Chronic Autonomic Dysfunction in SCI

Aims of this Session

• Describe autonomic dysfunction: physiology, pathophysiology in SCI

• Discuss lasting effects of autonomic dysfunction in SCI

• Describe severe autonomic dysreflexia, its recognition, treatment and prevention

• SCI affects the somatic (i.e. the sensory and motor pathways we are aware of and can control) nervous system below the level of the injury

• However the autonomic (i.e. ‘self-regulating’) nervous system is also affected, and, like the somatic central nervous system, the severity and extent of the damage is largely related to the level and neurological completeness of the injury

Autonomic Dysfunction: Physiology & Pathophysiology of SCI

What is the Autonomic Nervous System?

• The ANS maintains many body systems that need to run constantly without conscious effort: for example breathing, digestion, secretion and storage of urine, thermoregulation, circulation of blood.

• The ANS can be viewed as two systems, the sympathetic and parasympathetic, which respond to each other and the external environment in order to maintain an internal equilibrium while facilitating conscious response to challenges (‘flight or fight’)

Parasympathetic

Sympathetic

What is the Autonomic Nervous System?

• It is important to realise that the primary mode of action of the autonomic nervous system is the reflex: stimulus-response.

• As we have seen the parasympathetic and sympathetic tend to involve distinct levels of the spinal cord

• This means that the nature of the autonomic dysfunction in an individual is heavily influenced by the location and extent of the SCI

Autonomic Dysfunction: Physiology & Pathophysiology of SCI

Autonomic Dysfunction Landmarks

brain

C1-C7

T1-T6

T7-T12

L1-L5

S1-S5coccyx

sympathetic cardioaccelerator supply T6Profound spinal shockRisk of severe autonomic dysreflexia

LMN lesionNo spasmAreflexic NBDSevere erectile dysfunction

UMN lesion

Spasm

Reflex NBD

Reflex erection

Neurological Completeness of Injury: Risk of Severe Autonomic Episodes

24 5 63 0

119 28 48201 32

0%10%20%30%40%50%60%70%80%90%

100%

A B C D E

ASIA score

No AD

AD

High Risk Group: AIS ‘A’ Tetraplegics

• After spinal shock has subsided, there will be a persistent autonomic dyssynergy, again relative to level and density of lesion

• The parasympathetic and sympathetic systems will not be properly moderated or inhibited by each other, which will often result in hyperreflexia, particularly of the sympathetic system

• This will often have evident functional physiological consequences

Chronic Autonomic Dysfunction in SCI

Cardiovascular System

Signs Mechanism EffectHypotension

(postural)

Passive dilatation of blood vessels below injury (sympathetic inactivity)

Syncope (dizziness, fainting, visual disturbance) when sitting up suddenly

The BP is often very labile

Bradycardia Unopposed vagal stimulation(sympathetic inactivity)

Tetraplegics may often have a labile HR with a low resting pulse. This can lead to misdiagnosis

Poikilothermia Passive dilatation of blood vessels below injury(sympathetic inactivity)

Potential hypothermia

Respiratory systemMechanism Effect

respiration,

PO2

Diaphragmatic respiration

Nasal blockage, stuffiness

Vasodilation of face and air passages(compensatory sympathetic overactivity)

Often becomes interpreted that bladder or bowels are about to empty

Inability to expectorate effectively

Absent intercostals and auxiliary respiratory muscles

Chest infection

Gastrointestinal System

Signs MechanismNausea, vomiting, bloating

Slow gastrocolonic transit (sympathetic inactivity)

Constipation, faecal incontinence

Neurogenic bowel dysfunctions

‘Silent’ autonomic dysreflexia(sympathetic/parasympathetic dyssenergy with no somatic influence)

Skin

Signs Mechanism EffectMarks easily

Sweating, gooseflesh, flushing (often in response to sympathetic stimulation rather than heat or cold)

(sympathetic hyperreflexia)

Increased risk of pressure ulcers, discomfort

Poikilothermia (sympathetic dyssynergy)

Danger of causing burns to anaesthetic skin when attempting to correct hypothermia

Genitourinary System

Signs Mechanism EffectIntermittent oligouria

Poor renal perfusion when sitting due to postural hypotension

(sympathetic inactivity)

Reduced urine output when mobilising, with compensatory polyuria overnight

Dependent oedema of lower limbs

Retention of urine

Bladder reflexes absent/ineffective

Blocked urinary catheter

(sympathetic and parasympathetic dyssynergy)

Damage to upper urinary tract, infection and haematuria

Autonomic dysreflexia

Erectile and ejaculatory dysfunction

Disruption of reflex pathways Treatment required for erectile and ejaculatory dysfunctions

Amenorrhea Secondary to nutritional and metabolic deficits

Tends to resolve within 6/12, with resultant normal fertility

Chronic Autonomic Dysfunction in SCI

• Autonomic symptoms can be many and various

• Many of these can be distressing

• In the absence of normal somatic sensation these can be a useful aid to diagnosis

• Many SCI individuals ‘learn’ to interpret autonomic signs usefully

• Distressing autonomic symptoms can often be addressed rationally. For example:– Sweating often responds to

sympatheticomimetics (oxybutynin etc)– Postural hypotension is treated by gradual

mobilisation, and use of elastic stockings and abdominal binder. Sometimes ephedrine is used

• However attention must be given to any underlying cause- particularly bladder and bowel management

Chronic Autonomic Dysfunction in SCI

What is Autonomic Dysreflexia?

• Severe autonomic dysflexia is a sudden rise in blood pressure in response to a harmful stimulus (usually the increase in pressure in a body cavity caused by the collection of fluid)

• Untreated, this rise in blood pressure may continue and result in cerebrovascular events or even death

• The noxious stimulus triggers unmediated sympathetic reflex activity which causes massive vasoconstriction below the level of injury.

• This in turn causes a rise in central blood pressure which causes an alarming headache

• The area above the lesion tries to compensate with vasodilation, causing flushing and sweating

What is Autonomic Dysreflexia?

• In most cases the noxious stimulus is urine in the bladder (probably above 90% of new dysreflexia)

• In practice (outside of SCI Centres) this is usually due to a blocked catheter

What is Autonomic Dysreflexia?

• Bowel triggers are constipation, anal fissure, bleeding haemorrhoids etc

• Other (rarer) primary causes include infected pressure sores and abscesses, pus from an ingrowing toenail collecting behind the nail, and DVT

What is Autonomic Dysreflexia?

Recognition of Severe Autonomic Dysreflexia

• Non- drainage of urine

• Severe headache

• (raised BP)

• (sweating and flushed above lesion)

• Change catheter (do not attempt washout)

• (Give chemical vasodilator eg: GTN)

• Reassure

• (Elevate head)

Treatment of Severe Autonomic Dysreflexia

• Good bladder and bowel management:

– Regular catheter change

– Avoid constipation

Prevention of severe Autonomic Dysreflexia