FRCA Notes

Autonomic Dysfunction

This page comes under the brief curriculum item: 'disorders of the autonomic nervous system'.

Resources

Primary diseases

  • Familial dysautonomia
    • A congenital disorder arising from an autosomal recessive mutation on chromosome 9
    • Patients have hypertension, tachycardia, vomiting, sweating and altered personality
    • Death occurs from autonomic crises or aspiration; the mortality by 30yrs old is 50%

  • Multisystem atrophy (Shy-Drager syndrome)
    • A Parkinsons-plus syndrome presenting in late-middle age with ataxia, Parkinsonism and autonomic dysfunction
    • 80% are disabled within 5yrs and life expectancy post-diagnosis is <10yrs

  • Porphyria
  • Fabry's disease
  • Amyloidosis

Secondary (acquired) disorders

  • Diabetes mellitus
  • Chronic alcoholism; due to a direct toxic effect ± chronic liver disease ± associated nutritional deficit
  • Guillain-Barré syndrome
    • and other autoimmune processes such as SLE, Sjogren's
  • Parkinson's disease
  • Infectious diseases e.g. HIV, botulism, Lyme disease, tetanus, diphtheria, leprosy
  • As a paraneoplastic phenomenon


Symptoms Signs
Fainting Postural hypotension
Dizziness Episodic hypertension
GORD Cardiac conduction defects
Constipation Fixed heart rate
Nocturia Resting tachycardia
Impotence
Disordered sweating


  • Tests can be divided into:
    1. Bedside tests: lying/standing BP, sustained tonic muscular activity
    2. Laboratory tests: Valsalva manoeuvre, tilt-table testing

Lying/standing BP

  • A postural systolic drop of >20-30mmHg from lying to standing in a euvolaemic patient suggests autonomic dysfunction
  • A loss of sinus arrhythmia (e.g. on palpating pulse or on ECG) is abnormal

Sustained tonic muscular activity

  • If the autonomic nervous system is intact, a sustained hand grip should cause:
    • An increased heart rate
    • A rise in diastolic BP of 15mmHg
  • A rise in diastolic BP of <10mmHg suggests autonomic dysfunction

Valsalva manoeuvre

  • In autonomic dysfunction there may be a deficit in the baroreceptor reflex i.e. compensatory heart rate changes may not occur
  • During a Valsalva manoeuvre in a patient with autonomic dysfunction:
    • In phase 2 there is an excessive drop in BP, as no compensatory tachycardia occurs
    • In phase 4 there is no BP overshoot nor a reflex bradycardia

  • Can measure the patient's autonomic function as adjudged by the Valsalva ratio:

    • Valsalva ratio = max HR phase 2 / min HR phase 4

  • A ratio of <1.1 suggests autonomic dysfunction

Tilt-table testing

  • The patient's posture is altered by an adjustable table, from 0° to 80°
  • ECG and blood pressure are closely monitored
  • In autonomic dysfunction, postural hypotension and arrythmias are commonly seen

Perioperative management of patients with autonomic dysfunction


History and examination

  • Focussing on:
    • Aetiology underlying autonomic dysfunction
    • Nature and degree of symptoms
    • Existing medications e.g. fludrocortisone

Optimisation

  • Cardiac input if concern re: conduction defects
  • Premedication due to risk of gastric aspiration e.g. antacid of choice + metoclopramide
  • Ensure adequately fasted although aim to avoid hypovolaemia which may exacerbate cardiovascular effects

Monitoring and access

  • AAGBI
    • Consider 5-lead ECG or CM5 configuration to detect of silent myocardial ischaemia
  • Invasive arterial monitoring pre-induction
  • Central venous access may be required to optimise volume status

Anaesthetic technique

  • Use of neuraxial anaesthesia is controversial:
    • May be well tolerated as sympathetic tone is already reduced
    • May cause severe hypotension

  • For general anaesthesia
    • RSI technique due to risk of aspiration
    • There may be exaggerated or paradoxical cardiovascular responses to stimuli such as laryngoscopy
    • Patients may tolerate IPPV poorly if inadequately filled, with consequent hypotension
    • Laparoscopic surgery may cause greater haemodynamic instability compared to open surger
    • If changes to intra-operative positioning are required, they should be done slowly and in stages to minimise haemodynamic instability
    • Use depth of anaesthesia monitoring to titrate GA, especially as classical autonomic signs of inadequate anaesthesia may be absent

Drugs

  • There may be exaggerated responses to the cardiovascular effects of both IV and inhaled anaesthetic agents
  • Direct vasopressors should be readily available
  • Atropine should be available, but may cause a paradoxical bradycardia

Other care

  • Hypothermia can exacerbate cardiovascular autonomic neuropathy so should be avoided

  • Supplemental oxygen to minimise risk of silent myocardial ischaemia due to inadequate DO2
  • Consider HDU care, especially if ongoing cardiac monitoring is needed
  • Aggressively treat factors which may precipitate cardiovascular instability e.g. pain, bleeding