Carbon dioxide output in septic shock
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KeywordsSeptic Shock Cardiac Index Pressure Variable Treatment Efficiency Minute Ventilation
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.
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.
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).
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.