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In response to some insightful comments on post-arrest ventilation and PaCO2 by @_Brian_Mc_ , here's a thread on some of what we know about ventilation in the post-arrest period...
A large number of observational studies have demonstrated an association between post-arrest PaCO2 & a variety of outcomes. We summarized most of them here in the following @accpchest review: journal.chestnet.org/article/S0012-… 
In these retrospective data, hypocarbia has been consistently associted with poor outcome. The relationship b/w hypercarbia and outcome is less clear. All studies are subject to limitations, including ABGs drawn at variable time periods and not accounting for metabolic acidosis.
To address this, Kilgannon et al. @CooperEMed published a prospective cohort study (PMID 30452939 ) in which ABGs were drawn at 1 & 6h & adjusted for met acidosis. They found U-shaped association b/t PaCO2 & neuro outcome w/ optimal values of 68 & 51 (if metabolic acidosis) mmHg
Why might this be? Exact mechanism is not known, but here are a few possibilities:
1) Hyperventilation exacerbates hemodynamic effects of positive pressure ventilation. This is known during arrest (PMID: 15508657), but may also be true in post-arrest period.
1) Hyperventilation exacerbates hemodynamic effects of positive pressure ventilation. This is known during arrest (PMID: 15508657), but may also be true in post-arrest period.
2) Hypocarbia causes cerebral vasoconstriction and may worsen secondary ischemic injury. Conversely, mild hypercarbia may improve cerebral DO2. A small prospective study supports this hypothesis: PMID: 26903288.
3) Hypercarbia may mitigate the effects of ischemia-reperfusion injury. Lavani et al. reperfused chick myocytes in hypercarbic milleu and found decreased cell death and reactive oxygen species compared with hypocarbia and normal.
Where's the RCT, you ask? Well, @Eastwoodgm conducted a Phase 2 trial randomized pts to PaCO2 35-45 vs 50-55 for 24 hrs post-arrest. Found mild hypercarbia to be associated with lower levels of NSE and S100, biomarkers of neuronal injury and a (nonsignificant) 11% mortality diff.
While we eagerly await the results of @TAMEtrial (clinicaltrials.gov/ct2/show/NCT03…), here take-homes:
1) Avoid hypocarbia. Consistently associated with poor outcome.
2) Maintain high/normal PaCO2. Mild hypercarbia may be beneficial.
3) Get ABG early. EtCO2=/=PaCO2 in this population.
1) Avoid hypocarbia. Consistently associated with poor outcome.
2) Maintain high/normal PaCO2. Mild hypercarbia may be beneficial.
3) Get ABG early. EtCO2=/=PaCO2 in this population.
