Sonographic Evaluation of Intracranial Hemodynamics and Pressure after Out-of-hospital Cardiac Arrest: an Exploratory Sub-Study of the TAME Trial

Objective Targeted mild hypercapnia is a potential neuroprotective therapy after cardiac arrest. In this exploratory observational study, we aimed to explore the effects of targeted mild hypercapnia on cerebral microvascular resistance assessed by middle cerebral artery pulsatility index (MCA PI) and intracranial pressure estimated by optic nerve sheath diameter (ONSD) in resuscitated out-of-hospital cardiac arrest (OHCA) patients. Design, setting, participants and interventions Comatose adults resuscitated from OHCA were randomly allocated to targeted mild hypercapnia (PaCO2 50–55 mmHg) or targeted normocapnia (PaCO2 35–45 mmHg) for 24 h in the TAME trial. Main outcome measures Using transcranial Doppler and transorbital ultrasound, we obtained MCA PI and ONSD at 4, 24, and 48 h after randomization. Ultrasound parameters were compared between groups using a linear mixed effects model. Results Twelve consecutive patients were included, with seven patients in the mild hypercapnia group. MCA PI decreased from 4 to 24 h (p = 0.019) and was lower over the first 24 h in patients allocated to targeted mild hypercapnia compared with targeted normocapnia (p = 0.047). ONSD did not differ between groups or over time. Conclusion Cerebral microvascular resistance assessed by MCA PI decreased over 24 h and was lower in OHCA patients treated with targeted mild hypercapnia compared with targeted normocapnia. Targeted mild hypercapnia did not exert substantial effect on intracranial pressure as estimated by ONSD.