Trauma
Question 208 of 216
You have been asked to give a teaching session to a group of medical students. The topic of the session is "Electrical Injury". Regarding electrical injury, which of the following statements is INCORRECT?
Answer:
- VF is the commonest initial arrhythmia after high voltage AC shock; treat with prompt attempted defibrillation
- Asystole is more common after DC shock; use standard guidelines
Lightning Strike and Electrical Injuries
Environmental Emergencies / Trauma
Last Updated: 4th August 2021
Electrical injuries
Electrical injury is a relatively infrequent but potentially devastating multi-system injury with high morbidity and mortality. Most electrical injuries in adults occur in the workplace and are associated generally with a high voltage, whereas children are at risk primarily at home, where the voltage is lower (220V in Europe).
Factors influencing the severity of electrical injury include:
- Whether the current is alternating (AC) or direct (DC)
- Voltage
- Magnitude of energy delivered
- Resistance to current flow
- Pathway of current through the patient
- Area of contact
- Duration of contact
Pathophysiology:
- Contact with AC may cause tetanic contraction of skeletal muscle which may prevent physical release from the source of electricity
- Myocardial or respiratory failure may cause immediate death:
- Respiratory arrest may be caused by central respiratory depression or paralysis of the respiratory muscles
- Current may precipitate VF if it traverses the myocardium during the vulnerable period (analogous to an R-on-T phenomenon)
- Electrical current may also cause myocardial ischaemia because of coronary artery spasm
- Asystole may be primary, or secondary to asphyxia following respiratory arrest
- Current pathways
- Electric current follows the path of least resistance; conductive neurovascular bundles within limbs are particularly prone to damage
- Current that traverses the myocardium is more likely to be fatal
- A transthoracic (hand-to-hand) pathway is more likely to be fatal than a vertical (hand-to-foot) or straddle (foot-to-foot) pathway
- There may be extensive tissue destruction along the current pathway
Lightning strikes
- Electrocution from lightning strikes is rare but causes about 1000 deaths worldwide each year.
- Lightning strikes deliver as much as 300 kV over a few milliseconds
- Most of the current passes over the surface of the body in a process calls external flashover
- Both industrial shocks and lightning strikes cause deep burns at the point of contact; in industry, the points of contact are usually on the upper limbs, hands and wrists whereas with lightning they are mostly on the head, neck and shoulders
- Injury may also occur indirectly through ground current or current 'splashing' from a tree or other object that is struck by lightning
- Explosive force generated by a lightning strike may cause blunt trauma
- The pattern and severity of injury from a lightning strike varies considerably; death is caused by cardiac or respiratory arrest
- In those who survive the initial shock, extensive catecholamine release or autonomic stimulation may occur, causing hypertension, tachycardia, nonspecific ECG changes (including prolongation of the QT interval and transient T wave inversion) and myocardial necrosis; creatine kinase may be released from myocardial and skeletal muscle
- Lightning also causes various central and peripheral neurological problems
Treatment of lightning strike and electrical injuries
- Ensure any power source is switched off and do not approach the victim until it is safe
- High voltage electricity can arc and conduct through the ground for up to a few metres around the victim
- It is safe to approach and handle casualties after lightning strike although it would be wise to move to a safer environment
- Follow standard resuscitation guidelines
- Airway management can be difficult if there are electrical burns around the face and neck; intubate the trachea early in these cases and soft tissue oedema can cause subsequent airway obstruction; consider cervical spine immobilisation but this should not delay airway management
- Muscular paralysis, especially after high voltage, may persist for several hours; ventilatory support is required during this period
- VF is the commonest initial arrhythmia after high voltage AC shock; treat with prompt attempted defibrillation
- Asystole is more common after DC shock; use standard guidelines
- Remove smouldering clothing and shoes to prevent further thermal injury
- Give IV fluids if there is significant tissue destruction; maintain a good urine output to increase excretion of myoglobin, potassium and other products of tissue damage
- Consider early surgical intervention in patients with severe thermal injuries
- Conduct a thorough secondary survey to exclude injuries cause by tetanic muscular contraction or from the person being thrown by the force of the shock
- Electrocution can cause severe, deep soft tissue injury with relatively minor skin wounds because current tends to follow neurovascular bundles; look carefully for features of compartment syndrome, which will necessitate fasciotomy
- All patients who survive an electrical injury should be monitored in hospital if they have a history of cardiorespiratory problems or have had loss of consciousness, cardiac arrest, ECG abnormalities or soft tissue damage or burns
- Severe burns (thermal or electrical), myocardial necrosis, the extent of central nervous system injury, and secondary multiple system organ failure, determine the morbidity and long-term prognosis
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
