• In patients with severe abnormalities of the control system of breathing and of gas exchange, hypercapnia may result from relatively small increases in metabolic rate.
• The respiratory centers may be depressed directly or indirectly. In both instances, the increase in PaCO2 is due to decreased output of the respiratory centers.
• Causes of reduced respiratory muscle strength include neuromuscular disease, malnutrition, electrolyte abnormality, steroids, humoral mediators, thoracic deformity, deconditioning of respiratory muscles, peripheral fatigue, pulmonary hyperinflation, and rapid shallow breathing.
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