Autonomic Dysfunction

The clinical picture associated with pathology of the autonomic nervous system

1. The Hypothalamic-Pituitary axis,
2. The Ascending pathways in the brain from the basal ganglia
3. The Descending autonomic sympathetic and parasympathetic pathways from the hypothalamus to the viscera.

• N utritional deficiency - Vitamin B1, 3, 6, 12
• N eurological - Multiple sclerosis, Guilliane Barre, spinal cord injury
• E ndocrine - Diabetes, Porphyria, Addisons, Growth Hormone excess
• U nknown - Idiopathic
• R enal failure
• O ther! - Sarcoid
• P araneoplastic phenomena
• A utoimmune - Lupus, Rheumatoid, Sceloderma
• A bnormal Proteins - Multiple Myeloma
• T oxins and drugs - Alcohol and Ionizide
• H uman Imunodeficiency Virus
• Y Chromosome - Congenital

• Postural dizziness - elastic stockings, ephedrine, tyrosine, beta-blockers, mineralocorticoids e.g. fludrocortisone 0.1-0.3mg daily.
• Reflux oesophagitis and delayed gastric emptying - metoclopramide 10mg before meals.
• Nocturnal diarrhoea - metoclopramide 10mg 8 hourly, a short course of tetracycline may be of benefit to the patient.
• Post gustatory sweating - anticholinergics - propantheline hydrobromide before meals.
• Bladder dysfunction and urinary retention - regular voiding and antibiotics for infections.
• Impotence - counseling, pharmacological erections and penile implants.
• Cardiorespiratory arrest - maintain high FiO2 at all times.
• Pupillary abnormalities
• Thermal irregularities
• Skin colour abnormalities.

Tests for autonomic dysfunction.

1. Parasympathetic Heart rate response to a Valsalva manoeuvre . A correctly preformed Valsalva manoeuvre involves forced expiration, generating a pressure of 30mmHg, against a closed glottis for 5 seconds.

   Blood pressure, as it is a gauge pressure, increases at the beginning of the manoeuvre. The baroreceptors cause a transient decrease in heart rate during this period. The raised intrathoracic pressure impedes venous return which causes a decrease in cardiac output, and the blood pressure then gradually decreases to below baseline, despite the baroreceptors causing a progressive tachycardia and peripheral vasoconstriction. On release of glottic closure, the blood pressure will drop because it is a gauge pressure, further rising the heart rate. The compensatory reflexes combined with a now unimpeded venous return to the heart will cause the blood pressure to steadily rise, most often to above baseline until all the compensatory mechanisms and the heart rate have returned to normal These dramatic variations in heart rate are absent in autonomic dysfunction

2. Heart rate variation during quite inspiration and expiration is lost with autonomic dysfunction.

   Heart rate response to standing. In order to compensate for the decrease in blood pressure from the lying to standing position there is a reflex tachycardia which is maximal after ~ 15 beats. Blood pressure is restored to above baseline which causes a reflex brady cardia which is maximal after ~ 30 beats. Sympathetic

3. Postural hypotension.

   On standing the decreased blood pressure is usually compensated for by a reflex tachycardia and vasoconstriction, neither of these mechanism work well in autonomic dysfunction leading to a marked difference in systolic blood pressure between lying and sitting / standing. The normal is <10mmHg, pathological is when the difference is >30mmHg.

4. Blood pressure response to sustained handgrip.

   Sustained handgrip as measured by a dynamometer causes a reflex increase in heart rate and cardiac output without changing systemic vascular resistance, diastolic blood pressure thus normally increases.

Peri-operative management

Pre-operative History to elicit the cause of the neuropathy and the degree of symptomatology present. Co-morbid disease should be activly sought.

The examination is directed at finding evidence of cardiac decompensation and concommitant peripheral neuropathy.
A thorough airway evaluation is necessary.
Bed side examination for autonomic dysfunction generally involves finding postural hypotension and noting the heart rate response to a Valsalva manoeuvre.

Investigations area aimed at determining the degree of renal dysfuntion, checking the degree of myocardial ischaemi and cervical spine X rays for ligament laxity.

Premedication

• Decrease the amount of residual gastric volume - Metoclopramide 0.1mg/kg
• Increase the pH of the residual gastric volume - Ranitidine 2mg/kg nocte and mane orally combined with 0.3Molar sodium citrate, 30mls orally immediately prior to induction

Intra-operative Anaesthesia technique

Induction
Good pre-oxygenation followed by a rapid sequence intubation with a cuffed oral tracheal tube.
If a difficult larygoscopic view is anticipated then endotracheal intubation must be secured while the patient is awake
Centroneuraxial naesthesia is complicated by difficult blood pressure maintenance.
The presence of peripheral neuropathy must be well documented prior to any regional procedure

Maintenance
Inhalational anaesthesia with air, oxygen and a volatile agent titrated to effect Opioid supplementation must be done judiciously to avoid precipitate drops in blood pressure and post operative respiratory depression

Emergence
Complete reversal of any non-depolarising muscle relaxant to ensure excellent airway control. Extubate the patient only when fully awake and in the recovery position with good suction available.

Monitoring

• ECG for ischaemia and rhythm abnormalities.
• Arterial line pre-induction and connected throughout positioning of patient for beat to beat variations of blood pressure, with quick aggresive correction of hypotension - Phenylephrine 50 mg boluses, followed by an infusion of 0.15 to 1 mg/kg/min
• Central venous pressure and urine output for optimal fluid balance
• Temperature probe.

Positioning and padding
Slow controlled positioning is necessary to avoid sudden blood pressure changes.
These patients are at an increased risk of iatrogenic nerve injuries so excellent attention must be paid to padding vulnerable areas

Post operative
Supplemental oxygen (40%) and close respiratory monitoring for at least 24 hrs.
Close haemodynamic monitoring, with correction of hypotension for at least 24 hours
Good post operative analgesia - patient controlled analgesia or regional anaesthesia or nurse controlled, with anti-emetic prophylaxis