Renal Function in Respiratory Failure 265 



Hypercapnia. The effects of acute hypercapnia, usually 

 induced by inhalation of 5-10 per cent CO 2, have been 

 reviewed by Pitts (1953). There is a fall in plasma pH and a 

 rise in PCO2; the urine formed is acid, and the reabsorption 

 of filtered bicarbonate is virtually complete, although the 

 amount of filtered bicarbonate has been increased by the 

 experimental procedure. Enhancement of bicarbonate re- 

 absorption is the most striking change in renal performance 

 induced by acute hypercapnia ; and it persists when the fall in 

 plasma pH is prevented by infusion of bicarbonate, so that in 

 this context rise in pCOa seems to be the more relevant 

 stimulus to bicarbonate reabsorption. The reabsorption of 

 bicarbonate is also increased in subjects depleted of potassium, 

 in whom intracellular pH is probably decreased; so it seems 

 quite likely that the effect of raised pCOg on bicarbonate 

 reabsorption is mediated by a fall in the pH of the renal 

 tubule cells. Apart from this rather striking change in 

 bicarbonate excretion the output of electrolytes is not 

 significantly affected by short periods of hypercapnia, 

 although there is a transient water diuresis (Barbour et al., 

 1953). 



It is not clear how far the information obtained from 

 studies of acute hypercapnia can be applied to the situation 

 of chronic hypercapnia found in emphysematous patients. 

 Here, a steady state has been established at a new level of 

 plasma pH and bicarbonate concentration. The electrolyte 

 composition of plasma and red cells in emphysematous 

 patients is different in several respects from that of normal 

 people in whom a comparable hypercapnia has been induced 

 acutely by CO2 inhalation (Plattsand Greaves, 1957). For 

 example, the fall in pH is much smaller in the emphysematous 

 patients, and the chloride content of both cells and plasma is 

 lower than in acute respiratory acidosis. 



There are few observations on the renal response to chronic 

 respiratory acidosis in man. As part of a study on the effect 

 ofDiamox,Nadell (1953) reports observations on 24-hour speci- 

 mens of urine from two patients with respiratory acidosis. 



