Gastric mucosal systemic partial pressure of carbon dioxide (PCO2) gradient in experimental endotoxin shock in swinecomparison of two methods

Abstract

Objectives: Clinically applicable methods for continuous monitoring of visceral perfusion/metabolism do not exist. Gastric mucosal end-tidal partial pressure of carbon dioxide (PCO2) gradient has been used, but it has limitations, especially in patients with lung injury and increased dead space ventilation. We studied the agreement between gastric mucosal end-tidal (DPCO2gas) and gastric mucosal arterial PCO2 (D(t-a)PCO2) gradients, and especially the effect of dead space ventilation (Vd/Vt ratio) on the agreement. We hypothesized that DPCO2gas can be used as a semicontinuous indicator of mucosal arterial PCO2 gradient in sepsis. Design: A randomized, controlled animal experiment. Setting: National laboratory animal center. Interventions: Twelvehour infusion of endotoxin in landrace pigs. Measurements and results: We measured end-tidal PCO2 continuously, gastric mucosal PCO2 every 10 min (gas tonometry) and arterial PCO2 every 120 min. Carbon dioxide production and the Vd/Vt ratio were determined by indirect calorimetry. In the endotoxin group (n = 7) cardiac index increased and systemic vascular resistance decreased. Endotoxemia increased dead space ventilation by 27% (p = 0.001). Both DPCO2gas and D(t-a)PCO2 increased significantly in the endotoxin group (p < 0.0001 and p = 0.049, respectively). Control animals remained stable throughout the experiment. When we compared DPCO2gas and D(t-a)PCO2 (Bland-Altman analysis), the bias and precision were 0.9 and 0.9 kPa in the control group and 2.0 and 2.2 kPa in the endotoxin group, respectively. The disagreement between DPCO2gas and D(t-a)PCO2 increased as the Vd/Vt ratio increased. Conclusions: DPCO2gas is a clinically applicable method for continuous monitoring of visceral perfusion/metabolism. Septic lung injury and increased dead space ventilation decrease the accuracy of the method, but this may not be clinically important.