Hypo and Hypercapnea

Explain the physiological effects of hyperoxia, hypoxaemia, hypercapnia, hypocapnia, and carbon monoxide poisoning

Carbon dioxide is lipid soluble and can rapidly cross membranes, allowing it affect acid-base status in any compartment.

Hypercapnea

• Respiratory Effects

  • Increased respiratory drive via chemoreceptor stimulation

• CVS effects

  • Peripheral vasodilation
    • May cause tachycardia from sympathetic stimulation
  • Pulmonary vasoconstriction
  • Myocardial depression
    Intracellular acidosis.
  • Arrhythmogenic

• CNS effects
  • Increased CBF
  • Increased ICP secondary to increased CBF
  • SNS activation
  • CNS depression
    When PaCO₂ > 100mmHg

Hypocapnea

• Respiratory Effects
  • Left-shift of oxyhaemoglobin dissociation curve
  • Respiratory depression

• CVS effects
  • Myocardial depression
    Intracellular alkalosis.

• CNS effects

  • Decreased cerebral blood flow

• Electrolyte effects

  • Decreased serum K⁺
  • Decreased serum Ca²⁺
    Leads to paresthesias and twitches.
    • Ca²⁺ binds to H⁺ binding site on albumin

References

1. Brandis K. The Physiology Viva: Questions & Answers. 2003.