Introduction

The normal pH of extracellular fluid (range, 7.35 to 7.45) is unaffected by age. However, age-related changes do occur in certain respiratory and renal regulatory processes involved in maintaining normal pH, and the ability to respond to a challenge may be limited. For example, the ability to hyperventilate in response to acute metabolic acidosis may be blunted, leading to a further decline in pH. The aging kidney is slower to respond to an acid load, and the blood pH may take longer to recover. Many disorders common in the elderly (eg, heart failure, anemia, sepsis, diabetes mellitus, renal and pulmonary disease) can overwhelm the regulatory systems and contribute to acid-base disturbances. Also, many commonly used drugs (eg, salicylates, diuretics, laxatives) may precipitate acid-base disturbances. The combination of impaired homeostatic mechanisms and the high prevalence of drug use and disease in the elderly make acid-base disturbances common.