Is it an Emergency?

This is relevant for all animals belonging to Cnidarians (Jellyfish, Corals and Anemones).

Is it likely that a clinically relevant injection of venom has taken place?

Diagnostics

Inquire re:

time of the sting,
local pain,
muscle pain, in particular back pain.

Assess:

state of consciousness.

Measure:

blood pressure/pulse,
breathing (respiratory rate).

Observe/investigate:

the sting itself ("prints", which may enable differentiation of the cause Fig. 4.11).
extent of the sting (important for the distinction between "minor stings" and "major stings" in Chironex fleckeri and Chiropsalmus quadrigatus envenoming).
Eyes: conjunctivitis, corneal lesions.
Clinical signs of regional vascular insufficiency distal to a sting on the extremities.
Clinical signs of mononeuritis multiplex distal to a sting on the extremities.
Respiratory insufficiency/respiratory failure.
Clinical signs of shock (cardiogenic shock, anaphylactic shock).

Comments

With one exception, systemic signs of envenoming following cnidarian stings occur more or less immediately after the sting. Carukia barnesi causes the so-called "Irukandji syndrome", which manifests itself after a delay of a number of hours after an initially harmless local reaction.

Is it likely that the patient had an accident due to a venomous jellyfish?

Inquire

time of the sting
local, possibly regional pain
muscle pain, in particular back pain.

Assess

state of consciousness

Measure

blood pressure/pulse
respiratory rate
oxygen saturation (pulse oximeter)

Observe/investigate

the sting itself ("prints", which may enable differentiation of the cause - see above),.

extent of the sting (important for the distinction between "minor stings" and "major stings" in Chironex sp. envenoming),

conjunctivitis, corneal lesions,
clinical signs of regional vascular insufficiency distal to a sting on the extremities,
respiratory insufficiency/respiratory failure,
clinical signs of shock (cardiogenic shock, anaphylactic shock).