title: Clinical classification of tissue perfusion based on the central venous oxygen saturation and the peripheral perfusion index.
abstract: BACKGROUND
  We investigated whether combining the peripheral perfusion index (PI) and central venous oxygen saturation(ScvO2) 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 ScvO2 (70%) and critical PI (0.6) at T8, we assigned the patients to four categories: group 1 (PI ≤ 0.6 on ScvO2 < 70%), group 2 (PI ≤ 0.6 on ScvO2 ≥ 70%), group 3 (PI > 0.6 on ScvO2 < 70%), and group 4 (PI > 0.6 on ScvO2 ≥ 70%). The combination of low ScvO2(<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 ScvO2(>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 ScvO2(>70%) after resuscitation. The PI was correlated with the lactate, P(v-a)CO2, and ScvO2 in all the measurements (n = 404). These relationships are strengthened with abnormal PI (PI < 1.4) but not with normal PI (PI ≥ 1.4).
  
  
  CONCLUSIONS
  Complementing ScvO2 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 ScvO2 is normalized.
authors.affiliation: Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, 1 shuaifuyuan, Dongcheng District, 100730, Beijing, China. tjmuhhw@126.com.
authors.forename: Huaiwu
authors.initials: H
authors.lastname: He
authors.affiliation: Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, 1 shuaifuyuan, Dongcheng District, 100730, Beijing, China. iculong_yun@163.com.
authors.forename: Yun
authors.initials: Y
authors.lastname: Long
authors.affiliation: Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, 1 shuaifuyuan, Dongcheng District, 100730, Beijing, China. tjmuhhw@163.com.
authors.forename: Dawei
authors.initials: D
authors.lastname: Liu
authors.affiliation: Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, 1 shuaifuyuan, Dongcheng District, 100730, Beijing, China. icuwang_xiao_ting@163.com.
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, 1 shuaifuyuan, Dongcheng District, 100730, Beijing, China. xiangzhou_icu@163.com.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhou
mesh_terms: D001775:Blood Circulation / Q000502:physiology; D001784:Blood Gas Analysis; D016638:Critical Illness / Q000145:classification* / Q000401:mortality / Q000628:therapy; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012151:Resuscitation / Q000379:methods / Q000401:mortality; D016896:Treatment Outcome
chemical_list: D010100:Oxygen