Chapter 9: Acid-Base Balance

The body maintains blood pH within the narrow range of 7.35 to 7.45 through three integrated regulatory systems. Buffer systems, the fastest-acting defense, work immediately to neutralize excess hydrogen ions, with the carbonic acid-bicarbonate system serving as the primary buffer that maintains a critical 20:1 ratio. The respiratory system responds within seconds to minutes by increasing or decreasing ventilation to eliminate or retain carbon dioxide, while the kidneys provide the most comprehensive but slowest compensation over hours to days by selectively excreting or retaining hydrogen and bicarbonate ions. The chapter details four primary acid-base disturbances: respiratory acidosis results from hypoventilation caused by conditions like chronic obstructive pulmonary disease or airway obstruction, while respiratory alkalosis develops from hyperventilation due to fever, anxiety, or hypoxia. Metabolic acidosis, characterized by low bicarbonate levels, occurs with diabetic ketoacidosis or severe diarrhea and presents with Kussmaul's respirations, whereas metabolic alkalosis results from loss of hydrochloric acid through vomiting or excessive diuretic use. The chapter emphasizes the reciprocal relationship between potassium and acid-base status, where acidosis causes hyperkalemia as hydrogen ions enter cells and potassium exits, while alkalosis produces hypokalemia through the opposite mechanism. Arterial blood gas analysis provides the diagnostic foundation for identifying and classifying acid-base imbalances, requiring interpretation of pH, partial pressure of carbon dioxide, and bicarbonate concentration alongside assessment of appropriate compensatory responses. Clinical management strategies are tailored to the specific imbalance and may include oxygen administration, repositioning, breathing technique modification, insulin therapy, dialysis, or electrolyte replacement depending on the underlying cause and severity.