Transcript Top 10 Myths of Electrical Injury

Electrical Injuries
Robert Primavesi, MDCM, CCFP(EM)
Montreal General Hospital
McGill University Health Centre
Electrical Injuries
Goals
• To identify the important complications of
electrical injuries.
• To expose the pitfalls in diagnosis.
• To explore the controversies in management.
Electrical Injuries
Objectives
• Define the population at risk.
• Determine the factors predicting the severity of
injury.
• Differentiate between high-voltage and lowvoltage injuries.
• Recognize which patients require admission or
referral.
• Decide which patients need cardiac monitoring.
Top 10 Myths of Electrical Injury
*
Top 10 Myths of Electrical Injury
Myth #1
Electrical Injuries Are Uncommon
Electrical Injuries
Epidemiology
• 124 deaths in Quebec 19871992
• 5X additional patients
requiring emergency treatment
• 3-5% of all burn centre
admissions
• Bimodal distribution
– Toddlers
– Workforce
Top 10 Myths of Electrical Injury
Myth #2
Voltage Is the Most Important
Determinant of Injury
Electrical Injuries
Factors Determining Severity
OHM’S LAW: i = V / R
1.
2.
3.
V = voltage
i = current
R = resistance
Electrical Injuries
Factors Determining Severity
JOULE’S LAW:
Power (watts) = Energy (Joules)
time
=Vxi
2
=i xR
Electrical Injuries
Factors Determining Severity
Mucous membranes
Vascular areas
• volar arm, inner thigh
Wet skin
• Sweat
• Bathtub
Other skin
Sole of foot
Heavily calloused palm
Skin Resistivity - Ohms/cm2
100
300 - 10 000
1 200 - 1 500
2 500
10 000 - 40 000
100 000 - 200 000
1 000 000 - 2 000 000
Top 10 Myths of Electrical Injury
Myth #3
High Voltage Is More Likely to Kill Than
Low Voltage
Electrical Injury
Factors Determining Severity
• A momentary dose of
high voltage electricity is
not necessarily fatal.
• Low voltage is just as
likely to kill as high
voltage.
RK Wright, JH Davis. The investigation of electrical deaths: a report of 220 fatalities.
J. Forensic Sci. 1980; 25:514-521.
Cunningham PA. The need for cardiac monitoring after electrical injury. Medical Journa
of Australia. 154(11): 765-6, June 1991.
Top 10 Myths of Electrical Injury
Myth #4
The Extent of the
Surface Burn
Determines the
Severity of Injury
Electrical Injuries
Patterns of Injury
• Direct contact
– Direct tissue heating
– Contact burns (entry and
exit)
– Thermal burns
Top 10 Myths of Electrical Injury
Myth #5
The Pathway the Electrical Current Takes
Through the Victim Predicts the Pattern of
Injuries
Electrical Injuries
Patterns of Injury
Skin Resistivity
Least
Intermediate
Most
Nerves
Blood
Mucous membranes
Muscle
Dry skin
Tendon
Fat
Bone
Electrical Injuries
Effects of 60 Hz Current
1 mAmp
5 mA
6 mA
10 mA
20 mA
100 mA
6A
20 A
Threshold of perception
Maximum harmless current
Ground fault interrupter opens
“Let-go” current
Possible tetany of resp muscles
VF threshold
Defibrillation
Household circuit breaker opens
Top 10 Myths of Electrical Injury
Myth #6
• Electricity Kills by Causing Myocardial
Damage
• CK and/or Troponin Are Good Markers
for Myocardial Damage in Electrical
Injury
Electrical Injuries
Patterns of Injury
• James T., Riddick L., Embry J. Cardiac
abnormalities demonstrated post-mortem in four
cases of accidental electrocution and their potential
significance relative to non-fatal electrical injuries of
the heart. American Heart Journal. 120: 143-57,
1990
• Robinson N., Chamberlain D. Electrical injury to the
heart may cause long-term damage to conducting
tissue: a hypothesis and review of the literature. Int
J Cardiol. 53: 273-7, 1996
Top 10 Myths of Electrical Injury
Myth #7
All Patients With Electrical Injury Require
24 Hours of Cardiac Monitoring
Electrical Injuries
Cardiac Monitoring
• Alexander L. Electrical injuries of the nervous system. J
Nerv Ment Dis 1941; 94: 622-632
• Jensen PJ, et. al. Electrical injury causing ventricular
arrhythmias. Br heart J 1987; 57: 279-283
• Norquist C., Rosen CL., Adler JN., Rabban JT.,
Sheridan R. The risk of delayed dysrhythmias after
electrical injuries. Acad Emerg Med. 6: 393, 1999
Electrical Injuries
Cardiac Monitoring
Study
Voltage
No. of
patients
Initial ECG
= Normal
Initial ECG
= Abnormal
Late
Arrhythmias
1000
48
40
8
0
< 1000
35
31
4
0
Moran and
Munster
110 – 850
42
40
2
0
Kirschmair
and Denstl
220 – 900
19
15
4
0
Fatovitch and
Lee
240
20
18
2
0
Cunningham
240
70
59
11
0
Kreinke and
Kienst
> 220
31
29
2
0
Bailey, et. al.
120 and 240
120
119
1
0
> 220
73
69
4
0
Purdue and
Hunt
Wrobel
Arrowsmith
Electrical Injuries
Cardiac Monitoring
• Cardiac monitoring is not justified in
ASYMPTOMATIC patients,
• Or, in patients with only CUTANEOUS burns,
• Who had a normal ECG after a 120 v or 240 v
injury.
Top 10 Myths of Electrical Injury
Myth #8
ALL Patients Who Are Asymptomatic and
Who Have a Normal ECG After a 120V or
240V Injury Can Be Safely Discharged
From the ED
Electrical Injuries
Patterns of Injury
• Pregnancy
– Fetal monitoring is
mandatory for pregnant
patients
• Oral commisure burns
• Cataracts
• Delayed neuropsychological sequelae
Top 10 Myths of Electrical Injury
Myth #9
The HYDRO QUEBEC GUIDELINES
Provide the Standard of Care for Electrical
Injuries
Electrical Injuries
Summary - The Challenges
• Electrical injuries involve multiple body systems.
• Entry and exit wounds fail to reflect the true
extent of underlying tissue damage.
• Electrical current may cause injuries distant from
its apparent pathway through the victim.
• Controversies exist regarding indications for
admission and cardiac monitoring following low
voltage injuries.
Electrical Injuries
The Future
•
•
•
Surveillance electrographique des patients ayant
subi une électrisation: Étude prospective
multicentrique. Investigateur principal: Benoit
Bailey, MD MSc FRCPC
21 sites across Quebec – including RVH, MGH,
MCH
Primary objectives:
1. determine the prevalence of cardiac arrhythmias in
patients on initial ECG
2. determine the prevalence of late arrhythmias in patients
who undergo cardiac monitoring
• Secondary objectives:
– evaluate the importance of electrical injury in Quebec’s
EDs
– given a normal initial ECG, evaluate if late arrhythmias
develop in patients with tetany, current across the heart,
or with >1000V
– given a normal initial ECG, evaluate if late arrhythmias
develop in patients with PMHx of cardiac disease, or
decreased skin resistance
– evaluate the incidence of cardiac problems in the year
following electrical injury
• Secondary objectives, cont’d:
– accumulate prospectively an experience with applying the
Hydro Quebec protocol
– determine the utility of measuring CK, CK-MB in
predicting ECG abnormalities and the development of late
arrhythmias
– determine the utility of measuring Troponin in predicting
ECG abnormalities and the development of late
arrhythmias
Top 10 Myths of Electrical Injury
Myth #10
“er” is an Accurate
Reflection of Life in the ER
Electric Shock:
What Should You Do?
The victim:
Felt the current
pass through
his/her body
Yes
No
Was held by the
source of the
electric current
The current
passed through
the heart
Yes
No
Yes
1 second
or more
No
Yes
No
Lost
consciousness
No
Touched a voltage
source of more
than 1 000 volts
Yes
Cardiac Monitoring
24 hours
Electric Shock:
What Should You Do?
Page 2.
Touched a voltage
source of more
than 1 000 volts
Cardiac Monitoring
24 hours
Yes
No
Yes
Has burn marks
on his/her
skin
Yes
The current
passed through
the heart
No
Evaluate and treat burns
(surgical evaluation,
look for myogolbinuria, etc.)
No
Was thrown from
the source
Yes
Evaluate trauma
No
Is pregnant
Yes
Evaluate fetal
activity
No
BENIGN SHOCK
Reassure and discharge
Direction Services de Sante
Hydro Quebec, 1995