Autonomic Disturbances

Definition

Autonomic disturbances are disorders that affect the autonomic neurons of either or both the sympathetic and the parasympathetic nervous systems. Since the autonomic nervous system supplies almost every organ in the body, autonomic diseases influence localized organ function as well as integrated processes that control vital functions in the body such as arterial blood pressure and body temperature. The signs and symptoms present a wide spectrum, ranging from disorders of the cardiovascular system, such as postural hypotension and heart rate disturbances, to dysfunction involving the sudomotor, alimentary, urinary, or sexual systems, and eye and lacrimal glands in the body. Autonomic diseases may present at any age and may be hereditary or acquired. Neuroanesthesiologists may encounter autonomic disturbances most commonly in the setting of trauma patients (spinal cord injury (SCI), traumatic brain injury (TBI)), in diabetics (diabetic neuropathy) and alcoholics, and in patients of Guillain–Barré syndrome and Parkinson’s disease.

Pathophysiology and Causes

Autonomic disturbances may arise due to a dysfunction of the central or peripheral nervous system pathways. The autonomic nervous system has a craniosacral parasympathetic and a thoracolumbar sympathetic pathway.

Sympathetic outputs arise in brain and brain stem centers, descend into the spinal cord, and synapse with neurons in the intermediolateral cell mass in the thoracic and upper lumbar segments. Axons originating in the spinal cord synapse with cells in paravertebral ganglia, which, in turn, provide sympathetic output to remote target organs. Preganglionic sympathetic synapses use acetylcholine as the major neurotransmitter, while the postganglionic synapses use noradrenaline.

Parasympathetic outflow originates from the cranial and sacral segments, and these axons synapse in ganglia are located near their target organs. Acetylcholine is the major neurotransmitter in both pre- and postganglionic synapses.

Disruption at any level in the transmission pathway may cause autonomic disturbances.

Causes for autonomic neuropathy may be hereditary or acquired. The common causes are best classified on an etiological basis:

• 1.

  Aging

• 2.

  Trauma: TBI, SCI

• 3.

  Systemic diseases:

  • a.

    Diabetic neuropathy: the prevalence of autonomic impairment in diabetes is estimated to be ∼54% in type 1 and ∼73% in type 2 diabetic patients

  • b.

    Hepatic disease

  • c.

    Uremic neuropathy

  • d.

    Amyloidosis

  • e.

    Subacute combined degeneration

• 4.

  Infections: HIV, leprosy, and Chagas’ disease

• 5.

  Drugs and toxins: botulism, cancer chemotherapeutic drugs like vincristine and cisplatin, amiodarone, pyridoxine overdose

• 6.

  Immune mediated: Guillain–Barré syndrome, rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, Eaton–Lambert syndrome, anti-N-methyl-D-aspartate (NMDA) receptor encephalitis, etc.

• 7.

  Hereditary: Anderson–Fabry disease, MEN type 2B

• 8.

  Idiopathic

Dysautonomia frequently occurs in patients with severe TBI. A younger age and diffuse axonal injury could be risk factors for facilitating the development of dysautonomia. Almost 10% of patients with severe TBI have dysautonomic crises during their intensive care unit (ICU) stay. Dysautonomic crises determined a worse short-term neurologic recovery, a greater morbidity, and a longer ICU stay.

Autonomic dysreflexia (AD), seen in spinal cord injuries above T6 level, is a potentially dangerous clinical syndrome resulting in acute, uncontrolled hypertension, typically triggered by bladder or bowel distension.

AD is a clinical emergency. The patients usually give a history of headache, blurring of vision, spots in the visual field, nasal congestion, and a sense of anxiety or malaise.

There is significant rise in systolic and diastolic blood pressure (BP). An increase in systolic blood pressure of more than 20–30 mm Hg is considered a dysreflexic episode. This sudden increase in BP is associated with bradycardia. Clinically, the patient may have profuse sweating and flushing of the skin above the level of lesion. AD occurs more often in chronic stages of SCI but can occur early. It is more severe in complete tetraplegia than in incomplete lesions.

Signs and Symptoms

Postural hypotension is the most commonly recognized symptom of autonomic neuropathy. Any symptom affecting a single organ or system should be carefully evaluated for the possibility of an underlying disease.

The clinical features may be classified on the basis of system involvement.