Reduced Oxyhaemoglobin
Overview
The level of haemoglobin saturated by oxygen may be reduced in the context of reduced oxygen, right shift of the oxygen saturation curve, displacement of oxygen by carbon dioxide, or in the setting of haemoglobinopathies.
Causes of Reduced Oxyhaemoglobin
Reduced Environmental Oxygen
- High altitude
Hypoventilation
- CNS - drugs, trauma, encephalopathy, motor neurone disease, Guillain-Barré
- Muscular / neuromuscular - myaesthenia, paralytics, myopathy, fatigue, malnutrition
- Airway obstruction - foreign body, asthma, COPD, bronchiectasis
- Decreased compliance - interstitial lung disease
- Chest wall abnormalities
Ventilation / Perfusion Mismatch
- Physiological shunt - atelectasis, pulmonary oedema, pneumonia, ARDS
- Anatomical shunt - cardiac shunt e.g. tetralogy of Fallot
- Dead space - asthma, COPD, pulmonary embolus, heart failure
Other
- Right shift of the oxygen dissociation curve - acidaemia, hyperthermia, high 2,3-DPG
- Carbon monoxide poisoning
- Haemoglobinopathy - methaemoglobinaemia, foetal haemoglobin
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