Central venous oxygen saturation and carbon dioxide gap as resuscitation targets in a hemorrhagic shock

Abstract

Background: Fluid resuscitation is still a major challenge. We aimed to describe changes in central venous oxygen saturation (ScvO2 ) and venous-to-arterial carbon dioxide gap (dCO2 ) during an experimental stroke volume (SV) index (SVI)-guided hemorrhage and fluid resuscitation model in pigs.

Methods: Twelve anesthetized, mechanically ventilated pigs were bled till baseline SVI (Tbsl ) dropped by 50% (T0 ), thereafter fluid resuscitation was performed with balanced crystalloid in four steps until initial SVI was reached (T4 ). Statistical analysis was performed with Statistical Program for Social Sciences version 18.0; data are expressed as mean ± standard deviation.

Results: After bleeding, ScvO2 dropped (Tbsl = 78 ± 7 vs. T0 = 61 ± 5% P < 0.05) and oxygen extraction ratio increased (Tbsl = 0.20 ± 0.07 vs. T0 = 0.36 ± 0.05, P < 0.05). By T4 the ScvO2 normalized, but on average it remained 5% lower than at Tbsl (T4 = 73 ± 9% P < 0.05) and oxygen extraction also remained higher as compared with Tbsl (T4 = 0.24 ± 0.09 P = 0.001). ScvO2 showed significant correlation with SVI (r = 0.564, P < 0.001). dCO2 increased during hypovolemia (Tbsl :5.3 ± 2.0 vs. T0 :9.6 ± 2.3 mmHg, P = 0.001), then returned to normal by T4 = 5.1 ± 2.6 mmHg, and it also showed significant correlation with SVI (R = -0.591, P < 0.001) and oxygen extraction (R = 0.735, P < 0.001).

Conclusions: In this SV-guided bleeding and fluid resuscitation model, both ScvO2 and dCO2 correlated well with changes in SV, but only the dCO2 returned to its baseline, normal value, while ScvO2 remained significantly lower than at baseline. These results suggest that dCO2 may be a good hemodynamic endpoint of resuscitation, while ScvO2 is not strictly a hemodynamic parameter, but rather an indicator of the balance between oxygen delivery and consumption.