AIM: We hypothesized that microcirculatory dysfunction, similar to that seen in sepsis, occurs in post-cardiac arrest patients and that better microcirculatory flow will be associated with improved outcome. We also assessed the association between microcirculatory dysfunction and inflammatory markers in the post-cardiac arrest state. METHODS: We prospectively evaluated the sublingual microcirculation in post-cardiac arrest patients, severe sepsis/septic shock patients, and healthy control patients using Sidestream Darkfield microscopy. Microcirculatory flow was assessed using the microcirculation flow index (MFI) at 6 and 24h in the cardiac arrest patients, and within 6h of emergency department admission in the sepsis and control patients. RESULTS: We evaluated 30 post-cardiac arrest patients, 16 severe sepsis/septic shock patients, and 9 healthy control patients. Sublingual microcirculatory blood flow was significantly impaired in post-cardiac arrest patients at 6h (MFI 2.6 [IQR: 2-2.9]) and 24h (2.7 [IQR: 2.3-2.9]) compared to controls (3.0 [IQR: 2.9-3.0]; p<0.01 and 0.02, respectively). After adjustment for initial APACHE II score, post-cardiac arrest patients had significantly lower MFI at 6-h compared to sepsis patients (p<0.03). In the post-cardiac arrest group, patients with good neurologic outcome had better microcirculatory blood flow as compared to patients with poor neurologic outcome (2.9 [IQR: 2.4-3.0] vs. 2.6 [IQR: 1.9-2.8]; p<0.03). There was a trend toward higher median MFI at 24h in survivors vs. non-survivors (2.8 [IQR: 2.4-3.0] vs. 2.6 [IQR: 2.1-2.8] respectively; p<0.09). We found a negative correlation between MFI-6 and vascular endothelial growth factor (VEGF) (r=-0.49, p=0.038). However, after Bonferroni adjustment for multiple comparisons, this correlation was statistically non-significant. CONCLUSION: Microcirculatory dysfunction occurs early in post-cardiac arrest patients. Better microcirculatory function at 24h may be associated with good neurologic outcome.