Elsevier

Resuscitation

Volume 82, Issue 6, June 2011, Pages 696-701
Resuscitation

Clinical paper
Predictors of poor neurologic outcome in patients after cardiac arrest treated with hypothermia: A retrospective study

https://doi.org/10.1016/j.resuscitation.2011.02.020Get rights and content

Abstract

Introduction

Outcome studies in patients with anoxic-ischemic encephalopathy focus on the early and reliable prediction of an outcome no better than a vegetative state or severe disability. We determined the effect of mild therapeutic hypothermia on the validity of the currently used clinical practice parameters.

Methods

We conducted a retrospective cohort study of adult comatose patients after cardiac arrest treated with hypothermia. All data were collected from medical charts and laboratory files and analyzed from the day of admission to the intensive care unit until day 7, discharge from the intensive care unit or death using the Utstein definitions for the registration of the data.

Results

We analyzed the data of 103 patients. The combination of an M1 or M2 on the Glasgow Coma Scale or absent pupillary reactions or absent corneal reflexes on day 3 was present in 80.6% of patients with an unfavourable and 11.1% of patients with a favourable outcome. The combination of M1 or M2 and absent pupillary reactions to light and absent corneal reflexes on day 3 was present in 14.9% of patients with an unfavourable and none of the patients with a favourable outcome. None of the patients with a favourable outcome had a bilaterally absent somatosensory evoked potential of the median nerve. The value of electroencephalogram patterns in predicting outcome was low, except for reactivity to noxious stimuli.

Conclusions

No single clinical or electrophysiological parameter has sufficient accuracy to determine prognosis and decision making in patients after cardiac arrest, treated with hypothermia.

Introduction

Outcome studies in patients with anoxic-ischemic encephalopathy focus on the early prediction of an outcome no better than a vegetative state or severe disability. Clinical signs, electrophysiological and/or biochemical tests with a false positive rate of 0% and a narrow confidence interval are currently used early after cardiac arrest to identify a subset of patients with a poor prognosis.1

Hypothermia has a marked effect on the cerebral changes that occur during the post-cardiac arrest period by influencing metabolism, cerebral blood flow, inflammatory response and neuro-excitatory pathways.2 These hypothermia induced changes by itself may prolong the time to recovery of the brain. Sedatives additionally influence the time to regaining consciousness, and therefore prognostication after hypothermia. Midazolam is frequently used in patients after cardiac arrest.3 Hypothermia influences the metabolism of midazolam with an increase in plasma concentrations, possibly because of depressed cytochrome P 450(CYP)3A4 and CYP3A5 activity.4 Together with impaired hepatic and renal function that may occur as a result of whole-body ischemia–reperfusion, midazolam and its active metabolites can accumulate resulting in an unpredictably prolonged sedative effect.

Currently used predictors of outcome in patients with anoxic-ischemic encephalopathy are based on studies performed before the use of mild therapeutic hypothermia.1, 5 There is increasing evidence in the literature that these parameters may not be applicable to patients after hypothermia.6 We determined the effect of mild therapeutic hypothermia on the validity of the currently used clinical practice parameters as described by the Quality Standards Subcommittee of the American Academy of Neurology (AAN).1 In addition, we studied the natural course of the clinical neurological parameters of patients with post-anoxic encephalopathy during and after treatment with hypothermia.

Section snippets

Patients

We conducted a retrospective cohort study of consecutive adult patients with return of spontaneous circulation (ROSC) after cardiac arrest who were admitted to the ICU of the Radboud University Nijmegen Medical Centre between January 2007 and November 2009 and treated with mild hypothermia. The patients were identified from the National Intensive Care Evaluation (NICE) database using “cardiac arrest, with or without respiratory arrest” as the diagnosis on admission. Since no intervention was

Results

We identified 162 patients from the NICE database who were admitted to the ICU after cardiac arrest between January 2007 and November 2009. We excluded 43 patients that were not cooled to hypothermia and 16 patients because of missing data (most frequently because of transfer to another hospital) or failure to obtain the GOS. The data of the remaining 103 patients were analyzed.

Discussion

The prognosis of post-anoxic encephalopathy in patients treated with hypothermia is difficult to predict in an early phase. After treatment with mild hypothermia, the motor score of the GCS gradually improved during the first 7 days after ROSC. At day 3, the current clinical practice parameters such as the motor score, pupillary reflex or corneal reflex were unreliable in predicting a poor outcome. The predictive value of EEG patterns in predicting a poor outcome was low, except for reactivity

Conclusions

Our analysis clearly shows that no single clinical or electrophysiological parameter has sufficient accuracy to determine prognosis and decision making in patients after cardiac arrest, treated with hypothermia. We demonstrated that the current clinical AAN guidelines cannot be safely applied to these patients. Early prognostication in patients with post-anoxic encephalopathy will probably require a multimodal approach, combining a number of clinical and electrophysiological tests. Prospective

Conflict of interest statement

The authors declare that they have no competing interests.

Acknowledgement

None.

References (21)

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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2011.02.020.

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