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    98 Quantity of assimilated oxygen on 100 gr. of cerebral tissue
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    98 Quantity of assimilated oxygen on 100 gr. of cerebral tissue

    Cerebral oxygen consumption per 100 g: brain metabolism, measurement and causes of low and high values.

    The quantity of oxygen consumed per 100 g of brain tissue is the cerebral metabolic rate of oxygen (CMRO₂). The brain makes up about 2% of body weight but uses roughly 20% of the body's resting oxygen, almost entirely to produce ATP for maintaining ion gradients and transmitting nerve signals. It has practically no oxygen reserves, so consciousness is lost within seconds when supply stops. CMRO₂ was first measured in humans with the Kety–Schmidt nitrous oxide method, which also gave the classic value of cerebral blood flow of about 50 mL/100 g/min. In this application the value is linked to redox processes, lipid peroxidation and thyroid regulation.

    BrainMetabolismOxygen consumption
    Adults (this application)≈ 2.5–3.5 mL/100 g/min
    Children (this application)≈ 3.5–6 mL/100 g/min
    Brain share of resting O₂ use≈ 20%
    FormulaCMRO₂ = CBF × (CaO₂ − CjvO₂)
    Cerebral oxygen consumption per 100 grams of tissue: below 2.5 low, 2.5 to 3.5 adult range used by this application, 3.5 to 6 range for children Cerebral O₂ consumption (mL/100 g/min) Low below 2.5 2.5 Adults 2.5–3.5 3.5 Children 3.5–6
    Figure 1. Reference ranges of cerebral oxygen consumption used by this application. Children's brains have a higher metabolic rate than adults'.

    Measurement

    CMRO₂ = cerebral blood flow × (arterial O₂ content − jugular venous O₂ content)

    The reference methods are invasive or use special imaging: blood sampling from the jugular bulb together with cerebral blood flow measurement, and positron emission tomography (PET) with labelled oxygen. In intensive care, jugular venous saturation and brain tissue oxygen probes are used to judge whether oxygen supply matches demand.

    Clinical significance

    Low CMRO₂

    Anaesthesia and sedation (used therapeutically to protect the brain), hypothermia, coma, after cardiac arrest, advanced dementia, hypothyroidism, severe hypoglycaemia.

    High CMRO₂

    Seizures, fever, intense mental activity, agitation and delirium, stimulants, hyperthyroidism. Raised demand combined with reduced flow increases the risk of ischaemic injury.

    Seek emergency care

    for sudden confusion, loss of consciousness, seizures, or sudden weakness, numbness or speech difficulty.

    References

    1. Kety SS, Schmidt CF. The nitrous oxide method for the quantitative determination of cerebral blood flow in man: theory, procedure and normal values. J Clin Invest. 1948;27(4):476–483. doi:10.1172/JCI101994
    2. Claassen JAHR, Thijssen DHJ, Panerai RB, Faraci FM. Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation. Physiol Rev. 2021;101(4):1487–1559. doi:10.1152/physrev.00022.2020

    This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

    Published on 5 May 2024