When Cooling a Patient After Cardiac Arrest, Does Use of a Neuromuscular Blocking Agent Make Your Job Easier?

Post-arrest Therapeutic Hypothermia. Does Use of Neuromuscular Blockers Achieve Faster Cooling Time?

After successful resuscitation from cardiac arrest, cooling the whole body is a well established treatment that improves the chances of the brain recovering. This however, has to be done within a certain time-frame from the arrest. The purpose of this study is to explore the best way of dosing the muscle relaxing medications that are given during the cooling process.

Hypothesis: In the context of our institutional therapeutic hypothermia protocol, cisatracurium infusions lead to faster drops in core temperature when compared to cisatracurium prn boluses alone.

STUDY RATIONALE:

A large proportion of comatose survivors of cardiac arrest presenting to our intensive care units at London Health Sciences Centre (LHSC) undergo therapeutic hypothermia. Current evidence suggests that timely achievement of target temperatures is desirable to improve outcomes. At LHSC, this intervention is protocolized with a defined set of preprinted orders that includes a dosing regimen for neuromuscular blocking agents (NMBA's). Our preprinted protocol has been in place since January of 2004. Cisatracurium infusions were part of the therapeutic hypothermia protocol until October 2011. Since that time, our protocol has changed to cisatracurium prn boluses for any observed shivering. In this study we will examine if there has been any change in the times to achieving target temperatures with the implementation of this change. It is important to note that no other change in our protocol has taken place since it was first implemented, making our before and after comparison valid and fair.

Our hypothesis is that NMBA infusions lead to a faster drop in core temperatures when compared to NMBA prn boluses. If this were to stand true, we would expect cisatracurium IV infusions to result in faster reductions in core temperature when compared with cisatracurium prn boluses in the context of our therapeutic hypothermia protocol. Hypothermia has been known to cause a subclinical increase in muscle tone. This previously reported phenomenon has been named "microshivering". When attempting to reduce core temperatures, microshivering is likely a natural body response to try to restore body temperature back to normal. We therefore hypothesize that NMBA infusions are likely more effective at abolishing microshivering, which would be a desirable effect when trying to induce therapeutic hypothermia.

Although current American Heart Association (AHA) guidelines suggest considering the administration of NMBA's to facilitate induced hypothermia and control shivering. Their recommendation is to minimize the duration of NMBA use or if possible, avoid them altogether. After the publication of these guidelines our institutional protocol changed to prn boluses instead of the previous infusion orders. We therefore believe it is important to examine the effects of this change on our cooling protocol and potentially add to the growing body of knowledge in this field.

Inclusion Criteria:

• Admission to adult ICU (age ≥18 years) at London Health Sciences Centre
• Primary reason for ICU admission: postcardiac arrest
• Both in-hospital and out-of-hospital cardiac arrest will be included
• ICU admission between Jan 2008 and Dec 2012.

Exclusion Criteria:

- ICU admissions primarily for reasons other than cardiac arrest.