The ACEP Clinical Policies Committee regularly reviews guidelines published by other organizations and professional societies. Periodically, new guidelines are identified on topics with relevance to the clinical practice of emergency medicine. This article highlights recommendations for interventions to improve neurological outcomes in post­–cardiac arrest patients, which were developed by the American Academy of Neurology (AAN).

Roughly 300,000 people suffer from out-of-hospital cardiac arrest (OHCA) each year in the United States, but only about 6 to 9 percent of patients survive to hospital discharge.¹ Neurological injury remains a major determinate of morbidity and mortality in survivors. Targeted temperature management (TTM), which may include the avoidance of hyperthermia and therapeutic hypothermia, has been shown to improve neurological outcomes in post-arrest patients when initiated in the emergency department after return of spontaneous circulation (ROSC). In 2017, the AAN published a set of recommendations for management strategies to reduce neurological injury after cardiac arrest.²

The guidelines were developed from a systematic review and meta-analysis conducted by the AAN on literature from 1966 through August 2016. Below are highlights of their recommendations, focusing on aspects pertinent to emergency physicians.

Takeaway 1: Patients with atraumatic OHCA who are initially unresponsive after ROSC are likely to have lower mortality and better chances of favorable neurological outcomes if TTM is initiated.

This recommendation is supported by five Class I studies and multiple lower-quality studies demonstrating improved overall mortality and functional neurological outcomes in patients receiving some form of TTM. The benefits are greater for patients with an initial rhythm of ventricular tachycardia or ventricular fibrillation (VT/VF) compared to those with pulseless electrical activity (PEA)/asystole.

• Initial rhythm VT/VF: 16 percent more favorable neurological outcomes (95% CI; 4–27%) and 14 percent less mortality (95% CI; 3–26%) at six months.³
• Initial rhythm PEA/asystole: 6 percent more favorable neurological outcomes (95% CI; 3–9% percent) and 12 percent less mortality (95% CI; 8–16%) at hospital discharge.²

The number of post-OHCA patients needed to be treated (NNT) with cooling to benefit one patient with a positive neurologic outcome at six months is seven after VT/VF arrest and 17 after PEA/asystolic arrest.

Takeaway 2: At this time, no single temperature has been shown to be superior. Pick a temperature between 32°C and 36°C and stick with it.

While this is an ongoing area of research and a point of some debate among experts, the best evidence available has failed to show just how cold is “cold enough” for ideal TTM. In particular, one Class I study compared protocols based around 32°C versus 34°C, while another compared 33°C versus 36°C.^4,5 Neither found a significant difference in major outcomes. For now, different hospitals will use different protocols, so emergency physicians should just be aware of the protocol at their center.

Takeaway 3: There is no clear superiority of invasive cooling (through a central line or peritoneal catheter) versus noninvasive cooling methods (eg, cold saline boluses, cooling vests, etc.) with regard to mortality.

The AAN guideline found two Class III studies addressing this question, but both failed to show a benefit in mortality or neurological outcome for invasive versus noninvasive cooling strategies for TTM. Among this weak evidence, there was some suggestion that invasive cooling through a central line may provide less temperature variability, but it also is associated with more frequent bleeding complications. The bottom line is that more studies need to be done, and for now, emergency physicians should choose a method they have available at their institution and are most comfortable with.

Takeaway 4: There are a lot of interventions other than TTM that have been proposed to decrease OHCA neurological damage, but none cited by the AAN guideline are supported by strong evidence and they have less applicability to emergency physicians.

Some of the treatments reviewed were erythropoietin, corticosteroids, xenon gas, and others. None of these had strong evidence in their favor. Also, most of the therapies mentioned in the AAN guideline (other than TTM) are probably more applicable to the inpatient setting than interventions to be initiated in the emergency department.

Takeaway 5: Initiation of TTM in the out-of-hospital setting by EMS (with cooled saline boluses or other methods) is unlikely to add benefit to hospital-based TTM

Five Class I studies of moderate size failed to demonstrate benefit for out-of-hospital cooling when compared to initiation of cooling upon hospital arrival.

Conclusion

It is critical for emergency physicians to be familiar with their own center’s capabilities for TTM, and emergency physicians should work with other parties at their institution (ie, cardiology, neurology, and critical care) to create protocols and agreements to help facilitate effective TTM after ROSC for OHCA patients. Further research is needed to determine the optimal timing for initiation and the duration of TTM.

References

1. McNally B, Robb R, Mehta M, et al. Out-of-hospital cardiac arrest surveillance—Cardiac Arrest Registry to Enhance Survival (CARES), United States, October 1, 2005–December 31, 2010. MMWR Surveill Summ. 2011;60(8):1-19.
2. Geocadin RG, Wijdicks E, Armstrong MJ, et al. Practice guideline summary: reducing brain injury following cardiopulmonary resuscitation: report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology. 2017;88(22):2141-2149.
3. Hypothermia after Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med. 2002;346(8):549-556.
4. Lopez-de-Sa E, Rey JR, Armada E, et al. Hypothermia in comatose survivors from out-of-hospital cardiac arrest: pilot trial comparing 2 levels of target temperature. Circulation. 2012;126(24):2826-2833.
5. Nielsen N, Wetterslev J, Cronberg T, et al. Targeted temperature management at 33°C versus 36°C after cardiac arrest. N Engl J Med. 2013;369(23):2197-2206.

Dr. Harrison is a second-year emergency medicine resident at Beaumont Health in Royal Oak, Michigan.