(417) Sublingual Microcirculation Correlated With Ventilatory Ratio in Mechanically Ventilated Patients

Introduction: Sublingual microcirculatory impairment was observed in 20.6% of a heterogenous population of critically ill patients. Microcirculatory impairment involves microvascular beds of different organs including the lung. Impaired microvascular beds could theoretically result in mismatched lung perfusion and ventilation. Increased sublingual microcirculatory blood flow was reported to correlate with decreased dead space in ARDS patients. The high incidence of sublingual microcirculatory impairment in the heterogenous population of critically ill patients raised the question of whether respiratory dead space increased along with the altered sublingual microcirculation in this population. Respiratory dead space could be assessed using a bedside index, ventilatory ratio (VR). The aims of our study are to evaluate whether there were direct association between sublingual microcirculation and respiratory dead space assessed by VR, and to further explore their association with outcome in ventilated patients. We hypothesized that sublingual microcirculation was associated with VR and also with prognosis in this population.

Methods: Sublingual microcirculation was assessed in mechanically ventilated patients within 24 hours of ICU admission. The respiratory mechanics, blood gas analyses, hemodynamic variables and sublingual microcirculation were recorded at the same time. VR was defined as [minute ventilation (ml/min) × PaCO2 (mm Hg)] / (predicted body weight × 100 × 37.5).

Results: 80 consecutive patients were analyzed. The survivors had higher sublingual red blood cell velocity (RBCv), lower VR and peak airway pressure. RBCv weakly correlated with mean airway pressure (Pmean) (r = - 0.231, p = 0.039). Proportion of perfused vessels correlated with VR (r = - 0.366, p = 0.001), Pmean (r = - 0.272, p = 0.014) and positive end-expiratory pressure (r = - 0.249, p = 0.026). Increased RBCv was independently associated with decreased odds of ICU mortality (OR 0.99, p = 0.026). Patients with both low RBCv ( < 435um/s) and high VR (≥ 1.19) had the highest ICU mortality (42.9%).

Conclusions: Poor sublingual microcirculation is associated with VR and Pmean. A combination of low sublingual RBCv and high VR indicates highest ICU mortality in mechanically ventilated critically ill patients.