Disorders of Acid-Base Balance

Normal systemic arterial blood pH ranges between 7.35 and 7.45. Values below 7.35 indicate acidosis, while values above 7.45 indicate alkalosis. This narrow pH range is essential for maintaining proper enzyme function, cellular metabolism, and physiological processes throughout the body.

Respiratory acidosis occurs when arterial PCO2 exceeds 45 mm Hg, typically from shallow breathing or impaired gas exchange. Diseases like pneumonia, cystic fibrosis, and emphysema reduce the lungs' ability to eliminate carbon dioxide, causing CO2 accumulation and decreased blood pH. Understanding respiratory regulation of acid base balance helps explain these mechanisms.

Hyperventilation increases CO2 elimination, causing arterial PCO2 to drop below 35 mm Hg. This reduction in carbon dioxide lowers hydrogen ion concentration, raising blood pH above 7.45. Common triggers include oxygen deficiency, stroke, or severe anxiety that stimulates rapid breathing.

Metabolic acidosis results from decreased bicarbonate ion levels below 22 mEq/L due to excessive loss or acid accumulation, while respiratory acidosis stems from elevated CO2 levels. Metabolic acidosis occurs in conditions like persistent diarrhea or excessive alcohol consumption, whereas respiratory acidosis develops from lung disease or hypoventilation.

Metabolic alkalosis occurs when blood bicarbonate ion concentration exceeds 28 mEq/L, raising pH above 7.45. This develops from non-respiratory acid loss through vomiting or gastric suctioning, overconsumption of antacids or alkaline drugs, or endocrine disorders and severe dehydration. The roles of electrolytes chloride and bicarbonate are central to this condition.

Diarrhea causes metabolic acidosis by increasing bicarbonate ion loss through the gastrointestinal tract. As HCO3⁻ levels drop below 22 mEq/L, blood pH decreases below 7.35, creating an acidotic state. This represents one of the most common causes of metabolic acidosis in clinical practice.

Untreated acid-base disorders disrupt homeostasis and can cause severe physiological complications. Both respiratory and metabolic imbalances affect enzyme function, cellular metabolism, and organ performance. Restoring pH balance quickly prevents tissue damage and maintains the body's ability to sustain vital functions.