Hypothermia after long down times

You receive a patient resuscitated from cardiac arrest to a perfusing rhythm in your emergency department. History suggests a long ‘down time’: There was a ten minute duration of ‘no-flow’ (time from collapse to the start of resuscitation attempts).

Would this make you more likely or less likely to initiate targeted temperature management (TTM) and cool the patient to the recommended 32-34 degrees?

A recent study supports the suggestion that a longer no-flow time is associated with greater odds of survival with TTM compared with no TTM, than patients with shorter no-flow times. In other words, cooling the patient is more likely to make a difference in the ‘long down time’ patient, even though the overall survival in that group is obviously less.

Aim Mild therapeutic hypothermia has shown to improve long-time survival as well as favorable functional outcome after cardiac arrest. Animal models suggest that ischemic durations beyond 8 min results in progressively worse neurologic deficits. Based on these considerations, it would be obvious that cardiac arrest survivors would benefit most from mild therapeutic hypothermia if they have reached a complete circulatory standstill of more than 8 min.

Methods In this retrospective cohort study we included cardiac arrest survivors of 18 years of age or older suffering a witnessed out-of-hospital cardiac arrest, which remain comatose after restoration of spontaneous circulation. Data were collected from 1992 to 2010. We investigated the interaction of ‘no-flow’ time on the association between post arrest mild therapeutic hypothermia and good neurological outcome. ‘No-flow’ time was categorized into time quartiles (0, 1–2, 3–8, >8 min).

Results One thousand-two-hundred patients were analyzed. Hypothermia was induced in 598 patients. In spite of showing a statistically significant improvement in favorable neurologic outcome in all patients treated with mild therapeutic hypothermia (odds ratio [OR]: 1.49; 95% confidence interval [CI]: 1.14–1.93) this effect varies with ‘no-flow’ time. The effect is significant in patients with ‘no-flow’ times of more than 2 min (OR: 2.72; CI: 1.35–5.48) with the maximum benefit in those with ‘no-flow’ times beyond 8 min (OR: 6.15; CI: 2.23–16.99).

Conclusion The beneficial effect of mild therapeutic hypothermia increases with cumulative time of complete circulatory standstill in patients with witnessed out-of-hospital cardiac arrest.

The beneficial effect of mild therapeutic hypothermia depends on the time of complete circulatory standstill in patients with cardiac arrest
Resuscitation. 2012 May;83(5):596-601