64 - Hypoxic drive Myth and the Haldane effect

KYJ 64 - Hypoxic drive.
Can I use oxygen on my COPD patient?

Yes. Judiciously, and under  close observation, but Yes.

Hypoxic drive is a normal part of our primitive mechanism to breath. Literally hypoxic means "low oxygen".  So hypoxic drive means, when oxygen levels drop off in blood, chemical receptors in your carotid arteries and Aorta, detects low oxygen, and informs the respiratory centre in the brain.  This stimulates you to take another breath.

All humans have a hypoxic drive. But in the first few years of life a more powerful drive takes over.

Hypercapnic drive. If you are older than 3, and don't have severe gas trapping COPD, then you are breathing primarily because of this drive.  Hypercapnic drive means high Carbon Dioxide (CO2) drive.

As CO2 rises in your blood it lowers blood pH and causes blood to become acidic.  This acidic blood traveling through brain results in subtle lowering of CSF pH which, when detected in the Respiratory centre, is a powerful stimulant to initiate a breath.

In some CO2 retaining COPD patients  (not many), their Hypercapnic drive ceases to function effectively, causing them to rely on their hypoxic drive .   Traditionally we have been taught to avoid oxygenating these patients for fear of eliminating their will to breathe.  But this is an erroneous myth.  We will never completely destroy will to breathe.

So can I use oxygen on a person with hypoxic drive??? Yes. But we still want to minimise its use. Not because of respiratory suppression, but for a whole other reason.   The Haldane effect.

The Haldane effect is a physics principle that states that the more oxygen that haemoglobin can carry in blood, the less it can transport CO2.

So... Now stay with me!!

So... If I push your oxygen sats up, you can't carry CO2 and excrete it.  CO2 rises (is retained), exerting more and more acidosis.  

Now at a point, acidic blood becomes so acidic that it then will not allow haemoglobin to bind with oxygen,

So how much is enough.
23-28 % (nasal prongs) or Venturi mask.

What indications...
In severe COPD patients who are known CO2 retainers,  administer oxygen when their baseline sats drop below 88%.

All other patients - oxygenate to maintain sats over 93%

Summary
1.  Hypoxic drive is normal
2.  Oxygen to a patient with hypoxic drive causing respiratory rate depression is a MYTH.
3.  The Haldane effect inhibits CO2 transportation for excretion in over oxygenated COPD patients.

Give Oxygen Judiciously, and have a sound reason to use this poisonous gas.

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