Ace the Anesthesia Knowledge Test 1 (AKT-1) 2025 – Dive Into Dreamy Success!

Succinylcholine is a depolarizing neuromuscular blocker that produces its effects by mimicking acetylcholine at the neuromuscular junction, leading to sustained depolarization of the motor end plate. When assessing the effect of succinylcholine during train-of-four (TOF) stimulation, the distinction between Phase I and Phase II blocks is crucial.

During a Phase I block, which is associated with succinylcholine's initial action, there is a characteristic response on TOF stimulation. In this phase, the continuous stimulation leads to depolarization that results in muscle fasciculations, but over time, as the receptor becomes desensitized—despite being depolarized—the response diminishes. This absence of response to subsequent nerve stimulation is what is referred to as a "fade."

On the other hand, a Phase II block occurs after prolonged exposure to succinylcholine, where the neuromuscular junction behaves more like it would with non-depolarizing agents. In this Phase II block, although there is an initial response upon the first stimulus, subsequent responses do not return as the neuromuscular junction becomes desensitized, but there is no fade observed in the TOF response. This