Respiratory acidosis

Due to alveolar hypoventilation.

Associated with rapid production of carbon dioxide and failure of ventilation increases the partial arterial pressure of carbon dioxide.

Alveolar hypoventilation leads to an increased PaCO2 and in turn the increase in PaCO2 decreases the bicarbonate (HCO3)/PaCO2, decreasing the pH.

When impairment in ventilation occurs and removal of carbon dioxide by the lungs is less than the production of carbon dioxide in the tissues hypercapnia and respiratory acidosis occurs.

May be an acute or chronic process

In acute process the PaCO2 is increased above the normal range of 45 mm Hg and is accompanied by acidosis with a pH<7.35.

In the chronic process PaCO2 is elevated over the normal range but a normal or near normal pH secondary to renal compensation and elevated serum bicarbonate of greater than 30 mm Hg.

Acute disease results with an abrupt failure of ventilation.

Ventilation impairment may be a result of central nervous system depression by drugs, neuromuscular disease, cerebral disease or airway obstruction from asthma or COPD.

Chronic process may associated with COPD.

Hypoventilation in COPD involves decreased responsiveness to hypoxia and hypercapnia, increased ventilation-perfusion mismatch leading to increased dead space ventilation and decreased diaphragmatic function due to fatigue and hyperinflation.

Chronic process may be associated with obesity-hypoventilation syndrome, neuromuscular disorders and severe restrictive ventilatory defects as observed in interstitial fibrosis and thoracic deformities.

Generally, lung disease that interferes with alveolar gas exchange does not cause hypoventilation but can stimulate ventilation and hypocapnea related to hypoxia and if severe, can lead to respiratory muscle failure and secondary hypercapnia.

Metabolic changes that occur in the body result in the generation of volatile acid, carbon dioxide, and nonvolatile acids.

Fat and carbohydrate metabolism leads to the formation of large amount of carbon dioxide.

Carbon dioxide combines with water to form carbonic acid (H2CO3) and the lungs excrete the volatile fraction through ventilation and prevents acid accumulation.

Alterations in ventilation affecting the elimination of carbon dioxide can cause respiratory acid-base disorder.

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