Pediatric emergency medicine trisk 1962 1962
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TABLE 90.8
LIGHTNING VERSUS HIGH-VOLTAGE ELECTRICAL INJURY
Factor
Lightning
High voltage
Duration
Energy level
Prolonged
Much lower
Type of current
Shock wave
Cardiac arrhythmia
Burns
Brief
100,000,000 V
200,000 A
Direct
Present
Asystole
Superficial, minor
Renal failures
Rare
Fasciotomy and
amputation
Rare
Usually alternating
Absent
Ventricular fibrillation
Deep, frequently
obscured
Common secondary to
myoglobinuria
Common, early, extensive
Resistance is a major factor determining the amount of current flow through
tissue. The intensity of the electrical shock produced by a certain voltage can vary
with gender and age. Tissue injury is inversely related to resistance. Dry skin
provides resistance of approximately 40,000 ohms, whereas thick, callused palms
may provide up to 1 × 106 ohms. Thin, moist, or soiled skin lowers resistance to
the 300 to 1,000 ohm range. The highly vascular, moist oral mucosa has even
lower resistance.
The type of current is another important determinant of injury. Alternating
current (AC) at low voltage is able to induce tetanic muscle contraction and is,
therefore, more dangerous than direct current (DC). Normal household 60-Hz
current changes direction 120 times per second, a frequency that induces an
indefinite refractory state at neuromuscular junctions. The resultant muscle
contractions prevent the victim from releasing his grip (“locking-on”), thus
extending the duration of contact.
DC is used in medical settings for cardiac defibrillation, countershock, and
pacing. Currents as low as 1 mA may trigger ventricular fibrillation, and high
currents may damage the heart and conducting tissues directly. Lightning is
another example of DC, discharged in a single, massive bolt that lasts 1/10,000 to
1/1,000 second. The brevity of exposure makes deep thermal injury unlikely.
