 4.

Patient Transport and Management

• Early transport to a hospital appropriately equipped for rewarming has the potential to decrease complication rates and improve survival 4.
• Hypothermic patients with risk factors for imminent cardiac arrest (i.e., temperature <28°C, ventricular arrhythmia, systolic blood pressure <90 mmHg), and those who have already arrested, should be transferred directly to an ECLS center 5.
• Cardiac arrest patients should receive continuous cardiopulmonary resuscitation (CPR) during transfer, and modern postresuscitation care should be implemented following hypothermic arrest 5.

Temperature Management

• The International Liaison Committee on Resuscitation Advanced Life Support Task Force recommends targeted temperature management for adults with out-of-hospital cardiac arrest with an initial shockable rhythm at a constant temperature between 32 °C and 36 °C for at least 24 hours 6.
• Similar suggestions are made for out-of-hospital cardiac arrest with a nonshockable rhythm and in-hospital cardiac arrest, and the task force recommends against prehospital cooling with rapid infusion of large volumes of cold intravenous fluid 6.