What are the guidelines for using neuromuscular blocking agents (NMBA) with a laryngeal mask airway (LMA)?

Use of Neuromuscular Blocking Agents with LMA

Routine use of neuromuscular blocking agents (NMBA) for LMA insertion is not recommended, as LMA placement typically succeeds without paralysis and NMBA use may increase pharyngolaryngeal complications. 1

Primary Recommendation for Elective LMA Insertion

Do not routinely administer neuromuscular blocking agents for standard LMA insertion. 1 The evidence demonstrates:

• LMA insertion success rates are commonly high without muscle relaxants, with satisfactory ventilation conditions achieved in most patients 1
• Neuromuscular blockade increases postoperative pharyngolaryngeal discomfort (30.0% vs 13.8% without NMBA) and traumatic insertion events (32.5% vs 16.3% without NMBA) 2
• The LMA can be inserted without laryngoscopy or neuromuscular blockade 3, 4

When NMBA May Be Considered for LMA Insertion

Consider neuromuscular blockade only in specific circumstances:

• When using low-dose hypnotic and opioid induction protocols that provide inadequate jaw relaxation 1
• When propofol is not used as the induction agent, as non-propofol protocols have higher rates of adverse insertion events that decrease with neuromuscular blockade 1
• In patients with severe muscular dystrophy where controlled respiratory support is critical 5

The overall evidence quality remains low due to heterogeneity in anesthesia protocols, but the consistent finding across studies is that NMBA offers no advantage for routine LMA insertion 1.

Critical Indication: Airway Obstruction with LMA

Administer a neuromuscular blocking agent immediately when airway obstruction occurs with an LMA in place. 1 This represents a distinct clinical scenario:

• Glottic closure (incomplete/reversible obstruction): Deepen anesthesia first, then consider NMBA if obstruction persists 1
• Laryngospasm (complete glottic closure): Muscle relaxation is highly recommended, though propofol 0.25-0.8 mg/kg is effective in 77% of cases 1
• Suxamethonium is the preferred agent for laryngospasm as it is effective in all cases 1

Emergency Airway Management Context

In difficult airway scenarios, the LMA serves as a rescue device:

• Supraglottic airways are recommended when unanticipated difficult intubation and ventilation occur, to ensure oxygenation 1
• If NMBA was used and airway difficulties arise, antagonize muscle relaxation as part of the cannot-intubate-cannot-oxygenate (CICO) algorithm 1
• The LMA provides better oxygenation than face mask but does not protect against aspiration 3, 4

Practical Algorithm for NMBA Decision-Making

For elective cases:

1. Induce with adequate propofol dose (typically 2-3 mg/kg) and opioid
2. Insert LMA without NMBA
3. If insertion fails after 2-3 attempts, consider deeper anesthesia before adding NMBA 1

For airway obstruction:

1. Identify type: incomplete (glottic closure) vs complete (laryngospasm)
2. For incomplete: deepen anesthesia, jaw thrust, reposition LMA
3. For laryngospasm: propofol bolus 0.25-0.8 mg/kg first, then suxamethonium if refractory 1

Important Caveats

• Airway seal pressure may decrease in approximately 11% of patients after NMBA administration due to neck muscle relaxation, requiring verification of adequate seal under paralysis if NMBA is used intraoperatively 6
• The LMA does not protect against aspiration and should not be used in patients at risk for regurgitation 3, 4
• Proper patient screening is essential before choosing LMA over endotracheal intubation 3