Post-tetanic potentation

[drlee]

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My question pertains to the 1995 ABA ITE question 87. With recovery/reversal of nondepolarizing neuromuscular blockade, is there more or less post-tetanic potentation? 😕

 

[pgg]

My question pertains to the 1995 ABA ITE question 87. With recovery/reversal of nondepolarizing neuromuscular blockade, is there more or less post-tetanic potentation? 😕

More.

A 72-year-old man has had residual hemiparesis since having a cerebrovascular accident three years ago. Compared with the response of the unaffected limbs to nondepolarizing muscle relaxants, the hemiparetic limbs will show
(A) the same response
(B) greater depression of tetanus
(C) greater twitch depression
(D) less twitch depression
(E) less post-tetanic facilitation

The answer according to the key is D.

Patients with burns, denervation injury, and immobilization develop resistance to the effects of nondepolarizers because they produce extrajunctional receptors (also called immature or fetal receptors). This effect is localized to the injured or denervated muscles; other muscles are normal.

Less twitch depression (ie, a less intense block) is expected because of this resistance.

5 seconds of 50 Hz tetanic stimulation followed by 1 Hz single twitches starting 3 seconds later (or a TO4 if you're lazy) allows one to assess the intensity of neuromuscular blockade if the initial TO4 is flat [Miller 6th ed, p 1554]. The weaker the block, the more subsequent twitches will be facilitated by tetany. Therefore, one would expect more post-tetanic facilitation given the affected limb's resistance to nondepolarizers.

 

[Noyac]

More.



The answer according to the key is D.

Patients with burns, denervation injury, and immobilization develop resistance to the effects of nondepolarizers because they produce extrajunctional receptors (also called immature or fetal receptors). This effect is localized to the injured or denervated muscles; other muscles are normal.

Less twitch depression (ie, a less intense block) is expected because of this resistance.

5 seconds of 50 Hz tetanic stimulation followed by 1 Hz single twitches starting 3 seconds later (or a TO4 if you're lazy) allows one to assess the intensity of neuromuscular blockade if the initial TO4 is flat [Miller 6th ed, p 1554]. The weaker the block, the more subsequent twitches will be facilitated by tetany. Therefore, one would expect more post-tetanic facilitation given the affected limb's resistance to nondepolarizers.

Exactly.