Sublingual capillary de-recruitment with preserved recruitability in resuscitated patients with circulatory shock

Abstract Background Circulatory shock and multi-organ failure remain major contributors to mortality in critically ill patients, resulting in decoupling of macro- and microcirculatory function. Recent studies have identified the recruitment of microcirculatory diffusion capacity as reflected by an increase in functional capillary density (FCD) in response to a topical nitroglycerin (NG) administration as a mechanism to increase oxygen delivery to the tissue. However, the effect of circulatory shock on microcirculatory recruitability remains unclear. We hypothesized that circulatory shock leads to microcirculatory de-recruitment reflected by a lower FCD and lower RBCv, similar maximum recruitable FCD (FCDNG) and RBCV (RBCvNG), and increased microcirculatory recruitability (ΔFCDNG and ΔFCDNG). Methods Sublingual handheld vital microscopy measurements and assessment of microcirculatory recruitability were performed after initial fluid resuscitation in mechanically ventilated patients consecutively admitted to the tertiary medical ICU of the university hospital of Zurich. The presence of circulatory shock was defined as > 3 of the following: cardiac index (CI) < 2.2 l/min/m2, lactate > 2 mmol/l, vasopressor dependent index (VDI) > 3, Mottling score ≥ 2, capillary refill time (CRT) > 3s, mean arterial pressure (MAP) < 65 mmHg or the use of ECLC. FCD, FCDNG, and ΔFCDNG were assessed using the MicroTools advanced computer vision algorithm. Results 54 patients (57 ± 14y, BMI 26.3 ± 4.9kg/m2, SAPS 56 ± 19, 65% male) were included, 13 of which with circulatory shock (6 cardiogenic, 4 septic, 3 other). As compared to the controls, patients with circulatory shock presented with similar CI and MAP, but higher heart rate (p < 0.001), central venous pressure (p = 0.02), lactate (p < 0.001), CRT (p < 0.01), and Mottling score (p < 0.001). FCD and FCDNG were 15% and 10% lower in patients with circulatory shock (18.9 ± 3.2 to 16.9 ± 4.2, p < 0.01; 21.3 ± 2.9 to 19.3 ± 3.1; p = 0.03), while ΔFCDNG and ΔRBCvNG remained similar. Conclusion In patients presenting with comparable macrocirculatory status but clinical signs of impaired microcirculation and tissue hypoxia, monitoring of the sublingual microcirculation revealed signs of capillary de-recruitment and loss of recruitability potential suggesting microcirculatory tamponade associated with fluid resuscitation. These results indicate a potential benefit of monitoring microcirculation in critically ill patients in shock.