Abstract
BACKGROUND: The difference in partial pressure of carbon dioxide (PCO(2)) between mixed or central venous blood and arterial blood, known as the ∆PCO(2) or CO(2) gap, has demonstrated a strong relationship with cardiac index during septic shock resuscitation. Early monitoring of the ∆PCO(2) can help assess the cardiac output (CO) adequacy for tissue perfusion. OBJECTIVES: To investigate the value of ∆PCO(2) changes in early septic shock management compared with CO. METHODS: This observational prospective study included 76 patients diagnosed with septic shock admitted to Cairo University Hospital's Critical Care Department between December 2020 and March 2022. Patients were categorised by initial resuscitation response, initial ∆PCO(2) and 28-day mortality. The primary outcome was the relationship between the ∆PCO(2) and CO changes before and after initial resuscitation, with secondary outcomes including ICU length of stay (LOS) and 28-day mortality. RESULTS: Peri-resuscitation ∆PCO(2) changes predicted a ≥15% change in the cardiac index (CI) (area under the curve (AUC) 0.727; 95% CI 0.614 - 0.840) with 66.7% sensitivity and 62.8% specificity. The optimal ∆PCO(2) change cut-off value was <-1.85, corresponding to a <-22% threshold for a 15% cardiac index increase. The PCO(2) gap ratio (gap/gap ratio of T(1)- PCO(2) gap to T(0) -PCO(2) gap) also predicted a ≥15% change in cardiac index (AUC 745; 95% CI 0.634 - 0.855) with 63.6% sensitivity and 79.1% specificity. The optimal CO(2) gap/gap ratio cut-off value was <0.71. A significant difference in 28-day mortality was noted based on the gap/gap ratio. CONCLUSION: Peri-resuscitation ∆PCO(2) and the gap/gap ratio are useful non-invasive bedside markers for predicting changes in CO and preload responsiveness. CONTRIBUTION OF THE STUDY: The current study provides an insight to the PCO(2) gap changes during and after early resuscitation of septic shock patients, which correlate to cardiac output changes and might also serve as a fluid responsiveness indicator.