Significance of monitoring the gradients between transcutaneous PCO(2) and end-tidal PCO(2) in patients with septic shock

Abstract

Objective: To investigate the significance of monitoring the gradients between transcutaneous PCO(2) and end-tidal PCO(2) [P(c-et)CO(2)] in patients with septic shock. Method: Thirty-five mechanically ventilated patients with early septic shock were enrolled as the study group and 18 non-septic shock patients with stable hemodynamics as the control group between May 2014 and October 2016. The patients with septic shock were treated by early goal-directed therapy (EGDT) within 6 hours since hospitalization. The differences of baseline level of P(c-et)CO(2) and arterial lactate concentration (LAC) between the two groups and the variations of these indexes after EGDT in the study group were compared respectively. Results: The baseline levels of P(c-et)CO(2) and LAC in patients with septic shock were significantly higher than those of the control group [(26.0±16.2) mmHg vs (11.0±5.6) mmHg (1 mmHg=0.133 kPa) and (4.0±1.7) mmol/L vs (1.6±0.6)mmol/L, all P=0.000]. The area under receiver operator characteristic (ROC) curve (AUC) for baseline P(c-et)CO(2) and LAC was 0.924 (95%CI: 0.851-0.996) and 0.931 (95%CI: 0.872-1.000), respectively. P(c-et)CO(2) >12.6 mmHg and LAC >2.5 mmol/L could discriminate septic shock patients from those without shock with the same sensibility of 97% and the specificity of 83% and 78% respectively. With regard to the prognosis (Day 28) of the patients with septic shock, AUC for baseline P(c-et)CO(2) and LAC was 0.709 (95%CI: 0.533-0.886) and 0.714 (95%CI: 0.545-0.883), respectively. P(c-et)CO(2) >20.0 mmHg and LAC>3.6 mmol/L could discriminate survivors from non-survivors with the same sensibility of 92% and the same specificity of 76%. All the patients in the study group completed EGDT within 6 hours after admission, 20 (57.1%) passed EGDT and 17 (85.0%) survived, 15 (42.9%) failed EGDT and 4 (26.7%) survived, and the survival rates were significantly different (F=9.844, P=0.001). After EGDT, P(c-et)CO(2) (21.0±9.5 mmHg) and LAC(3.3±2.5 mmol/L)reduced significantly compared with the baselines (P=0.008 and P=0.046), and the associated AUC was 0.905(95%CI: 0.792-1.000) and 0.747 (95%CI: 0.576-0.917)respectively. P(c-et)CO(2) > 16.5 mmHg and LAC > 3.1 mmol/L could discriminate survivors from non-survivors with the sensibility of 97% and 91%, and the specificity of 78% and 69%, respectively. Conclusions: P(c-et)CO(2) >12.6 mmHg could play the same role as LAC in recognizing early septic shock. EGDT was an effective therapy for the septic shock and P(c-et)CO(2) reflected efficacy. P(c-et)CO(2)>20 mmHg before EGDT and >16.5 mmHg after EGDT both could predict the 28 d prognosis of patients with septic shock, and the effect of the former was equal to that of LAC, but the latter was better than LAC.