The effect of red blood cell transfusion on peripheral tissue oxygen delivery and consumption in septic patients

The impact of blood transfusion on tissue oxygen delivery (DO₂) and tissue oxygen consumption (VO₂) is a subject of current clinical studies. The primary objective of this observational study is to evaluate and measure the parameters involved in determining DO₂ and VO₂, in early phase of septic patients. A secondary objective of this study is to assess the potential benefit of blood transfusion on tissue metabolism by serial measurements of lactic acid (Ac. Lac.).

A group of 29 patients were studied, each patient received between one to three units of fresh packed red blood cells (pRBC). Clinical and paraclinical criteria for sepsis as well as the plasma value of haemoglobin (Hb) below 10g/dL represented the inclusion criteria in this study. We evaluated Hb, haematocrit (HCT), arterial blood oxigen saturation (SAO₂), central venous oxygen saturation (SCVO₂), parameters which are involved in determination of DO₂ and VO₂, before and after the transfusion of one unit of pRBC. Values of Ac. Lac. were also assessed in order to determine the type of metabolism (aerobic or anaerobic). SCVO₂, SAO₂, Hb, HCT and Ac. Lac. were determined using Epoc blood analyser. The cardiac output (CO) and systemic vascular resistance (SVR) were monitored during blood transfusion, using Vigileo monitor (Edward's Life Science, PreSep catheter kit). SAO₂ was also monitored by pulse-oximetry.

Changes in Hb, HCT and SCVO₂ before and after pRBC transfusion (which further determine VO₂) were statistically significant (P<0.001). A statistically significant increase (P<0.001) was obtained in Ac. Lac. values, before and after pRBC transfusion. SAO₂ and CO directly involved in producing DO₂, were clinically monitored during blood transfusion and the results remained constant.

Results obtained in this clinical study show an increase in DO2 in critically ill septic patients and also an increase in oxygen tissue uptake which is similar to VO2, clearly pointing out the benefit of pRBC transfusion. The benefits of pRBC transfusion on tissue metabolism in critically ill septic patients remain elusive because of lactic acid values increase during and after transfusion. Based on our findings we recommend that Hb values used as a single trigger for pRBC transfusion should be further studied and that additional parameters such as SCVO₂ and lactic acid should be considered as possible triggers for transfusion. Values of Hb and HCT should never be neglected.