Abstract： Objective To detect the changes of central venous-to-arterial carbon dioxide difference (P(cv-a)CO2) during early goal-directed therapy (EGDT) in patients with septic shock and evaluate its' value in predicting adequate resuscitation and prognosis. Methods From April 2009 to October 2010,26 septic shock patients were enrolled in the study.EGDT was performed in all the patients immediately after enrollment.According to the whether they achieved early goal with in the 6 hour or not,patients were separated to EGDT achievement and un-achievement groups.At the onset and after the 6 hours EGDT,mean arterial pressure (MAP),cardiac index (CI),central venous oxygen saturation (ScvO2 ),oxygen delivery ( DO2 ),oxygen comsumption ( VO2 ),oxygen extraction ratio ( O2 ext ),lactate,P ( cv-a ) CO2 were recorded.The Acute Physiology and Chronic Health Evaluation Ⅱ (APACHE Ⅱ ) score and 28 day mortality were compared between 2 groups. Results There were no significant difference of age and sex between the 15 patients who achieved early goals and 11 patients who did not. EGDT un-achievement patients had higher APACHE Ⅱ score (21±5) and 28 day mortality (9/11) when compared with EGDT achievement patients (t =2.985,x2 =4.547,P ＜ 0.05 ). In EGDT un-achievement group,MAP,CI,DO2,VO2,O2ext,ScvO2,Lac,P(cv-a) CO2 were comparable between the onset and 6 hours after EGDT.However,in EGDT achievement group,MAP ((90 ± 9) mmHg( 1 mmHg =0.133 kPa)),CI ((4.0 ±1.8) L · min 1 · m-2),DO2( (596± 274) ml · min-1 · m 2),ScvO2(76.9％ ±4.1％ ) increased,and P(ev-a) CO2 ( (4.2 ± 2.7 ) mmHg) decreased significantly after 6 hours of EGDT ( t values were - 3.393,-2.985, - 2.103 and - 3.195 respectively,all P ＜ 0.05 ).The changes of P(cv-a) CO 2 between the onset and 6 hours after EGDT,demonstrated high value for predictability of outeome,according to the area under the ROC curve (AUC) was O.839 ( P =0.004).As a predictor for death,increasing of P(cv-a) CO2 after 6 hours of EGDT has a sensibility of 100％ and specificity of 60％. Conclusions Increasing of P(ev-a)CO2 after EGDT purports inadequate tissue perfusion in patients with septic shock. Changes of P(cv-a) CO 2 during EGDT demonstrated a useful tool to evaluate adequate resuscitation and prognosis.