Stage 2 block (Phase II block) is seen with:
Ref: Miller Textbook of Anaesthesia. 6th edition.Explanation:Succinyl Choline - Mechanism of action1. Phase 1 block (depolarizing)Succinylcholine is the only clinically useful depolarizing blocking drug.Its neuromuscular effects are like those of acetylcholine except that succinylcholine produces a longer effect at the myoneural junction.Succinylcholine reacts with the nicotinic receptor to open the channel and cause depolarization of the motor end plate, and this in turn spreads to the adjacent membranes, causing contractions of muscle motor units.Because succinylcholine is not metabolized effectively at the synapse, the depolarized membranes remain depolarized and unresponsive to subsequent impulses (ie, in a state of depolarizing block).Furthermore, because excitation-contraction coupling requires end plate repolarization ("reprintmg") and repetitive firing to maintain muscle tension, a flaccid paralysis results.This so-called phase 1 (depolarizing) block is thus augmented, not reversed, by cholinesterase inhibitors.2. Phase II block (desensitizing)With continued exposure to succinylcholine, the initial end plate depolarization decreases and the membrane becomes repolarized.Despite this re polarization, the membrane cannot easily be depolarized again because it is desensitized.The mechanism for this desensitizing phase is unclear, but some evidence indicates that channel block may become more important than agonist action at the receptor in phase II of succinylcholine' s neuromuscular blocking action.Later in phase II. the characteristics of the blockade are nearly identical to those of a nondepolarizing block (ie, a nonsustained twitch response to a tetanic stimulus), with reversal by acetylcholinesterase inhibitors.
Suxamethonium
Isoflurane
Sevoflurane
Enflurane
Depolarising Neuromuscular Blocking Agents