Carbon dioxide output in septic shock

Introduction

Tissue hypoperfusion with concomitant hypoxia is a leading sign of septic shock. Despite increased DO₂ after volume administration, VO₂ remains low. Our hypothesis was that in this setting, lower CO₂ output would also occur. We calculated anaerobic output of CO₂ and found its small proportion to complete CO₂ output.

Methods

We measured the output of CO₂ as well as the venous–arterial difference in CO₂ concentration (v–aDCO₂) in 25 patients in septic shock. All patients were mechanically ventilated, and the circulatory volume and pressure variables were monitored and changed according to pulmonary catheter findings.

CO₂ output was measured by use of our own technical innovation; a 5 l balloon was placed on the expiratory outlet and the CO₂ concentration was measured by standard capnograph. Minute ventilation was measured by a volume monitor over an ascending and a descending line.

Results

In 10 survivors VCO₂ was higher than in nonsurvivors at the baseline (189 ± 10 vs 173 ± 14, P = 0.0005). The cardiac index was also higher (3.1 ± 0.27 vs 2.7 ± 0.6, P = 0.03). There was no significant difference in v–aDCO₂ (7.3 ± 1.6 vs 7.3 ± 1.4, P = 0.95).

During resuscitation VCO₂ increased markedly in survivors (P = 0.0004), whereas in nonsurvivors only an increasing trend was noted, but it did not reach statistical significance (P = 0.12).

Conclusion

We conclude that this simple and noninvasive test of measurement of VCO₂ in patients in septic shock may be useful in early detection of metabolic disarrangements caused by hypoxia, as well as outcome of disease. It may also be used as a measure of treatment efficiency.