Question 14

Describe the pharmacology of oxygen.

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College Answer

Candidates who approached this question in a structured pharmacology approach were able to score well, outlining the pharmaceutics, pharmacodynamics, and pharmacokinetics. Many candidates limited their pharmacodynamic discussion to adverse effects of oxygen only or listed effects without demonstrating understanding of their mechanism or consequences which limited their ability to score marks. 


Physico-chemical properties of oxygen

  • Oxygen (O2)is a diatomic gas with a density and viscosity slightly higher than that of air. 
  • Conventional "wall" oxygen is delivered at approximately 4 atmospheres of pressure (415 kPa) and is close to 0°C at the wall outlet.


  • As an inhaled agent via a selection of fixed or variable performance delivery devices
  • As intravenous or intra-arterial infusion of well-oxygenated blood (i.e. ECMO)
  • Externally (as in hyperbaric oxygen therapy)


  • Pulmonary absorption (250ml/min with 21% FiO2, at rest)
  • Cutaneous absorption (under 1ml/min at normal atmospheric pressure)
  • Oral (and other) mucosal absorption (usually, nil)


  • Metabolised in all tissues (mainly brain, heart and skeletal muscle)
  • Mainly metabolised by cytochrome c mitochondrial enzymes (90%)
  • Zero-order clearance kinetics, roughly 200ml/minute
  • Main metabolites are CO2 and H2O, cleared via the lung and renally. 

Indications for use

  • Supplementation (in hypoxemia)
  • Prophylaxis (in pre-oxygenation for anaesthesia)
  • As an antidote (carbon monoxide toxicity)
  • Therapeutic uses:
    • As an antibiotic (hyperbaric oxygen for deep anaerobic infections)
    • To decrease the volume of air-filled body cavities by denitrogenation (eg. pneumothorax and pneumoencephalus)
    • In management of decompression sickness


  • Bleomycin use (leads to pulmonary fibrosis)
  • Paraquat toxicity (worsens ARDS)
  • Aspiration of acid (worsens ARDS)


  • Drying of mucous membranes and inspissation of secretions
  • Inflammatory tracheobronchitis
  • Decreased central respiratory drive (minimally)
  • Hypecapnoea in "CO2 retainers" mainly by virtue of V/Q mismatch and Haldane effect
  • Absorption atelectasis
  • Increased left-to-right shunting in ASDs
  • Increased peripheral vascular resistance
  • Cerebral and coronary vasoconstriction
  • Euphoria
  • Retrolental fibroplasia of the newborn
  • Decreased erythropoiesis


  • Visual changes and seizures (hyperbaric) 
  • Toxicity from free radicals (worsening ARDS)


  • Few uses are evidence-based
  • Evidence does not support the use of supraphysological oxygen in most cases, i.e. hyperoxia is discouraged.


O'Driscoll, B. R., et al. "BTS guideline for oxygen use in adults in healthcare and emergency settings." Thorax 72.Suppl 1 (2017): ii1-ii90.

Ogryzlo, E. A. "Why liquid oxygen is blue." Journal of Chemical Education 42.12 (1965): 647.

Bitterman, Haim. "Bench-to-bedside review: oxygen as a drug." Critical Care 13.1 (2009): 205.