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Ultrasound gel causes inflammation in subcutaneous tissue and muscle in Wistar rats. Dr Paul Lee-Archer Royal Children’s Hospital Brisbane, Australia. Background. Ultrasound guided procedures are increasingly being used in anaesthesia
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Ultrasound gel causes inflammation in subcutaneous tissue and muscle in Wistar rats Dr Paul Lee-Archer Royal Children’s Hospital Brisbane, Australia
Background • Ultrasound guided procedures are increasingly being used in anaesthesia • Hollow needles introduce small amounts of gel into tissues • Ultrasound gel is designed to be topical only, its safety as an injectable has not been assessed • This study aimed to determine what effect ultrasound gel has on subcutaneous tissue and muscle
Background • Current evidence mainly limited to case reports of contact dermatitis • Preservatives and stabilisers implicated in these reactions • Infection/contamination risk • Report of cell lysis in FNA samples contaminated with gel • Exact composition of gels not always known
Methods • 20 Wistar rats anaesthetised and injected with Parker Aquasonic 100 sterile ultrasound gel • Two injection sites: • Subcutaneously in chest • Intramuscularly in thigh • Corresponding sites on opposite side of the body injected with saline to act as a control
Methods • After seven days the rats were euthanised, sites examined and tissue harvested • Slides of the tissue samples were prepared • The examining pathologist was blinded as to which samples were controls
Results • Macroscopically, the ultrasound gel injection sites developed a hard, mobile lump and some skin necrosis • Microscopically all the ultrasound gel samples exhibited a florid inflammatory reaction • The presence of giant cells suggests a foreign-body reaction
Results Fig 1. Site of subcutaneous ultrasound gel injection exhibiting swelling and skin necrosis seven days after injection.
Conclusions • Ultrasound gel causes inflammation in rat tissue • Limitations: • Rat model may not be representative • Relatively large volumes used • Only one brand of ultrasound gel tested • Is there any clinical relevance?
Conclusions • Possible solutions • Avoid injecting through a layer of gel • Use a different medium such as sterile water • Develop a new ultrasound gel that is safe to inject
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