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 [[[Amyotrophic lateral sclerosis|ALS]]], guillain-Barré syndrome, muscular dystrophy.
• 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 mechanisms 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 decreased due to hyperinflation and fatigue.
  • Obesity hypoventilation syndrome (OHS).