Oxygen extraction index measured by near infrared spectroscopy--a parameter for monitoring tissue oxygenation?

The objective was to assess the ability of near infrared spectrophotometry (NIRS) to detect changes in tissue oxygenation due to alterations in oxygen delivery. Ten hemodynamically stable preterm neonates with a median gestational age of 27.9 weeks (range 25.1-31.2), a median birth weight of 840g (range 690-1310), and a postnatal age of 29 days (range 2-45) were included in this prospective trial. Tissue oxygenation of the lower leg was measured by NIRS and the oxygen extraction index (OEI) was calculated prior and after a transfusion of 10-20 ml/kg body weight packed red blood cells. The OEI decreased from 0.31 (range 0.13-0.39) to 0.24 (range 0.12-0.36, p<0.005). This decrease correlated positively with the weight matched amount of packed red cell transfusion (r2=0.40, p<0.05) and with the increase in hematocrit (r2=0.58, p<0.005). The OEI obtained by a NIRS may allow to monitor changes in tissue oxygenation.