[A thermodynamic model to predict oxygen consumption and peripheral blood flow of the newborn infant (author's transl)].

The continuous evaluation of the oxygen consumption and peripheral blood flow is technically difficult and practically not feasible in the newborn infant. We attempted to assess these two variables by means of a thermodynamic model, where only a set of geometrical variables and a set of temperatures have to be measured. The body is represented by a central cylinder (head, trunk) and a peripheral cylinder (extremities) and the heat flux therein is described by mathematical formulas. Only steady state conditions are considered. From the heat flux "surface leads to environment" the oxygen consumption and from the heat flux "central cylinder leads to peripheral cylinder" the peripheral blood flow is derived. On the patient only one core temperature (rectum) and two skin temperatures--one on the chest and the other one on the calf--have to be measured. The validity of the model was tested in 17 healthy newborns (body weight 1,100-3,850 g) and 6 diseased newborns (body weight 1,500-3,400 g). Comparing the computed oxygen consumption to values from the literature for a similar group showed good agreement. In 7 newborns the calculated oxygen consumption correlated well (r = 0.88, p less than 0.01) with the directly and synchroneously measured oxygen consumption. Indirect proof that the model also gives a reasonable index for the peripheral blood flow was obtained by relating the computed peripheral blood flow a) to values from the literature for a similar group and b) by demonstrating the dependence of the (calculated) peripheral blood flow on the haematocrit (r = -0.58, p less than 0.01).