Monocyte subsets predict mortality after cardiac arrest

After successful cardiopulmonary resuscitation (CPR), many patients show signs of an overactive immune activation. Monocytes are a heterogeneous cell population that can be distinguished into 3 subsets by flow cytometry (classical monocytes [CM: CD14(++)CD16(‐)], intermediate monocytes [IM: CD14(++)CD16(+)CCR2(+)] and non‐classical monocytes [NCM: CD14(+)CD16(++)CCR2(‐)]). Fifty‐three patients admitted to the medical intensive care unit (ICU) after cardiac arrest were included. Blood was taken on admission and after 72 h. The primary endpoint of this study was survival at 6 months and the secondary endpoint was neurological outcome as determined by cerebral performance category (CPC)‐score at 6 months. Median age was 64.5 (49.8‐74.3) years and 75.5% were male. Six‐month mortality was 50.9% and survival with good neurological outcome was 37.7%. Monocyte subset distribution upon admission to the ICU did not differ according to survival. Seventy‐two hours after admission, patients who died within 6 months showed a higher percentage of the pro‐inflammatory subset of IM (8.3% [3.8‐14.6]% vs. 4.1% [1.5–8.2]%; P = 0.025), and a lower percentage of CM (87.5% [79.9–89.0]% vs. 90.8% [85.9–92.7]%; P = 0.036) as compared to survivors. In addition, IM were predictive of outcome independent of time to ROSC and witnessed cardiac arrest, and correlated with CPC‐score at 6 months (R = 0.32; P = 0.043). These findings suggest a possible role of the innate immune system in the pathophysiology of post cardiac arrest syndrome.