Respiratory acidosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Vamsikrishna Gunnam M.B.B.S [2]

Overview

Respiratory acidosis is a clinical condition that occurs when the lungs are not able to remove enough of the carbon dioxide (CO2) produced by the body. Respiratory acidosis may be classified into two groups: Acute respiratory acidosis and Chronic respiratory acidosis.

Classification

Acute respiratory acidosis

• Acute respiratory acidosis occurs when PaCO2 is increased above the upper limit of the reference range >45 mmHg with an accompanying acidemia (ie, pH <7.35).

• In patients with pure acute respiratory acidosis, the levels of hypercapnia and bicarbonate correctly predicts the pH.
• In contrast, for patients who develop acute respiratory acidosis, the measured pH will be higher than predicted.
• Acute respiratory acidosis occurs due to the result of sudden failure of ventilation. This failure may be due to central nervous system(CNS) disease or any drug-induced respiratory depression.
• Inability to ventilate sufficiently , due to paralysis like for eg, myasthenia gravis, amyotrophic lateral sclerosis [ALS], Guillain-Barré syndrome, muscular dystrophy.see
• Airway obstruction, usually seen in relation to asthma or chronic obstructive pulmonary disease (COPD) patients.

Chronic respiratory acidosis

• Chronic respiratory acidosis occurs when PaCO₂ is elevated above the upper limit of the reference range ie >45 mmHg.
• But the pH is at the lower limit of normal or near-normal pH (eg, pH 7.33 to 7.35) secondary to renal compensation (secretion of acid from the distal tubule).
• Secondary to many pathologies Chronic respiratory acidosis may occur like for eg in patients who are suffering with chronic obstructive pulmonary disease (COPD) and involve multiple mechanisams which are as follows
  • In conditions like hypoxia and hypercapnia the responsiveness is decreased .
  • Increased in dead space ventilation due to increased ventilation-perfusion mismatch.
  • function of Diaphragm decresed due to hyperinflation and fatigue.
  • Obesity hypoventilation syndrome (OHS).