vasopressin in severe acidosis post arrest?

Overheard in resus recently: "if the patient is profoundly acidotic post arrest, I use vasopressin, as adrenaline/epinephrine is ineffective at low pH".

I'd heard the second statement before, but not the first.  Curious, I went down an internet rabbit warren of not-very-good evidence.

Firstly, I couldn't find much evidence that adrenaline is ineffective at low pH (though plenty that suggests adrenaline causes low pH, but that's another thing entirely).  The best study I could find (in vitro, on mammary arteries, open access here) suggests the contrary is true for adrenaline, at pH's down to 6.8.  

Secondly, there's no comparative data on the effect of vasopressin over adrenaline in post cardiac arrest syndrome.  The statement overheard may come from an interpretation of Wenzel et al's paper (open access) comparing vasopressin with epinephrine in out of hospital arrest, where patients who were asystolic (hence probably profoundly acidotic?) may have done better with vasopressin.  12 asystolic patients survived to hospital discharge in the vasopressin group, compared with 4 in the epinephrine group ... but many more were comatose or vegetative, compared with epinephrine alone.  Interpreting this is totally speculative, this study wasn't powered for these findings - but I can't find any other evidence that's relevant.

The European Resuscitation Council guidelines for cardiac arrest in special circumstances (an open access must-read with loads of useful guidance) states that there may be role for vasopressin if adrenaline fails.  In anaphylaxis, which is a hypoxic and acidotic state, as a rule.

The Resuscitation Council UK guidance (an open access absolutely must-read, for a succinct evidence-based summary of post arrest care) generally advocates noradrenaline +/- dobutamine for post arrest cardiac dysfunction.  But first line, I will still use judicious fluid boluses, and then epi/adrenaline - I can make up a 5mcg/ml infusion in seconds, which is much more realistic in a busy resus, with an extremely unstable patient.  If that stabilises them, my ICU colleagues have time to switch to Noradrenaline +/- dobutamine, and probably to curse me for inducing lactic acidosis...

How do you manage post-cardiac arrest circulatory dysfunction in the resus room?
​~Lou Mitchell~