Abstract & Commentary

Neuroprognostication in Patients Receiving Therapeutic Hypothermia Following Cardiac Arrest

By David J. Pierson, MD, Editor, Professor Emeritus, Pulmonary and Critical Care Medicine, University of Washington, Seattle, is Editor for Critical Care Alert.

Although current guidelines recommend delaying neuroprognostication during therapeutic hypothermia following resuscitation from cardiac arrest, this review of 55 consecutive patients so managed found that a "poor prognosis" designation was arrived at during the hypothermia period in most of them, including six patients who were eventually discharged with a favorable neurologic outlook.

Source: Perman SM, et al. Timing of neuroprognostication in postcardiac arrest therapeutic hypothermia. Crit Care Med 2012;40:719-724.

Therapeutic hypothermia (TH) has been widely adopted as a management strategy for patients who remain comatose after return of spontaneous circulation following cardiac arrest, as the only therapeutic intervention shown to favorably influence neurologic outcomes. Because sedation and paralysis are used, and because hypothermia itself depresses neurologic function, current guidelines recommend deferring neuroprognostication until the TH period is completed. In this retrospective review of patients managed with post-cardiac arrest TH in the medical and cardiac ICUs of two University of Pennsylvania hospitals, the authors sought to determine when neuroprognostication took place, how it was done, and what the patient outcomes were.

During the 3.5-year period covered by the study, TH was carried out by means of a protocol. Adult patients who had return of spontaneous circulation following cardiopulmonary resuscitation after primary cardiac arrest and whose Glasgow Coma Scale scores were less than 6 were included, so long as they did not have do-not-resuscitate status or another specific contraindication. Hypothermia (32-34° C) was induced using cold intravenous saline and external cooling body wraps, and was maintained for 24 hours once the target temperature was attained. Active rewarming at 0.25-0.50° C/h was then undertaken. Sedating and paralyzing agents were used throughout the TH period, the latter being discontinued once normothermia was reached. For this study, the "intra-TH" period was defined as extending from resuscitation through 15 hours following attainment of normothermia. Patients who survived to discharge were designated according to cerebral performance category as good (full function), moderate cerebral disability (disabled but independent), severe cerebral disability (conscious but disabled and dependent), coma/vegetative state (unconscious), or dead or brain dead.

Of 55 patients who initially met entry criteria and whose charts were reviewed, six were excluded for various a priori reasons, leaving 49 patients (59% male, mean age 56 years). Of these, 28/49 (57%) had documentation of an "intra-TH" poor prognosis in the chart. Documentation occurred prior to achievement of target hypothermia in five patients, during the 24-hour hypothermia period in eight, during rewarming in five, and within the first 15 hours after rewarming in 10. Of the 28 patients assigned a poor prognosis during the TH protocol, 18 (64%) were still receiving sedation and paralytic drugs at the time. Neurology consultation was obtained in 21 of the 28 "poor prognosis" patients, 24 of whom also underwent head computed tomography. Most of the "poor prognosis" designations were assigned by the primary managing team, while the neurology consultant advised waiting until post-TH for prognostication in 43% of instances. Most of the patients assigned an "intra-TH" poor prognosis had a do-not-resuscitate order signed within 48 hours thereafter. Of the 28 patients given an "intra-TH" poor prognosis, 20 (71%) did not survive to discharge, while six (21%) of them were eventually discharged with a cerebral performance score of "good."

Commentary

This study found that, in the authors' institution, patients managed with post-arrest TH were often assigned a poor prognosis before completion of the TH regimen, which included sedation and muscle relaxation as part of the protocol. The timing and mechanism of prognostication varied greatly. As the authors point out, further research is clearly needed to determine how best to evaluate the neurological prognosis in patients treated with TH.

In addition to anoxic brain injury, which is the primary target for neurologic assessment following cardiac arrest, sedatives, and paralytics, the effects of hypothermia on their metabolism and clearance, and the hypothermia itself may all contribute to assignment of an inappropriately poor prognosis. The fact that several patients who were discharged in good neurologic condition were initially assigned a poor prognosis prior to completion of the TH protocol emphasizes the importance of not concluding too hastily that the patient has little or no chance of meaningful recovery in the context of TH and its associated interventions.