Oxygen transport—1. Basic principles

Editor - In an otherwise excellent article, "ABC of oxygen - Oxygen
Transport -1. Basic principles" surely the table labelled "Causes of
Hypoxaemia" should have been "Some Causes of Hypoxaemia", as any candidate
for a higher examination would find the examiner unsatisfied with a such a
list as that. It omits many important causes, some requiring rapid or even
immediate recognition if serious harm to a patient is to be avoided. I do
not intend to provide an exhaustive list now, but some omissions spring to
mind instantly.

Before the category "Alveolar hypoventilation" should come one
entitled "Hypoxic Gas Mixtures" to include for example high altitude,
house fires and accidental (iatrogenic or otherwise).

Under "Alveolar hypoventilation" I would expect some mention of
respiratory obstruction to include inhaled foreign bodies amongst others,
and under "Ventilation-perfusion mismatch" a class called circulatory
failure to include massive pulmonary embolism, myocardial infarction and
so on.

There is no mention of excessive oxygen consumption, but patients
with malignant hyperpyrexia demonstrate low haemoglobin saturations, and
if hypoxaemia is held to mean "Low blood oxygen content" as opposed to
just hypoxia (low oxygen tension), then there needs to be an "Impaired
blood oxygen carrying capacity" category to include the real and
functional (e.g. carbon monoxide poisoning) anaemias.

1. Treacher DF, Leach RM ABC of oxygen. Oxygen transport -1. Basic
principles. BMJ 1998 1302:1306 (7 May)