Respiratory acidosis is a clinical condition associated with lungs dysfunction in order to remove excess carbon dioxide (CO2) from the body. Respiratory acidosis may be classified into two groups: Acute respiratory acidosis and Chronic respiratory acidosis.

• Respiratory acidosis is classified into acute and chronic groups, depending on the duration.

• 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, in 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 respiratory muscle paralysis disorders including myasthenia gravis, amyotrophic lateral sclerosis [[[Amyotrophic lateral sclerosis|ALS]]], guillain-Barré syndrome, muscular dystrophy.
• Airway obstruction, usually seen in patients with asthma or chronic obstructive pulmonary disease (COPD).^[1][2]

• 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).
• Chronic respiratory acidosis may occur secondary to many diseases such as chronic obstructive pulmonary disease(COPD) and Obesity hypoventilation syndrome (OHS) that involve multiple mechanisms including^[3][4][5][6]
  • In conditions with 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.