Page 471 - Clinical Application of Mechanical Ventilation

Pharmacotherapy for Mechanical Ventilation 437

TABLE 13-10 Adverse Effects of Neuromuscular Blocking Agents

Histamine Cardiovascular
Agents Release Impairment Clinical Considerations

Depolarizing
Succinylcholine Moderate Moderate Caution with plasma cholinesterase
(Anectine, Quelicin) disorder

Nondepolarizing
Pancuronium bromide Minimal Moderate Steroidal-based
(Pavulon) Use corticosteroids with caution
Atracurium (Tracrium) Moderate Minimal Not affected by organ dysfunction

Vecuronium bromide Not likely Minimal Steroidal-based
(Norcuron) Use corticosteroids with caution

Rocuronium (Zemuron) Minimal Minimal Use corticosteroids with caution
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depleting oxygen, generating excessive carbon dioxide, spiking body temperature,
and causing circulatory collapse and death if not treated immediately. The fastest
way to detect MH is by monitoring with capnography (to detect rapid increase in
exhaled CO ) when administering succinylcholine and volatile anesthetics. The pre-
2
ferred treatment for MH is dantrolene sodium (Halsall et al., 2003).

Evaluation of Neuromuscular Blockade

To prevent unintentional overdosing, clinicians must establish an objective method of
monitoring the depth of paralysis. This is especially meaningful in the management of
patients with potential for drug accumulation secondary to renal or hepatic dysfunction.
A peripheral nerve stimulator is a valuable tool used to monitor the degree of neu-
romuscular blockade in patients who are pharmacologically paralyzed. It can measure
the degree of blockade by measuring the number of muscle twitches in response to four
sequential stimuli delivered over a two-second period. This is called a Train-of-Four
(ToF) stimulus. Two electrodes are placed along a nerve path where electrical stimuli
are delivered at a frequency of 2 Hz (four times in 0.5-sec intervals). As the degree of
blockade increases, the number of elicited responses (muscle twitches) decreases. The
ulnar, facial, and posterior tibial nerves are commonly used because they are superficial
and easy to locate. Figure 13-5 shows the electrode placement along the ulnar nerve.
Most recommendations for ToF monitoring suggest titration of neuromuscular
blocker to one or two twitches (. 80% to 90% muscular blockade) in 2 sec, which
is the current practice in using ToF monitoring. However, ToF of three twitches gen-
erally corresponds closely to 80% muscular blockade. This lighter level of muscular
blockade may be adequate to assure patient-ventilator synchrony and lower airway
pressures and to optimize oxygen delivery in most patients (Strange et al., 1997).

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