ESTIMATION OF INTRAPULMONARY SHUNT IN RESUSCITATION - USE OF A NOMOGRAM

  • 1 January 1975
    • journal article
    • research article
    • Vol. 11  (5) , 659-681
Abstract
Acutely ill patients often show rapid and sometimes concomitant changes in hemodynamics, pulmonary exchange and O2-uptake. PaO2 [arterial O2 tension] reflects the interrelationships between these 3 factors. The .ovrhdot.Qs/.ovrhdot.Qt time shunt is computed by taking 2 simultaneous blood samples, one systemic arterial, the other mixed venous, with the patient inhaling pure O2 for 20 min. In estimating the fraction of total cardiac output unsaturated in pulmonary transit, .ovrhdot.Qs/.ovrhdot.Qt is practically used as a selective test for pulmonary gas exchange. A nomogram is proposed showing in terms as .ovrhdot.Qs/.ovrhdot.Qt shunt the variations of PaO2, of HbO2 saturation and of arterialvenous difference of O2 concentrations. Blood gas changes during treatment of shock or of acute respiratory insufficiency are explained by use of this nomogram. In 14 patients with hypovolemic or septic shock, the rapid infusion of 500 ml of fluid gelatin (Plasmagel) increased .ovrhdot.Qs/.ovrhdot.Qt (from 27 to 33%) with mild variation of PaO2 (from 195 to 217 torr). A Dextran 40,000 infusion (n = 10) increased PaO2 from 191 to 291 torr, while .ovrhdot.Qs/.ovrhdot.Qt shunt remained constant (25%). The i.v. of dopamine (n = 9) markedly increased the shunt (from 27 to 42%, while PaO2 slightly decreased (from 137 to 113 torr). By adding a continuous positive expiratory pressure of 10 cm H2O (n = 17), PaO2 increased from 63 to 114 torr and shunt decreased from 44 to 29%. The use of the nomogram in these 4 series graphically showed the fundamental role of variations in arterial-venous difference of O2 concentrations on changes of PaO2. The limits of the method and the significance of .ovrhdot.Qs/.ovrhdot.Qt shunt are discussed.