Both depolarizing and non-depolarizing agents can be used to facilitate tracheal intubation. Only non-depolarizing agents are used to maintain blockade during surgery or to facilitate mechanical ventilation on intensive care.
However, the two classes of NMBs produce neuromuscular blockade in different ways. Succinylcholine is the only available depolarizing muscle relaxant.
Table 1 summarizes the important clinical differences between these two classes.
Study the table and decide which of the two classes of NMBs is best for elective and which for emergency surgery, then select the links below:
|
|
Depolarizing |
Non-depolarizing |
|---|---|---|
|
Speed of onset |
fast |
slower |
|
Activation before block? |
yes, see twitching |
no |
|
Speed of offset |
fast |
slower |
|
May require reversal of blockade? |
no |
yes |
Table 1 Features of the two types of NMBs
Standard induction
This is indicated for routine cases requiring muscle paralysis when an induction agent is followed by a non-depolarizing agent.
The non-depolarizing neuromuscular agent should only be given once it has been confirmed that the airway can be maintained using simple mask ventilation.
If the patient then proves impossible to intubate after being paralyzed, simple mask ventilation may be used to keep the patient oxygenated and anaesthetized.
'Can't intubate' is not a disaster but 'can't intubate, can't ventilate' may well turn into one. Be sure you can mask-ventilate the patient prior to giving a non-depolarizing neuromuscular blocker.
Rapid Sequence Induction
This is indicated in situations where the patient is at risk of aspiration of gastric contents.
Preoxygenation is followed by an induction agent and then immediately by the depolarizing neuromuscular blocker succinylcholine, without checking for mask ventilation.
There are two reasons for this:
In RSI, the wear-off profile of succinylcholine is more important than its onset profile.