30.18
Disorders of Acid-Base Balance
The human body maintains a precise pH range of arterial blood between 7.35 and 7.45. Deviations result in either acidosis (pH < 7.35) or alkalosis (pH > 7.45). These conditions…
The normal pH range of systemic arterial blood is between 7.35 and 7.45.
An arterial blood pH and bicarbonate concentration below 7.35 and 20 mEq/L indicates acidosis, while pH and a bicarbonate concentration above 7.45 and 20 mEq/L indicates alkalosis. These conditions can be respiratory or metabolic.
Respiratory imbalances result from changes in the partial pressure of CO2.
Respiratory acidosis occurs when arterial PCO2 exceeds 45 mm Hg, in diseases like pneumonia, or emphysema.
In respiratory alkalosis, arterial PCO2 drops below 35 mm Hg, caused by oxygen deficiency, stroke, or anxiety.
Metabolic imbalances result from changes in blood pH.
Metabolic acidosis occurs when bicarbonate ion levels drop below 22 mEq/liter due to excessive ion loss in conditions like persistent diarrhea or excessive alcohol consumption.
In metabolic alkalosis, arterial bicarbonate ion concentration exceeds 28 mEq/liter due to vomiting, diuretics, or excessive intake of alkaline drugs.
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Q1: What is the normal pH range of arterial blood?
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.
Q2: What causes respiratory acidosis?
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.
Q3: How does hyperventilation lead to respiratory alkalosis?
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.
Q4: What is the difference between metabolic acidosis and respiratory acidosis?
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.
Q5: What causes metabolic alkalosis?
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.
Q6: How does diarrhea contribute to metabolic acidosis?
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.
Q7: Why is prompt intervention critical for acid-base disorders?
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.