Myth: COPD & Hypoxic drive.

Myth: Administration of high concentration of oxygen to COPD patient will cause them to loss their hypoxic drive and resulting in hypoventilation and type 2 respiratory failure.

Truth:

  • High oxygen concentration is dangerous in this type of patient. Because it cause oxygen induce hypercapnia.
  • Oxygen induced hypercapnia in COPD patient contributed by:
  1. Increased V/Q mismatch: damage alveolar(hypoventilate) with low PaO2 will have low blood flow due to feedback vasoconstriction. By giving high oxygen concentration, this will increase PaO2 in the damage alveolar and cause increase in blood flow to the damage alveolar. However the alveolar can’t perform as normal alveolar and cause high V/Q mismatch. The blood flow through this alveolar doesn’t get much gas exchange.
  2. Haldane effect: high concentration oxygen will saturate hemoglobin. The oxygenated hemoglobin bind CO2 with less affinity compare to deoxygenated hemoglobin, thus transport of CO2 is impaired and cause increase in CO2. This effect contribute to 25% of hypercapnia.

So,

    Target SpO2: 88-92%.
    Titrate FiO2 to the lowest possible to achieve SpO2 88-92%.

Reference:

1. https://lifeinthefastlane.com/ccc/oxygen-and-co2-retention-in-copd/#comment-298600

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3682248/#!po=54.3478

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