Episodic or transient loss of consciousness is a common problem. The important causes of blackout are presented in TABLE 75.4. The history is important to determine whether the patient is describing a true blackout or episodes of dizziness, weakness or some other sensation.
Table 75.4Clinical features of blackouts ||Download (.pdf) Table 75.4 Clinical features of blackouts
|Cause ||Precipitants ||Subjective onset ||Observation ||Recovery |
|Reflex syncope || |
|Warning of feeling ‘faint’, ‘distant’, ‘clammy, sweaty’ || |
|Cardiac syncope including POTS syndrome ||Various ||May be palpitations ||Pale || |
May be flushing
|Autonomic syncope ||Postural change orthostasis, food alcohol ||Warning (feels faint) ||Pale ||Rapid |
|Respiratory syncope || |
|Warning (feels faint) ||Pale ||Rapid |
|Carotid sinus syncope || |
Carotid pressure (e.g. tight collar + turning neck)
|Warning (feels faint) ||Pale ||Rapid |
|Migrainous syncope || |
|Scotomas ||Pale || |
Nausea and vomiting
|Epilepsy || |
|Aura with complex partial seizures (CPS) ||Automatism (e.g. fidgeting, lip smacking) with CPS || |
The clinical features of various types of blackouts are summarised in TABLE 75.4.
Epilepsy is the commonest cause of blackouts. There are various types, the most dramatic being the tonic–clonic seizure in which patients have sudden loss of consciousness without warning. See CHAPTERS 54 and 84.
The typical features (in order) of a tonic–clonic convulsion are:
aura (sensory or psychological feelings)
initial rigid tonic phase (up to 60 seconds)
convulsion (clonic phase) (seconds to minutes)
mild coma or drowsiness (15 minutes to several hours)—postictal confusion
cyanosis, then heavy ‘snoring’ breathing
eyes rolling ‘back into head’
± tongue biting
± incontinence of urine or faeces
It should be noted that sphincter incontinence is not firmly diagnostic of epilepsy. In less severe episodes the patient may fall without observable twitching of the limbs.5
In atonic epilepsy, which occurs in those with tonic–clonic epilepsy, the patient falls to the ground and is unconscious for only a brief period.
Orthostatic intolerance and syncope
In syncope there is a transient loss of consciousness but with warning symptoms and rapid return of alertness following a brief period of unconsciousness (seconds to 3 minutes). The three main syndromes that are outlined in CHAPTER 54 are reflex syncope, postural orthostatic tachycardia syndrome and autonomic failure.
Relevant features of reflex syncope or vasovagal or common faint (see TABLE 75.4):
occurs with standing or, less commonly, sitting
warning feelings of dizziness, faintness or true vertigo
nausea, hot and cold skin sensations
fading hearing or blurred vision
sliding to ground (rather than heavy full-length fall)
rapid return of consciousness
pallor and sweating and bradycardia
often trigger factors (e.g. emotional upset, pain)
The patient invariably remembers the onset of fainting. Most syncope is of the benign vasomotor type and tends to occur in young people, especially when standing still (e.g. choir boys). It is the main cause of repeated fainting attacks.
The treatment is to avoid precipitating causes (e.g. prolonged standing, especially in the sun) and bend forwards with the head down or lie down with premonitory signs. ‘Smelling salts’ (ammonium carbonate) can be carried and used in these circumstances.
This uncommon event may occur after micturition in older men, especially during the night when they leave a warm bed and stand to void. The cause appears to be peripheral vasodilatation associated with reduction of venous return from straining.
Severe coughing can result in obstruction of venous return with subsequent blackout. This is also the mechanism of blackouts with breath-holding attacks.
This problem is caused by pressure on a hypersensitive carotid sinus (e.g. in some elderly patients who lose consciousness when their neck is touched).
Syncope on exertion is due to obstructive cardiac disorders, such as aortic stenosis and hypertrophic obstructive cardiomyopathy.