Understanding Anesthesiology - The Global Regional Anesthesia ...

Contraindications
Opioids must not be given to those with a known allergy.
Intravenous opioids must not be given in settings
where one is not able to support ventilation.
Caution should be used when administering opioids to
patients with hypovolemic or cardiogenic shock, where
the blunting of sympathetic tone may exacerbate hypotension.
Non-Depolarizing Muscle Relaxants
The decision to use non-depolarizing muscle relaxants
during maintenance of anesthesia depends on both the
type of surgical procedure and the type of anesthetic.
Some procedures require muscle relaxation to facilitate
exposure (e.g. intra-abdominal surgery). In other cases,
muscle relaxation is required because patient movement
would be detrimental (e.g. neurosurgery, ophthalmic
surgery). In a balanced technique, the use of muscle
relaxants decreases the requirements of the other
agents and facilitates mechanical ventilation.
Historically, the choice of succinylcholine versus a nondepolarizing
muscle relaxant (NDMR) for use during
induction of anesthesia was a decision which balanced
the need for rapid airway control against the side effects
of succinylcholine. With the introduction of the
rapidly acting non-depolarizing agent, rocuronium, the
use of succinylcholine has steadily declined. In the rare
circumstance where succinylcholine is used to facilitate
intubation, a NDMR is given after the effects of succinylcholine
have worn off. However, in the vast majority
of cases NDMR is given at induction to provide relaxation
for both intubation and surgery.
Mechanism of action
In order to appreciate how NDMR cause muscular paralysis,
one must have a basic understanding of how
neuromuscular transmission occurs (Figure 20). Normally
a nerve impulse travels the length of the nerve to
arrive at the motor nerve terminal where it causes release
of acetylcholine (Ach) into the synaptic cleft. The
Ach then binds to post-synaptic nicotinic Ach receptors
causing a conformational change in those receptors.
This conformational change leads to a change in membrane
permeability of sodium and potassium causing
depolarization of the post-junctional membrane. The
propagation of this action potential leads directly to
muscular contraction. NDMR interfere with this process
by binding to the post-synaptic Ach receptors
thereby acting as a competitive inhibitor to Ach.
Dose, onset, duration, elimination and effects
The choice of which muscle relaxant to use is influenced
by the speed of onset, duration of action, method
of elimination and side effect profile of the various
agents. Except in the case of very brief procedures,
NDMR are used for relaxation during maintenance of
anesthesia. Commonly-used NDMR are rocuronium
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