Objective To investigate the significance of monitoring P(c-a)CO2 (the gradients between transcutaneous PCO2 and arterial PCO2) in patients with septic shock.Method 31 patients with early septic shock were enrolled as the study group and 20 patients with stable hemodynamics as the control group from Fab.2013 to Sept.2014 in our Intensive Care Unit (ICU).The patients with septic shock were treated guided by early goal directed therapy (EGDT) within 6 hours since hospitalization.The differences of baseline P(c-a) CO2 levels and other index as arterial lactate (LAC) concentration between two groups and the variations of these indexes after EGDT in the study group were compared respectively.Results The baseline levels of P(c-a)CO2 and LAC in patients with septic shock were significantly higher than in patients of control group: (21.2 ± 10.1) mmHg vs.(7.5 ±4.6), P =0.000, and (4.0±2.4) mmol/ Lvs.(1.6 ± 0.5), P =0.000.The areas under receiver operator characteristic (ROC) curve (AUC) for baselineP(c-a)CO2 and LAC were 0.918 (95％ CI: 0.843-0.992) and 0.840 (95％ CI: 0.719-0.962) respectively.A threshold of 14.0 mmHg for P(c-a)CO2 and 2.1 mmol/L for LAC discriminated patients with septic shock from without shock with the same sensibility of 83.9％ and the same specificity of 90.0％, respectively.With regard to prognosis (Day 28), AUC for baseline P(c-a)CO2 and LAC were 0.739 (95％ CI: 0.562-0.917) and0.702 (95％ CI: 0.514-0.889) respectively.A threshold of 21.5 mmHg for P(c-a) CO2 and 3.9 mmol/L for LAC discriminated survivors from nonsurvivors with the same sensibility of 71.4％ and the same specificity of 70.6％ respectively.31 patients in the study group completed EGDT within 6 hours after the admission, 16 (51.6％) passed EGDT and 13 (81.3％) survived, 15 (48.4％) failed EGDT and 4 (26.7％) survived, and survival rates were significantly different, F =9.314, P =0.004.After EGDT, P(c-a) CO2 (18.8 ± 9.4) mmHg and LAC (3.3 ± 2.4) mmol/Lreduced significantly compared with the baselines, all P =0.000.AUC then for P(c-a) CO2 and LAC were 0.742 (95％ CI: 0.562-0.921) and 0.769 (95％ CI: 0.593-0.945), respectively.A threshold of 18.3 mmHg for P(c-a)CO2 and 3.1 mmol/L for LAC discriminated survivors from nonsurvivors with the same sensibility of 71.4％ and the specificity of 71.4％ and of 76.5％ respectively.P(c-a) CO2 and LAC of patients passed EGDT reduced significantly compared with those failed EGDT: (14.8 ± 7.5) mmHgvs.(23.6±9.6) mmHg (P=0.012)、 (2.5±1.5) mmol/L vs.(4.3±2.9) mmol/L (P=0.038), and so did with their baseline : (14.8±7.5) mmHgvs.(18.0±8.1) mmHg, (P=0.042)、 (2.5±1.5) mmol/Lvs.(3.2±1.8) mmol/L, P=0.043.In patients failed EGDT, P(c-a)CO2 and LAC changed little after EGDT, from (24.6 ± 9.2) to (23.6 ± 9.6) mmHg (P =0.238) and from (4.8 ± 2.5) mmol/L to (4.3 ± 2.9) mmol/L (P =0.629).When baseline levels were compared between patients passed EGDT with those failed EGDT, P(c-a) CO2 was (18.0 ±8.1) mmHg vs.(24.6 ± 9.2) mmHg (P =0.042), LAC was (3.2 ± 1.8) mmol/L vs.(4.8 ± 2.5) mmol/L (P =0.050).Conclusions P(c-a) CO2 ＞ 14.0 mmHg could play a role in recognizing early septic shock.EGDT was an effective therapy for the disease and P(c-a)CO2 level could reflect the efficacy of EGDT.P(c-a)CO2 ＞ 21.5mmHg before EGDT and P(c-a) CO2 ＞ 19.3 mmHg after EGDT both could predict the prognosis of patients with septic shock.All above correlated well with LAC and represented a new efficient technique to assess tissue microperfusion.