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Blackouts or loss of consciousness

Evidence-based medicine

Gerry Morrow

Monday, 11 March 2019

AdobeStock_162202477.jpgA blackout is defined as a transient, spontaneous loss of consciousness (TLoC) followed by complete recovery. Blackouts are common. In the UK, 1 in 2 people will experience a blackout at some point in their lives, the most common underlying cause being vasovagal syncope.

Approximately 3% of accident and emergency department visits in the UK are thought to be due to blackouts. One meta-analysis of adults presenting to emergency departments with syncope found that 29% related to situational, orthostatic or vasovagal syncope. Heart disease was diagnosed in 10.4% of people, most frequently bradyarrhythmia (4.8%) and tachyarrhythmia (2.6%). One third of all patients were discharged without a formal diagnosis.

The commonest causes of blackouts are neurally-mediated reflex syncope, orthostatic hypotension, cardiac abnormalities (such as bradycardia, tachycardia or low cardiac output), epileptic seizures (ES) and psychogenic non-epileptic seizures (PNES).  

Making a definitive diagnosis of the cause of the blackout is a challenge faced by all GPs, paramedics and emergency department clinicians specifically because of the lack of unique distinguishing clinical features in these patients.

Clearly, in a TLOC situation the importance of a management plan based on an accurate diagnosis allows for appropriate risk stratification, avoidance of misdiagnosis and false reassurance for individuals who may be at high risk of complications for an underlying cardiological or neurological pathology.

A recent attempt to collate symptom-based data, examination findings and investigation results into an easy-to-use tool to assist in resolving the diagnostic dilemma of blackouts was unsuccessful. The authors used questionnaires, witness testimony, ictal and post-ictal findings to assist clinicians facing the TLoC conundrum.

Unfortunately, the authors were forced to conclude that when faced with a patient who has blacked out, where a compelling diagnostic reason has been excluded (such as an arrhythmia) the most appropriate management is likely to require referral to a clinician with expertise in the diagnosis and treatment of seizures.  

This conclusion is supported by the current NICE quality standards on blackouts. In particular, where they assert that a cardiological cause should be excluded if possible, in these patients. The NICE guideline on epilepsies diagnosis and management also advises that if there is diagnostic doubt that a seizure has occurred specialist referral should be urgent.

This still leaves us with the problem of how to deal with patients who have a brief loss of consciousness, spontaneous recovery, non-witnessed in the absence of a clear and defined underlying pathological process causing the episode.

The best guidance appears to be that we exclude red flags, (such as serious injuries sustained during the episode, any signs of heart failure, or new heart murmurs, the presence of ECG abnormalities, TLoC during exertion or a family history of sudden cardiac death under the age of 40 or an inherited cardiac condition) and then exercise our well-honed clinical judgement in other patients to access further specialist assessment, where appropriate. 

At present therefore, the challenge of definitive diagnosis in TLoC is yet to be solved.

Author's Image

Gerry Morrow

With a keen interest in evidence-based medicine and patient involvement, Gerry has over twenty years’ experience working as a GP, based initially in Worcester and then in the rural practice of Allendale. Now Medical Director of Clarity Informatics, a leading IT healthcare solutions provider, Gerry is leading a globally recognised team of clinicians and researchers, and is also directly responsible for the production and delivering of Clarity’s clinical guidance which forms the clinical content of NICE’s Clinical Knowledge Summaries (CKS) service. Gerry is also a clinical non-executive director of the North East Ambulance Service, responsible for operating patient transport and ambulance response services across a region covering 3,200 square miles and a population of 2.7 million people.
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