Electrical injuries occur from heat damage to tissues (eg. burns, vessel thrombosis, compartment syndrome) or from the effects of current on excitable tissues (eg. cardiac arrest, seizures, asphyxia from apnoea, and so on). The most important determinants of severity are magnitude of the current (amperage) and the duration of exposure. In the ICU, electrical injury patients will likely end up intubated because of coma, difficult to ventilate because of heart failure, and in a state of rhabdomyolysis from damaged muscle tissue. The burns aspect is well explored in the chapter dedicated to burns injuries.
Electrical injuries came up for the first time in Question 3 from the first paper of 2016. Specifically, this question asked for factors which influence the severity of burns caused by electricity, as well as potential causes of reduced lung in the recently electrocuted patient. Among the things you could potentially know about electrocution, these issues are probably not the most important. However, because they were in the exam, they are discussed in some detail. More relevant detail is asked about in Question 27 from the second paper of 2017; that time the college has asked the canddiates to manage an electrocuted patient in a more conventional "how'd you manage this patient" sort of way.
As far as published literature goes, there are three main resources. In Oh's Manual, there is an entire chapter dedicated to this topic ( Electrical safety and injuries by Lester AH Critchley, Chapter 83 pp. 844). For those who want to read further, Critchley references Theodore Bernstein's 1994 paper. Bernsetein is an electrical engineer who is a world authority on electrocution and specifically on the electric chair (“From a purely historical point of view,” he says, “it’s a fascinating subject. As long as you don’t think too much about the people being killed.”) The candidate with unlimited time may also wish to explore the excellent (free to read) review by A.C Koumbourlis (2002). Solid attention to lightning injury is offered by Price and Cooper (2006). These resources were all used in equal measure to form the summary below.
Determinants of severity in electrical injury
Factors determining the severity of electrical injuries in general
- Size of the current: the greater the current (in amperes) the worse the injury. This is the most important determinant of electrical injury; the severity is the most directly related to amperage. Current in excess of 5A can cause sustained asystole.
- Duration of the current: the longer the duration of exposure, the worse the burn
- Magnitude of the voltage: the higher the voltage, the greater the damage
- Type of current (AC is more dangerous than DC) - the domestic 50Hz frequency is said to be the most dangerous in terms of causing asystole
- Tissues traversed by the current: the most important examples being the brain and heart.
- Contact conduction vs. arcing: i.e. current arcing though ionised air causes surface flash burns which may be diffuse, whereas contact with an electrode causes burns at the specific site of contact.
- Presence of a surface conductor, eg. water. Wet skin has its normally high resistance reduced a hundred-fold, with a much larger
- Subcutaneous conduction: most of the resistance to current is by the dry skin. Once it is penetrated, the resistance is greatly reduced. Resistance of the blood and muscles is approximately 20-50 times less than that of the skin (500-1000 Ohm vs 100,000 Ohm). Microshock can be the consequence, which is a risk to ICU patients who have various conductive materials suspended in their bodies.
Factors determining the severity of electrical burns specifically
- As per Kombourlis, "The severity of the burn depends on the intensity of the current, the surface area, and the duration of exposure."
- Magnitude of the current is most important factor. Current in excess of 1A is enough to cause skin burns.
- Duration of exposure is the next most important factor.
- Surface area of exposure is an important determinant of burn severity and depth: if one has a wide surface area exposed, the current is distributed across all of it, and the damage is relatively minor- whereas if all of the current was concentrated in a small area, the burn would be deep and severe. This is the rationale behind making big wide electrode pads for cardioversion.
- Magnitude of the voltage does not seem to matter (Ferreriro et al, 1998)
- Current and voltage significant enough to cause severe burns are also usually enough to cause asystole.
- Severity of the burn cannot be assessed externally: the damage is frequently to deep structures, and there may be severe coagulative myonecrosis with minimal external skin damage. Normal burns staging does not apply.
Patterns of injury associated with specific electrical injuries
- Direct current causes the characteristic violent spasmodic muscle contraction; the victim is typically "thrown" somewhere, but is rarely killed per se. The first model of the electric chair (by Thomas Edison) used direct current, and it was notoriously difficult to kill people with it.
- Alternating current causes tetanic contraction of muscle, characteristically preventing the person from letting go of the conductor. This increases the duration of exposure and is therefore more lethal. Alternating current is also more likely to causes sustained asystole.
- Traumatic injuries: you don't exactly lower yourself carefully to the ground after being electrocuted. People are either thrown against something, fall off a ladder, or collapse in some other equally dramatic manner.
- High voltage tends to result in arcing, which causes burns.
- Arcing current causes direct tissue damage by exposure to ionised superheated air, which are typically skin burns.
- Lightning strike is a form of high voltage arcing current, and tends to damage people in at least four distinct ways. You may be hit directly, or be injured by standing next to an object which explodes after being hit directly, or be standing on the electrified ground with a potential difference between one's legs (in which case current enters one leg and exits via the other). Alternatively, the lightning might simply pass over the body, causing explosive damage to the clothes but causing little harm to the tissues themselves (in which case, all the damage is done by your burning clothes).
- Pile of dead rescuers: the electrical injury is the stereotypical case of "D" being important in the "DR ABC" of basic life support. Characteristically, good samaritans come to the aid of a collapsed person, fail to recognise the electrical danger, and join them in death after trying to check for response.The electrocuted victim becomes the conductor which electrocutes the rescuer. Even the ground itself may be a danger in the context of high voltage injuries.
Specific organ system involvement in electrical injuries
- Airway electrical injuries causing airway compromise are usually not seen to any great extent in the adult population. Airway issues in electrical injuries relate more to the acute need to intubate and ventilate the unconscious electrocuted patient. However, in the paediatric population acute electrical airway injuries are well known from toddlers chewing on power cords (Pitts et al, 1969).
- Inhalational burn injuries: particularly in high voltage scenarios, people tend to be exposed to a volume of vapourised conductor. The author can recall an anecdote involving a patient who was involved in an attempt to illegally harvest copper wire. A high-voltage transformer suddenly discharged into that wire, causing it to change into a superheated cloud of rapidly expanding copper vapour. Even in the absence of such exotic injuries, electrocution can occur in the context of a fire, and inhalational injuries are common.
- Difficult ventilation due to poor lung compliance: This answers part (b) from Question 3 from the first paper of 2016. " List the potential causes of poor lung compliance", they asked. This is weird, because according to Koumbourlis, "there are no specific injuries to the lungs or the airways directly attributable to electric current." In view of this, the author was forced to concoct an imaginative list of respiratory complications for a condition which usually has none.
- Pulmonary oedema due to heart failure or enthusiastic fluid resuscitation
- Pneumothorax from CPR
- Burns causing reduced chest wall compliance
- Thoracic compartment syndrome (myonecrosis of the intercostal muscles)
- Sustained tetany: especially with AC at household frequency (50-60Hz), which can induce "an indefinite refractory state at the neuromuscular junction" (Koumbourlis, 2002), causing sustained tetanic contraction.
- Abdominal compartment syndrome (myonecrosis of the abdominal muscles, or circumferential burns)
- Lung contusions from CPR, being thrown, or blast damage
- Aspiration due to unconsciousness
- Asystole or ventricular fibrillation are a common consequence of electrical injuries. Low voltage current will usually cause VF, whereas high voltage current will usually cause asystole.
- CPR usually follows
- Myocardial stunning may result
- Myocardial necrosis will be caused by direct myocardial injury
- Arrhythmias are usually self-limiting, unless you have some other reason for arrhythmia.
Circulatory failure and shock
- Cardiogenic shock may result from a stunned or infarcted myocardium. If asystole occurred, sinus rhythm will usually return after the current is turned off - but then the person remains apnoeic, and they will arrest again.
- Coronary artery thrombosis may develop if there was direct cardiac electrical injury
- Vessel thrombosis may occur. Blood vessels are naturally ideal conduits for electricity and typically get the worst of the electrical injury.
- Large vessel aneurysms: Small vessels are more likely to thrombose; in larger vessels the higher flow is protective, but they get damage to the media of the walls, resulting in aneurysm formation or rupture.
- Compartment syndrome is the usual consequence of significant vascular injury, be it venous or arterial.
Neurological and sensory sequelae
- Unconsciousness which may be only transient
- Respiratory arrest if the current has passed through the brain
- Ruptured ear drums due to local blast trauma
- Fixed dilated pupils due to massive catecholamine release
- Seizures, which may progress to chronic epilepsy
- Corneal ulceration from exposure to ultraviolet radiation (this is given off by arcing current, and is a well-known cause of corneal damage in the welder who refuses to wear his mask).
- Cataracts from heat damage to the lens.
- Hypoxic brain injury due to asphyxia
- Monoparesis (one limb affected by paralysing nerve damage)
- Spinal cord damage
- Dysautonomia or sympathetic dystrophy
- Myonecrosis may occur due to direct coagulative heat damage
- Compartment syndrome may damage muscles which remain "uncooked", but which share a compartment with heat-damaged muscles
- Interruption of blood supply can knock out whole limbs.
- Damage tends to be concentrated around bones. Bone offers the greatest resistance to current, and therefore generates the greatest amount of heat during electrical injury.
Renal failure and electrolyte derangement due to rhabdomyolysis
- In a practical sense, rhabdomyolysis from electrical injury is no different to the rhabdomyolysis from any other cause. This topic is discussed in detail elsewhere (see: "Rhabdomyolysis as a cause of acute kidney injury"). The key features are
- Raised CK
- High serum phosphate
- High serum potassium
Intensive care management of severe electrical injuries
- Transthoracic echo: cardiac function needs to be assessed
- CT of the extremities: myonecrosis may be hidden; deep burns may have no external manifestations
- CK enzyme levels: rhabdomyolysis is the most fearsome delayed complication
- Urinary myoglobin
- Ophthalmic examination: disabling eye damage may follow lightning strike
- Debridement and amputation of damaged muscle
- Fasciotomy of limbs affected by compartment syndrome
- Vigorous fluid resuscitation aiming for a high urine output and alkaline urine. Parkland and similar formulae do not apply.
Considerations for defibrillation and cardioversion
- If they have just been electrocuted and are now in VF, is more electricity really the answer? Surprisingly, yes. One should not be deterred from following the normal ALS algorithm.
- A- the patient will remain intubated at least until airway injury is excluded
- B- mandatory ventilation may be weaned as lung compliance improves
- C- inotropes may be required to maintain a satisfactory cardiac output.
- D- anticonvulsants may be required
- E- electrolyte derangement of rhabdomyolysis needs to be monitored
- F- watch for renal failure. CVHDF/SLED may be required
- G- enteral nutrition may be commenced.
- ulcer prophylaxis is even more important: these patients have a higher than average risk of gastric ulcers (Curlings ulcers, as UpToDate refers to them).