Early detection of cardiovascular instability by monitoring oxygen uptake and carbon dioxide production

The oxygen uptake and carbon dioxide production were measured in 21 patients in sepsis during conventional hemodynamic resuscitation. We assumed that in the state of low oxygen delivery, carbon dioxide is increasingly eliminated from the body. We hypothesized that this condition can be recognized from the VCO₂/VO₂ relationship.

VO₂ and VCO₂ were measured by analysis of expired gas by metabolic monitor; hemodynamics was monitored by pulmonary artery catheter. Cardiac output was determined by thermodilution, oxygen transport variables were gauged according to standard formulas using samples from peripheral arterial and mixed venous blood from pulmonary artery.

The patients were monitored for 6 hours. Lower values of VO₂ were followed with higher values of VCO₂. There was a high coefficient of negative correlation between cardiac index and respiratory quotient (r = -0.85; P = 0.002). The similar correlation, as expected, was found between oxygen delivery and respiratory quotient (r = -0.75; P = 0.01). The positive correlation was detected between respiratory quotient and venous–arterial CO₂ difference (v–aDCO₂) (r = 0.79; P = 0.016).

Our preliminary conclusion was that cardiovascular instability in patients with sepsis can be recognized from variations in VO₂ and respiratory quotient.