Original Contribution
Blood ammonia is a predictive biomarker of neurologic outcome in cardiac arrest patients treated with therapeutic hypothermia

https://doi.org/10.1016/j.ajem.2011.10.009Get rights and content

Abstract

Purpose

The aim of this study was to investigate the value of commonly examined laboratory measurements, including ammonia and lactate, in predicting neurologic outcome of out-of-hospital cardiac arrest (OHCA) patients treated with therapeutic hypothermia (TH).

Methods

This was a retrospective cohort study of patients with a return of spontaneous circulation after OHCA who were treated with TH between February 2007 and July 2010. We measured typical blood measurements on arrival at the emergency department. The subjects were classified into 2 groups: the good neurologic outcome group (Cerebral Performance Category [CPC] 1-2 at 1 month) and the poor neurologic outcome group (Cerebral Performance Category 3-5). We compared blood biomarker levels and basal characteristics between the 2 groups. Logistic regression analyses were performed to determine independent biomarkers that predict poor neurologic outcome.

Results

A total of 117 patients were included. Between the 2 groups, significantly different levels of blood measurements included hemoglobin level, pH, Pao2, Paco2, base excess, albumin, glucose, potassium, chloride, bilirubin, phosphorous, and ammonia. In multivariate analyses, blood ammonia level (>96 mg/dL; odds ratio [OR], 7.240; 95% confidence interval [CI], 1.718-30.512), noncardiac causes (OR, 46.215; 95% CI, 9.670-220.873), and time interval from collapse to return of spontaneous circulation (>33 min; OR, 5.943; 95% CI, 1.543-22.886) were significantly related to poor neurologic outcome.

Conclusion

Among the blood measurements on emergency department arrival, blood ammonia (>96 mg/dL) was the only independent predictive biomarker of poor neurologic outcome. Thus, higher blood ammonia level was associated with poor neurologic outcome in OHCA patients treated with TH.

Introduction

Out-of-hospital cardiac arrest (OHCA) occurs in about 1 in 2500 adults in the developed world each year [1]. However, despite advances in postcardiac arrest care, the survival rate to hospital discharge with good neurologic outcome after OHCA remains low [2], [3].

Therapeutic hypothermia (TH) is a proven standard therapy used to reduce brain injury in comatose survivors with cardiopulmonary arrest (CPA). Recently, the use of mild therapeutic hypothermia (MTH) in comatose survivors with CPA, which is commonly used worldwide, was evaluated as part of the chain for cardiopulmonary resuscitation (CPR) and emergency cardiac care [4].

Although early and accurate prognostication of neurologic outcome is important and an essential component of postcardiac arrest care, it is difficult and challenging. Therefore, many investigators have previously evaluated predictive biomarkers, including brain-specific biomarkers, such as S-100 protein and neuron-specific enolase in survivors with CPA [5], [6]. However, most studies were performed in patients who were not treated with TH, and most general hospitals are not able examine biomarkers.

Recently, 2 studies revealed that laboratory findings including serum ammonia and lactate levels were predictors of neurologic outcome in postcardiac arrest patients [7], [8]. However, in those studies, only a small proportion of patients received TH, which is one of standard therapy, and the number of patients who had good neurologic outcome was relatively small.

Thus, the aim of this study was to investigate the association between neurologic outcome and common laboratory measurements, including ammonia and lactate level on arrival in the emergency department (ED) and the value of these measurements as predictive factors of neurologic outcome in OHCA patients treated with TH.

Section snippets

Study population

The setting of the study was university hospital ED with an annual patient volume of 90 000. We conducted a single-center and retrospective cohort study between February 2007 and July 2010 at a tertiary hospital located in Incheon city, South Korea. This study was approved by the institutional review board of our hospital.

The subjects of the present study consisted of patients aged 18 years or older who were successfully resuscitated after nontraumatic OHCA and then treated with TH. We excluded

Basal characteristics of study patients

We have tried TH in 140 patients during the study period, and TH was discontinued because of hemodynamic instability and refractory arrhythmias despite treatment in 3 patients. So, 137 patients have reached at the target temperature and finished TH protocol. Two patients who were already diagnosed with chronic renal failure and 18 patients who were referred from another hospital after ROSC were excluded. Finally, the remaining 117 patients were enrolled in this study. Thirty-four patients

Discussion

The patients who achieve ROSC after OHCA had neurologic injury, cardiovascular dysfunction, and multiple organ failure because of whole body ischemia-reperfusion injury called “postcardiac arrest syndrome (PACS)” [10]. Whole body ischemia-reperfusion causes multiorgan damage and results in changes in various laboratory measurements. However, studies concerning the changes and mechanism of the underlying laboratory measurements and influence of these in the neurologic outcome of postcardiac

Conclusions

Among the blood laboratory measurements on ED arrival, blood ammonia levels greater than 96 mg/dL were only independent predictive biomarker of poor neurologic outcome for OHCA patients treated with MTH. Thus, higher blood ammonia levels on ED arrival was associated with poor neurologic outcome in OHCA patients who were treated with TH.

However, further prospective and multicenter studies are needed to evaluate the exact mechanisms and determine the cutoff values.

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