Influence of Cooling Duration on Efficacy in Cardiac Arrest Patients

A multicenter, randomized, adaptive allocation clinical trial to determine if increasing durations of induced hypothermia are associated with an increasing rate of good neurological outcomes and to identify the optimal duration of induced hypothermia for neuroprotection in comatose survivors of cardiac arrest.

Cardiac arrest is a common and devastating emergency of the heart and the brain. More than 380,000 patients suffer out of hospital cardiac arrest (OHCA) each year in the US. Improvements in cardiac resuscitation (the early links in the "chain of survival" for patients with OHCA) are tempered by our limited ability to resuscitate and protect the brain from global cerebral ischemia.

Neurological death and disability are common outcomes in survivors of cardiac arrest. Therapeutic cooling of comatose patients resuscitated from shockable rhythms markedly increases the rate of good neurological outcome, but poor outcomes still occur in as many as 50%, and the benefit of cooling in those resuscitated from asystole and pulseless electrical activity has not been shown in a randomized study.

Objectives:

The overarching goal of this project is to identify clinical strategies that will increase the number of patients with good neurological recovery from cardiac arrest. We hypothesize that longer durations of cooling may improve either the proportion of patients that attain a good neurological recovery or may result in better recovery among the proportion already categorized as having good outcomes.

Primary Objectives:

1. To determine, in each of two populations of adult comatose survivors of cardiac arrest (those with initial shockable rhythms and those with pulseless electrical activity (PEA)/asystole), the shortest duration of cooling that provides the maximum treatment effect as determined by a weighted 90 day modified Rankin score B. To determine, in each of two populations of adult comatose survivors of cardiac arrest (those with initial shockable rhythms and those with PEA/asystole), whether increasing durations of cooling are associated with better outcomes or recovery implying efficacy of hypothermia to no cooling.

Secondary Objectives:

To characterize the overall safety and adverse events associated with duration of cooling To characterize the effect of duration of cooling on neuropsychological outcomes To characterize the effect of duration of cooling on patient reported quality of life

Design:

This study is a randomized, response-adaptive, duration (dose) finding, comparative effectiveness clinical trial with blinded outcome assessment. The design is based on a statistical model of response as defined by the primary endpoint, a weighted 90-day mRS, across the treatment arms. The design will fit patient outcome data to a duration response model (separately for shockable and non-shockable rhythms), in which the potentially non-linear association between durations of cooling and the primary endpoint are estimated. All conclusions about the treatment arms are based on this model. The functional form of the duration-response model is flexible and able to fit many different shapes for the duration-response curve. Specifically it is parameterized to identify up to two change-points in the treatment effect across arms, allowing it to fit an increasing, decreasing, flat, plateau, or U-shape duration-response curve.

Subjects will initially be equally randomized between 12, 24, and 48 hours of cooling. After the first 200 subjects have been randomized, additional treatment arms between 12 and 48 hours will be opened and patients will be allocated, within each rhythm type, by response adaptive randomization. As the trial continues, shorter and longer duration arms may be opened. Specifically, a 6-hour duration arm will be opened if the emerging duration-response curve from 12 hours is flat. Similarly, a 60-hour or 72-hour duration arm will be opened if the emerging duration response curve shows an increasing treatment benefit through 48 hours.

This trial will have frequent interim analyses to stop the trial early for futility if it is highly likely that no treatment arm offers a greater benefit then the 6-hour duration arm.

Primary Outcome Measure:

The primary outcome measure will be the modified Rankin scale at 90 days after return of spontaneous circulation. The mRS will be analyzed as a weighted score incorporating both the proportion of subjects achieving a good neurological outcome and degree of residual functional impairment among those with good neurological outcomes.

Study Population:

Comatose adult survivors of out of hospital cardiac arrest that have already been rapidly cooled using a definitive temperature control method (endovascular or surface) will be enrolled in the emergency department or intensive care unit. Hub and spoke hospitals from the SIREN network will be enriched with high potential ancillary Hubs. Approximately 50 hospitals are anticipated to each enroll an average of 9 subjects per year.

Randomization:

Central computerized randomization by web-based interface will be used. Subjects will be potentially randomized over the course of the trial to the following possible durations of cooling (in hours): 6, 12, 18, 24, 30, 36, 42, 48, 60, and 72. The first 200 patients will be randomized 1:1:1 to the 12, 24, and 48-hour durations only. After this initial "burn in" period, response adaptive randomization will be used to allocate subjects to durations inclusive of 12 to 48 hours initially, and then subsequently to the 6, 60 or 72 hour durations if specified conditions are met and the emerging duration-response curve suggests that the maximum treatment benefit might be on those durations. The response adaptive randomization probabilities for each arm will be determined separately for the two rhythm type populations. Randomization probabilities will be updated monthly, or approximately every 38 patients based on the expected accrual rate.

Consent:

Eligible patients for this trial will not have capacity to provide informed consent. Written informed consent from a legally authorized representative will be required.

Intervention:

The intervention will be random allocation to duration of cooling after cardiac arrest. Cooling in the study will be by a definitive temperature control method to a target temperature of 33 deg C. Any endovascular or surface cooling system with closed loop feedback will be allowed. Duration of cooling will be measured from the time that cooling with a definitive device is initiated in the hospital. As part of routine medical care, cooling may be initiated by emergency medical service (EMS) or in the emergency department. Eligibility will require that a temperature of <34 degrees C be obtained by 240 minutes after cardiac arrest. After the allocated duration of cooling is completed, controlled rewarming will be performed. Rewarming to a temperature of 36.5 deg C will occur over the shorter of 24 hours or a rewarming period equal to the allocated duration of cooling. Definitive cooling devices may be used for maintenance of normothermia after rewarming is complete. A clinical standardization guideline will be followed to reduce the effects of practice variability. Key physiologic and practice variables will be tracked and compliance with clinical standardization and deviation from physiologic targets reported back to study teams.

Statistical Analysis for the Primary Outcome Measure:

We will model the mean weighted mRS at 90 days across the treatment arms. The weighted mRS incorporates both the proportion of subjects achieving a good neurological outcome and degree of impairment among those with good neurological outcomes. The primary analysis is conducted separately for each rhythm type, allowing for a different treatment effect by rhythm type, and has two components. First, we identify the most likely target duration, where the target duration is the shortest duration that achieves the maximum treatment effect (Objective A). Second, we calculate whether the efficacy of any duration is superior to any shorter duration of cooling indicating a positive duration response (Objective B). Establishing a positive duration response implies confirmation that cooling is effective in improving outcome or recovery versus normothermia, when a normothermia control arm is not clinically acceptable.

A maximal sample size of 1800 subjects enrolled over 4 years (estimated accrual rate of 37.5 subjects/month) is anticipated.

Investigational Device Exemption