Mild Hypothermia Induction in Out-of-Hospital Cardiac Arrest Patients - Mild Hypothermia Induction in Out-of-Hospital Cardiac Arrest Patients
The goal of the pilot trial was to evaluate prehospital induction of mild hypothermia with a rapid infusion of 4°C normal saline compared with usual care in patients with an out-of-hospital cardiac arrest.
Patients Screened: 559
Patients Enrolled: 125
Mean Follow Up: Hospital discharge or death
Mean Patient Age: Mean age, 66 years
Age ≥18 years, resuscitated with return of pulse by paramedics from nontraumatic out-of-hospital cardiac arrest (defined as being unconscious as a result of a sudden pulseless collapse), had an esophageal temperature of ≥34°C, were intubated, had intravenous access, and were unresponsive
Traumatic cardiac arrest, ability to follow commands
Temperature difference: at hospital arrival minus at randomization in the field
Patients were randomized to standard care (n = 62) or standard care plus induction of mild hypothermia (n = 63) using a rapid infusion of up to 2 L of 4°C normal saline as soon as paramedics had resuscitated the patient from the out-of-hospital cardiac arrest. Patients in the cooling group also received pancuronium (7-10 mg) and diazepam (1-2 mg). The trial was conducted in Seattle, Washington, by Medic One, a paramedic group comprised of 78 paramedics in seven paramedic units serving nine acute care hospitals. Upon arrival at the hospital, patients were treated according to the physician preference rather than the study protocol.
The out-of-hospital cardiac arrest was witnessed in 70% of patients; CPR was initiated prior to paramedic arrival in 43% of patients. Initial rhythm was ventricular fibrillation (VF) in 41% of cases, asystole in 31%, pulseless electrical activity in 27%, and unknown in 1%. Of the 63 patients randomized to prehospital cooling, eight did not receive any saline and only 12 received the full 2 L of saline. There was no difference in the time from paramedic arrival to hospital arrival between groups (46 minutes for cooling vs. 47.5 minutes for usual care, p = NS).
The primary endpoint of temperature difference at hospital arrival minus at randomization in the field was lower in the cooling group compared with the usual care group (-1.24°C vs. 0.10°C, p < 0.001). There was no difference in frequency of re-arrest after randomization (24% for cooling vs. 21% for usual care, p = 0.70). Death prior to hospital admission occurred in 22% of the cooling group and 23% of the no cooling group; an additional 44% and 48%, respectively, died during the hospitalization, with only 33% and 29%, respectively, discharged alive.
In patients arriving at the hospital alive, first heart rate measured in the emergency department was higher in the cooling group (101 bpm vs. 84 bpm, p = 0.025), as was first systolic blood pressure (125 mm Hg vs. 106 mm Hg, p = 0.051). Other early arrival measures were similar between groups, including need for pressors, diuretics, and heart rate and blood pressure 4 hours after hospital arrival.
Among patients with an out-of-hospital cardiac arrest, prehospital induction of mild hypothermia with a rapid infusion of 4°C normal saline was feasible and was associated with a greater reduction in temperature compared with usual care in this pilot trial.
Prior studies have shown that mild hypothermia induced in patients resuscitated from VF can improve neurological recovery and survival. However, hypothermia was generally induced 4-8 hours after resuscitation in these trials. The present study sought to evaluate the feasibility and effect on body temperature of early prehospital hypothermia induction, with the hypothesis that earlier hypothermia closer to the time of resuscitation would maximize its benefits.
It should be noted that few patients received the full 2 L of saline and some did not receive any saline in the cooling arm. Despite this limitation and the inability to obtain temperatures at both time points in several patients, the strategy was effective in reducing body temperature to a greater degree in the cooling arm. A larger trial would be needed to evaluate the impact of prehospital cooling on clinical outcomes such as survival and neurologic recovery.
Kim F, Olsufka M, Longstreth WT, et al. Pilot Randomized Clinical Trial of Prehospital Induction of Mild Hypothermia in Out-of-Hospital Cardiac Arrest Patients With a Rapid Infusion of 4°C Normal Saline. Circulation. 2007;115:3064-3070.
Keywords: Pancuronium, Resuscitation, Out-of-Hospital Cardiac Arrest, Diazepam, Cardiopulmonary Resuscitation, Ventricular Fibrillation, Diuretics, Blood Pressure, Heart Arrest, Heart Rate, Hypothermia, Induced
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