Continuous Compressions, Incomplete Ventilation? A Retrospective Analysis of mCPR in Admitted ED Patients

<b>Background/Objectives</b>: Mechanical cardiopulmonary resuscitation (mCPR) devices offer consistent chest compressions during prolonged resuscitations and transport, but their impact on ventilation and patient outcomes remains unclear. This study aimed to compare gas exchange, metabolic parameters, and clinical outcomes in patients with ongoing manual versus mechanical CPR upon arrival at the emergency department (ED) after out-of-hospital cardiac arrest (OHCA). <b>Methods</b>: We conducted a retrospective analysis of 394 consecutive adult patients with non-traumatic OHCA admitted to a metropolitan cardiac arrest center between January 2019 and December 2024. Patients were categorized into three groups: Return of spontaneous circulation (ROSC) on arrival (n = 240), ongoing manual CPR (n = 107), and ongoing mechanical CPR (n = 47). Gas exchange and metabolic parameters were obtained from initial arterial blood gas (ABG) analysis and monitor readings. The primary outcome was survival to hospital discharge; secondary outcomes included 24 h survival and neurological status at discharge (CPC 1-2). <b>Results</b>: Survival to hospital discharge was significantly higher in the manual CPR group (8.4%) compared to 0% in the mechanical CPR group (<i>p</i> = 0.04). Both groups showed severe acidosis and hypercapnia upon ED arrival; however, PaCO₂ levels were significantly higher in the mCPR group (83.0 ± 25.5 mmHg vs. 72.3 ± 21.6 mmHg, <i>p</i> = 0.01). ROC analysis identified lactate (AUC = 0.765) and pH (AUC = 0.743) as the strongest predictors of survival, while EtCO₂ had limited prognostic value (AUC = 0.541). <b>Conclusions</b>: In patients with refractory out-of-hospital cardiac arrest admitted with ongoing cardiopulmonary resuscitation, mechanical CPR was associated with higher PaCO₂ levels on emergency department arrival compared with manual CPR, while other gas exchange parameters did not differ significantly. Given the limited sample size and small number of survivors, these findings are exploratory and hypothesis-generating, underscoring the need for prospective studies on ventilation during continuous chest compressions.