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Transient loss of consciousness ('blackouts') in over 16s – NICE guideline

This National Institute for Health and Care Excellence (NICE) guideline covers assessment, diagnosis and referral for people over 16 who have had a transient loss of consciousness (TLoC; also called a blackout). It aims to improve care for people with TLoC by specifying the most effective assessments and recommending when to refer to a specialist.

Key recommendations

Initial assessment

  • Ask the person who has had the suspected TLoC, and any witnesses, to describe what happened before, during and after the event. Try to contact by telephone witnesses who are not present. Record details about:
    • circumstances of the event
    • person's posture immediately before loss of consciousness
    • prodromal symptoms (such as sweating or feeling warm/hot)
    • appearance (for example, whether eyes were open or shut) and colour of the person during the event
    • presence or absence of movement during the event (for example, limb-jerking and its duration)
    • any tongue-biting (record whether the side or the tip of the tongue was bitten)
    • injury occurring during the event (record site and severity)
    • duration of the event (onset to regaining consciousness)
    • presence or absence of confusion during the recovery period
    • weakness down one side during the recovery period.
  • Record a 12-lead electrocardiogram (ECG) using automated interpretation. Treat as a red flag (see recommendation if any of the following abnormalities are reported on the ECG printout:
    • conduction abnormality (for example, complete right or left bundle branch block or any degree of heart block)
    • evidence of a long or short QT interval, or
    • any ST segment or T wave abnormalities.
  • Record carefully the information obtained from all accounts of the TLoC. Include paramedic records with this information. Give copies of the ECG record and the patient report form to the receiving clinician when care is transferred, and to the person who had the TLoC.
  • Refer urgently for cardiovascular assessment, with the referral reviewed and prioritised by an appropriate specialist within 24 hours, anyone with TLoC who also has any of the following.
    • an ECG abnormality (see recommendations and
    • heart failure (history or physical signs).
    • TLoC during exertion.
    • family history of sudden cardiac death in people aged younger than 40 years and/or an inherited cardiac condition.
    • new or unexplained breathlessness.
    • a heart murmur.
  • Consider referring within 24 hours for cardiovascular assessment, as above, anyone aged older than 65 years who has experienced TLoC without prodromal symptoms.
  • Diagnose uncomplicated faint (uncomplicated vasovagal syncope) on the basis of the initial assessment when:
    • there are no features that suggest an alternative diagnosis (note that brief seizure activity can occur during uncomplicated faints and is not necessarily diagnostic of epilepsy) and
    • there are features suggestive of uncomplicated faint (the 3 'P's) such as:
      • Posture – prolonged standing, or similar episodes that have been prevented by lying down
      • Provoking factors (such as pain or a medical procedure)
      • Prodromal symptoms (such as sweating or feeling warm/hot before TLoC).

Further assessment and referral

  • Refer people who present with one or more of the following features (that is, features that are strongly suggestive of epileptic seizures) for an assessment by a specialist in epilepsy; the person should be seen by the specialist within 2 weeks (see the NICE guideline on epilepsies: diagnosis and management).
    • a bitten tongue
    • head-turning to one side during TLoC
    • no memory of abnormal behaviour that was witnessed before, during or after TLoC by someone else
    • unusual posturing
    • prolonged limb-jerking (note that brief seizure-like activity can often occur during uncomplicated faints)
    • Confusion following the event
    • prodromal déjà vu, or jamais vu (see glossary, appendix C)
  • Consider that the episode may not be related to epilepsy if any of the following features are present:
    • prodromal symptoms that on other occasions have been abolished by sitting or lying down
    • sweating before the episode
    • prolonged standing that appeared to precipitate the TLoC
    • pallor during the episode. 
  • Do not routinely use electroencephalogram (EEG) in the investigation of TLoC (see the NICE guideline on epilepsies: diagnosis and management).

Specialist cardiovascular assessment and diagnosis

  • Carry out a specialist cardiovascular assessment as follows:
    • Reassess the person's:
      • detailed history of TLoC including any previous events
      • medical history and any family history of cardiac disease or an inherited cardiac condition
      • drug therapy at the time of TLoC and any subsequent changes.
    • Conduct a clinical examination, including full cardiovascular examination and, if clinically appropriate, measurement of lying and standing blood pressure.
    • Repeat 12-lead ECG and obtain and examine previous ECG recordings.
    • On the basis of this assessment, assign the person to one of the following suspected causes of syncope:
      • suspected structural heart disease
      • suspected cardiac arrhythmic
      • suspected neurally mediated
      • unexplained.
    • Offer further testing as directed by recommendations to or other tests as clinically appropriate.
  • For people with a suspected cardiac arrhythmic cause of syncope, offer an ambulatory ECG and do not offer a tilt test as a first-line investigation. The type of ambulatory ECG offered should be chosen on the basis of the person's history (and, in particular, frequency) of TLoC. For people who have:
    • TLoC at least several times a week, offer Holter monitoring (up to 48 hours if necessary). If no further TLoC occurs during the monitoring period, offer an external event recorder that provides continuous recording with the facility for the patient to indicate when a symptomatic event has occurred.
    • TLoC every 1–2 weeks, offer an external event recorder. If the person experiences further TLoC outside the period of external event recording, offer an implantable event recorder.
    • TLoC infrequently (less than once every 2 weeks), offer an implantable event recorder. A Holter monitor should not usually be offered unless there is evidence of a conduction abnormality on the 12-lead ECG.
  • Do not offer a tilt test to people who have a diagnosis of vasovagal syncope on initial assessment.
  • For all people with unexplained syncope (including after negative carotid sinus massage test in those for whom this is appropriate), offer ambulatory ECG (see recommendation Do not offer a tilt test before the ambulatory ECG.

TLoC is very common: it affects up to half the population in the UK at some point in their lives. TLoC may be defined as spontaneous loss of consciousness with complete recovery. In this context, complete recovery would involve full recovery of consciousness without any residual neurological deficit. An episode of TLoC is often described as a 'blackout' or a 'collapse', but some people collapse without TLoC and this guideline does not cover that situation. There are various causes of TLoC, including cardiovascular disorders (which are the most common), neurological conditions such as epilepsy, and psychogenic attacks.

This guideline aims to define the appropriate pathways for the initial assessment, diagnosis and specialist referral of people who have had TLoC, so that they receive the correct diagnosis quickly, efficiently and cost effectively, leading to a suitable management plan. The approach of the Guideline Development Group was to produce a guideline in the form of an algorithm, pointing clinicians and patients towards those areas where guidance already exists (such as the guidance on epilepsy [NICE clinical guideline 20]; replaced by NICE clinical guideline 137), and providing new guidance in other areas, namely for people with syncope.

You can read the guideline on NICE's website.