Electrical Injuries and their Sequelae

Patients presenting with electrical injuries have problems that can range from the very trivial to the fatal (in which case, they are said to have been electrocuted). If patients survive the initial exposure, the outlook is generally very good with few permanent injuries as a result.

• Electric burn injuries account for about 3-4% of burns units admissions. ²
• Electricians and linesmen are at highest risk.
• For every death, there are 2 serious injuries and 36 reported electric shocks.
• Death most often occurs in young males.
• Most deaths occur in the spring and summer months.
• Water greatly increases the risk of fatality.

Electrical current causes damage either through thermal injury or through physiological changes. There are several factors that affect the degree of damage and that are related in the following way:

Current

Type of currentThis may be direct or alternating. The latter is significantly more dangerous in a number of respects:

• It may result in tetanic muscular contraction so preventing the casualty from letting go of the source.
• An alternating current of any more than 10mA induces sweating. Skin moisture decreases its resistance (see below).
• Human tissue is most sensitive to frequencies between 40 and 150 Hz. The frequency best suited for household use is about 50 Hz, so making household current particularly dangerous. This is all the more salient as this is the frequency that is capable of producing ventricular fibrillation.

• 1mA = threshold of perception resulting in tingling sensation.
• >10mA = muscular tetany preventing release of grip from current source.
• >50mA = pain and severe breathing difficulties.
• 100mA = ventricular fibrillation.

Voltage²

Generally, the greater the voltage, the greater the damage (the exception being with high tension voltage: above this level, greater voltage doesn't necessarily influence the degree of injury ³). This is accentuated or limited by the resistance of the tissue that the electricity passes through (see below):

• < 50V: no danger.
• 240V: UK household supply (±10%). This creates small, deep entrance and exit wounds.
• > 1000V = "high tension voltage": there is often extensive tissue damage and limb loss. Contact with > 70,000 V is invariably fatal.
• 100 million V: Lightning. This is quite different from a high voltage electric shock and is treated separately below.

Resistance

This varies in different tissues and will have a great influence on the extent of any injuries.

Contact duration

Most contacts are short (the person is often thrown back from the current source) but if this is prolonged through loss of consciousness or tetany (with subsequent inability to let go), damage is increased.

Point of entry³

This influences the degree of immediate and long-term neurological impairment (paralysis, anaesthesia) but does not appear to influence the degree of renal impairment or cataract formation. If the path to the exit point does not go through the heart, the point of entry does not affect the cardiac system either.

There are a few general points worth noting:

• At a cellular level, the injury resembles a crush injury more than it does a burn. The electrical current will pass through low resistance tissues in preference, causing necrosis along the way.
• There will be a range of clinical manifestations with different effects on different organs.
• Beware of the size of the cutaneous wound: deep structures are classically involved and damage tends to be more severe than the skin wounds suggest.

Burns²

• Range from first degree to third degree: there is typically a depressed charred central area with surrounding oedema. There may be several entry and exit wounds.
• Arc burns are produced by the passage of a current of electricity from the source to the ground and may be associated with extensive skin damage.
• Flame burns occur when the current ignites clothing.

Cardiac system

• Ventricular fibrillation (VF) is the usual cause of immediate death from electrocution; this occurs immediately.
• Other arrhythmias have been reported: sinus tachycardia, non-specific S-T and T wave changes and occasionally, atrial fibrillation.
• Acute myocardial infarction has been reported.

Nervous system

• Acute complications: these include respiratory arrest, seizures, altered mental state, amnesia, coma and expressive dysphasia. Motor deficits have also been reported.
• Delayed complications: these include spinal cord injury and reflex sympathetic dystrophy (a chronic pain syndrome which may present with an intense burning sensation, aching, sweating or abnormal sweating of the affected area).
• Peripheral nerve injury: this may occur in the presence or the absence of concurrent soft tissue injury - the prognosis is good in the latter case.

Renal system

• Acute renal failure (secondary to myoglobinuria).
• High output renal failure (less common).
• Transient renal changes: oliguria, albuminuria, haemoglobinuria, renal casts.

Effects on the vascular system

Large and small vessel thrombosis may occur resulting in surrounding tissue damage. There may also be immediate or delayed haemorrhage.

Musculoskeletal effects

• Muscle cell disruption occurs, releasing myoglobin and creatinine phosphokinase.
• Tetanic muscle contractions can result in bone fractures and dislocations.
• Secondary injuries arise from being thrown back from the source.

Long term damage

• Cataract formation is well documented after significant electrical injury.
• Psychological sequelae: the degree is not necessarily related to the amount of physical injury and problems may last for years.

• General points: there is little information available about electric shocks during pregnancy and the accepted high rate of mortality may be due to publication bias. However, it is well documented that fetal skin is 200 X less resistant than the skin post-natally so less electricity may cause significantly more harm. Indeed, an amount enough to cause minimal injury to the mother may be lethal to the fetus. Furthermore, the path of transmission becomes important here: the current path may completely bypass the maternal heart but if it travels through the uterus, the fetus may be seriously injured.
• Fetal harm: other than cardiac arrest, fetal complications include intrauterine growth retardation, oligohydramnios, reduction in fetal movements and spontaneous abortion.
• Therapeutic electric shocks (such as defibrillation): these are safe on account of the current path followed which does not include the uterus.

• Separate the patient from the source using a non-conducting instrument (e.g.: rubber, wood) and if possible, turn off electrical supply. It is particularly important not to touch the patient before the power has been turned off in high voltage situations, even with non-conducting material.
• Commence cardiopulmonary resuscitation if required. VF is the most common arrhythmia.
• Summon help - early defibrillation provides the best chance of survival.

• Once in the emergency department, a full survey should be carried out including basic blood tests with a particular note of the renal function. ECG is mandatory. Check βHCG and tetanus status. Pregnant women should have an urgent ultrasound scan, even for apparently minor shocks.
• Minor shocks: if the patient is asymptomatic and has a normal ECG, they can safely be discharged with reassurance. ² If the patient is pregnant and is well with a normal ultrasound scan of the fetus, liaise with the obstetric team before discharge.
• Mild to moderate shocks: arrhythmias and neurological sequelae (such as aphasia) require simple observation and tend to resolve spontaneously (there are no reports of delayed lethal arrhythmias). Offer simple analgesia for muscle pain from tetany.
• Treat more severe sequelae accordingly (e.g.: volume replacement, treatment of acidosis, myoglobinuria or musculoskeletal injury secondary to trauma from being thrown away from source).
• Even if the shock was relatively minor, there may be a degree of psychological distress or shock - be aware of this and offer support as required.

• Mortality: if the initial shock is survived, the chances of survival are excellent.
• Morbidity: this depends on the extent of the soft tissue and other associated injuries but recovery from injuries tends to be good.

• Provision of information (via leaflets, health visitors, talks etc) is the key to prevention.
• Cover plugs with safety sockets.
• Never mix water and electricity.
• Always use licensed electricians.

Physics of lightning

Lightning occurs when particles moving in a thunderstorm create static electricity and negative charge builds up at the bottom of the cloud. When the difference between this and the positively charge ground is great enough, an electrical discharge occurs.

Clinical effects

• The clinical effects are very different from a high voltage shock on account of the brief and instantaneous time of exposure and the fact that it is a direct current. The popular belief that lightning is invariably fatal is wrong (the mortality rate is in fact about 30%).
• Immediate effects - cardiac arrest (asystole) which may revert but which may be followed by a secondary hypoxic arrest. There may be chest pains, muscle aches and neurological deficits (ranging from unconsciousness to transient muteness which tends to resolve within 24h). Contusions and tympanic rupture have also been reported.
• Delayed effects - limb paralysis is common with flaccidity also being observed. The peripheral pulses may not be palpable and the skin takes on a mottled blue appearance. 'Feathery' cutaneous burns (Litchenberg flowers) may occur immediately or over several hours but tend to heal well. Cataract formation, retinal detachment, optic nerve dysfunction, myoglobinuria, sensorineural deafness and vestibular dysfunction have all been reported.
• Pregnancy - there is a high rate of fetal death, even where maternal survival occurs.
• Flashover effect - this is where the current passes over and around the casualty's body but not through it. Clothes and shoes are torn apart but there are only superficial skin wounds (unless the clothes catch fire and burn the skin before being blasted off).²

Immediate management

• After the lightning has struck, the victim is safe to touch.
• Commence immediate cardiopulmonary resuscitation (CPR) - this may prevent the secondary hypoxic cardiac arrest.
• Carry out CPR even if the casualty appears dead (pupils may be fixed and dilated as a result of muscular paresis - they do not necessarily represent brain death).
• Most lightning strikes are unwitnessed and the patient may simply present as unconscious or confused - send to emergency department for assessment.

Further management

• As described above, most strikes are unwitnessed. Tell-tale clues include a casualty (or multiple casualties) found outdoors on a stormy day, exploded clothing, cutaneous burns (linear, punctate or feathery) and tympanic membrane rupture.
• Carry out full trauma assessment to look for immediate effects and initiate resuscitation as appropriate. ECG is mandatory and CT of the head may be indicated where consciousness deteriorates. If the patient is conscious, don't forget to document the visual acuities.
• Check tetanus prophylaxis status.
• Liaise with relevant departments (medical, renal, audiological medicine and ophthalmology) for monitoring of delayed effects.
• Consider differential diagnoses including cerebrovascular event, spinal cord injury, seizure, closed head injury, Stokes-Adams attack, myocardial infarction, overdose.

Outcome

Generally excellent for those who survive the initial strike. The outcome is coloured by the quantity and severity of secondary trauma.