11 Neurological and muscular disorders

Cerebrovascular disease 244

Parkinson's disease 246

Anaesthesia in spinal cord lesions 250

Myasthenia gravis 256

Multiple sclerosis 262

Guillain–Barré syndrome 264

Motor neuron disease (amyotrophic lateral sclerosis)  265

Dystrophia myotonica 266

Muscular dystrophy 268

Jane Halsall

Malignant hyperthermia 270

Make provision for therapy if oral antiepileptic medication cannot be given.

Full drug history, including timing of antiepileptic therapy should be noted.

The effect of the condition on lifestyle and the eligibility to hold a driver's licence should be noted.

Sedative premedication, if necessary, may be achieved with benzodiazepines. Long-acting drugs such as diazepam (10mg PO) or lorazepam (2–4mg PO) are useful.

Maintain antiepileptic therapy up to the time of surgery.

All currently used anaesthetic agents are anticonvulsant in conventional doses. Thiopental is powerfully anticonvulsant and may be a preferred induction agent in the poorly controlled epileptic.

Muscle relaxation is best achieved by drugs without a steroid nucleus (e.g. atracurium, cisatracurium) since enzyme induction by all commonly used anticonvulsant drugs (especially phenytoin, carbamazepine, and the barbiturates) will lead to rapid metabolism of vecuronium and rocuronium.

Avoid hyperventilation and consequent hypocarbia since this will lower seizure threshold.

Regional anaesthesia may assist in preservation of, or early return to, oral intake. Be aware of maximum local anaesthetic doses.

Use antiemetic agents unlikely to produce dystonias (e.g. cyclizine 50mg IV/IM, domperidone 30–60mg PR, ondansetron 4mg IV).

Record any epileptiform activity in the perioperative period carefully. The misdiagnosis of postoperative shivering/dystonic movements on induction as epilepsy may have profound implications.

Day case anaesthesia is suitable for those with well-controlled epilepsy (seizure free for 1yr or nocturnal seizures only). Patients should be warned of the potential for perioperative convulsions.

Epileptic patients may be prone to seizures during the rapid emergence from propofol anaesthesia.

Profound suppression of abnormal EEG activity is usually noted during propofol infusion.

Propofol has also been reported to be effective in status epilepticus in ICU.

They are thought to be related to embolism of platelet and fibrin aggregates released from areas of atherosclerotic plaque. The risk of stroke in untreated patients is said to be ∼5% per annum with a mortality of ∼30% per episode.

Patients with a history of TIA should be investigated and assessed by a specialist vascular service if practical. Doppler flow studies, with or without angiography, are indicated in all cases of recurrent TIA or those that have occurred despite aspirin therapy.

Delay of all but urgent or emergency surgery is warranted until Doppler studies are performed. At present only those with a history of TIA with good recovery and a surgically accessible lesion of either >80% stenosis or ‘ragged’ plaque are routinely referred for carotid surgery. Crescendo TIA is considered by some as an indication for urgent carotid surgery.

Hemiplegia of <6–9 months’ duration is associated with exaggerated hyperkalaemic response to suxamethonium.

Take a full drug history—continue antihypertensive drugs until operation.

Warfarin should be discontinued and substituted with heparin (unfractionated or LMWH as per local protocol) if necessary.

Aspirin is discontinued only if the consequences of haemorrhage are significant (e.g. tonsillectomy, neurosurgery) (see pp. 222–225).

Document the nature of any ischaemic events and any residual neurological deficit. These may range from transient blindness (amaurosis fugax) to dense hemiplegia. This will help in differentiating new lesions arising in the perioperative period that may require urgent therapy.

Ask about precipitating events. Vertebrobasilar insufficiency is most likely to be precipitated by postural changes and neck positioning.

Thromboprophylaxis is advisable unless contraindicated (e.g. low-dose LMWH).

Ensure that pressor and depressor agents are available prior to induction. Use agents with which you are familiar. Maintain blood pressure as close as practical to preoperative levels to maintain cerebral blood flow. Useful pressors are ephedrine/metaraminol; useful depressors are opiods/labetalol/esmolol/GTN.

Blood pressure may ‘swing’ excessively during surgery due to the interactions of anaesthesia, antihypertensives, and the surgical stimulation on a relatively rigid vascular system. IV fluid replacement should be proactive rather than reactive, with large-bore IV access and invasive central pressure monitoring if large fluid shifts are expected.

Ensure that neck positioning is neutral and avoids movements associated with syncope.

Induction of anaesthesia may result in dangerous hypotension followed by extreme hypertension on intubation. Careful IV induction is indicated. Cover for intubation may be provided by opioids (e.g. alfentanil 500–1000µg or fentanyl 150–250µg).

Avoid hyperventilation. Hypocarbia is associated with reduced cerebral blood flow and therefore cerebral ischaemia. The combination of hypotension and hypocarbia must be avoided.

Examine the patient early in the postoperative period to determine any change in neurological status. New neurological signs will require urgent referral to a neurologist/vascular surgeon and urgent treatment if possible.

Parkinsonism is due to an imbalance of the mutually antagonistic dopaminergic and cholinergic systems of the basal ganglia. Pigmented cells in the substantia nigra are lost, leading to reduced dopaminergic activity. There is no reduction in cholinergic activity.

Drug therapy of parkinsonism is aimed at restoring this balance by either increasing dopamine or dopamine-like activity or reducing cholinergic activity within the brain.

Drug therapy in parkinsonism is limited by severe side effects (nausea and confusion), especially in the elderly. Up to 20% of patients will remain unresponsive to drug therapy.

Monoamine oxidase B (MAO-B) inhibitors (e.g. selegiline) act by reducing central breakdown of dopamine. Selegiline has fewer drug interactions than the non-specific MAO inhibitors, but may cause a hypertensive response to pethidine and dangerous CNS excitability with SSRI and tricyclic antidepressants (see p. 284).

Ergot derivatives such as bromocriptine, cabergoline, lisuride, and pergolide act by direct stimulation of dopamine receptors. They are usually reserved for adjuvant therapy in those already on l-dopa or those intolerant of the side effects of l-dopa.

Entacapone is an adjuvant agent capable of reducing the dose of l-dopa and increasing the duration of its effect. It is usually reserved for those experiencing ‘end of dose’ deterioration after long-term dopaminergic therapy.

Other adjuvant dopaminergic agents are ropinirole, pramipexole, amantadine, apomorphine, and tolcapone.

There are no parenteral dopaminergic agents currently available for use in parkinsonism.

These agents are indicated as first-line therapy only when symptoms are mild and tremor predominates. Rigidity and sialorrhoea may be improved by these agents but bradykinesia will not be affected.

This class of drug is useful for drug-induced parkinsonism but not in tardive dyskinesia.

Parenteral formulations exist for procyclidine and benzatropine, making these useful for acute drug-induced dystonias.

Pallidotomy is primarily for those with rigidity and bradykinesia, although the tremor (if present) may also be reduced.

Deep brain stimulation using implantable devices is becoming more commonplace. There is no literature at present relating to incidental anaesthesia in patients with these devices, but it would seem prudent to contact the manufacturer or team responsible for insertion of the device before using diathermy. If diathermy is necessary, bipolar should be used, as far as practical from the device or lead. Device function should be checked after surgery.

Postural hypotension may be evidence of both dysautonomia and drug-induced hypovolaemia and should warn of possible hypotension on induction or position changes during surgery.

Drug-induced arrhythmias, especially ventricular premature beats, are common, although they are usually not clinically significant.

Respiratory function may be compromised by bradykinesia and muscle rigidity as well as by sputum retention. Chest radiograph, lung function tests, and blood gases may be indicated.

Difficulty in voiding may necessitate urinary catheterisation. Postoperative urinary retention may be a potent cause of postoperative confusion.

The severity of the underlying disease should be determined and other likely problems anticipated, e.g. akinesia, muscle rigidity, tremor, confusion, depression, hallucinations, and speech impairment.

Premedication is usually unnecessary unless distressing sialorrhoea is present. Consider glycopyrronium (200–400µg IM) as an antisialogogue.

The presence of preoperative sialorrhoea or dysphagia is a sign of gastrointestinal dysfunction. Airway control with intubation by rapid sequence induction may be indicated.

Maintain normothermia to avoid shivering.

There is no evidence that any anaesthetic technique is superior to any other.

Analgesia: IV morphine is useful if regional or local analgesia is not possible (PCA may prove difficult for the patient). Oral analgesia may be difficult to administer with coexisting dysphagia (a nasogastric tube may be necessary).

Postoperative physiotherapy should be arranged if rigidity is disabling.

Nasogastric tube insertion may be needed if GI dysfunction is present to allow early return of oral medication.

Prolonged GI dysfunction postoperatively may lead to severe disability since no parenteral dopaminergic therapy is currently available.

Serotonin antagonists, e.g. ondansetron 4mg IV and granisetron 1mg IV slowly, may be useful rescue agents in PONV if domperidone alone is ineffective.

Antihistamine derivatives (e.g. cyclizine 50mg IV/IM).

Spinal shock follows rapidly and is characterised by hypotension and bradycardia due to loss of sympathetic tone. It is most common after high cord lesions (above T₇). There is associated loss of muscle tone and reflexes below the level of the lesion. Vagal parasympathetic tone continues unopposed, causing profound bradycardia or asystole—especially on tracheal suction/intubation. This phase may last from 3d to 8wk. Paralytic ileus is common.

Reflex phase: as neuronal ‘rewiring’ occurs, efferent sympathetic discharge returns, along with muscle tone and reflexes.

Obstetric: labour, cervical dilation, etc.

Bowel obstruction/faecal impaction

Acute abdomen

Fractures

Rarely, minor trauma to skin, cutaneous infection (bedsores).

If no apparent cause, examine carefully for unrevealed trauma or infection, catheterise, and check for faecal impaction.

If simple measures fail, consider:

Abnormal response to the Valsalva manoeuvre with continued drop in blood pressure (no plateau) and no overshoot with release.

Profound postural hypotension with gradual improvement after initial injury (never to normal). Changes in cerebral autoregulation reduce its effect on CBF and consciousness in the non-anaesthetised patient.

Lesions above C3—apnoea.

Lesions at C3/4/5—possible diaphragmatic sparing, some respiratory capacity. Initial lesions may progress in height with shock and oedema, with recovery as the oedema improves, leading to a marked improvement in respiratory capacity.

Below C5—phrenic sparing, intercostal paralysis. Recruitment of accessory muscles is necessary to improve respiratory capacity (this may take up to 6 months).

Paralysis of abdominal muscles severely affects the ability to force expiration, reducing the ability to cough.

The FVC is better in the horizontal or slight head-down position due to increased diaphragmatic excursion.

Bronchial hypersecretion may occur.

Poor thermoregulation due to isolation of central regulatory centres from information pathways, inability to use muscle to generate heat, and altered peripheral blood flow.

Muscle spasms and spasticity occur due to intact reflexes below the level of the lesion. They can be caused by minor stimuli. Baclofen and diazepam may be used, the former increasingly via epidural infusion.

Reduced bone density leading to increased risk of fractures. There is heterotopic calcification around the joints in up to 20% of patients.

Poor peripheral perfusion—pressure sores and difficult venous access.

Anaemia, usually mild.

Tendency to thrombosis and pulmonary embolism. Some centres warfarinise tetraplegics 5d after initial presentation.

There is delayed gastric emptying in tetraplegics (up to 5 times longer).

Recommendations vary as to the period of potential risk. Practically—avoid suxamethonium from 72hr following the initial injury. There are no reports of clinically significant hyperkalaemia with suxamethonium after 9 months.

Extreme care should be taken if cervical spine injury is suspected.

Preload with fluid (500–1000ml crystalloid) to reduce hypotension.

Central line insertion may be necessary to manage fluid balance and guide appropriate inotrope therapy.

If complete, is the proposed surgery below the sensory level? (Is anaesthesia necessary?)

Has there been spinal instrumentation? (Potential problems with spinal/epidural anaesthesia.)

Is the cervical spine stable/fused/instrumented? (Potential intubation difficulty.)

Is postural hypotension present? (Likely to be worsened by anaesthesia.)

Is there a history of autonomic dysreflexia (paroxysmal sweating and/or headache) and, if so, what precipitated it?

In cervical lesions, what degree of respiratory support is necessary?

Are there contractures, or pressure sores?

U&Es—renal impairment

Liver function tests—possible impairment with chronic sepsis

Pulmonary function tests (FVC)—mandatory with all cervical lesions due to potential respiratory failure.

Minor peripheral surgery below a complete sensory level is likely to be safe without anaesthesia.

Even with minor peripheral surgery, minimal stimulation may provoke muscular spasm that may require anaesthesia to resolve. Local anaesthetic infiltration may prevent its occurrence.

Care should be taken with high lesions (T₅ and above) or patients with a history of autonomic dysreflexia undergoing urological procedures.

If the decision is made to proceed without anaesthesia, IV access is mandatory and ECG, NIBP, and pulse oximeter should be applied.

An anaesthetist should be present on ‘standby’ for such procedures.

Despite the theoretical risk of gastro-oesophageal reflux there appears to be no increased risk of aspiration. If intubation is necessary for the desired procedure, anticholinergic pre-treatment is recommended.

Those with cervical cord lesions are likely to require assistance with ventilation under general anaesthesia. If IPPV is performed in tetraplegics, blood pressure may drop precipitously. Fluid preloading and vasopressors (e.g. ephedrine) may be required.

With the exception of paralysis to facilitate intubation, neuromuscular blockade is unlikely to be necessary unless troublesome muscular spasm is present.

Care should be taken to preserve body temperature (wrapping or forced-air warming blankets). Position with respect to pressure areas.

Fluid management may be difficult as blood volume is usually low, and with high cord lesions reflex compensation for blood loss is absent. Fluid preloading coupled with aggressive replacement of blood losses with warmed fluid is recommended.

Unlikely to cause cardiovascular instability since sympathetic tone is already low prior to blockade.

No reported adverse effect of spinal injection of local anaesthetics or opioids on neurological outcome.

Avoids risks of general anaesthesia.

Spinal anaesthesia is more common than epidural anaesthesia as it is technically easier and more reliable in preventing autonomic dysreflexia. Use standard doses of local anaesthetic agents (bupivacaine ‘heavy’ or plain). Intrathecal opioids appear to confer no advantage.

There is difficulty in determining the success or level of blockade in complete lesions. Incomplete lesions are tested as usual.

Temperature should be monitored and hypothermia actively treated.

Analgesia should be provided by conventional means.

Dysreflexia may occur and require drug treatment after removal of precipitating causes (such as pain and urinary retention).

Reduced respiratory reserve with increased risk of respiratory failure and pneumonia. Increased oxygen demand.

Increased anaemia due to haemodilution.

Labour is a potent cause of autonomic dysreflexia in those with lesions above T₅ (dysreflexia may be the first sign of labour in such patients).

Increased risk of premature labour (increasing risk with higher level injury).

Increased risk of thromboembolic complications.

Labour pains will not be felt in complete lesions above T5. Lesion between T₅ and T₁₀—some awareness of some contractions.

Epidural analgesia is usually possible in those with high cord lesions without vertebral instrumentation at the level of catheter insertion.

Spinal anaesthesia is usually possible for elective Caesarean section and may be achievable with both single-shot and microcatheter techniques, irrespective of the presence of spinal instrumentation.

General anaesthesia may proceed with the precautions outlined above.

Hypotension is not usually a problem after adequate fluid preloading (at least 1 litre of crystalloid or colloid). However, hypotension from any cause should be treated aggressively in those with high lesions due to the lack of compensatory mechanisms and a tendency to progressive hypotension. Aortocaval compression should be avoided by careful positioning for the same reasons.

Autonomic dysreflexia has been reported up to 48hr after delivery. If successful block is achieved it would appear prudent to leave the epidural in situ for this time.

Failure to establish adequate epidural blockade may necessitate drug treatment of autonomic dysreflexia (see above).

Management is usually with oral anticholinesterase medication with or without steroid therapy.

Severe disease may require immunosuppressant therapy, plasmapheresis, or immunoglobulin infusion.

Plasmapheresis depletes plasma esterase levels, prolonging the effect of suxamethonium, mivacurium, ester-linked local anaesthetics, and remifentanil.

Suxamethonium may have an altered effect—patients may be resistant to depolarisation due to reduced receptor activity, requiring increased dose. This, in conjunction with treatment-induced plasma esterase deficiency, leads to an increased risk of non-depolarising (Phase II) block.

Any degree of bulbar palsy is predictive of the need for both intra- and postoperative airway protection.

Those who have significant respiratory impairment are more likely to require postoperative ventilation.

Take a full drug history and determine the effect of a missed dose of anticholinesterase. Those with severe disease may be very sensitive to dose omission.

Premedication should be minimal.

Avoid use of neuromuscular blocking drugs if possible. Intubation/ ventilation is often achievable using non-paralysing techniques.

Non-depolarising drugs should be used sparingly. Monitor the response with a nerve stimulator. Initial doses of ∼10–20% of normal are usually adequate.

Consider topical LA to the airway.

Short- and intermediate-duration non-depolarising drugs such as atracurium, mivacurium, vecuronium and rocuronium are preferable to longer-acting drugs.

Reversal of neuromuscular blocking drugs should be achievable with standard doses of neostigmine if preoperative symptom control has been good (see below). Avoidance of reversal is preferred since further doses of anticholinesterase may introduce the risk of overdose (cholinergic crisis). Drugs with spontaneous reversal such as atracurium are optimal.

Reversal of neuromuscular blockade using new agents such as sugammadex has been suggested as complete reversal of any drug-induced blockade by rocuronium or vecuronium may be achieved without the need for neostigmine. It may also reduce the confusion between postoperative weakness due to disease and neuromuscular blockade.

Consider insertion of a nasogastric tube if difficulty with bulbar function is anticipated and early return of oral therapy required.

Extubation is possible if neuromuscular function is assessed as adequate using nerve stimulation. Beware of preoperative bulbar function abnormality. The best predictor of safe extubation is >5s head lift.

Regional anaesthesia may reduce the need for postoperative opioids and the risks of respiratory depression.

Facilities for postoperative ventilation should be available.

If doubt exists as to the ease of intubation, consider awake techniques.

If suxamethonium is used, do not use any other neuromuscular blockade until muscle function has returned and no fade is present.

In the event of gastrointestinal failure, parenteral therapy is indicated.

Duration of disease >6yr.

A history of coexisting chronic respiratory disease.

Dose requirements of pyridostigmine >750mg/d.

A preoperative vital capacity of <2.9l.

The best monitors of postoperative respiratory capacity are:

Repeated peak flow measurements.

Vital capacity should be at least twice tidal volume to allow for cough.

Best results are achieved in those with normal or hyperplastic thymus.

The approach most commonly used is trans-sternal. Transcervical approaches provide less satisfactory access for surgery.

Thoracoscopic thymectomy is gaining acceptance, although its reputed benefit of reduced complications and need for postoperative ventilation is yet to be proven.

Anaesthetic management follows the same general principles outlined above, although all patients need postoperative care in HDU or require ventilation for a short period in the early postoperative period.

Fewer than 8% of patients requiring sternotomy for thymectomy need ventilation for >3hr postoperatively.

Almost all patients will require a degree of muscle relaxation if preoperative preparation has been optimal. Postoperative analgesia can be achieved satisfactorily with epidural or PCA.

It is not reversed by anticholinesterase therapy and muscle weakness is improved by exercise.

Associated dysautonomia may manifest as dry mouth, impaired accommodation, urinary hesitance, and constipation.

Unlike myasthenia gravis, patients with myasthenic syndrome are sensitive to both depolarising and non-depolarising neuromuscular blocking drugs.

Reduced doses should be used if the disease is suspected. Maintain a high index of suspicion in those undergoing procedures related to diagnosis and management of carcinoma of the lung.

Respiratory failure due to both respiratory muscle failure and bulbar palsy may be a feature in end-stage disease.

Symptoms are characterised by symptomatic episodes of variable severity with periods of remission for several years.

Permanent weakness and symptoms develop in some patients, leading to increasingly severe disability.

Demyelinated nerve fibres are sensitive to heat. A temperature rise of 0.5°C may cause a marked deterioration in symptoms.

Respiratory function may be affected. Bulbar palsy causes increased risk of aspiration and reduced airway reflexes in the postoperative period.

Regional anaesthesia does not affect neurological symptoms, but it may be medicolegally prudent to document discussion of relative risks before embarking on nerve or plexus blockade.

Centroneuraxial blockade has been associated with recurrence of symptoms. However, this is reduced by use of minimal concentrations of local anaesthetic/opioid in combination.

Epidural analgesia for labour is not contraindicated—keep LA concentration to a minimum. There is widespread use of spinal anaesthesia for Caesarean section in patients with multiple sclerosis in the UK.

Suxamethonium is associated with a large efflux of potassium in debilitated patients and should be avoided.

Response to non-depolarising drugs is normal, although caution and reduced dosages are indicated in those with severe disability.

Careful cardiovascular monitoring is essential since autonomic instability leads to marked hypotensive responses to drugs and sensitivity to hypovolaemia.

Temperature is important and should be monitored in all patients. Pyrexia must be avoided and should be treated aggressively with antipyretics (paracetamol 1g PR/PO), tepid sponging, and forced-air blowers. Hypothermia may delay recovery from anaesthesia.

The more rapid the onset of symptoms, the more likely the progression to respiratory failure. Impending respiratory failure may be evidenced by difficulty in swallowing and phonation due to pharyngeal muscle weakness.

Inability to cough is a marker of severe respiratory impairment and usually indicates the need for intubation and ventilation.

Autonomic dysfunction is common.

Autonomic dysfunction leads to potential severe hypotension during induction of anaesthesia, initiation of positive pressure ventilation, and postural changes under anaesthesia or recovery.

Hydration should be maintained with wide-bore IV access and pressor agents (ephedrine 3–6mg bolus IV) prepared prior to induction.

Tachycardia due to surgical stimulus may be extreme and atropine may elicit a paradoxical bradycardia.

Suxamethonium should be avoided due to potential catastrophic potassium efflux. The risk of hyperkalaemia may persist for several months after clinical recovery.

Non-depolarising muscle relaxants may not be needed and should be used cautiously.

Epidural analgesia is useful and may avoid the need for systemic opioid analgesia. Epidural opioids have been used to manage distressing paraesthesia in these patients.

Patients remain mentally competent up to the point of terminal respiratory failure, leading to ethical and moral difficulty in the provision of long-term ventilation.

Respiratory support is likely to be necessary, both during surgery and in the postoperative period.

Autonomic dysfunction leads to potentially severe hypotension during induction of anaesthesia, initiation of positive pressure ventilation, and postural changes under anaesthesia or recovery.

Hydration should be maintained with wide-bore IV access if necessary and pressor agents (ephedrine/metaraminol) prepared prior to induction.

Suxamethonium should be avoided due to potential catastrophic potassium efflux.

Non-depolarising agents should be used in reduced dosage if necessary and their action monitored with a nerve stimulator.

The main clinical features are related to muscular atrophy, especially of facial, sternomastoid, and peripheral muscles.

Progressive deterioration/atrophy of skeletal, cardiac, and smooth muscle over time leads to a deterioration in cardiorespiratory function and a (possibly severe) cardiomyopathy.

Further respiratory deterioration occurs due to degeneration of the central nervous system, leading to central respiratory drive depression.

Progressive bulbar palsy causes difficulty in swallowing/clearing secretions and an increased risk of aspiration.

Degeneration of the cardiac conduction system causes dysrhythmia and atrioventricular block.

Mitral valve prolapse occurs in ∼20% of patients.

There is mental deterioration after the second decade.

Endocrine dysfunction may lead to diabetes mellitus, hypothyroidism, adrenal insufficiency, and gonadal atrophy.

Death usually occurs in the fifth or sixth decade.

Pregnancy may aggravate the disease and Caesarean section is more common due to uterine muscle dysfunction.

Therapy is supportive using antimyotonic medications such as procainamide, phenytoin, quinine, and mexiletine.

Seek signs of cardiac failure and dysrhythmia.

Gastric emptying may be delayed. Premedication with an antacid (ranitidine 150–300mg PO) or a prokinetic (metoclopramide 10mg PO) may be indicated.

ECG to exclude conduction defects and echocardiography for myocardial dysfunction.

U&Es and glucose to exclude endocrine dysfunction.

Non-depolarising drugs are safe to use but do not always cause muscle relaxation. Use of a nerve stimulator may provoke muscle contraction, leading to misdiagnosis of tetany.

Reversal with neostigmine may also provoke contraction. Non-depolarising agents with short action and spontaneous reversal (atracurium, mivacurium) are preferred.

Reversal of rocuronium and vecuronium is possible without the use of neostigmine using sugammadex.

Intubation and maintenance of anaesthesia can often be achieved without the use of any muscle relaxant.

Invasive arterial monitoring is indicated for significant cardiovascular impairment.

Even small doses of induction agents can produce profound cardio-respiratory depression.

Bulbar palsy increases the need for intubation under general anaesthesia.

Regional anaesthesia does not prevent muscle contraction. Troublesome spasm may be helped by infiltration of local anaesthetic directly into the affected muscle. Quinine (600mg IV) and phenytoin (3–5mg/kg IV slowly) have been effective in some cases.

High concentrations of inhaled anaesthetics should be avoided because of their effect on myocardial contraction and conduction.

Patient warmth must be maintained. Postoperative shivering may provoke myotonia.

Analgesia is best provided, if possible, by regional or local block to avoid the systemic depressant effects of opioids.

Autosomal recessive: limb-girdle, childhood, congenital

Autosomal dominant: facioscapulohumeral, oculopharyngeal.

Onset of symptoms of muscle weakness at 2–5yr.

The patient is usually confined to a wheelchair by 12yr.

Death usually by 25yr due to progressive cardiac failure or pneumonia.

Cardiac: myocardial degeneration leading to heart failure and possible mitral valve prolapse. Evidence of heart failure is often apparent by 6yr (reduced R wave amplitude and wall motion abnormalities). Isolated degeneration of the left ventricle may lead to right outflow obstruction and right heart failure.

Respiratory: progressive respiratory muscle weakness, leading to a restrictive ventilation pattern, inadequate cough, and eventual respiratory infection and failure.

Possible vascular smooth muscle dysfunction, leading to increased bleeding during surgery.

Associated progressive and severe kyphoscoliosis.

Disease progression may be tracked by serum creatinine kinase levels. These are elevated early in the disease but reduce to below normal as muscles atrophy.

CXR, spirometry, and blood gases may be indicated by respiratory symptoms.

Echocardiography is mandatory if the patient is wheelchair bound—myocardial and valve function can be assessed.

Reduced gut muscle tone leads to delayed gastric emptying and increased risk of aspiration.

An antisialogogue such as glycopyrronium may be needed if secretions are a problem.

Careful IV induction of anaesthesia with balanced opioid/induction agent.

Potent inhalational anaesthetics should be used cautiously in these patients because of the risk of myocardial depression.

Suxamethonium should be avoided because of potassium efflux and potential cardiac arrest.

Non-depolarising neuromuscular blockers are safe, although reduced doses are required. Nerve stimulator monitoring should be used.

Respiratory depressant effects of all anaesthetic drugs are enhanced and postoperative respiratory function should be monitored carefully. Those with pre-existing sputum retention and inadequate cough are at high risk of postoperative respiratory failure and may need prolonged ventilatory support.

Regional analgesia is useful to avoid opioid use and potential respiratory depression after painful surgery. Caudal epidural may be technically easier to perform than lumbar epidural in those with kyphoscoliosis.

It is inherited as an autosomal dominant condition and caused by loss of normal Ca²⁺ homeostasis at some point along the excitation–contraction coupling process on exposure to triggering agents. Any defect along this complex process could result in the clinical features of MH and may explain why differing chemical agents trigger MH and the heterogeneity seen in DNA studies.

The most likely site is the triadic junction between the T tubules, involving the voltage sensor of the dihydropyridine receptor (DHPR), and the ryanodine receptor, a Ca²⁺ efflux channel on the sarcoplasmic reticulum (SR).

About 70% of MH families are linked to the RYR1 gene located on chromosome 19q. Over 200 mutations have been identified in RYR1 but only 29 have evidence of causality. Other loci have been identified (e.g. chromosomes 1, 3, and 7) but only for small numbers of families.

Mortality rates have fallen dramatically from 70–80% to 2–3% due to increased awareness, improved monitoring standards, and the availability of dantrolene.

Commonly seen in young adults, males > females, but this may be a lifestyle rather than a true sex difference.

Used to be more frequent in minor operations, e.g. dental/ENT, due to anaesthetic technique, i.e. when suxamethonium and vapour were commonly used.

Previous uneventful anaesthesia with triggering agents does not preclude MH; 75% of MH probands (index cases) have had previous anaesthesia prior to their MH crisis.

Annual UK incidence of confirmed MH cases is falling (currently ∼10–15/yr) due to changes in anaesthetic techniques, e.g. decreased use of suxamethonium, increased use of TIVA and local anaesthesia. However, there is an increased referral rate due to increased index of suspicion.

Muscle signs: masseter spasm after suxamethonium, generalised muscle rigidity, hyperkalaemia, high CK, myoglobinuria, renal failure.

The two most important early signs are unexplained, unexpected, increasing heart rate and ETCO₂.

If possible abandon surgery; if not convert to ‘MH safe’ technique (volatile free); allow approximately 15min to ensure that the patient is stabilised. Monitor ETCO₂ and temperature, and consider an arterial line.

Additional MH signs increase the likelihood of MH significantly: 50–60% if metabolic signs present, 70–80% if muscle signs present.

Investigations that are particularly useful are the initial and 24hr creatine kinase (CK) and examination of the first voided specimen for myoglobinuria, indicating evidence of muscle damage.

Prolonged severe muscle stiffness greatly in excess of the ‘normal scoline pains’ may occur.

MMS may be the first indication of a previously unsuspected muscle disease, particularly the myotonic conditions. Perform resting CK and EMG. Consider neurological opinion.

In the meantime warn the patient and family of the potential implications of MH.

MH is not a diagnosis to be made lightly without adequate follow-up.

Unless MH can be clearly excluded on clinical grounds the patient/family will be offered screening to confirm or refute the clinical diagnosis.

The proband is always screened even if the clinical reaction is undoubted. If the proband cannot be screened (e.g. died or too young) the most appropriate relative is screened (e.g. parents of a young child).

The IVCT follows a European MH Group (EMHG) protocol exposing muscle tissue to halothane and separately to caffeine under preset conditions in a dedicated laboratory.

The diagnosis is considered positive if the muscle contracts in response to halothane and/or caffeine.

There is a potential for ‘false positive’ MH diagnoses in order to ensure the accuracy of the MH negative diagnosis. The combined EMHG data indicate a specificity of 93.6% and sensitivity of 99%.

If the proband is confirmed as MH susceptible by IVCT, they are screened for the 29 RYR1 mutations currently used for diagnostic purposes by the EMHG for DNA testing of MH.

If a mutation is identified in the proband, family members can be offered an initial DNA blood test for the familial mutation; if a mutation carrier, they are classified as MH susceptible without a muscle biopsy; if mutation negative, a confirmatory biopsy is required for reasons of safety because MH is complex with a small incidence (∼5–10%) of discordant results within families.

If a mutation is not identified in the proband, family members are offered IVCT only.

Family screening is organised on the basis of the autosomal dominant pattern of inheritance, so relatives with a 50% risk are screened first, i.e. parents, siblings, and children; the latter are not screened until aged 10–12yr.

The purpose of family screening is to identify the small number of individuals in a family who are susceptible to MH rather than labelling the whole family. Screening will involve only a small proportion of the family.

Once identified as MH susceptible the MH unit can provide written information about MH, warning cards/discs, and information about the British MH Association (BMHA), a patient support charity.

MH centres should co-ordinate family screening to ensure the appropriate method of testing is offered.

Preoperative questioning about personal and family anaesthetic history is essential to identify potential MH patients.

It is not absolutely essential to screen suspected cases prior to surgery, providing careful individual assessment has been made of the risks involved.

An MH ‘safe’ technique, i.e. avoiding suxamethonium and all anaesthetic volatile agents, may not pose any additional risk in many circumstances, but will do so in certain situations, e.g. when the preferred technique would have necessitated use of these agents.

All local anaesthetic agents are safe.

Dantrolene is not required prophylactically because of its side effects, but should be readily available.

Standard monitoring is adequate, i.e. ECG, NIBP, SaO₂, ETCO₂. A baseline core temperature should be established before the procedure and monitored ∼4hr postoperatively.

If no volatile-free machine is available, remove all vaporisers and circuitry from the machine and ventilator, including soda lime, and purge with oxygen for 20–30min. Use new circuits/soda lime/LMAs/ETT, etc.

The MH unit can be contacted for further advice if required.

If anaesthesia is urgent and more details unavailable, proceed as for an MH-susceptible patient.

History of postoperative myoglobinuria (red/black urine).

Renal failure in otherwise healthy patient.

Postoperative pyrexia. Establish timing of the pyrexia in relation to surgery. If intraoperative/immediate recovery period was uneventful with the pyrexia developing later on the ward, MH is not implicated. If timing is unclear, the likelihood of MH is low but cannot be excluded.

Take a thorough history of the event. If possible obtain old records and seek further advice from the MH centre. If surgery is urgent proceed as if MH susceptible and resolve problem later.

Mother MH susceptible:

Father MH susceptible (fetus at risk)

Heat stroke and King–Denborough syndrome remain controversial (see p. 314).

Neuroleptic malignant syndrome and sudden infant death syndrome are not associated with MH (see p. 287).

The British MH Association (BMHA) is a charitable patient support group which provides the ‘hotline’, warning cards/discs, translations for travel abroad, and newsletters, as well as fundraising for research. Secretary: Mrs A. Winks, 11 Gorse Close, Newthorpe, Nottingham NG16 2BZ. Tel: 01773 717901.

There are 16 MH centres in Europe. Contact the European MH Group Secretary Dr P.J. Halsall (address above) for further details or see the EMHG website: http://www.emhg.org.

For the USA and Canada contact MHAUS, 39 East State St, PO Box 1069, Sherburne, NY 13460, USA. Tel: in North America, 1-800-MH-Hyper; outside North America, 1-315-464-7079; http://www.mhaus.org. Hotline: 1-800-98-MHAUS.

For Australia contact Dr Neil Street, Anaesthetic Dept, The New Children's Hospital, Westmead, NSW, PO Box 3515, Parramatta 2124. Tel: (02) 9845 0000; Fax: (02) 9845 3489.

For New Zealand contact Dr Neil Pollock, Anaesthetic Dept, Palmerston North Hospital, Mid Central Health, Palmerston North Tel: (06) 3569169; Fax: (06) 3508566.