Effects of fluid challenge on gastric mucosal PCO2 in septic patients

Objective: To determine the effects of fluid challenge on systemic hemodynamic variables and gastric intramucosal partial pressure of carbon dioxide (PCO2) in septic patients. Design: Short-term interventional study. Setting: Medical-surgical intensive care unit in a university hospital. Patients: Twenty-four adult patients with severe sepsis or septic shock requiring volume replacement. All patients were studied within 24 h of onset of severe sepsis or septic shock. Interventions: Five hundred milliliters of a 6% hydroxyethyl starch (HES) solution were administered in 30 min. Measurements and results: Complete hemodynamic data, blood samples, and gastric mucosal PCO2 (automatic gas capnometry) determinations were obtained at baseline and 15 min after the end of fluid infusion. After fluid challenge, cardiac index (CI) increased from 3.8 (range 2.9-4.2) to 4.2 (range 3.1-4.9) l/min m(-2) (p<0.05). The PCO2 gap decreased from 9.8 (range 6.9-26.0) to 8.5 (range 6.6-17.4) min Hg (p<0.05), but important individual variations were observed. We failed to observe significant relationships between changes in Cl and in PCO2 gap, or between indices of preload (pulmonary artery occluded pressure, right atrial pressure, and pulse pressure variations) and changes in PCO2 gap. In addition, changes in PCO2 gap and in (v-a) CO2 were not related; however, changes in PCO2 gap were related to baseline PCO2 gap (p=0.003), PEEP (p=0.02), and cumulative doses of vasopressors (p=0.02). Conclusions: The effects of fluid challenge on gastric mucosal PCO2 are variable and related to baseline PCO2 gap rather than to systemic variables. In general, rapid volume infusion decreases PCO2 gap, but this effect is more pronounced in patients with presumably impaired mucosal perfusion.