What is Blood-Gas Partition Coefficient?
Rahul's Noteblog Notes on Pharmacology What is Blood-Gas Partition Coefficient?
Blood-Gas Partition Coefficient:
The potency of anesthesia depends upon the anesthetic partial pressure in the CNS. Anesthetic transfer into the brain begins only after the blood has been fully saturated (i.e., when the partial pressure of anesthetic in blood is equal to the partial pressure of inspired air).
The onset of anesthetic action is determined by the speed of transfer of anesthetic to the brain. Anesthetics that are highly soluble in the brain have high blood-gas partition coefficients.
Nitrous oxide (NO) has a blood-gas partition coefficient of 0.47 L, thus, it is dissolves poorly in blood.
Ether, on the other hand, has a blood-gas partition coefficient of 12 L, thus, it dissolves very well in blood.
It should also be noted that gases with high-blood gas coefficients have a slower onset of action, higher solubility in blood, and slow equilibrium with the brain. On the other hand, gases with low blood-gas coefficients have a faster onset of action, lower solubility in blood, and fast equilibrium with the brain.
Conclusion:
Highly solule anesthetics exert a lower tension in arterial blood, i.e., the lower the anesthetic arterial blood tension, the higher the blood-gas partition coefficient. Thus, a highly soluble anesthetic is characterized by a high arteriovenous gradient (high tissue uptake) and slow onset of action.
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