Noninvasive Carbon Dioxide Gradient (NICO2G) during Hemorrhagic Shock.

摘要

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.