Respiratory Acidosis

Respiratory acidosis is an acid-base disturbance characterized by reduced alveolar ventilation and manifested by hypercapnea (partial pressure of arterial carbon dioxide [Paco2] greater than 45 mm Hg). Respiratory acidosis can be acute (resulting from sudden failure in ventilation) or chronic (resulting from long-term pulmonary disease).

The prognosis depends on the severity of the underlying distUrbance and the patient's general clinical condition.

Causes

Factors that predispose a patient to respiratory acidosis include:

• drugs, such as narcotics, anesthetics, hypnotics, and sedatives, which depress the respiratory control center's sensitivity
• central nervous system (CNS) trauma, such as medullary injury, which may impair ventilatory drive
• chronic metabolic alkalosis, which may occur when respiratory compensatory mechanisms attempt to normalize pH by decreasing alveolar ventilation
• neuromuscular diseases, such as Guillain-Barre syndrome, myasthenia gravis, and poliomyelitis, in which respiratory muscles fail to respond properly to respiratory drive, reducing alveolar ventilation.

In addition, respiratory acidosis can result from an airway obstruction or parenchymal lung disease that interferes with alveolar ventilation or from chronic obstructive pulmonary disease (COPD), asthma, severe adult respiratory distress syndrome, chronic bronchitis, large pneumothorax, extensive pneumonia, and pulmonary edema.

Signs and Symptoms

Symptoms of the diseases that cause respiratory acidosis are usually noticeable, and may include shortness of breath, easy fatigue, chronic cough, or wheezing.

When respiratory acidosis becomes severe, confusion, irritability, or lethargy may be apparent.

Diagnostic tests

Arterial blood gas (ABG) analysis confirms respiratory acidosis when Paco2 is greater than the normal 45 mm Hg; pH is typically below the normal range of; 7.35 to 7.45; and bicarbonate levels are normal in acute respiratory acidosis but elevated in chronic respiratory acidosis.

Treatment

The goal of treatment is to correct the source of alveolar hypoventilation. If alveolar ventilation is significantly reduced, the patient may need mechanical ventilation until the underlying condition can be treated. This includes bronchodilators, oxygen, and antibiotics in COPD; drug therapy for conditions such as myasthenia gravis; removal of foreign bodies from the airway in cases of obstruction; antibiotics for pneumonia; dialysis to eliminate toxic drugs; and correction of metabolic alkalosis.

Dangerously low pH levels (less than 7.15) can produce profound CNS and cardiovascular deterioration and may require administration of I.V. sodium bicarbonate. In chronic lung disease, elevated carbon dioxide (CO2) levels may persist despite 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.