Hypoxemia and pulmonary gas exchange during hemodialysis

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Abstract
With measured values of arterial blood gas tensions, of expired respiratory gas fractions and volume of the expired ventilation, the determinants of alveolar O2 tension (PAO2) were used to evaluate their influence on the development of the arterial hypoxemia that occurs in spontaneously breathing patients undergoing hemodialysis using an acetate dialysate. Dialysis produced no significant changes in the alveolar-arterial O2 tension gradient (AaDo2). The extracorporeal dialyzer removed an average of 30 ml.cntdot.m-2.cntdot.min-1 of CO2. The pulmonary gas exchange ratio (R) dropped from a mean predialysis value of 0.81 to 0.62 (P < 0.001). The arterial CO2 tension remained constant throughout; the minute ventilation, both total (P < 0.01) and alveolar (P < 0.01), decreased during dialysis. This decrease in ventilation accounts for more than 80% of the fall in PAO2. During dialysis there was a decrease (P < 0.001) in arterial O2 tension (PaO2), which varied among the individuals from 9 to 23% of control. During the postdialysis hour PaO2 returns to control values concomitant with increase in ventilation. The quantitative gas exchange relationships among R, alveolar ventilation and AaDo2 predict the PaO2 values actually measured.

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