FRCA Notes

Perioperative Care for Patients with Neuromuscular Disorders

Resources

  • Neuromuscular diseases are a heterogenous group of conditions affecting neuromuscular transmission
  • They may be classified as either:
    • Congenital or acquired
    • Pre-junctional, post-junctional or affecting the neuromuscular junction itself

Charcot-Marie-Tooth

  • Chronic peripheral neuromuscular denervation
  • Muscle atrophy leading to limb and spinal deformities
  • Sensory disturbance occurs as well as muscle weakness
  • Restrictive lung defect may develop from spinal deformity

  • Particular anaesthetic conduct:
    • Avoid suxamethonium
    • Effects of non-depolarising NMBA may be prolonged

Friedrich's ataxia

  • Autosomal recessive ataxic syndrome
  • Skeletal muscle weakness and progressive limb ataxia
  • Frequently have myocardial degeneration, which leads to cardiac failure
  • The diaphragm is often impaired and can lead to respiratory failure

  • Particular anaesthetic conduct:
    • Avoid suxamethonium
    • Caution with negatively inotropic agents due to myocardial involvement

  • Muscular dystrophies - see separate page
  • Myotonias - diseases characterised by a tendency to myotonic contractures
    • Myotonic dystrophy - see separate page
    • Myotonia congenita
    • Familial hyperkalaemic periodic paralysis
    • Familial hypokalaemic periodic paralysis
  • Metabolic disorders
  • Mitochondrial disorders

Myotonia congenita

  • Autosomal dominant; 4/100,000
  • Due to reduced chloride conductance and increased excitability
  • Widespread muscle hypertrophy and therefore prolonged muscular contraction following stimulation
  • There isn't typically muscle weakness though they may get palatopharyngeal dysfunction which can lead to aspiration risk

  • Particular anaesthetic conduct:
    • Avoid factors that may precipitate myotonia inc. suxamethonium
    • Treat myotonia with sodium channel antagonists
    • Avoid anti-cholinergic drugs

Familial hyperkalaemic periodic paralysis

  • Autosomal dominant; 1/100,000
  • Dysfunctional sodium channel leads to hyperexcitability followed by a period of inactivity and weakness
  • Flaccid paralysis associated with increased K+ concentrations and precipitated by cold, hunger and stress
  • Respiratory muscles are usually spared

  • Particular anaesthetic conduct:
    • May need pre-operative potassium depletion with loop diuretics
    • Avoid drugs that can increase K+ concentrations inc. suxamethonium and potassium-containing fluids
    • Avoid hypothermia
    • Have calcium available to rapidly treat life-threatening hyperkalaemia
    • Minimise fasting time and infuse glucose-containing fluids whilst fasting
    • Volatiles and non-depolarising NMBA safe

Familial hypokalaemic periodic paralysis

  • Rare autosomal dominant condition characterised by DHP gene mutation and calcium channel dysfunction
  • Severe muscle weakness and asymmetrical paralysis associated with hypokalaemia
  • May be crossover with MH mutations that increase risk of hyperexcitable states in those with this condition

  • Particular anaesthetic conduct:
    • Avoid sux., and only use short-duration non-depolarising NMBAs
    • Can use volatile agents with caution
    • Avoid anxiety and peri-operative potassium shifts

Metabolic disorders

  • Muscle cramps, myoglobinuria and myalgia can occur due to interrupted muscle metabolic pathways

  • Particular anaesthetic conduct:
    • Aggressive metabolic monitoring
    • Adequate hydration ± forced diuresis to prevent myoglobinuria
    • Glucose ± amino acid infusion
    • Avoid hypothermia

Mitochondrial disorders

  • Myopathies due to primary mitochondrial dysfunction
  • Difficult to anaesthetise as most anaesthetic drugs depress mitochondrial function
  • May have swallowing difficulty and respiratory failure post-operatively

  • Particular anaesthetic conduct:
    • Require access to pacing equipment in theatre as total AV block can occur
    • Strict glucose monitoring and control
    • Avoid prolonged starvation, stress and lactate-containing solutions
    • Low dose volatile anaesthetic and ketamine
    • Avoid LA and propofol due to their mitochondrial-depressant effects

Pre-junctional

Junctional


Perioperative management of the patient with neuromuscular disease


History and examination

  • Thorough history ande examination;
    • Disease state and course
    • Coalescing comorbidities

  • Thorough assessment of respiratory function, with high incidence of respiratory complications in this population due to:
    • Difficult intubations
    • Disease involvement of pharyngeal and respiratory muscles
    • Progressive spinal deformities

  • Thorough assessment of cardiac function
    • Patient may not be aware of cardiac dysfunction as their disease limits their ability to stress their heart

Investigations

  • Bloods: FBC, U&E, LFT, clotting studies, G&S

  • Assess respiratory function
    • Pulmonary function tests
    • CXR
    • Baseline ABG
  • Assess cardiac function
    • ECG
    • TTE

Monitoring and access

  • AAGBI
  • ± Invasive arterial monitoring
  • Often close intra-operative glucose monitoring is necessary

Regional anaesthesia

  • Advantageous in those with significant cardiac or respiratory involvement
  • Avoid in those with rapidly progressive neurological disease in order to distinguish regional anaesthesia from disease progression
  • Sympathetic blockade can exacerbate autonomic dysfunction

General anaesthesia

  • TIVA is generally preferred to volatile anaesthesia in those with Duchenne's dystrophy due to risk of MH and rhabdomyolysis
  • Volatiles may exacerbate cardiac dysfunction due to vasodilatory and arrhythmogenic properties

NMBA

  • Suxamethonium
    • Proliferation of foetal type nAChR may lead to hyperkalaemia and rhabdomyolysis if sux. is used
    • Fasciculations may cause TMJ spasm and prevent ventilation
    • Can be used in myasthenia gravis although may require 2x dose due to relative resistance

  • Non-depolarising NMBA
    • Most patients with neuromuscular disease are relatively sensitive to non-depolarising NMBA
    • Use can lead to post-operative respiratory and GI (dysphagia) complications
    • Avoid use if possible, using alternative means to acheive intubation and a still patient e.g. remifentanil infusions, IV lidocaine
    • If used, use 10-20% of the normal dose and monitor depth of blockade
    • Atracurium (/mivacurium) may be preferable as it avoids the need for reversal agents, which may also contribute to myotonias

Thermoregulation

  • Patients may be vulnerable to both hypo- and hyper-thermia

  • Hypothermia
    • Due to low muscle activity + exacerbated by anaesthesia
    • Aim for patient to be normothermic before induction
    • Maintain temperature in usual fashion
    • Hypothermia can induce myotonia, increase sensitivity to NMBA, aggravate rhabdomyolysis and affect multiple organ physiology

  • Hyperthermia
    • May arise due to muscle contractions from myotonia, malignant hyperprexia or anaesthetic-related rhabdomyolysis, to which some patients are susceptible
    • High index of suspicion of MH

  • Plan for overnight stay; patients with neuromuscular disease are unsuitable for day case anaesthesia
  • Likely to require post-operative HDU due to availability of monitoring, rapid access to PPV if needed and ability to provide more robust analagesia
  • Other care e.g. anti-emesis, VTE prophylaxis as standard

Rhabdomyolysis

  • May be spontaneous due to myotonia, suxamethonium-induced, related to MH or from anaesthetic-related rhabdo.
  • Management is as standard for rhabdomyolysis

Autonomic dysfunction

  • May lead to severe hypotension after IV induction or regional anaesthesia
  • There may be increased sensitivity of ɑ- and β-adrenoreceptors and therefore cautious dosing of sympathomimetics

  • Gastric dysmotility increases risk of regurgitation/aspiration

Myotonias

  • Myotonic contractures can occur due to permanent sodium influx/chloride efflux, rendering the muscle membrane hyperexcitable
  • Induced by a number of anaesthesia-related events, such as:
    • Suxamethonium
    • Anticholinesterases i.e. neostigmine
    • Opioids
    • Hypothermia
    • Shivering
    • Acidosis

  • Management
    • Do not respond to peripheral nerve, regional nerve or neuromuscular blockade
    • Sodium channel antagonists (e.g. LA) or other anti-arrhythmic agents are drugs of choice

Cardiac complications

  • Presence of cardiomyopathy and conduction abnormalities can cause serious mortality in peri-operative period, exacerbated by catecholamine release
  • Appropriate pre-operative assessment and screening is necessary
  • Treat all patients as high risk with:
    • Low threshold for invasive monitoring
    • Consideration of HDU care post-operatively

Respiratory complications

  • Respiratory failure is the commonest cause of death in those with neuromuscular disease, due to:
    • Bulbar weakness → aspiration
    • Poor pharyngeal and respiratory muscle tone
    • OSA and progressive spinal deformity → restrictive lung defect

  • Investigate respiratory function appropriately pre-operatively
  • Extubate as soon as possible to avoid weakening of respiratory muscles