Pathophysiology:
Snake venom is mostly watery in nature. It consists of numerous enzymes,
proteins, aminoacids, etc., Some of the enzymes are proteases, collagenases, arginine
ester hydrolase, hyaluronidase, phospholipidase, metallo-proteinases, endogenases,
autocoids, thrombogenic enzymes, etc., These enzymes also act like toxins on different
tissues of the body, and are grouped under neurotoxins, nephrotoxins, hemotoxins,
cardiotoxins, cytotoxins etc., resulting in organ dysfunction / destruction. Enormous
clinical and experimental works have been published on the pathophysiology of snake
bite in relation to different species of snakes.
The quality and quantity of enzymes and other clinical constituents vary with
species and subspecies, and the response of the victims to those substances are also
variable, thus resulting in dissimilar features in different individuals. For example
hyaluronidase allows rapid spread of venom through subcutaneous tissues by disrupting
mucopolysaccharides, and phospholipase A2 has esterolytic effect on the red blood
cell membrane and causes hemolysis. It also promotes muscle necrosis. Thrombogenic enzymes promote formation of weak fi brin clot, which activates plasmin and results
in consumptive coagulopathy and hemorrhagic consequences. Venom of some snakes
causes neuromuscular blockade at pre or post synaptic level. In addition to above it
causes endothelial cell damage which results in increased vascular permeability. In
short, snake venom acts on various parts / systems / organs of the body. Venom also
causes endothelial cell damage which results in increased permeability.
Symptoms and signs:
An international expert on snakebite, the late Dr. Alistair Reid of the Liverpool
School of Tropical Medicine found out that only 10 to 15% of venomous bites end
in death. The possibility of survival, even without treatment, is incredibly good in
80-90% of cases. One of the reasons for this is that many snakebites are by nonvenomous
snakes. Secondly, a large percentage of venomous snakebites are dry bites
i.e., the snake does not always inject venom. Sometimes, it might inject only a tiny
quantity of venom. The snake can inject the quantity of venom it wants. This is an
entirely voluntary process. Hence, one can never know how much venom was injected
except by observing the progression of the symptoms. In other words the recovery
in snakebite without even treatment is great. Every traditional healer uses this fact
to his / her advantage and propagates his / her own method to treat snakebite viz.,
herbal details, “snakestone” or mantra, or plain soda water and most villagers would
be happy to go to him.
Also, every one should remember the systemic action of venom and the extent
varies from one snake to another. Complications and outcome due to snakebite may
also vary from each other and can’t be predicted by any means. Moreover, the status
of poisoning cannot be judged by the bite mark, reaction to envenomation, size or the
type of snake. Hence, one has to observe for signs and symptoms which may develop
within 24 to 48 hours.
The symptoms and signs of Viperine and Elapid envenomation as well as lateonset
envenomation are listed below.
General symptoms and signs of Viperine envenomation
Local effects
• Swelling and local pain with or without erythema or discoloration at the site
of bite
• Tender enlargement of local lymphnodes as large molecular weight Viper
venom molecules enter the system via the lymphatics.
• Effects due to coagulopathy and hemorrhagic consequences
• Bleeding from the gingival sulci and other orifi ces.
• Epistaxis.
• The skin and mucous membranes may show evidence of petechiae, purpura
and ecchymoses.
• The passing of reddish or dark-brown urine or declining or no urine output.
• Lateralising neurological symptoms and asymmetrical pupils may be indicative
of intra-cranial bleeding.
• Vomiting.
• Acute abdominal tenderness which may suggest gastro-intestinal or retro
peritoneal bleeding.
• Hypotension resulting from hypovolaemia or direct vasodilation.
• Low back pain, indicative of early renal failure or retroperitoneal bleeding.
Other effects
• Muscle pain indicating rhabdomyolysis.
• Parotid swelling, conjunctival oedema, sub-conjunctival haemorrhage.
General symptoms and signs of Elapid envenomation
Local effects
• Swelling and local pain with or without erythema or discoloration at the site of
bite (Cobra).
• Local necrosis and / or blistering / bullae (Cobra).
Neurotoxic effects
• Descending paralysis, initially of muscles innervated by the cranial nerves,
commencing with ptosis, diplopia, or ophthalmoplegia. The patient complains
of diffi culty in focusing and the eyelids feel heavy. There may be some
involvement of the senses of taste and smell.
• Problems of vision, breathing and speech.
• Paralysis of jaw and tongue may lead to upper airway obstruction and aspiration
of pooled secretions because of the patient’s inability to swallow.
• Numbness around the lips and mouth, progressing to pooling of secretions,
bulbar paralysis and respiratory failure.
• Hypoxia due to inadequate ventilation can cause cyanosis, altered sensoriun
and coma. This is a life threatening situation and needs urgent intervention.
• Paradoxical respiration, as a result of the intercostal muscles paralysis is a
frequent sign.
• Krait bites often present in early morning with paralysis that can be mistaken
for a stroke. Stomach pain which may suggest submucosal haemorrhages in
the stomach.
Other effects
• Stomach pain which may suggest submucosal haemorrhages in the stomach
(Krait).
• Eye pain and damage due to ejection of venom into the eyes by spitting cobra
(as observed in Africa)
[If features of renal failure are noted search for other causes / mechanisms]
Late-onset envenomation
The patient should be kept under close observation for at least 24 hours. Many
species, particularly the Krait and the Hump-nosed pit viper are known for the length
of time it can take for symptoms to manifest. Often this can take between 6 to 12 hours.
Late onset envenoming is a well documented occurrence. This is also particularly
pertinent at the start of the rainy season when snakes generally give birth to their
young. Juvenile snakes (young ones), 8-10 inches long, tend to bite the victim lower
down on the foot in the hard tissue area, and thus any signs of envenomation can take
much longer to appear.
Overlapping symptoms and signs
Russells Viper envenomation can also manifest with neurotoxic features. This can
sometimes cause confusion and further work is necessary to establish how wide this
might be. Development of neurotoxic features in Russells Viper bite are believed to be
pre synaptic or Krait like in nature. It is for this reason that a doubt is expressed over
the response of both species to Neostigmine. Clinical aspects and therapeutic response
in relation to some of the poisonous snakes in India is provided in Table no. 3
| Feature | Cobras | Kraits | Russells Viper | Saw Scaled Viper | Hump Nosed Viper |
| Local Pain/ Tissue Damage | YES | NO | YES | YES | YES |
| Ptosis/ Neurological Signs | YES | YES | YES! | NO | NO |
| Haemostatic abnormalities | NO | NO! | YES | YES | YES |
| Renal Complications | NO | NO | YES | NO | YES |
| Response to Neostigmine | YES | NO? | NO? | NOT Applicable |
NOT Applicable |
| Response to ASV | YES | YES | YES | YES | NO |
[* If features of renal failure are noted search for other causes / mechanisms]
Sea snakes:
Sea snake bites are reported rarely among fi shermen and / or their family members
living in the seashore area as well as among those who walk on the seashore. To begin
with there may be local pain which may be insignifi cat which appears within 60 to 90
minutes. There may not be obvious local swelling. Systemic manifestations noticed
among poisonous sea snake bite are neurological involvement, severe muscle pain,
rigidity, renal failure, hyperkalemia and fi nally cardiac arrest.
Criteria for diagnosis
An approach to snakebite is provided in Annexures VIII and IX. The criteria to
diagnose poisonous snakebite in a given clinical setting are:
a. Systemic envenomation in the form of coagulopathy and neurotoxicity.
b. Local envenomation (Table no: 4). Features of local envenomation – are grouped
under the mneumonic “PONDS”.
Table No :4 : Details of local envenomation
• Pain- pain at the site of bite, swelling and regional lymphnode
• Oozing- sero / sanguinous oozing from the site of bite
• Node- development of an enlarged tender lymphnode draining the bitten
limb
• Discoloration- discoloration at the site of bite
• Swelling – swelling is seen at the site of the bites on the digits (toes and
especially fi ngers); local swelling develops in more than half of the bitten
limb immediately (in the absence of the tourniquet) and swelling extends
rapidly beyond the site of bite (eg. beyond the wrist or ankle within a few
hours of bites on the hands or feet)
Complications and Outcome
Complications in snake envenomation are due to the heterogenous composition of
the venom. In addition the quantity and quality of the venom and the response of the
individual to the components of venom infl uence the clinical course, complications
and outcome. The complications of venom are observed in various systems viz., the
hematological, vascular, renal, respiratory, cardiovascular, endocrine, gastrointestinal,
muscular and dermatological system.
In addition to the anti snake venom, the envenomed individual requires supportive
treatment for the complications arising out of snakebite as well as the consequences of
the complication. One must also remember to look for complications developing after
infusion of Inj.anti snake venom and get prepared to treat them also.
The outcome of snakebite depends upon amount of envenomation, bite to needle
time, individual’s response to envenomation, the complications that develop following
snakebite and response to treatment. Till the patient has recovered, one cannot predict
the complications and outcome.
Investigations
20 Minutes Whole Blood Clotting Test (20WBCT)
The 20 Minutes Whole Blood Clotting Test (20WBCT) is considered as the most
reliable test for coagulation and can be carried out at the bedside without specialised
training. It can also be carried out in the most basic settings. It is signifi cantly superior
to the ‘capillary tube’ method of establishing clotting capability and is the preferred
method of choice in snakebite. The advantages, requirements and procedure for
20 WBCT are provided in in Table no: 5
Table No. 5: 20 Minutes Whole Blood Clotting Test (20WBCT)
Advantages
• The most
reliable test of
coagulation.
• Can be carried
out, at the
bedside.
• Does not
require
specialised
training.
Requirements
Dry glass test tube
(clean and new)
• 2ml disposable
syringe
• Cotton
• Antiseptic solution
• Clean gloves (one
pair)
• (The test tube
must not have
been washed with
detergent, as this
will inhibit the
contact element
of the clotting
mechanism)
Procedure
Wash hands with soap and water.
• Wear the gloves
• Collect 2ml blood from the
peripheral vein of the unaffected
limb
• Remove the needle and pour the
blood along the walls of the test
tube
• Keep the test tube untouched and
unshaken in a safe place near
the patient’s bedside at ambient
temperature for 20 minutes
• Note the time
• After 20 minutes the test tube is
gently tilted and if the blood is
still liquid then the patient has
incoagulable blood.
If the 20WBCT is normal in a suspected case of poisonous snakebites, the test
should be carried out every 30 minutes from admission for three hours and then hourly
after that. If incoagulable blood is discovered, the 6 hourly cycle will then be adopted
to test for the requirement of repeat doses of ASV. This is due to the inability of the
liver to replace clotting factors under 6 hrs.
Other Useful Tests:
• Clinical test:
– PR / BP / RR / Postural Blood Pressure
• Laboratory studies:
– Haemoglobin / PCV / Platelet Count/ PT / APTT / FDP / D-Dimer
– Peripheral Smear / Blood grouping / Rh typing
– Urine Tests for Proteinuria / RBC / Haemoglobinuria / Myoglobinuria
– Biochemistry for Serum Creatinine / Urea / Electrolytes / Oxygen Saturation
• Imaging studies :
– X-Ray Chest / CT / Ultrasound (whenever required)
• Others
– Electrocardiogram
– Special investigations depending upon clinical status.
– Ocular fundus examination