Induced hypothermia using large volume, ice-cold intravenous fluid in comatose survivors of out-of-hospital cardiac arrest:: a preliminary report
Introduction
Out-of-hospital cardiac arrest is common and associated with a poor prognosis, with less than 3% of patients surviving to good outcome at hospital discharge [1]. Patients who are initially successfully resuscitated by emergency medical services often remain unconscious because of severe anoxic brain injury [2]. Recently, clinical trials of induced hypothermia (IH) have shown improved outcome in comatose survivors of out-of-hospital cardiac arrest [3], [4], [5]. These studies used surface cooling with ice packs [3], [4] or forced cold air cooling [5], however, these techniques of surface cooling had significant limitations. Firstly, these are relatively slow methods of decreasing core temperature, with a 0.9 °C/h decrease in core temperature using ice packs [3], [4] and 0.3 °C/h using forced cold air cooling [4]. Secondly, the covering of the patient with ice packs or cooling blankets during resuscitation is inconvenient for medical and nursing staff. Finally, the use of ice packs or refrigerated units (for forced air cooling) limit the use of these techniques to the hospital environment.
Since there is evidence from animal studies that outcome is improved if cooling is initiated during resuscitation or immediately after return of spontaneous circulation [6], [7], the development of a technique to induce hypothermia which is feasible in the out-of-hospital setting may further improve outcome. We hypothesized that a rapid intravenous infusion of large volume (30 ml/kg), ice-cold (4 °C) lactated Ringers solution would be an effective alternative to surface cooling for the induction of mild hypothermia. We report our preliminary experience with this technique.
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Materials and methods
The study was undertaken in the Emergency Department (ED) of Dandenong Hospital in Melbourne, Victoria, Australia. Patients were eligible for inclusion in the study if they arrived unconscious at the ED after resuscitation by paramedics from out-of-hospital cardiac arrest. Exclusion criteria included children (<18 years), possible pregnancy (females<50 years), coma possibly due to cerebrovascular accident or head trauma, cardiogenic shock (systolic blood pressure<90 mmHg despite adrenaline
Results
There were 22 patients enrolled in the study between March 2000 and May 2002. The demographics of the patients are shown in Table 1. The mean total collapse to return of spontaneous circulation time of 27 min (range 12–48 min) is consistent with our previously published clinical studies of induced hypothermia [3], [4]. The cardiac arrests were witnessed in all 14 patients with an initial cardiac rhythm of ventricular fibrillation and four of the remaining eight patients.
The vital signs and
Discussion
Recent clinical studies suggest that IH improves outcome in patients with anoxic brain injury following resuscitation from out-of-hospital cardiac arrest and is not associated with adverse side-effects [3], [4], [5]. In a preliminary study, we used IH in 22 adult patients with coma following resuscitation from pre-hospital cardiac arrest [3]. Hypothermia (33 °C) was induced in the ED using surface cooling with ice packs and maintained for 12 h in the ICU. Compared with 22 historical controls,
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