Spider and marine envenomation

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Red flags

• Funnel-web envenomation is the only ANZ spider bite that kills — sweating, fasciculations, hypertension and pulmonary oedema within minutes mandate funnel-web antivenom two vials IV repeated until controlled, not observation.
• Pressure immobilisation is for funnel-web only — do not apply it to red-back bites, jellyfish stings or blue-ringed octopus bites; it prolongs red-back pain and is irrelevant to the marine syndromes.
• Vinegar (acetic acid) inactivates box-jellyfish nematocysts; freshwater or rubbing triggers further discharge. In an unidentified tropical sting, douse with vinegar first.
• Box jellyfish can cause cardiac arrest within minutes, especially in a child — start CPR, douse with vinegar, give box-jellyfish antivenom three vials IV plus magnesium 2 to 4 g IV, and continue resuscitation.
• Blue-ringed octopus envenomation produces a fully awake, paralysed, apnoeic patient — intubate and ventilate for 4 to 15 hours and recovery is complete; there is no antivenom and neostigmine does not help.
• Irukandji syndrome presents 5 to 40 minutes after an apparently trivial sting with severe back and abdominal pain, hypertension and a rising troponin — admit and observe for cardiomyopathy; intracerebral haemorrhage is the feared complication.
• Red-back spider antivenom may be no better than placebo — the RAVE study cast doubt on its efficacy; lead with analgesia, reserve antivenom for refractory pain, and give it intravenously in a monitored area because anaphylaxis to the equine protein is well described.