The Vitals: Dysautonomia

Dysregulation of the ANS, or Dysautonomia, results in imbalances between sympathetic and parasympathetic outflow to target organs. Based on the affected organ/organs, clinical symptoms may manifest as paroxysmal episodes of sympathetic or parasympathetic hyperactivity or even as hyper-exaggerated responses to normal stimuli.

Treating this condition can be tricky.  Life-threatening fluctuations in vital parameters such as heart rate and blood pressure demand immediate attention; however, in some occasions, treatment leads to hyper-exaggerated responses that are similarly life-threatening. In Guillain-Barré Syndrome, for example, drug sensitivity may be so heightened that treating dangerously high blood pressures may result in dangerously low ones. Through primarily retrospective studies, there is emerging data suggesting the use of opioids such as morphine and fentanyl as an effective strategy.  Opioids have proven effective at controlling blood pressure with the added safety benefit of less risk of hypotension. If additional control is needed or opioids prove ineffective, intravenous antihypertensives such as labetalol and nicardipine are likely a better choice, over long-acting oral agents, due to their short-acting effects which can be quickly titrated. Continuous blood pressure monitoring via an arterial line may be useful particularly in highly labile patients and especially if there is consideration towards starting an oral agent.

Mechanically ventilated patients also need to be monitored for sudden, paroxysmal episodes of hypotension and orthostasis. This is typically the result of uncontrolled parasympathetic and vagal hyperactivity. Potentially useful strategies include avoiding prolonged periods in the supine position along with compression stockings. In refractory cases, oral alpha-agonists (e.g. midodrine) or fludrocortisone can be effective. Patients should also be monitored for paroxysmal episodes of bradycardia caused by vagal hyperactivity. Paroxysmal bradycardia may be mild; however, patients may even occasionally experience brief periods of asystole during common patient maintenance activities such as tracheal suctioning! Consideration for pacemaker placement, either transvenous or permanent, may be the optimal strategy in such scenarios.  If sinus tachycardia is observed, first consider whether it is being caused by an acute physiological disturbance such as pain, hypovolemia, fever, or infection before initiating beta blockers. To avoid unnecessary and repetitive blood cultures it should be recognized that temperature fluctuations are frequently observed in these patients. 

The enteric nervous system is another division of the ANS. Disruption may result in clinically significant ileus and in severe cases, bowel perforation! In this setting, it may be helpful to consider either replacing opioids or stopping them altogether. Prokinetic agents like neostigmine may be considered dangerous in the setting of vagal hyperactivity due to an increased risk of bradyarrhythmia or asystole. Maximizing gastric motility with the use of enemas and stool softeners along with opioid-antagonists may be helpful. If all else fails and colonoscopy is unavailable, manual dis-impaction may be the only way to decompress. Get in there!