Neuromuscular blocking agents produce skeletal muscle paralysis by inhibiting the action of acetylcholine at the neuromuscular junction. Depolarizing agents (succinylcholine; Table III–10) depolarize the motor end plate and block recovery; transient muscle fasciculations occur with the initial depolarization. Nondepolarizing agents (atracurium, pancuronium, and others; see Table III–10) competitively block the action of acetylcholine at the motor end plate, preventing depolarization. Therefore, with nondepolarizing agents, no initial muscle fasciculations occur and a flaccid paralysis is produced.
The neuromuscular blockers produce complete muscle paralysis with no depression of CNS function (they are positively charged and water-soluble compounds that do not cross the brain-blood barrier rapidly). Thus, patients who are conscious will remain awake but be unable to move, and patients with status epilepticus may continue to have seizure activity despite paralysis. Furthermore, the neuromuscular blockers do not relieve pain or anxiety and have no sedative effects.
produces the most rapid onset of neuromuscular blockade. After intravenous administration, total paralysis ensues within 30–60 seconds and lasts 10–20 minutes. It is hydrolyzed rapidly by pseudocholinesterase, an enzyme present in the vascular compartment but not at the neuromuscular junction (NMJ). Therefore, a relatively small fraction of the administered dose reaches the site of action, and diffusion from the NMJ back into the intravascular space determines metabolism. Larger (1.5 mg/kg IV in adults) rather than smaller doses should be used for rapid-sequence intubation (RSI).
Rocuronium, a nondepolarizing agent, also has a rapid onset of effect. However, the duration of the blockade (22–94 minutes) is considerably longer than that of succinylcholine. Sugammadex, a specific and rapid reversal agent for rocuronium, has been approved for use in the United Kingdom, Sweden, Germany, and Finland, but at the time of this writing it has not been approved in the United States.
The onset and duration of several other neuromuscular blockers are described in Table III–10.
Table III-10 Selected Neuromuscular Blockers |Favorite Table|Download (.pdf)
Table III-10 Selected Neuromuscular Blockers
Dose (All Intravenous)
0.6 mg/kgb (children: 1 mg/kgc) over 10–20 seconds; repeat as needed.
0.4–0.5 mg/kg (children <2 years: 0.3–0.4 mg/kg).
0.15–0.2 mg/kg (children 2–12 years: 0.1 mg/kg), then 1–3 mcg/kg/min to maintain blockade.
0.05–0.08 mg/kg (children: 0.03–0.05 mg/kg), then 0.005–0.01 mg/kg every 30–45 minutes to maintain blockade (children may require more frequent dosing).
0.15–0.25 mg/kg (children: 0.2 mg/kg), then 0.1 mg/kg every 15 minutes or by continuous infusion; start with 0.01 mg/kg/min and maintain with average adult dose of 0.006–0.007 mg/kg/min (children: 0.014 mg/kg/min).
0.06–0.1 mg/kg; then 0.01–0.02 mg/kg every 20–40 minutes as needed to maintain blockade.
0.05–0.1 mg/kg (adjust for renal function); then 0.01–0.015 mg/kg every 17–175 minutes (children may be less sensitive and require more frequent dosing).
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