Regional hypoxia and partial pressure of carbon dioxide gradients: what is the link?

Excerpt

Gut hypoperfusion is often suspected in critically ill patients but identifying it can be difficult. The usual diagnostic tools, such as echography or CT scan, are not sensitive enough and can only detect extreme situations. Global hemodynamic measurements are commonly performed in critically ill patients and provide essential information. Nevertheless, gut hypoperfusion is still often unrecognized, either because of the development of regional blood flow alterations, even when cardiac output is maintained, or because gut blood flow may paradoxically be preserved when cardiac output is decreased. The measurement of hepatic venous oxygen saturation may be useful to evaluate the adequacy of splanchnic blood flow [1]. In addition, an elevated gradient between mixed-venous and hepatic venous oxygen saturation is suggestive of hepato-splanchnic VO₂/DO₂ dependency [2]. Unfortunately, this measurement reflects total hepato-splanchnic blood flow, including not only portal, but also hepatic, arterial blood flow. Hence, gut hypoperfusion can still occur even when hepatic venous oxygen saturation is maintained [3]. Ideally portal blood should be sampled, but this is not feasible in clinical practice. Hepatic vein lactate measurements [4] can also be used to detect splanchnic hypoxia, but similar limitations apply to these measurements. In addition, lactate measurements can be influenced by other factors than tissue hypoxia [5]. …