On a regular basis, I have been asked to give opinion as to the mechanism of an otherwise unexplained motor vehicle accident.  This may have involved car, bus or lorry where third parties have been injured.  Occasionally, it involves a bicycle whereby the injured cyclist subsequently claims, that they must have struck a pothole even though they have no memory of it. It is my impression that the legal process is often not aware of the concept of an isolated clinical event that could contribute to the understanding or even be the cause of some of the tragedies that occur.



The Usual Scenario

The usual instruction involves a letter from the solicitors acting for a Defendant.  The individual with no prior medical history or obvious cause suddenly finds themselves on the wrong side of the road or on the pavement, resulting in a collision either with an unfortunate pedestrian or pedestrians or generating a head-on collision with obvious consequences.  The individual will have no knowledge of the accident until after the event.



Non Pathological Reasons

In the current climate, it is often assumed that such accidents occur as a consequence of poor concentration or distraction, such as might occur from mobile phone usage.  The same might apply for lighting a cigarette or looking down in order to tune a radio or similar.


For the purposes of this article, it will be assumed that none of those distractions have taken place or that no evidence has been provided to suggest an individual may have “volitionally” contributed to the collision.



Physiological Reasons for Accidents

An accident might occur because an individual is drowsy, excessively tired or just falls asleep at the wheel.  These situations are outside the brief of this particular article but would always need consideration when dealing with the mechanism of an accident.



Pathological (and Physiological) Causes of Altered Awareness
or Loss of Consciousness Phasio

Altered awareness or a loss of consciousness is much more common than would normally be realised by the lay public mind.   Vasovagal fainting also known as syncope or a simple faint would be the most common mechanism by far.  Such episodes however rarely occur when an individual is sitting down or driving.  On the whole such activity leads to an increase in the pulse and an elevation rather than a reduction in blood pressure.  There could however be circumstances whereby an individual may be more likely to faint.  This would apply if they were unduly tired, had not eaten before embarking on a long drive, in the midst of menstruation, worse the wear for a previous night of alcohol consumption without eating the following morning or as a consequence of taking prescribed medication which can lower blood pressure.


It could well be argued I suspect within the legal process, that driving under these circumstances is unwise and more than a material contribution beyond reasonable doubt, to the mechanism by which an accident has taken place.



Causes of Blackouts

Once a faint has been excluded, then it is necessary to consider what other causes could lead to a loss or altered consciousness.

The preservation of consciousness requires the integrity of the back part of the brain known as the brain stem.  We have in this part of the brain arousal nuclei that are responsible for maintaining conscious awareness.  Both hemispheres or the cerebral cortex also need to be functioning normally for preservation of consciousness.  Under a number of circumstances either both hemispheres or the brain stem can switch off leading to a state of reduced or lost consciousness.



Heart Rhythm Disturbance

The brain requires a blood supply.  Blood is pumped from the heart supplying all the organs of the body.  There are four arteries that can carry blood away from the heart up to the brain.  If for any reason the blood flow in these vessels is restricted for more than four seconds than consciousness will be altered or lost. 


This may occur as a consequence of a heart rhythm disturbance whereby the heart literally stops for various medical reasons or goes so fast or so slowly that the heart cannot pump sufficient blood into the peripheral circulation.


The electrical fault of the heart may be caused by a problem with the blood supply to the heart itself.  If an individual has a heart attack or what is known medically as a myocardial infarction, then a heart rhythm disturbance may occur such as ventricular fibrillation, heart block or asystolic cardiac arrest that will lead to a loss of consciousness without the individual necessarily having any awareness that catastrophe is about to happen.


Doctors use the term “Stokes-Adams” attacks to describe the loss of consciousness that associates with heart block, when the electrical integrity of the heart is so impaired that the heart literally stops for a short period of time.  Clearly if the heart does not restart itself, then this would be the condition of cardiac arrest and the individual will die if the circulation is not restored within a few minutes.  On the whole, such a situation is easy to diagnose and would not lead to any challenge with regard to a diagnosis.


Likewise in the aftermath of an accident the investigation that should be carried out would demonstrate that there was significant cardiac disease to explain what had happened.




In all age groups an epileptic fit may arise.  This occurs as a consequence of an abnormal electrical discharge in the brain.  When this electrical discharge spreads through the hemispheres and then down into the brain stem, an individual will blackout suffering an epileptic fit.  This can manifest itself in many ways.  The lay experience of epileptic seizures, suggests that people will not just lose consciousness, but will shake and go rigid and often wet themselves or bite their tongue.  In reality there are a whole range of different epileptic fits and individuals may just lose consciousness or have altered awareness, without having any other manifestations of an epileptic fit.  Such seizures often challenge the diagnostic process clinically let alone when they arise within the legal arena.


It is also important to differentiate between an epileptic fit which is an isolated or single episode as opposed to a diagnosis of epilepsy, which by definition is a recurring tendency to have epileptic fits.  Within the legal scenario of a car accident inevitably there should not be a diagnosis of epilepsy, as the individual should not be driving in any case unless they have gone one year seizure free.



Investigation of Black Outs

Any individual who suffers a blackout at the wheel of a car demands investigation.  If there is any suggestion of altered consciousness or awareness, then the driver should consult their GP soonest and be referred for appropriate investigation.  By far the most important part of the assessment of a blackout or “funny turn” is the history.  In clinical practice, neurologists will do everything they can to get a primary history which would normally be from a witness.  Usually the individual who has had the “funny turn” will not know what happened, although they may have had some awareness leading into it.  The extent of that awareness is a fundamental part of the diagnosis often.


It is the witness account that will spell out precisely the circumstances of the funny turn and then what the individual looked like during the episode.  If there is any post event confusion or automatic or strange behaviour, then this will be very important.  The presence or absence of incontinence or tongue biting will not be pathognomonic of a seizure, but could be suggestive as would be the post event confusional state, severe headache and drowsiness.


The problem with road traffic accidents is that the blackout or funny turn, may then be complicated by serious injury including a head and underlying brain injury, trying to unravel those elements that are secondary to the brain injury as opposed to the initiating event, can be particularly challenging.

If there are any witness accounts to the accident such as the driver desperately trying to control the car, then this would be fundamental and suggesting that there was no loss of consciousness.  If on the other hand, the individual makes a sudden manoeuvre and is seen either slumped over the wheel or not reacting to it, then this would suggest that the conscious process has at least been diminished, so that they have not reacted to the situation.
Psychologists might I suppose reflect on the concept of “frozen with fear” such that no response is made, but that would normally emerge with the appropriate history taking.


A number of tests can be carried out. These tests should include analysis of blood samples to exclude anaemia and other conditions that might arise and lead to a blackout.  For instance, measurements of a blood glucose might reveal albeit the rare possibility, that somebody has a condition known as hypoglycaemia that is a low blood sugar that could alter conscious awareness.  There are other biochemical abnormalities that can also be investigated by simple blood investigation.


There should be an MRI brain scan to make sure that there is no underlying cerebral pathology or scarring.  A brain wave test known as an EEG or electro encephalogram may be helpful but usually not diagnostic.  There can be a resting EEG, an EEG carried out in the setting of sleep deprivation or even ambulatory EEG recordings, whereby an individual wears the EEG electrodes for at least 24 or 48 hours to see if there are any abnormal electrical discharges.


Cardiac investigation clearly needs to be carried out including monitoring the heart rhythm over at least 24 hours and undertaking an echocardiogram to make sure that there is no other cardiac anomaly that could explain the event.


Often under these circumstances all the tests are normal.  That does not mean that the episode did not occur, what it means is that it is so intermittent that the testing process cannot reveal an obvious cause.


The GP will usually invoke the help of a consultant neurologist and/or a consultant cardiologist to help with the analysis.



I Have Had a Blackout at the Wheel and Caused Injury – What Should I Do?

Any individual who is involved in a road traffic accident and does not know how it happened should report the event to their GP.  If they have been injured themselves in the accident, then hopefully investigation will start via the A&E Department where they should have been taken.  If there is no injury, then it is inconsistent to perceive that an accident caused by altered awareness has occurred and the individual not sought medical advice.

Any individual who has had an event at the wheel leading to an accident or not is under a duty to report the event to the DVLA in order to determine the length of time during which they should not drive in order to be safe.


It is possible that an individual would be ignorant of their requirement under the law to notify of an event.  Usually if the police are involved and they perceive that there has been altered consciousness or awareness then they would usually report the matter to DVLA themselves.



Matters for the Legal Process to Consider

Irrespective of being Defendant or Prosecution instructed, it is necessary to obtain all the GP and hospital records.  These may give clues to the mechanism of the attack or the veracity of the Defendant.


From the Defendant perspective, it is useful to know that a mobile phone has not been used and that the individual was not smoking, taking drugs or having any current medical problem which should have prevented them from driving in the first place.


The behaviour of the Defendant in the aftermath of the event is also important and a clear account from any witnesses, as to the behaviour of the Defendant at the time that the car was out of control very helpful.


If consciousness is maintained and an individual loses control, then you would expect frantic activity at the wheel to try and correct the vehicle.

If an individual appears slumped over the wheel or not responding, then this is powerful evidence supporting that there was in fact some kind of altered consciousness or awareness.


Given the tragedies that can occur under these circumstances, it is almost a pity that both sides of the legal process do not work together in order to determine the most likely mechanism of an incident.

Perhaps with a greater realisation that between 0.5 and 2% of all people will have a blackout at some stage in their lives, will assist in the understanding of why it is so important to try and work out the mechanism of the event.


If an individual has their first blackout in a bath or swimming pool, they will drown.


In the writer’s own practice tragically the first fit in a young mother led to the drowning of her baby that she was bathing at the time.


First fits have led to obvious car accidents, falling off roofs or ladders and suffering severe burns when the first fit occurred under the wrong circumstance.

Just because a third party is injured rather than the Defendant does not make them necessarily guilty of an offence, but there is a need to explore all of the possibilities.  There also should be a consistent behaviour of the Defendant in order to make sure that they are as safe as possible with regard to any future events happening.