Pressure immobilisation bandages in first-aid treatment of jellyfish envenomation: current recommendations reconsidered

Objective: To evaluate whether applying pressure equivalent to that of pres sure immobilisation bandages (PIB) causes release of additional venom from discharged jellyfish nematocysts. Design: In-vitro experiment - the venom beads released from electrically ac tivated Chiropsalmus sp. nematocysts were viewed under direct microscopy be fore and after applying 40 mmHg pressure (replicating the pressure of PIE); and saline washings of discharged nematocysts before and after applying pr essure were tested for toxicity (time to ventricular standstill after injec ting into live prawns). Results: Applying 40 mmHg pressure caused the venom beads to visibly increa se in size, consistent with pressure expressing further venom from the disc harged nematocysts. First washings of the nematocyst shafts before compress ion produced ventricular standstill in prawns within 60 seconds (n=3); seco nd washings did not produce standstill during 540 seconds of observation (n =3); and washings after applying 40 mmHg pressure showed a return of toxici ty, with ventricular standstill in all prawns within 180 seconds (n=3). Conclusion: Discharged nematocysts are by no means empty and harmless. Appl ying pressure results in further release of nematocyst venom. The currently recommended practice of applying PIE in the initial treatment of patients stung by a jellyfish may exacerbate the envenomation, and thus should not b e recommended.