Clinical paper Effects of mild hypercapnia on myocardial injury after out-of-hospital cardiac arrest. A sub-study of the TAME trial

Purpose: Mild hypercapnia did not improve neurological outcomes for resuscitated out-of-hospital cardiac arrest (OHCA) patients in the Targeted Therapeutic Mild Hypercapnia After Resuscitated Cardiac Arrest (TAME) trial. However, the effects of hypercapnic acidosis on myocardial injury in patients with cardiac arrest is unexplored. We investigated whether mild hypercapnia compared to normocapnia, following emergency coronary intervention, increased myocardial injury in comatose OHCA-patients with AMI. Methods: Single-centre, prospective, pre-planned sub-study of the TAME trial. Patients were randomised to targeted mild hypercapnia (PaCO2 = 6.7-7.3 kPa) or normocapnia (PaCO2 = 4.7-6.0 kPa) for 24 h. Myocardial injury was assessed with high-sensitive cardiac troponin T (hs-cTnT) measured at baseline, 24, 48 and 72 h. Haemodynamics were assessed with right heart catheterisation and blood-gas analyses every 4th hour for 48 h. Results: We included 125 OHCA-patients. 57 (46%) had an AMI, with 31 and 26 patients randomised to hypercapnia and normocapnia, respectively. Median peak hs-cTnT in AMI-patients was 58% lower in the hypercapnia-group: 2136 (IQR: 861-4462) versus 5165 ng/L (IQR: 2773-7519), p = 0.007. Lower average area under the hs-cTnT curve was observed in the hypercapnia-group: 2353 (95% CI 1388-3319) versus 4953 ng/L (95% CI 3566-6341), P-group = 0.002. Hypercapnia was associated with increased cardiac power output (CPO) and lower lactate levels in patients with AMI (P-group < 0.05). hs-cTnT, lactate and CPO were not significantly different between intervention groups in OHCA-patients without AMI (p > 0.05). Conclusions: Mild hypercapnia was not associated with increased myocardial injury in resuscitated OHCA-patients. In AMI-patients, mild hypercapnia was associated with lower hs-cTnT and lactate, and improved cardiac performance.