Acid-Base Balance – Definition and Disorders
The acid-base balance refers to the equilibrium between acids and bases in the human body, measured by blood pH. It is essential for all physiological functions and must be tightly regulated.
Things worth knowing about "Acid-Base Balance"
The acid-base balance refers to the equilibrium between acids and bases in the human body, measured by blood pH. It is essential for all physiological functions and must be tightly regulated.
What Is the Acid-Base Balance?
The acid-base balance refers to the carefully regulated equilibrium between acid-forming and alkaline (basic) substances in the human body. This balance is expressed by the pH value of the blood. In a healthy individual, blood pH is maintained between 7.35 and 7.45, representing a slightly alkaline environment. Even small deviations from this narrow range can have life-threatening consequences, as virtually all biochemical reactions in the body depend on a stable pH.
Regulation of Acid-Base Balance
The body uses three main mechanisms to maintain pH stability:
- Blood buffer systems: The most important is the bicarbonate-carbonic acid buffer system, which can neutralize excess acids or bases within seconds. Hemoglobin and plasma proteins also serve as buffers.
- Respiratory system (lungs): By exhaling carbon dioxide (CO₂), the body can rapidly reduce acid levels. Breathing rate is adjusted accordingly to fine-tune pH.
- Kidneys: The kidneys provide long-term pH regulation by retaining bicarbonate or excreting hydrogen ions (H⁺). This process takes hours to days but is highly precise.
Disorders of Acid-Base Balance
When blood pH falls outside the normal range, the condition is classified as either acidosis (excess acid) or alkalosis (excess base). These disorders are further categorized by their underlying cause:
Acidosis (pH below 7.35)
- Respiratory acidosis: Results from inadequate ventilation of the lungs, such as in chronic obstructive pulmonary disease (COPD), causing CO₂ to accumulate in the blood.
- Metabolic acidosis: Caused by conditions such as kidney failure, uncontrolled diabetes mellitus (diabetic ketoacidosis), severe diarrhea, or poisoning.
Alkalosis (pH above 7.45)
- Respiratory alkalosis: Occurs during hyperventilation, for example due to anxiety or high altitude exposure, as too much CO₂ is exhaled.
- Metabolic alkalosis: May result from prolonged vomiting, excessive use of antacids, or certain diuretics.
Symptoms of Acid-Base Disorders
Disruptions of the acid-base balance can present with a wide range of symptoms, including:
- Nausea and vomiting
- Rapid or deep breathing (known as Kussmaul breathing in severe acidosis)
- Muscle weakness or cramps
- Confusion and altered consciousness
- Cardiac arrhythmias
- Tingling in the hands and feet (common in alkalosis)
Diagnosis
Diagnosis is typically established through an arterial blood gas (ABG) analysis, in which blood is drawn from an artery. This test measures pH, partial pressure of CO₂ (pCO₂), partial pressure of oxygen (pO₂), and bicarbonate levels (HCO₃⁻). Electrolytes such as potassium and sodium, as well as the anion gap, are also evaluated to identify the precise cause of the disorder.
Treatment
Treatment is always directed at the underlying cause:
- For respiratory acidosis, improving ventilation is the priority — through bronchodilators, breathing therapy, or mechanical ventilation in severe cases.
- For metabolic acidosis, the primary disease is treated (e.g., insulin administration in diabetic ketoacidosis), and intravenous sodium bicarbonate may be given if needed.
- For alkalosis, triggering factors are addressed, such as electrolyte replacement (potassium) or breathing exercises to normalize respiratory rate.
Clinical Significance
A stable acid-base balance is a fundamental requirement for the proper functioning of all organ systems and enzyme pathways in the body. Acid-base disturbances frequently accompany serious illnesses and require careful monitoring and management in clinical settings. They are particularly critical in intensive care units, where patients with sepsis, renal failure, or severe trauma are treated.
References
- Silbernagl, S. & Lang, F. (2016). Color Atlas of Pathophysiology. 3rd Edition. Thieme Publishing, Stuttgart.
- World Health Organization (WHO): Chronic respiratory diseases and metabolic regulation. Available at: https://www.who.int
- Kellum, J. A. (2007). Disorders of acid-base balance. Critical Care Medicine, 35(11), 2630-2636. PubMed PMID: 17828044.
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