Muscle Relaxation (PICU)

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Prevent muscle shivering in control of hyperthermia during active cooling. 4. ... When intubating ensure ventilation is possible before muscle relaxation.
Paediatric Critical Care

Muscle Relaxation Important points: 1. Ensure adequate depth of anaesthesia before administering muscle relaxation and for duration of its action. 2. High risk intubations: e.g. potentially difficult intubation, upper airway obstruction or mediastinal mass, always plan for a “can’t intubate, can’t ventilate scenario” post administration of muscle relaxation.

Indications for muscle relaxation 1. Safe transfer of patient (inter / intra hospital) 2. Facilitate/ manipulate ventilation (e.g. bronchiolitis/ ARDS, CO2 control) 3. Prevent muscle shivering during active cooling 4. Post operative stability (e.g. LTR patients or high risk cardiac surgery)

Pancuronium

Rocuronium

Atracurium

Suxamethonium

Indication

Intubation and intermittent paralysis

Intubation and intermittent paralysis

Rapid sequence induction or acute intubation following loss of airway

Dose (IV)

0.1 mg/kg

1 mg/kg

Intubation and intermittent paralysis 0.5mg/kg 25% of dose

Use standard dose

Agent

Myasthenia gravis dose Onset of action

25% of dose

25% of dose

3-5 minutes

4-5minutes

30 -45 seconds

Duration of action

45-60 min

30 min

Metabolism

Hepatic to active metabolites

Hepatic

Excretion

50% urine, 10% bile

50% unchanged in bile and 20% urine

Prolonged action

Renal failure (use same dose). See drug list below*

Hepatic dysfunction (use same dose) See drug list below*

(intubation)

30 seconds

30-45mins

3-5 min

Ester hydrolysis and Hofmann elimination 10% excreted unchanged in urine Not confirmed even in hepatic or renal disease Isoflurane, aminoglycosides, lithium, magnesium salts prolong action

Carbamazepine & phenytoin reduce efficacy

Drug interactions

Histamine release causing flushing, bronchospasm and transient drop in blood pressure.

Side effect

Vagolytic (tachycardia does not contraindicate but avoid in tachyarrhythmia)

Anaphylaxis rare but possible

Malignant hyperthermia risk

Safe in malignant hyperthermia

Safe in malignant hyperthermia

Safe in malignant hyperthermia Known anaphylaxis. Caution in asthma or cardiovascular instability due to potential for histamine release

Contraindications

Tachyarrhythmia’s

Known anaphylaxis

Storage

Fridge drug 2-8 oC . Light sensitive.

Fridge drug. Keep at 2-8 oC Unopened vial stable at 25 oC for 1 month

2 mg/kg IV (always use with atropine)

Fridge drug. Keep at 2-8 oC. Unopened vial stable at 25 oC for 14 days

Hydrolysed by plasma cholinesterase 10% excreted unchanged in urine Plasma cholinesterase deficiency (genetic or acquired). Propofol (competes with enzyme) Cholinesterase inhibitors – organophosp. Digoxin potentiates arrhythmias. Precipitates thiopentone Bradycardia (muscarinic effect.) always use with atropine. Histamine release (avoid in asthma) Increases K (0.5 mmol/L). Anaphylaxis. Contraindicated. Malignant hyperthermia trigger Muscle injury (burns, rhabdomyolysis, trauma, denervation injury/cord transection) undiagnosed or central/minicore myopathy Fridge drug 2-8 oC Unopened vial stable at 25 oC for 24 hrs

To reverse non depolarising muscle relaxants (rocuronium, pancuronium) use Neostigmine 50mcg/kg AND Glycopyrolate 10mcg/kg. To reverse Rocuronium in children > 2 years: sugammadex 2mg/kg may be used. This will reverse neuromuscular blockade from rocuronium within 5-15 minutes. You must wait 24 hours before re-administering rocuronium. The action of Rocuronium/Pancuronium prolonged by ↓K, ↓Ca, ↑Mg, ↑Na, hypothermia, antibiotics (gent, vanc, clindamycin), antiarhythmics (lignocaine, verapamil).

Monitoring neuromuscular blockade 1. 2. 3. 4.

Avoid continuous infusions and use intermittent bolus if regular muscle relaxation required. This reduces the risk of critical care polyneuropathy. To asses the degree of neuromuscular block use Train of Four test (TOF) using a nerve stimulator. With ECG clips attached over the ulnar nerve at the wrist, press the TOF button (A). This sends 4 equal strength nerve stimuli in rapid succession and produces a repetitive full strength twitch of the stimulated muscle if no muscle relaxant is present. Absent twitch after TOF = full neuromuscular blockade.