What are the recommended muscle relaxants and their dosages for clinical use?

Recommended Muscle Relaxants and Dosing for Clinical Use

Primary Agents for Tracheal Intubation

For routine tracheal intubation, rocuronium 0.6 mg/kg IV is the recommended initial dose, providing intubation conditions within 1-2 minutes with approximately 31 minutes of clinical relaxation under opioid/nitrous oxide/oxygen anesthesia. 1

Rocuronium Dosing Algorithm

Standard Intubation:

• Initial dose: 0.6 mg/kg IV provides median onset of 1 minute (range 0.4-6 minutes), with most patients ready for intubation within 2 minutes 1
• Lower dose option: 0.45 mg/kg IV provides onset in 1.3 minutes, with 22 minutes of clinical relaxation 1
• Maintenance doses: 0.1-0.2 mg/kg administered at 25% recovery of control, providing 12-24 minutes of additional blockade 1

Rapid Sequence Intubation:

• Rocuronium 0.9-1.2 mg/kg IV provides excellent intubating conditions in less than 2 minutes, comparable to succinylchonium 2, 1
• While suxamethonium provides superior intubation conditions more frequently than rocuronium (RR = 0.86), when comparing suxamethonium 1.0 mg/kg with rocuronium >0.9 mg/kg, no superiority of suxamethonium was found 2
• Rocuronium is preferred over suxamethonium to avoid the numerous serious side effects associated with depolarizing agents 2

Continuous Infusion:

• Initial rate: 10-12 mcg/kg/min to counteract spontaneous recovery, then reduce to 5-9 mcg/kg/min for maintenance 1
• Initiate only after early evidence of spontaneous recovery from bolus dose 1
• Mandatory Train-of-Four (TOF) monitoring at the adductor pollicis muscle to guide dosing 3

Atracurium Dosing Algorithm

Standard Intubation:

• Initial dose: 0.4-0.5 mg/kg IV (1.7-2.2 times ED95) provides good/excellent intubation conditions in 2-2.5 minutes 4
• Maximum block achieved at 3-5 minutes, with clinical duration of 20-35 minutes under balanced anesthesia 4
• Maintenance doses: 0.08-0.1 mg/kg required at 20-45 minute intervals 4

Continuous Infusion:

• Initial rate: 9-10 mcg/kg/min to counteract spontaneous recovery, then 5-9 mcg/kg/min for maintenance 4
• Some patients may require rates as low as 2 mcg/kg/min or as high as 15 mcg/kg/min 4

Special Clinical Situations

Renal or Hepatic Failure

Atracurium or cisatracurium are the preferred agents in renal/hepatic failure due to organ-independent elimination (Hofmann reaction and ester hydrolysis). 2, 5

• No dose modification required for initial dosing of any muscle relaxant, including rocuronium, atracurium, or cisatracurium 2
• Atracurium's active metabolite laudanosine accumulates in renal failure but does not reach concentrations causing adverse effects even after 72-hour infusions 2
• Cisatracurium generates significantly lower amounts of laudanosine due to higher potency 2

Patients on Pyridostigmine

Reduce rocuronium maintenance doses by 50-75% in patients on chronic pyridostigmine therapy, with mandatory TOF monitoring. 3

• Initial dose should not be modified 3
• Pyridostigmine increases acetylcholine at the neuromuscular junction, directly antagonizing non-depolarizing relaxants 3
• Sugammadex is preferred over neostigmine for reversal in these patients 3

Obese Patients

Dose rocuronium based on actual body weight, not ideal body weight. 1

• Dosing by ideal body weight results in longer time to maximum block, shorter clinical duration (25 minutes), and inadequate intubating conditions 1

Pediatric Patients (≥2 years)

No dose adjustment required for rocuronium or atracurium in children ≥2 years old. 4, 1

• Rocuronium 0.6 mg/kg provides time to maximum block in approximately 1 minute across all age groups 1
• Recovery is shortest in children (36.7 minutes) and longest in infants (59.8 minutes) 1

Infants (1 month to 2 years):

• Atracurium 0.3-0.4 mg/kg under halothane anesthesia 4
• Maintenance doses required with slightly greater frequency than adults 4

Cardiovascular Disease

Reduce initial dose to 0.3-0.4 mg/kg of atracurium, given slowly or in divided doses over one minute. 4

• This applies to adults, children, or infants with significant cardiovascular disease 4
• Also recommended for patients with history of severe anaphylactoid reactions or asthma 4

Potentiation by Inhalational Anesthetics

Reduce rocuronium infusion rates by 30-50% in the presence of steady-state enflurane or isoflurane anesthesia. 1

• Halothane has only marginal (20%) potentiating effect, requiring smaller reductions 4
• For atracurium, reduce infusion rate by approximately one-third with enflurane or isoflurane 4
• Initial intubating dose of atracurium should be reduced to 0.25-0.35 mg/kg under steady-state isoflurane or enflurane 4

Critical Safety Considerations

Muscle relaxants are recommended to reduce pharyngeal and laryngeal injury during intubation (GRADE 1+). 2

• Use of muscle relaxants reduces pharyngeal/laryngeal injury rate from 18.7% to 9.7% 2
• Muscle relaxant-free intubation is an independent risk factor for difficult intubation 2

For supraglottic device insertion, routine muscle relaxant use is probably not recommended (GRADE 2). 2

• Success rates are commonly high without relaxants when adequate propofol and opioid doses are used 2
• Consider muscle relaxants only when hypnotic/opioid doses are low 2

Quantitative neuromuscular monitoring is mandatory when administering muscle relaxant infusions, continuing until TOF ratio ≥0.9. 3

• Failure to monitor can lead to residual blockade, occurring in approximately 28% of pediatric patients 3
• Peripheral nerve stimulator use minimizes overdosage and assists in evaluating recovery 1, 4