194 Toxinology Emergencies
SNAKE BITES(ii) Give the appropriate species-specific monovalent antivenom if
the snake species has been positively identified on VDK (or by an
expert herpetologist).
(a) start with two vials (2000 units) in brown snake envenoming,
occasionally up to 10 vials (10 000 units) for critical cases
(b) give up to two vials (6000 units) for tiger snake envenoming;
one or two vials (6000 to 24 000 units) for taipan; and start
with one vial for envenoming by black snake (18 000 units)
and death adder (6000 units).
(iii) Get expert advice urgently if the snake species is still unknown in
an envenomed patient
(a) tiger snakes are the only terrestrial venomous snake native to
Tasmania, simplifying the use of antivenom in that state
(b) in the other Australian states, give polyvalent antivenom two
to four vials i.v. This is more expensive and carries a greater
risk of anaphylaxis.
(iv) Give antivenom slowly by i.v. infusion over 30 min after 1 in 10
dilution with normal saline
(a) give an undiluted neat bolus of antivenom as a life-saving
measure if the patient is in cardiac arrest or has circulatory
collapse.
(v) Pre-treatment with adrenaline (epinephrine) is unhelpful,
but adrenaline must be available as there is the possibility of
anaphylaxis to the horse-serum derived antivenom:
(a) the risk of an immediate-type hypersensitivity reaction to
antivenom is 41% for polyvalent and tiger snake antivenom
and 10% to brown snake antivenom, but overall only 5%
reactions are severe anaphylaxis.
4 Give tetanus prophylaxis according to the patient’s immune status.
5 Refer all patients with signs of systemic envenomation to ICU or the local
toxicology unit.
6 Remove the pressure-immobilization bandage and observe carefully those
patients who remain systemically well, with no clinical signs of envenoma-
tion and who have normal initial laboratory blood tests.
(i) Repeat the laboratory tests 1 h after bandage removal, including
INR, aPTT and CK.
(a) treat with antivenom if they become abnormal, of if the
patient develops any clinical signs of envenoming.
(ii) Observe the patient for a further 12 h prior to discharge, with
careful clinical examination looking particularly for delayed
neurotoxicity or myotoxicity.
(iii) Repeat the same laboratory tests including INR, aPTT and CK
at 6 h and again at 12 h after bandage removal. If these remain
normal and the patient is well, discharge.