Lungs, kidneys and acid-base

The maintenance of normal blood pH depends crucially on synergy of action between lungs and kidneys, so that students of acid-base physiology must become familiar with the interrelatedness of kidney and lung function in both health and disease. 

This interrelatedness is the central theme of a recently published review that was first presented at the 51st International Respiratory Congress of the American Association for Respiratory Care in San Antonio, Texas in December of last year.  The paper begins with consideration of the physiological connection between lungs and kidneys for maintenance of blood pH by reference to the Henderson-Hasselbach equation. 

This defines pH in terms of measured pCO₂ (the respiratory component) and bicarbonate, HCO₃^- (the renal component). The concept of respiratory compensation for bicarbonate abnormality and renal compensation for pCO₂ abnormality is addressed. 

There follows a descriptive account of three diseases that affect both kidneys and lungs: Wegener’s granulomatosis, systemic lupus erythematosus and Goodpasture’s syndrome.

The main focus of the article, however, is the various respiratory complications that can affect those with chronic renal failure. These include pulmonary edema, pleural effusion, respiratory infections, pulmonary calcification, urinothorax (a rare complication of urinary obstruction, characterized by the presence of urine in the pleural space) and sleep apnea (which apparently affects around 60 % of hemodialysis patients).

Iatrogenic effects are also discussed, including hemodialysis-related hypoxemia and adverse effects of mechanical ventilation on the kidneys, a subject of current research interest.