Clinical classification of tissue perfusion based on the central venous oxygen saturation and the peripheral perfusion index

Introduction: We investigated whether combining the peripheral perfusion index (PI) and central venous oxygen saturation(ScvO(2)) would identify subsets of patients for assessing the tissue perfusion and predicting outcome during the resuscitation in critically ill patients. Methods: A total of 202 patients with central venous catheters for resuscitation were enrolled in this prospective observational study. The arterial, central venous blood gas and the PI were measured simultaneously at the enrollment (T0) and 8 h (T8) after early resuscitation. Based on the distribution of the PI in healthy population, a cutoff of PI >= 1.4 was defined as a normal PI. Moreover, the critical value of PI was defined as the best cutoff value related to the mortality in the study population. The PI impairment stratification is defined as follows: a normal PI(>= 1.4), mild PI impairment (critical value < PI < 1.4) and critical PI impairment (PI <= critical value). Results: The PI at T8 was with the greatest AUC for prediction the 30-day mortality and PI is an independent risk factor for 30-day mortality. Moreover, a cutoff of PI < 0.6 is related to poor outcomes following resuscitation. So, based on cutoffs of ScvO(2) (70 %) and critical PI (0.6) at T8, we assigned the patients to four categories: group 1 (PI <= 0.6 on ScvO(2) < 70 %), group 2 (PI <= 0.6 on ScvO(2) >= 70 %), group 3 (PI > 0.6 on ScvO(2) < 70 %), and group 4 (PI > 0.6 on ScvO(2) >= 70 %). The combination of low ScvO(2)(< 70 %) and PI(<= 0.6) was associated with the lowest survival rates at 30 days [log rank (Mantel-Cox) = 87.518, p < 0.0001]. The sub-group patients who had high ScvO(2)(> 80 %) at T8 were with low mortality and high PI. Moreover, the normal PI (>= 1.4) did not show a better outcome than mild impaired PI (0.6-1.4) patients who had a normalized ScvO(2)(> 70 %) after resuscitation. The PI was correlated with the lactate, P(v-a)CO2, and ScvO(2) in all the measurements (n = 404). These relationships are strengthened with abnormal PI (PI < 1.4) but not with normal PI (PI >= 1.4). Conclusion: Complementing ScvO(2) assessment with PI can better identify endpoints of resuscitation and adverse outcomes. Pursuing a normalized PI (>= 1.4) may not result in better outcomes for a mild impaired PI after ScvO(2) is normalized.