Hydrofluoric Acid Toxicity
By Edouard Bastarache
I - Background:
A -
Hydrofluoric acid (HF) is one of the strongest inorganic acids.
Its use is mainly industrial, including glass etching, metal
cleaning and electronics manufacturing. It may be found in home
rust removers. Exposure is usually accidental, often due to
inadequate use of protective measures.
B -
HF burns are a unique clinical entity. Dilute solutions penetrate
deeply before dissociating, causing delayed injury and symptoms.
Burns to the fingers and nail beds may leave the overlying nails
intact.
C -
Severe burns are those following exposure to concentrated HF (50%
or greater) to 1% or more " body surface area ", HF of any
concentration to 5% or more " body surface area ", or inhalation
of HF fumes from a 60% or stronger solution. The vast majority of
cases involve only small areas of exposure, usually on the
digits.
II - Pathophysiology
:
Tissue damage is caused by two
mechanisms. A corrosive burn from the free hydrogen ions and a
chemical burn from tissue penetration of the fluoride ions.
Fluoride ions penetrate and form insoluble salts with calcium and
magnesium. Soluble salts are also formed with other cations but
dissociate rapidly, releasing the fluoride ion allowing further
tissue destruction.
III-Mortality/Morbidity :
Local effects include tissue destruction
and necrosis. Burns may involve underlying bone.
Systemic fluoride ion poisoning from
severe burns is associated with hypocalcemia, hyperkalemia,
hypomagnesemia and sudden death. Deaths have been reported from as
little as 2.5% " body surface area " burn from concentrated
acid.
IV - History
:
A -
The time to onset of symptoms is related to the concentration of
the HF. Solutions of 14% produce symptoms immediately. Solutions
of 12% may take up to an hour. Solutions of 7% or less may take
several hours before onset of symptoms, resulting in delayed
presentation, deeper penetration of the undissociated HF and a
more severe burn.
B -
Concentrated solutions cause immediate pain and produce a surface
burn similar to other common acids with erythema, blistering and
necrosis.
C -
The pain is typically described as deep, burning, or throbbing and
is often out of proportion to apparent skin involvement.
D -
A history of potential exposure to cleaning solutions should be
obtained in the last 24 hours including :
1- Concentration of acid.
2- Duration of exposure.
3- Use of protective measures.
4- Other agents in the solution.
E -
Symptoms of hypocalcaemia such as tetany, Chvostek's sign and
Trousseau's sign (although these are often absent even with marked
hypocalcemia).
Medications and intercurrent illness
predisposing to hypocalcaemia or hypomagnesaemia
V- Physical
:
A -
Weaker solutions penetrate before dissociating. Surface
involvement in these cases is minimal and may even be
absent.
B -
Three categories of appearance
:
1- A white burn mark and/or erythema and
pain.
2- A white burn mark and/or erythema and
pain, plus edema and blistering.
3- A white burn mark and/or erythema and
pain, swelling and blistering, plus necrosis.
C -
Ocular burns present with severe pain.
D -
Inhalation burns may develop acute pulmonary edema.
VI - Lab Studies
:
A
- Electrolytes : Severe disturbances can occur, especially
hypocalcemia, hypomagnesemia and hyperkalemia.
B -
Imaging Studies :
Radiographs :
CXR, if pulmonary edema is suspected; to
look for pulmonary edema
Digital - if burns to the fingers to
evaluate bone integrity.
C -
Other Tests :
ECG - Cardiac monitoring is necessary if
the burn is significant.
Arrhythmias are a primary cause of
death. Monitor for Q-T prolongation from hypocalcemia or signs of
hyperkalemia.
VII - Treatment
:
A - Prehospital Care :
1 - Skin Burns :
a - Treatment for HF burns includes
basic life support and appropriate decontamination, followed by
neutralization of the acid by the use of calcium gluconate. If
exposure occurs at an industrial site, obtain and transport any
treatment literature available.
b - Acute life threats are assessed and
managed in the usual manner. EMS personnel use gloves, masks and
gowns, if necessary.
c - Remove soiled clothing. Initially
decontaminate by irrigation with copious amounts of water.
d - Ice packs on the affected area may
alleviate symptoms. If calcium gluconate gel is available, apply
liberally to the affected area.
2 - Inhalation injuries
: oxygen, and 2.5% calcium
gluconate nebulizer.
3 - Transport the patient to the nearest appropriate medical
facility.
B - Emergency Department Care
:
1 - Skin Burns :
a - Remove soiled clothing.
b - Decontaminate by irrigation with
copious amounts of water.
c - Assess and manage life threats as
with any other cause.
d - Commence comprehensive monitoring
for significant exposures.
e - Intravenous 10% calcium gluconate
should be administered early if there is any evidence of
hypocalcemia.
f - Application of 2.5% calcium
gluconate gel to the affected area. If the proprietary gel is not
available, constitute by dissolving 10% calcium gluconate solution
in 3 times the volume of a water soluble lubricant such as KY gel.
g - For burns to the fingers, retain gel
in a latex glove.
h - If pain persists for more than 30
minutes after using calcium gluconate gel, further treatment is
required. Subcutaneous infiltration of calcium gluconate (not the
chloride salt as it is an irritant and may itself cause tissue
damage) is recommended at a dose of 0.5 ml of a 10% solution per
square centimeter of surface burn extending 0.5 cm beyond the
margin of involved tissue.
2 - Burns to the digits
: Local infiltration of
digits is not reccommended due to pain, disfugurement and
potential complications.
Alternatives are :
a - IV regional calcium gluconate
: 10-15 ml of 10% calcium
gluconate plus 5,000 units of heparin diluted up to 40 ml in 5%
dextrose. Using a Bier's ischemic arm block technique, the
solution is infused intravenously and the cuff released when the
first of the following occur: pain from the digits is resolved;
the cuff is more painful than the burn, or 20 minutes of ischemic
time has elapsed.
Treatment can be repeated after 4 hours
if needed.
b - Intra-arterial calcium gluconate
: An arterial catheter is placed
in the radial or brachial artery as needed to perfuse the affected
digits. The solution of 10 ml of 10% calcium gluconate in 40 ml of
5% dextrose is infused over a 4 hour period, followed by further
infusions repeated after 4-8 hours, if necessary.
Several treatments may be needed.
Continuous ECG and clinical
monitoring is essential during these procedures.
3 - Ocular burns :
Irrigate generously with sterile water
or saline for at least 5 minutes. Local anaesthetic may be
required. If pain persists, irrigate with a 1% solution of calcium
gluconate by diluting the 10% solution in 10 times the volume of
normal saline.
Undiluted 10% calcium gluconate
should NOT be used.
4 - Inhalation burns
:
All exposures to the head and neck
should arouse suspicion of pulmonary involvement. If there is any
doubt, admission for observation is advised.
Specific treatment includes: 100% oxygen
by mask, 2.5% calcium gluconate by nebulizer with 100% oxygen,
continuous pulse oximetry, ECG and clinical monitoring.
5 - Pulmonary
edema is treated along
conventional lines as needed.
Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
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