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Respiratory Acidosis

An acid-base disturbance characterized by reduced alveolar ventilation and manifested by hypercapnia (partial pressure of arterial carbon dioxide [Paco2,] greater than 45 mm Hg), respiratory acidosis can be acute (from a sudden failure in ventilation) or chronic (as in long­term pulmonary disease). The prognosis depends on the severity of the underlying disturbance, as well as the patient's general clinical condition.

Causes

Respiratory acidosis can be caused by diseases or conditions that affect the lungs themselves, such as emphysema , chronic bronchitis , asthma , or severe pneumonia . Blockage of the airway due to swelling, a foreign object, or vomit can induce respiratory acidosis. Drugs like anesthetics, sedatives, and narcotics can interfere with breathing by depressing the respiratory center in the brain. Head injuries or brain tumors can also interfere with signals sent by the brain to the lungs. Such neuromuscular diseases as Guillain-Barré syndrome or myasthenia gravis can impair the muscles around the lungs making it more difficult to breathe. Conditions that cause chronic metabolic alkalosis can also trigger respiratory acidosis.

Signs and symptoms

Acute respiratory acidosis produces CNS disturbances that reflect changes in the pH of cerebrospinal fluid rather than increased carbon dioxide levels in cerebral circulation.

Effects range from restlessness, confusion, and apprehension to somnolence, with a fine or flapping tremor (asterixis), or coma. The patient may complain of headaches and exhibit dyspnea and tachypnea with papilledema and depressed reflexes. Unless the patient is receiving oxygen, hypoxemia accompanies respiratory acidosis.

This disorder may also cause cardiovascular abnormalities, such as tachycardia, hypertension, atrial and ventricular arrhythmias and, in severe acidosis, hypotension with vasodilation (bounding pulses and warm periphery

Diagnosis

Respiratory acidosis may be suspected based on symptoms. A blood sample to test for pH and arterial blood gases can be used to confirm the diagnosis. In this type of acidosis, the pH will be below 7.35. The pressure of carbon dioxide in the blood will be high, usually over 45 mmHg.

Treatment

Effective treatment of respiratory acidosis is designed to correct the underlying source of alveolar hypoventilation. Significantly reduced alveolar ventilation may require mechanical ventilation until the underlying condition can be treated.

In COPD, treatment includes bronchodilators, oxygen, corticosteroids and, frequently, antibiotics; drug therapy for conditions such as myasthenia gravis; removal of foreign bodies from the airway; antibiotics for pneumonia; dialysis or charcoal to remove toxic drugs; and correction of metabolic alkalosis. An elevated Paco2 may persist in a patient with COPD despite optimal treatment.

Prevention

Do not smoke. Smoking leads to the development of many severe lung diseases that can lead to respiratory acidosis.

Losing weight may help prevent obesity hypoventilation syndrome.