Autonomic Hyperactivity Syndromes

Fig. 7.1

(a) Admission CT scan showing temporal right contrecoup hemorrhage, right subdural hematoma, subarachnoidal hematoma, and basal skull fracture. (b) Autonomic monitoring day 1: fluctuations of heart rate, blood pressure according to intracranial pressure fluctuations. Upper trace (white) heart rate, lower trace (red) systolic and diastolic blood pressure. (c) Autonomic monitoring day 3: increased frequency of fluctuations. Upper trace (white) heart rate, lower trace (red) systolic and diastolic blood pressure

7.1.1 Introduction

One of the most dangerous expressions of autonomic disease is autonomic hyperactivity, usually caused by a profound sympathetic increase.

Causes of autonomic hyperactivity include acute intracranial lesions (e.g., severe head trauma, hemorrhage, brain stem lesions) [1], spinal cord lesions causing autonomic dysreflexia, peripheral neuropathies (e.g., Guillain-Barré), drugs (intoxications), and alcohol withdrawal [2].

Features of autonomic hyperactivity

Fluctuations in
- Blood pressure
- Heart rate
- Respiratory function
- Body temperature
May include
- Agitation
- Sweating
- Flushing
- Piloerection
- Pupillary dilatation
- Muscle tone increase

Autonomic hyperactivity may mount in severe complications.

Parasympathetic increase, especially acute loss of modulation, might also cause severe or even life-threatening complications (hypotonia or bradycardia, paralytic ileus, or bladder dysfunction). They are much less common but occur in, e.g., patients suffering autonomic dysreflexia or generalized seizures.

Consequences of autonomic hyperactivities are baroreceptor reflex failure, heart rate fluctuations, ECG changes (see Fig. 7.1b, c), cardiac arrhythmias, blood pressure disturbances, chemoreceptor reflex failure, and respiratory complications in variable degrees. The most severe of these complications is the collapse of the cardiovascular function. Apart from measuring blood pressure, heart rate, and oxygenation, blood flow might be already evaluated at bedside (skin color, skin temperature). During intensive care monitoring, invasive circulation measurements are needed. Provocation factors should be avoided.

Provocative factors/triggers

Pain including intestinal pain during bowel movement and body manipulation during nursing
Tracheal suctioning
Catheterization
Bladder distention
Pressure on the carotid sinus
Eyeball pressure
Loud and sudden noise

Autonomic hyperactivity needs urgent attention in identifying the lesion site and monitoring the patient.

7.2 Diagnosing Autonomic Involvement

In contrast to autonomic tests presented in Chaps. 2, 3, and 4, autonomic standard investigations are rarely accessible at an intensive care or critical care units. However, these patients are monitored, and several biosignals are of great help in hinting to autonomic disorders.

7.2.1 ECG [3]

The heart frequency is an important biomarker of autonomic dysfunction in intensive care patients. Tachycardia, bradycardia, or arrhythmia indicates sympathetic or parasympathetic overactivity (see Table 7.1). In addition, autonomic innervation of the heart leads to altered ECG morphologies. These include prolonged PQ and QT interval, T wave, and ST and U interval morphologies.

Table 7.1

Typical symptoms and causes of autonomic hyperactivity syndromes

Syndrome	Symptoms	Possible causes
Increased sympathetic drive	Hypertension, arrhythmia, ECG changes, hyperhidrosis	SAH, ICH, stroke
Sympathetic deafferenciation	Hypotension, orthostatic intolerance, bradycardia, anhidrosis	Acute lesion cervical spinal cord
Increased parasympathetic drive	Bradycardia, reflex asystole, hypersalivation, diarrhea	GBS, brain stem lesion, side effect of cholinergic drugs
Parasympathetic deafferenciation	Tachycardia, intestinal atonia, dry mouth, dry eyes	GBS, side effect of anticholinergic drugs
Complete autonomic deafferenciation	Hhypotonia, orthostatic intolerance, autonomic atonia	GBS, pandysautonomia, brain death
Changing vegetative states	Symptom oscillations from increased sympathetic to parasympathetic drive	GBS, tetanus
Intracranial pressure	Hypertension, bradycardia	ICH, cerebral edema, SDH

Adapted from Autonome Störungen et al. [3]

7.2.1.1 Blood Pressure

As discussed in Chaps. 1 and 3, the sympathetic nervous system regulates the arterial vessel constriction. Blood pressure is therefore a strong marker for sympathetic innervation in intensive care patients. This biomarker is best monitored “beat to beat” employing an arterial catheter. In patients with autonomic dysfunction, blood pressure trends might be valuable to monitor autonomic dysfunction.

7.2.1.2 General Management Considerations

Patients with autonomic hyperactivity should be managed at critical care wards including basic monitoring of ECG, temperature, respiratory frequency, continuous blood pressure, fluid balance (eventually invasive), and blood oxygenation.

As soon as the patient is initially stabilized, elaborate evaluation of the condition causing autonomic hyperactivity is necessary to initiate optimal treatment. Pursuing an approach as presented in Table 7.1 might prove valuable to derive an etiologic differential diagnosis.

Even if the condition is already well established at the onset of autonomic hyperactivity (e.g., head trauma, intracranial hemorrhage), reevaluation is mandatory, to exclude secondary complications such as hydrocephalus, drug effects, seizures, increasing brain edema, systemic inflammatory response syndrome (SIRS), or multiple organ dysfunction syndrome.

General management considerations include concise fluid management to maintain euvolemic conditions, exclusion or early treatment of infection, sufficient analgesia or analgosedation if necessary, and focused attention to triggering factors.

7.3 Syndromes

7.3.1 Sympathetic Hyperactivity

Autonomic storm is considered in patients suffering extensive activation of the sympathetic nervous system. This activation might have three different pathophysiological mechanisms: sympathoadrenal discharge, Cushing’s response, and end diencephalic “seizures.”
Typical signs of sympathoadrenal discharge are hypertension, tachycardia, increased cardiac output, and decreased vascular resistance. Autonomic hyperactivity is caused by increased sympathetic nerve activity due to severe CNS lesions, either with sympathetic neural discharge or excessive adrenal activity.
Cushing’s response on the contrary shows hypertension but bradycardia as well as slow irregular breathing. Causes are acute distortion of the lower brain stem or cerebral hematomas.
Diencephalic “seizures” are characterized by acute hypertension, tachycardia, pupillary dilatation, and often extensive sweating. The pathophysiology is unclear; there is no convincing evidence for epileptic discharge. Causes might be closed head injuries resulting in a decorticate state or widespread axonal injury.

7.3.2 Specific Syndromes

7.3.2.1 Head Trauma

Paroxysmal sympathetic hyperactivity is a regular complication of head trauma patients. Disconnections involving the posterior corpus callosum and posterior limb of the internal capsule may play a role in the pathogenesis [4]. Paroxysms often start 5–7 days after injury, eventually starting earlier, and follow a regular pattern for several times a day. Diagnosis might be achievable quite early [5]. Each episode may last from less than 1 h to 10 h. It might be present from 1 week to several months. The diagnosis of paroxysmal sympathetic hyperactivity was proposed if four of six criteria are present in the absence of other potential causes [6]: