Original Contribution
Outcome and adverse events with 72-hour cooling at 32°C as compared to 24-hour cooling at 33°C in comatose asphyxial arrest survivors

https://doi.org/10.1016/j.ajem.2013.11.046Get rights and content

Abstract

Purpose

Studies suggest that the current therapeutic hypothermia (TH) protocol does not improve outcomes in adult asphyxial arrest survivors. We sought to compare the effect of 24-hour cooling at 33°C vs that of 72-hour cooling at 32°C on outcomes and the incidence of adverse events in unconscious asphyxial arrest survivors.

Methods

Retrospectively collected data on 79 consecutive asphyxial arrest patients treated with TH from January 2006 to March 2013 were analyzed. Forty-one patients who presented between January 2006 and January 2011 formed the 33°C-24 h group, whereas 38 patients who presented between February 2011 and March 2013 formed the 32°C-72 h group. The primary outcome was neurologic outcome at 30 days following arrest. The secondary outcomes were all-cause mortality at 30 days following arrest and the incidence of adverse events.

Results

The Kaplan-Meier curve showed no significant difference in survival over time during the 30 days after arrest between the 2 groups (P = .608). Good neurologic outcome was achieved in only 2 patients (2.5%) of the overall cohort, despite TH. One of the 32°C-72 h group (2.6%; 95% confidence interval, 4.7%-13.5%) had a good neurologic outcome, as did one of the 33°C-24 h group (2.4%; 95% confidence interval, 4.3%-12.6%) (P = 1.000). There were no significant differences in the rates of adverse events between the 2 groups.

Conclusion

The present study did not demonstrate an advantage of 72-hour cooling at 32°C in unconscious asphyxial arrest patients compared with 24-hour cooling at 33°C.

Introduction

Randomized clinical trials reported that therapeutic hypothermia (TH) improved the rates of neurologically intact survival to hospital discharge in adults who remained comatose after resuscitation from ventricular fibrillation (VF) out-of-hospital cardiac arrest (OHCA) [1], [2]. Based on these studies, the current resuscitation guidelines recommend cooling at 32°C to 34°C for 12 to 24 hours, particularly if the initial rhythm is VF or pulseless ventricular tachycardia (VT) [3]. In a study that included 1145 OHCA patients, Dumas et al [4] reported that TH was associated with significantly better outcomes in patients with VF or pulseless VT but not in patients with pulseless electric activity (PEA) or asystole. There is a well-known link between cardiac arrest (CA) cause and the first cardiac rhythm. In the study by Dumas et al, extracardiac causes of arrest were found in 87% of patients with PEA or asystole [4]. Asphyxia is one of the most prevalent extracardiac causes of arrest. Although the use of TH has not been studied to a significant extent in asphyxial arrest patients, studies suggest that the currently recommended cooling protocol does not improve outcomes in unconscious asphyxial arrest survivors [5], [6]. Our previous study included 13 survivors of asphyxial arrest after near hanging treated with cooling at 33°C for 24 hours and showed that all patients but 1 (92.3%) had poor neurologic outcomes at the time of hospital discharge [6].

Asphyxial arrest is known to result in more severe brain injuries than VF CA for the same duration does [7]. Data from animal experiments suggest that the beneficial effect of TH decreases as the severity of the insult increases [8]. Meanwhile, several studies suggest that cooling for a longer duration than the currently recommended duration may have a better impact on outcomes [9], [10]. In a gerbil model of global cerebral ischemia and reperfusion, cerebral damage was reduced as the duration of hypothermia increased [9]. In studies in neonates with peripartum asphyxia, TH for 72 hours significantly improved neurologic outcomes as compared with intensive care alone without TH [11], [12]. Although it remains to be elucidated which target temperature (32°C-34°C) is more efficacious, cooling at 32°C yielded better outcomes than cooling at 34°C in a recent study that included 36 comatose OHCA survivors [13]. Therefore, comatose survivors resuscitated from asphyxial arrest may benefit from cooling at 32°C for a longer duration than the currently recommended duration.

At our hospital, TH at 33°C for 24 hours has been used for unconscious OHCA survivors since 2004. According to our local policy, TH has also been used in unconscious patients after asphyxial arrest since 2006, unless the patient has a contraindication. Despite the implementation of TH, most unconscious survivors resuscitated from asphyxial arrest had poor outcomes. Thus, in February 2011, we began using cooling at 32°C for 72 hours in unconscious asphyxial arrest survivors. In this retrospective study of unconscious asphyxial arrest patients, we hypothesized that cooling at 32°C for 72 hours would improve outcomes without increasing the risk of adverse events as compared with cooling at 33°C for 24 hours. Thus, the aim of this study was to compare the effect of cooling at 33°C for 24 hours vs that of cooling at 32°C for 72 hours on outcomes and the incidence of adverse events during the intensive care period.

Section snippets

Study design and population

This was a retrospective observational cohort study using the medical records of patients who had been treated with TH, following asphyxial arrest, at a university-affiliated, 1005-bed hospital capable of providing comprehensive post-CA care. Our institutional review board approved this study. The subjects included in this study were consecutive unconscious asphyxial arrest survivors treated with TH between January 2006 and March 2013. The definitive cause of arrest was confirmed through

Clinical characteristics of patients

From January 2006 to March 2013, a total of 343 adult unconscious CA survivors were treated with TH at our institution (Fig. 1). Of these, 79 patients had asphyxia as an arrest cause and were included in this study. Forty-one patients who presented between January 2006 and January 2011 formed the 33°C-24 h group, whereas 38 patients who presented between February 2011 and March 2013 formed the 32°C-72 h group. The clinical characteristics of the 2 groups were generally similar, although the

Discussion

In the present study, survival with a good neurologic outcome was achieved in only 2.5% of the overall cohort despite TH, with no differences in mortality or neurologic outcomes being found between the 2 cooling protocols.

Data from animal experiments and neonates with peripartum asphyxia suggest that TH can improve the outcomes of comatose arrest patients, even when the cause of arrest is asphyxia [11], [12], [17], [18]. However, TH did not appear to improve the outcomes of comatose asphyxial

Conclusions

In the present study, which compared 72-hour cooling at 32°C and 24-hour cooling at 33°C in unconscious asphyxial arrest patients, survival with a good neurologic outcome was achieved in only 2.5% of the patients despite TH, with no intergroup differences in mortality or neurologic outcome. Considering the poor outcomes of the patients in the present study, efforts should be urgently made to find effective treatments for this devastating injury.

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    Funding sources/disclosures: The authors have no relevant financial information or potential conflicts of interest to disclose.

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