At the Laos Friends
Hospital for Children (LFHC), in Luang Prabang, Laos, it was 9pm when a
Hmong father brought his 11-year-old son into the ER with a chief complaint
of snake bite to leg, a green snake.
They were farmers and lived one hour away. Prior to leaving their
village they’d visited a local healer who had incised the bite and sucked at
the wound, then applied a tourniquet. The father and patient had taken a moped
to LFHC.
Earlier in the week an Australian PEM attending had given
the whole team an entertaining lecture on Southeast Asian snake bites. All of a
sudden it wasn’t entertainment!
The Lao nurses placed the patient on a stretcher in the ER,
instructed him to lie as still as possible. By the time I arrived they’d removed
the tourniquet, hooked him up to the monitor, placed an IV, and were washing
the bitten leg with soap and water. My Lao physician colleague was examining
the patient, noting the normal vital signs, no cranial nerve (ptosis) abnormalities, headache, respiratory
compromise, cardiovascular abnormalities, vomiting, weakness, mental status
changes, or oozing from the wound/gums. The right shin with 2 fang bites was
slightly swollen and tender.
We were reassured, but not confident that the patient would
remain stable. First of all, what snake was it? Was the green snake venomous or
not? Was it a young or an old snake? Was it a dry bite or not? If it was a
venomous snake, was it a minimal, moderate or severe envenomation? If it was a venomous snake, was it a
neurotoxic or hematotoxic (coagulopathic) snake? So many unknowns.
The laboratory had closed for the night, so no PT or INR
levels were available to determine if this was a vipid envenomation. My Lao
colleagues were all recent graduates, and none of us had managed snake bites
before! We reviewed what we knew of snakes bites.
# SE Asia is the most snake bite
affected region of the world.
# 70% of snake
bites are from non venomous species.
# Only 50% of bites
from venomous snakes actually envenomate the patient.
That was reassuring! What should we do?
1st Aid:
#Immobilize the limb (and the patient), but do
not wrap the limb.
#Calm
the patient and family.
#Clean
the wound and update tetanus vaccination.
We’d done that. What about the symptoms of snake
envenomation?
# Snake venom is a complex mix of toxic
proteins and enzymes that singly and in combination are responsible for the
toxic effects.
# Viperidae snakes include true
vipers (the dangerous Russell’s
Viper) and pit vipers (crotalines): bites cause local tissue damage and
necrosis, systemic coagulopathy and platelet dysfunction with hemorrhage, and
sometimes toxic cardiovascular and nervous system symptoms. Patients have
persistent bleeding from fang bites, gums, even intracranial hemorrhage,
rhabdomyolysis, with multiorgan failure often the cause of death.
#Elapidae (cobras, kraits, sea
snakes) bites cause local tissue necrosis (but some kraits and sea snakes don’t
cause local envenomation), and systemic neurotoxins causing a descending
paralysis, (starting with bilateral ptosis) progressing to respiratory
paralysis and failure. Some kraits have a delayed onset with prolonged duration
of paralysis, some can also cause rhabdomyolysis and renal failure (like sea
snakes).
What kinds of snakes
are in Laos?
# 22 of those are venomous snakes.
What if the snake
wasn’t green?
# Cobras are the most venomous: the
king cobra is highly intelligent,
it’s neurotoxic venom has been known to kill an elephant (yikes!) – but it’s
not green.
#Malayan krait is
shy, neurotoxic and nocturnal, 50% of its bites to humans are fatal, even after
treatment!
#Malayan pit viper is
aggressive, and hematotoxic, but survival is good.
#Russell’s viper – an
irritable snake with a powerful hematotoxic venom causing pain, swelling,
bleeding, decreased blood pressure and heart rate. It has the highest mortality
and morbidity.
What if it was a
green snake?
#Green tree viper
–not known to be a very deadly species, but is dangerous because it bites the
head, neck and shoulder areas (can be deadly bites).
#Green keelback, white lipped green
pit viper, Gumprech’s green pit viper, Vogel’s green pit viper?
How could we diagnose
viper coagulopathic envenomation without a lab?
20 minute whole blood clotting
test (2ml venous blood in a glass vessel, let stand for 20 min, tip the vessel
once, if blood still liquid and runs out, the patient has hypofibrinogenemia as
a result of venom induced coagulopathy – likely viper bite). Our 20 minute blood coagulated.
What is the treatment
for snake bites?
# Give appropriate antivenom if
symptoms develop, keep giving it until symptoms resolve.
#Supportive
care: local wound care (debridement as needed), respiratory support (intubation
and ventilation if respiratory paralysis), and hemorrhagic shock (coagulopathy, bleeding)
and acute renal failure (rhabdomyolysis) management.
We would do our best given the limited local resources.
Did our hospital even have antivenom?
Our patient was stable and asleep by now.
My Lao colleague and I found the keys to the pharmacy and
went looking for antivenom. In the pharmacy fridge, we found 2 vials of
antivenom – written in Thai. Luckily each one had 3 photos of snakes, and one
vial had a photo of a green snake! We were set. But what if one vial wasn’t
sufficient? The recommendation was to give antivenom till symptoms resolved. We
were unsure of the supply of antivenom in the city of Luang Prabang, and the
Provincial Hospital next door didn’t have any.
Antivenom Treatment:
# Pit Vipers: CroFab replaces the Antivenom (Crotalidae)
Polyvalent (ACP) manufactured by Wyeth laboratories. ACP antivenom may still be used, but has
higher incidence of allergic reactions and serum sickness. No pretreatment is necessary with CroFab, as
the incidence of allergic reactions is minimal.
# Elapidae Snakes: Decision to administer this snake antivenom
is complicated; symptoms are delayed, so if the snake and puncture wounds are
positively identified, treatment is usually administered, as neurologic
symptoms are difficult to reverse once they’ve started. However, as many bites don’t result in
significant envenomation, watchful waiting has been more recently
employed. Recommendation is to
immediately evacuate, then plan for antivenom administration.
We closely monitored our patient throughout the night. His
father climbed into his bed and they both slept soundly all night, unlike us.
But 12 hours later as we finished morning rounds, father and son were up and
looking for breakfast.
A lucky boy, and staff!
Summary
Snakes bites are a
significant and under reported medical and public health problem. Estimates are
of over 2.5 M bites/year with over 130,000 deaths/year worldwide.
Bites by non venomous
snakes are common.
Bites by venomous
snakes are not always accompanied by injection of venom (dry bites).
1st Aid
recommended in all snake bites:
#Reassure patient, avoid panic and stress that can mimic early
envenomation.
#Immobilize patient and bitten extremity with a splint or
sling.
#Rapidly transport patient to a medical facility (walking should
be avoided as muscle contractions promote venom distribution) with antivenom.
#Avoid local bite interventions: no incision and sucking
wound, tourniquet, chanting, herbal medications, or snake stones.
