====== Management of Anaphylaxis to Antivenom ======

===== AUSTRALIAN SNAKEBITE PROJECT (ASP) GUIDELINES =====

==== (i) Preparation prior to commencing antivenom. ====

a. We do not recommend routine premedication with antihistamines or steroids\\
b. Dedicate one small bore (18-20 G in adults) IV line to antivenom administration and one large bore IV line (16-14 G in adults) for emergency resuscitation.\\
c. Prepare 1L Normal Saline (20 ml/kg in children) ready to give under pressure.\\
d. Prepare adrenaline 1:1000 (1mg in 1 mL) drawn up to a dose of 0.01 mg/kg (max. 0.3 mg, i.e. max 0.3 mL) and label “adrenaline for i.m. injection only (dose in mg)”.\\
e. Prepare an i.v. infusion of adrenaline 1mg in 100 mL (controlled by infusion pump or syringe driver) ready to attach by a side arm to the resuscitation line. Anti-reflux valves must be attached above the side arm on any other infusions using this i.v., to prevent adrenaline going back up into the other fluid bags. To prevent erroneous administration, do not attach the adrenaline infusion unless it is needed.\\
f. Record blood pressures on the other side to the fluid/adrenaline infusion, to avoid pronged cuff inflations and thus extravasation of infusion fluids.

==== (ii) Management of a reaction (In addition to study procedures – see ASP Datasheet 4) ====

a. Most reactions are related to the rate of antivenom infusion, and cause flushing, hypotension and bronchospasm. Some mild reactions resolve with temporary cessation of the antivenom infusion and recommencing it at a slower rate.\\
b. Envenomed patients may be severely coagulopathic, so it is important to be cautious when giving adrenaline to avoid blood pressure surges, which might lead to intracerebral haemorrhage.\\
c. Initial management of severe reactions (sudden hypotension, bronchospasm):

  * i. Suspend the antivenom infusion.
  * ii. Lie the patient flat (if not already), commence high flow/100% oxygen and support airway/ventilation as required.
  * iii. Rapid infusion of 1L N Saline (20 mL/kg in children) over 2-3 minutes.
  * iv. Adrenaline i.m. into the lateral thigh, 0.01 mg/kg to maximum of 0.3 mg (alternatively, those experienced with i.v. adrenaline infusions may proceed directly to this, as below).
  * v. Liaise with toxicology service regarding ongoing management.

d. For reactions that do not respond to initial management:

  * i. If hypotensive, repeat Normal Saline bolus as above (up to 50 mL/kg may be required).
  * ii. Commence i.v. infusion of adrenaline (0.5-1 mL/kg/hour, of 1 mg in 100 mL) and titrate according to response; monitor BP every 3-5 minutes (using the arm opposite to the infusion); beware that as the reaction resolves adrenaline requirements will fall, the blood pressure will rise and the infusion rate will need to be reduced.
  * iii. Consider nebulised salbutamol for bronchospasm, nebulised adrenaline for upper airway obstruction, and i.v. atropine for severe bradycardia.
  * iv. Seek advice urgently from the local/regional ED Consultant &/or ICU Consultant.

===== REFERENCES =====

Snakebite and Spiderbite Management Guidelines SA. Prof. Julian White

Government of South Australia Department of Health Guideline Ref G0034, August 2006

ASP Reaction Management Guidelines V1 9 Feb 2008

[[http://www.bmj.com/cgi/content/full/327/7427/1332|McLean-Tooke APC. Adrenaline in the treatment of anaphylaxis: what is the evidence? BMJ 2003;327:1332-1335]]