The Noninvasive Carbon Dioxide Gradient (NICO2G) during Hemorrhagic Shock
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
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Hemorrhagic shock HS is a setting in which both pulmonary and cutaneous perfusion may be impaired. The goals of this study were 1 to evaluate the relationship between end-tidal etCO2, transcutaneous tPCO2, arterial carbon dioxide PaCO2, and lactate during lethal HS and 2 to assess the effect of progressive HS on those variables and on a new variable, the non-invasive CO2 gradient NICO2G, or difference between tPCO2 and etCO2. Ten consciously sedated swine were hemorrhaged, by means of an computerized exponential protocol, of up to 80 estimated blood volume EBV over 20 min. EtCO2, tPCO2, PaCO2, and lactate measurements were taken at baseline and every 5 min thereafter, i.e., after 25, 44, and 62 total blood volume hemorrhage TBVH, and at cardiac arrest CA. CA occurred on average at 67 TBVH. Data were analyzed by linear regression and one-way repeated measures analysis of variance ANOVA and are presented as means or - SD. Results 49 paired measurements were made. There was no overall relationship between non-invasive CO2 variables and PaCO2 PaCO2 vs. tPCO2 r2 0.002 p 0.78 PaCO2 vs. etCO2 r to the 2nd 0.0002 p 0.93. Rather, NICO2G increased at each level of blood loss 4.0 or - 24.9 at baseline, 6.3 or - 35.7 at 25 TBVH, 25.0 or - 37.6 at 44 TBVH, 55.0 or - 33.9 at 62 TBVH, and 70.0 or - 33.2 at CA p less than 0.05. Similarly, tPCO2 increased and etCO2 decreased at each level. Linear regression of NICO2G and lactate showed a better correlation than was observed for the other 2 variables NICO2G r2 0.58 tPCO2 r2 0.46 etCO2 r2 0.26. Conclusions During HS, non-invasive CO2 monitors lose accuracy for approximating the PaCO2, but gain usefulness as hemodynamic monitors. Also, by combining data from 2 different organ systems, NICO2G demonstrated improved correlation with lactate than did either etCO2 or tPCO2 alone.
- Anatomy and Physiology
- Medicine and Medical Research