Evaluating the Prognosis of Patients with Septic Shock associated with Ventilator induced Pneumonia Using Variance of Arterial and Venous CO2 versus Serum Lactate

Abstract

Background:

Ventilator-associated pneumonia (VAP) is a common complication in critically ill patients, often leading to septic shock. Early and accurate prognostication of septic shock patients with VAP is crucial for optimizing treatment strategies. This study aimed to compare the prognostic value of monitoring arterial and venous carbon dioxide (CO2) variance with serum lactate levels in patients with septic shock related to VAP.

Materials and Methods:

We conducted a prospective observational study in a tertiary care centre over a period from October 2022 to September 2023. We enrolled 150 patients diagnosed with septic shock secondary to VAP. Patients were divided into two groups based on the monitoring method: Group A, where arterial and venous CO2 variance was measured, and Group B, where serum lactate levels were measured. Demographic data, clinical characteristics, and outcomes were recorded. The primary outcome was 28-day mortality.

Results:

In Group A, arterial and venous CO2 variance was found to be significantly higher in non-survivors compared to survivors (mean variance 5.2 ± 1.3 mmHg vs. 2.8 ± 0.9 mmHg, p < 0.001). In Group B, serum lactate levels were also higher in non-survivors (mean lactate level 4.9 ± 1.2 mmol/L vs. 2.1 ± 0.7 mmol/L, p < 0.001). However, the area under the receiver operating characteristic curve (AUC-ROC) for predicting 28-day mortality was higher in Group A (0.87, 95% CI 0.80-0.94) compared to Group B (0.78, 95% CI 0.70-0.86). The sensitivity and specificity for a cutoff value of 3.5 mmHg for CO2 variance in Group A were 82% and 79%, respectively, while for a cut off value of 3.0 mmol/L in Group B, the sensitivity and specificity were 73% and 72%, respectively.

Conclusion:

Monitoring arterial and venous CO2 variance appears to be a more sensitive and specific prognostic marker for septic shock related to VAP compared to serum lactate levels. The higher AUC-ROC and improved sensitivity and specificity suggest that CO2 variance may help identify patients at higher risk of mortality earlier in their clinical course. Further research is needed to validate these findings and incorporate CO2 variance monitoring into routine clinical practice.