Nailfold videocapillaroscopy - a novel method for the assessment of hemodynamic incoherence on the ICU.

Background: Loss of hemodynamic coherence is a phenomenon in critically ill patients. Due to inflammatory events and endothelial remodeling, macro- and microhemodynamics are decoupled from each other, resulting in microcirculatory disturbances and end organ ischemia despite adequate vital parameters. So far, quantification of perfusion of vessels with < 100 μm diameter on the intensive care unit (ICU) was regularly performed with incident darkfield (IDF) microscopy. Nailfold videocapillaroscopy (NVC), however, is an established and easy method for visualization of the microcirculation in chronic diseases. We here evaluated NVC in critically ill patients and compared its use with consensus microcirculatory assessment of IDF-microscopy.

Methods: A new score, the capillary microcirculation (CapMic) score summarizing the microcirculation of the nail fold at four regions of digitus III, IV and V in a number between 0 (= no microcirculation) and 1 (= completely preserved microcirculation) was first established in 10 healthy volunteers and compared to the Microangiopathy Evolution Score (MES) standardized for NVC in chronic diseases. Then, n = 60 critically ill patients were recruited from a surgical ICU. Consensus-defined IDF scores and NCV data were compared at a single time point.

Results: Evaluation of the CapMic score in 10 healthy volunteers at rest and under iatrogenic limb ischemia showed robust changes (0.80 ± 0.03 vs. 0.51 ± 0.12, p < 0.001). In critically ill patients, the IDF microscopy parameters "proportion of perfused vessels" (PPV) and "microvascular flow index" (MFI) inversely correlated with the MES (Spearman's R = -0.590, p < 0.001; Spearman's R = -0.585, p < 0.001). There was a positive correlation between PPV and the CapMic score (Spearman's R = 0.714, p < 0.001) and between MFI and the CapMic score (Spearman's R = 0.711, p < 0.001) and an inverse correlation between MES and the CapMic score (Spearman's R = -0.610, p < 0.001). Both sublingual and nailfold microcirculation deteriorated under rising norepinephrine- and crystalloid volume-requirements.

Conclusion: NVC-imaging provides comparable information on the microcirculation in critically ill patients compared to sublingual IDF microscopy. NCV could represent a new, additional method for diagnosing microcirculatory parameters on the ICU.