Page 632 - ACCCN's Critical Care Nursing

Emergency Presentations 609

TABLE 22.11 Characteristics and clinical manifestations of snake venom 156,165,166

Toxin Effects Signs and symptoms
Neurotoxin Blocks transmission at the neuromuscular junctions, causing l Ptosis (drooping of upper eyelids)
skeletal and respiratory muscle flaccid paralysis, either l Diplopia (double vision)
presynaptic and/or postsynaptic. l Ophthalmoplegia (partial or complete paralysis of
eye movements)
l Fixed, dilated pupils
l Muscle weakness
l Respiratory weakness, paralysis
Haemotoxin Causes coagulopathies, resulting in either: l Bleeding from bite wounds
l defibrination with low-fibrinogen, unclottable blood, but usually l Bleeding at venipuncture sites
with a normal platelet count; or l Haematura
l direct anticoagulation with normal fibrinogen and platelet count.
Both cause an elevated prothrombin ratio (INR).
Myotoxin Causes myolysis, resulting in generalised destruction of skeletal l Muscle weakness
muscles with high serum creatine kinase and leading to l Muscle pain on movement
myoglobinuria and occasionally severe hyperkalaemia. l Red or brown urine, which tests positively to blood

mobilise, to minimise distribution of any injected venom. To identify the likely snake involved and the correct anti-
Once applied the pressure immobilisation bandage is not venom required, a bedside snake venom detection kit
removed until the patient is in a hospital that is stocked (SVDK) is used at the bite site or with urine. A swab of
with antivenom. 164 the washings from the bite is collected by leaving the
pressure immobilisation bandage on and creating a
A brief and focused history explores the time and circum- window over the bite site to expose the area. Testing takes
stances of the bite, a description of the snake (colour, about 25 minutes. If there are signs of systemic envenom-
length), geographical location and the application of any ation, urine can be used to perform the test; blood should
first aid. The patient is assessed for general symptoms be avoided, as it is unreliable. A positive result indicates
including headache, nausea, vomiting, abdominal pain, that venom from a particular snake is present, but does
collapse, convulsions and anxiety (these alone do not not mean that systemic envenomation has occurred,
indicate envenomation), 164,165 as well as blurred or double while a negative result does not exclude systematic
vision, slurred speech, muscle weakness, respiratory dis- envenomation. 163,165
tress, bleeding from the bite site or elsewhere, and pain
and swelling at the bite site and associated lymph nodes.
Patients with suspected snake bite are located in an acute Practice tip
area with full monitoring available, with symptomatic
patients placed in a resuscitation area. The patient requires Whole blood clotting time is performed by drawing 10 mL
IV access and collection of blood for pathology tests venous blood and placing in a glass test tube. If the blood has
including FBC, UEC, CK and full coagulation studies. not clotted within 10 minutes, a coagulopathy is likely to exist,
Unnecessary venipunctures should be avoided, including suggesting envenomation. 166
sites where it may be difficult to control bleeding should
it occur. Healthcare settings with no ready access to
pathology services may need to perform whole blood In patients with known snake bite and systemic enven-
clotting time testing at the bedside to assess for any omation, antivenom administration is required if there is
coagulopathy. any degree of paralysis, significant coagulopathy, any
myolysis (myoglobinuria or CK >500), or unconscious-
All probable snake bites require observation for at least ness or convulsions. In an asymptomatic patient with
12 hours, as some serious symptoms may be delayed. 164,165 normal pathology and a negative or positive SVDK, it is
Assess for tachycardia, hypotension or hypertension, and likely that envenomation has not occurred. In this case,
a falling oxygen saturation, respiratory rate, forced vital the pressure immobilisation bandage is removed under
capacity (FVC) or peak expiratory flow rate (PEFR), indi- close observation in a resuscitation area. The patient is
cating respiratory muscle paralysis. 165 Frequent neuro- fully reevaluated including repeat blood test, assessing
logical observations focus on identification of muscle coagulation parameters, within 1–2 hours after removal
weakness and paralysis; note any ptosis, diplopia, of the pressure bandage. If the patient’s condition remains
dysphagia, slurred speech, limb weakness or an altered unchanged, further observation and repeat blood
level of consciousness. Insert an indwelling catheter for tests at 6 and 12 hours are required. Patients with no
close monitoring of urine output and presence of evidence of envenomation after 12 hours may be
any myoglobin. discharged. 163,167