Autonomic Nervous System

Guillain-Barré Syndrome and the Autonomic Nervous System
Gareth J. Parry, M.D. Professor and Head
Department of Neurology University of Minnesota

The autonomic nervous system controls those functions of our bodies that we do not have to think about such as heart beat, blood pressure, sweating bowel and bladder function and sexual function. The weakness in GBS patients, including weakness of breathing muscles, so dominates the clinical picture that abnormalities of autonomic function often go unrecognized or is completely ignored. However, they significantly impact patient comfort during the early evolution of the illness. In addition, with the tremendous improvement in the care of ventilator dependent patients over recent years, abnormalities of cardiac autonomic function have come to constitute a major cause of death from GBS. Furthermore, these deaths are preventable with early recognition and appropriate treatment.

The most important form of autonomic instability in terms of survival is that which affects the heart and blood vessels. Tachycardia (rapid heart beat) is seen in many perhaps a majority of patients with GBS. By itself, this is not particularly important but as an indicator of early autonomic problems it is critical and is the principle reason why every GBS patient should have heart monitoring when first admitted to the hospital. About 20% of patients may have more serious cardiac arrhythmias. These do not always need treatment but are a reason for continued close cardiac monitoring. Some patients with serious irregularities of heart beat may require medication to stabilize the cardiac rhythm. In others, the heart beats too slowly and sometimes there are long pauses which may result in loss of consciousness. These latter patients may need a pacemaker to control the heart rhythm.

Hypotension (low blood pressure) is common in GBS and is usually made worse when the patient is upright (postural hypotension). Thus, patients may faint when they get up from bed. I have seen this problem many times, particularly in men who may have difficulty passing their urine when lying in bed. A kind-hearted nurse helps the patient to stand to urinate and the patient promptly gets very light-headed and may faint. In addition, involvement of the autonomic nerves to the bladder makes urination more difficult, compounding the problem. The same difficulties may be experienced during physical therapy. Other patients may develop severe hypertension. This may be sustained but is more often paroxysmal so that the patient may have periods of hypotension alternating with severe hypertension. Great care must be exercised in treating the elevated blood pressure because it is usually short lived. Medication may produce dramatic falls in blood leisure to dangerously low levels.

A number of factors may exacerbate autonomic instability. Mild hypoxia (lack of oxygen) may induce or exacerbate cardiac arrhythmias and this may be the first clue that a patient is developing respiratory failure. Succinylcholine, which is a drug frequently used to relax the muscles when patients are intubated in preparation for artificial ventilation, also induces cardiac arrythmias and should be avoided if possible in GBS patients. In addition, the act of intubation may cause arrythmias and every effort should be made to avoid emergency intubation by inexperienced personnel. By recognizing incipient respiratory failure before it becomes overt, these risks can be avoided or at least minimized. Plasmapheresis may also exacerbate autonomic instability. Both hypotension and cardiac arrhythmias may occur during the plasma ex-change and patients should continue on cardiac monitoring throughout the procedure. In patients who have objective evidence of autonomic instability I prefer to use intravenous immune globulin (IVIg), rather than plasmapheresis, to treat GBS patients.

Other autonomic problems that may occur include difficulty urinating which often necessitates catheterization, and constipation. Both are exacerbated by the inactivity resulting from the weakness. Abnormal sweating (drenching sweats) and flushing may also occur and may be mistaken for infection although fever is not present.

The severity of the autonomic instability is usually proportional to the severity of weakness but may still be seen in mildly involved patients. That is why I recommend cardiac monitoring for all patients for at least 24 hours or while the weakness continues to progress. The problems caused by autonomic instability are short lived and amenable to treatment so long term prognosis is excellent. However, constant vigilance during the acute phase of the disease is critical if an optimal course good outcome is to be achieved.