33% of candidates passed this question.

Candidates were expected to describe the pharmacology of oxygen under the following headings: pharmaceutics / preparation, mechanism of action, indications/uses, administration methods, pharmacokinetics, pharmacodynamics and toxicity.

Given the breadth of the question the detail of answers will be inherently limited by time however some specific details were important. Pharmaceutics included the properties of oxygen and its manufacturing and storage.

Administration by inhalation may be via fixed and variable performance devices. Indications included causes of hypoxaemia but there are others such as de-nitrogenation of gas filled spaces, and various indications for hyperbaric O2 therapy. Mechanism of action involved mentioning oxidative phosphorylation occurring in the mitochondria where O2 functions as the final electron acceptor.

Other mechanisms include biochemical pathways requiring O2 as a substrate, and generation of reactive oxygen species by neutrophils and macrophages for antimicrobial purposes. Pharmacokinetics required a description of diffusion across alveolar membrane, binding to Hb and the small amount in solution, metabolism in mitochondria and excretion subsequently of CO2 and H20.

Answers were elevated by quantitation of O2 uptake, O2 carriage, mention of importance of pressure gradients (O2 cascade) and O2 stores.

Pharmacodynamics required mention of systemic vasoconstriction, effects on the respiratory system such as de-nitrogenation of gas filled spaced, absorption atelectasis, inhibition of hypoxic pulmonary vasoconstriction and risk of hypercapnia in select patients with COPD.

Side effects involve reactive oxygen species, and awareness of dose and time of exposure as relevant factors.

There is a risk of delirium/seizures in hyperbaric oxygen, and longer-term risks of pulmonary toxicity and to the premature neonate of retrolental fibroplasia and retinopathy.