Therapeutic neuromuscular blockade is a routine part of intraoperative
anesthetic management for many surgeries and is occasionally appropriate
in the ICU in order to facilitate certain forms of mechanical ventilation,
prevent patient movements that may harm the patient, facilitate
procedures, decrease oxygen consumption, or prevent muscle spasm
in certain diseases. Therapeutic paralysis involves the administration
of neuromuscular blocking agents to interfere with the synaptic
transmission at the neuromuscular junction and thereby prevent or
decrease the force of muscle contractions. These drugs are administered
in boluses or by continuous infusion and their effects can be monitored
by patient observation or with peripheral nerve stimulators similar
to those used in the operating room.
- ▪ Neuromuscular blocking agent: A drug that interferes
with normal acetylcholine-mediated synaptic transmission (Figure
12-1) by blocking acetylcholine’s actions at the postsynaptic
receptors (Figure 12-2).
- ▪ Depolarizing neuromuscular blocking agents (ie, succinylcholine)
depolarize the neuromuscular junction causing initial release of
acetylcholine followed by paralysis, and are not typically used in
the ICU because of their very short duration and the potential for
potassium release on administration.
- ▪ Non–depolarizing muscle-blocking agents (NMBs)
interfere with the action of acetylcholine at the postsynaptic receptor
and are typically used for ICU administration.
- ▪ Train-of-four (TOF) monitoring is a technique by which
the effects of NMBs can be monitored objectively involving the administration
of a series of four successive electrical stimulations over a peripheral
nerve. The force of contraction of a muscle enervated by that nerve
is monitored (Figure 12-3) and monitoring can be performed at a
variety of locations (Figure 12-4).
Normal synaptic transmission, where acetylcholine (orange
circles) acts as the neurotransmitter from the nerve to the muscle.
Paralytic agents (green triangles) interfere with the
actions of acetylcholine in the junction.
The degree of paralysis is monitored by administering
a series of electrical impulses over a nerve and monitoring the
contraction of a muscle enervated by that nerve (ulnar nerve and
in this case).
Several common sites for monitoring in the ICU including
the wrist, the forehead, and the ankle.
- ▪ Clinical indications
- —Chemical paralysis is indicated to facilitate certain
nonphysiologic approaches to mechanical ventilation such as inverse-ratio
ventilation, airway pressure-release ventilation, or independent lung-ventilation
that may be indicated in diseases such as adult respiratory distress
syndrome (ARDS) or obstructive pulmonary diseases.
- —Paralysis may be indicated to prevent the
patient from muscle movements that may result in harmful consequences,
such as ...