CO2 gap changes compared with cardiac output changes in response to intravenous volume expansion and/or vasopressor therapy in septic shock.

Abstract

The difference in partial pressure of carbon dioxide (PCO2) between mixed or central venous blood and arterial blood, known as the ∆PCO2 or CO2 gap, has demonstrated a strong relationship with cardiac index during septic shock resuscitation. Early monitoring of the ∆PCO2 can help assess the cardiac output (CO) adequacy for tissue perfusion. To investigate the value of ∆PCO2 changes in early septic shock management compared with CO. 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 ∆PCO2 and 28-day mortality. The primary outcome was the relationship between the ∆PCO2 and CO changes before and after initial resuscitation, with secondary outcomes including ICU length of stay (LOS) and 28-day mortality. Peri-resuscitation ∆PCO2 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 ∆PCO2 change cut-off value was <-1.85, corresponding to a <-22% threshold for a 15% cardiac index increase. The PCO2 gap ratio (gap/gap ratio of T1- PCO2 gap to T0 -PCO2 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 CO2 gap/gap ratio cut-off value was <0.71. A significant difference in 28-day mortality was noted based on the gap/gap ratio. Peri-resuscitation ∆PCO2 and the gap/gap ratio are useful non-invasive bedside markers for predicting changes in CO and preload responsiveness. The current study provides an insight to the PCO2 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.