Acid–base disturbances

Acid–base disturbances are a group of conditions characterized by changes in the normal acid-base balance of the blood. The body's acid-base balance is meticulously regulated to maintain the arterial blood pH within a narrow range of 7.35 to 7.45, which is necessary for the proper functioning of metabolic processes and efficient enzyme activity. Disturbances in this balance can lead to acidosis (pH < 7.35) or alkalosis (pH > 7.45), each of which can be further classified as either respiratory or metabolic, depending on the primary cause of the pH imbalance.

Classification

Acid-base disturbances are classified into four main categories:

• Respiratory acidosis: This occurs when there is an accumulation of carbon dioxide (CO2) due to decreased ventilation, leading to an increase in carbonic acid in the blood.
• Respiratory alkalosis: This is caused by excessive loss of CO2 through hyperventilation, resulting in a decrease in carbonic acid.
• Metabolic acidosis: This results from an increase in acid production or a decrease in bicarbonate (HCO3-), leading to a decrease in blood pH.
• Metabolic alkalosis: This occurs when there is an excessive loss of acid or an increase in bicarbonate, leading to an increase in blood pH.

Causes

The causes of acid-base disturbances vary depending on the type:

• Respiratory acidosis can be caused by conditions that impair lung function, such as chronic obstructive pulmonary disease (COPD), pneumonia, and drug overdose leading to respiratory depression.
• Respiratory alkalosis is often caused by conditions that lead to hyperventilation, such as anxiety, pain, or high altitude exposure.
• Metabolic acidosis can result from kidney failure, diabetic ketoacidosis, or ingestion of certain toxins, such as methanol or ethylene glycol.
• Metabolic alkalosis can be caused by excessive vomiting, diuretic use, or hyperaldosteronism.

Symptoms

Symptoms of acid-base disturbances vary widely and can include fatigue, confusion, nausea, vomiting, shortness of breath, and changes in heart rate. Severe disturbances can lead to coma or death if not promptly treated.

Diagnosis

Diagnosis of acid-base disturbances involves a detailed patient history, physical examination, and laboratory tests. Arterial blood gas (ABG) analysis is the gold standard for assessing acid-base status, providing precise measurements of pH, partial pressure of carbon dioxide (PaCO2), and bicarbonate (HCO3-). The anion gap may also be calculated to help determine the cause of metabolic acidosis.

Treatment

Treatment of acid-base disturbances focuses on correcting the underlying cause. In cases of respiratory acidosis, improving ventilation is key. This may involve treating lung infections, reducing airway obstruction, or using mechanical ventilation in severe cases. For respiratory alkalosis, rebreathing into a paper bag or using sedatives to reduce hyperventilation may be effective. Metabolic acidosis may require administration of bicarbonate to raise blood pH, while metabolic alkalosis might be treated with volume repletion and potassium replacement.

Prevention

Prevention of acid-base disturbances involves managing chronic conditions that can lead to disturbances, such as COPD and kidney disease, and avoiding substances that can cause metabolic acidosis or alkalosis.