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Can higher MAP post cardiac arrest improve neurologic outcomes?



CHICAGO – A European clinical trial that targeted a mean arterial blood pressure after cardiac arrest higher than what the existing guidelines recommend found that the approach was safe, improved blood flow and oxygen to the brain, helped patients recover quicker, and reduced the number of adverse cardiac events, although it did not reduce the extent of anoxic brain damage or improve functional outcomes, the lead investigator reported at the American Heart Association scientific sessions.

Dr. Koen Ameloot of East Limburg Hospital in Genk, Belgium.

Dr. Koen Ameloot

The Neuroprotect trial randomly assigned 112 adult survivors of an out-of-hospital cardiac arrest who were unconscious upon admission to two study groups: early goal-directed hemodynamic optimization (EGDHO), in which researchers used a targeted mean arterial pressure (MAP) of 85-100 mm Hg and mixed venous oxygen saturation between 65% and 75% during the first 36 hours after ICU admission; and the standard care group, in which they used the guideline-recommended MAP target of 65 mm Hg, said Koen Ameloot, MD, of East Limburg Hospital in Genk, Belgium.

“EGDHO clearly improved cerebral perfusion and oxygenation, thereby for the first time providing the proof of concept for this new hemodynamic target,” Dr. Ameloot said. “However, this did not result in the reduction of the extent of anoxic brain hemorrhage or effusion rate on MRI or an improvement in functional outcome at 180 days.”

He noted the trial was predicated on improving upon the so-called “two-hit” model of cardiac arrest sequelae: the first hit being the no-flow and low-flow period before achieving restoration of spontaneous circulation; the second hit being hypoperfusion and reperfusion injury during ICU stay.

Dr. Ameloot referenced a study in which he and other coauthors reported that patients with a MAP target of 65 mm Hg “experience a profound drop of cerebral oxygen saturation during the first 12 hours of ICU stay that may cause additional brain damage” (Resuscitation. 2018;123:92-7).

The researchers explored the question of what is the optimal MAP if a target of 65 mm Hg is too low, Dr. Ameloot said. “We showed that maximal brain oxygenation is achieved with a MAP of 100 mm Hg, while lower MAPs were associated with submaximal brain perfusion and higher MAPs with excessive after-load, a reduction in stroke volume, and suboptimal cerebral oxygenation.”

During the 36-hour intervention period, the EGDHO patients received higher doses of norepinephrine, Dr. Ameloot said. “This resulted in significant improvement of cerebral oxygenation during the first 12 hours and was paralleled by significantly higher cerebral perfusion in the subset of patients in whom Doppler measurements were performed,” he said. “While patients allocated to the MAP 65 mm Hg target experienced a profound drop of cerebral oxygenation during the critical first 6-12 hours of ICU stay, cerebral oxygenation was maintained at 67% in patients assigned to EGDHO.”

However, the rate of anoxic brain damage, measured as the percentage of irreversibly damaged anoxic voxels on diffusion-weighted MRI – the primary endpoint of the study – was actually higher in the EGDHO group, 16% vs. 12%, Dr. Ameloot said. “The percentage of anoxic voxels was only a poor predictor of favorable neurological outcome at 180 days, questioning the validity of the primary endpoint,” he said. He also noted that 23% of the trial participants did not have an MRI scan because of higher than expected 5-day rates of death.

“The percentage of patients with favorable neurological outcome tended to be somewhat higher in the intervention arm, although this did not reach statistical significance at ICU discharge and at 180 days,” Dr. Ameloot said. He noted that 42% of the intervention group and 33% of controls in the full-analysis set (P = .30) and 43% and 27%, respectively, in the per-protocol set (P = .15) had a favorable neurological outcome, as calculated using the Glasgow-Pittsburgh Cerebral Performance Category scores of 1 or 2, at 180 days.

The study did not reveal any noteworthy differences in ICU stay (7 vs. 8 days, P = .13) or days on mechanical ventilation (5 vs. 7, P = .31), although fewer patients in the EGDHO group required a tracheostomy (4% vs. 18%, P = .02). The intervention group also had lower rates of cardiac events, including recurrent cardiac arrest, limb ischemia, new atrial fibrillation, and pulmonary edema (13% vs. 33%; P = .02), Dr. Ameloot said.

Future post-hoc analyses of the data will explore the hypothesis that higher blood pressure leads to improved coronary perfusion and reduced infarct size, thus improving prognosis, he added.

“Should this trial therefore be the definite end to the promising hypothesis that improving brain oxygenation might reduce the second hit in post–cardiac arrest patients? I don’t think so,” Dr. Ameloot said. He noted a few limits to the study: that the perfusion rate on MRI was a poor predictor of 180-day outcome; that more patients than expected entered the trial without receiving basic life support and with nonshockable rhythms; and that there was possibly less extensive brain damage among controls at baseline. “Only an adequately powered clinical trial can provide an answer about the effects of EGDHO in post–cardiac arrest patients,” Dr. Ameloot said.

Dr. Ameloot had no financial relationships to disclose.

SOURCE: Ameloot K et al. AHA 2018, Abstract 18620

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