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February 16, 1990

Severe Alkalosis During Assisted Ventilation in Chronic Obstructive Pulmonary Disease

JAMA. 1990;263(7):950. doi:10.1001/jama.1990.03440070036027

To the Editor.—  The excellent review by Drs Schmidt and Hall1 only briefly touches on a problem that I feel requires greater attention when caring for patients with chronic obstructive pulmonary disease who are receiving ventilatory assistance. That is severe alkalosis, which develops not only owing to hyperventilation in these carbon dioxide retainers but also secondary to an increase in the "strong ion difference" (often called "an increase in bicarbonate or base excess") and to a decrease in the concentration of nonvolatile weak acids.2-4 The strong ion difference is the difference between the sum of the concentrations of all of the strong cations (Na+, K+, Ca, and Mg) and the strong anions (Cl-, SO4=, and organic acids) and is normally approximately + 42 mEq/L. The nonvolatile weak acids are largely composed of the plasma proteins, with a very minor contribution from inorganic phosphate.The increase in strong ion