Central Venous-to-ArterialCO2Gap Is a Useful Parameter in Monitoring Hypovolemia-Caused Altered Oxygen Balance: Animal Study

Abstract

Monitoring hypovolemia is an everyday challenge in critical care, with no consensus on the best indicator or what is the clinically relevant level of hypovolemia. The aim of this experiment was to determine how central venous oxygen saturation (ScvO2) and central venous-to-arterial carbon dioxide difference (CO2 gap) reflect hypovolemia-caused changes in the balance of oxygen delivery and consumption. Anesthetized, ventilated Vietnamese minipigs (n = 10) were given a bolus followed by a continuous infusion of furosemide. At baseline and then in five stages hemodynamic, microcirculatory measurements and blood gas analysis were performed. Oxygen extraction increased significantly, which was accompanied by a significant drop in ScvO2 and a significant increase in CO2 gap. There was a significant negative correlation between oxygen extraction and ScvO2 and significant positive correlation between oxygen extraction and CO2 gap. Taking ScvO2 < 73% and CO2 gap >6 mmHg values together to predict an oxygen extraction >30%, the positive predictive value is 100%; negative predicted value is 72%. Microcirculatory parameters, capillary perfusion rate and red blood cell velocity, decreased significantly over time. Similar changes were not observed in the sham group. Our data suggest that ScvO2 < 73% and CO2 gap >6 mmHg can be complementary tools in detecting hypovolemia-caused imbalance of oxygen extraction.

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

“…In a recent study, aiming to achieve oxygen extraction < 27% as target endpoint, which means keeping ScvO 2 > 73%, reduced the number of organ failures and hospital stay after surgery . In our previous experiments, ScvO 2 showed good correlation with oxygen extraction . However, it is an important finding of the current study that ScvO 2 remained significantly lower at the end of resuscitation as compared with baseline despite that SV has reached its baseline value.…”

“…This also means that reaching the physiological value of the dCO 2 does not mean adequate tissue oxygenation. In a recent animal experiment, we found that adding dCO 2 to ScvO 2 for predicting hypovolemia‐caused increase of VO 2 /DO 2 > 30% improved positive predictive value from 85% to 100% …”

Measured and calculated variables of global oxygenation in healthy neonatal foals

“…5 • 48 In dogs with experimentally induced hypovolemia, low or decreasing Scvo 2 and high or increasing Pcvco 2 -Paco 2 were detected after administration of furosemide, which reflected changes in global oxygen balance and altered microcirculatory blood flow in hypovolemia. 24 As expected in the present study, Sao 2 was significantly higher at all times than was Scvo 2 ; mean Sao 2 over all times was 95 ± 1.7% , which is similar to measurements in healthy neonatal foals reported elsewhere. 49…”

Goal-Directed Resuscitation Aiming Cardiac Index Masks Residual Hypovolemia: An Animal Experiment

“…Indeed, in patients under general anesthesia the S cv O 2 is often higher than 80%, which is due to the reduced oxygen demand and consumption; hence, higher values should be considered as “normal” [ 30 , 31 ]. Furthermore, in our previous experiments, S cv O 2 showed good correlation with oxygen extraction [ 32 , 33 ]. Therefore, as interpretation of absolute values may prove difficult in different conditions evaluation of the changes of S cv O 2 may be more helpful.…”