Ultrasound gel causes inflammation in subcutaneous tissue and muscle in Wistar rats

Dr Paul Lee-ArcherRoyal Children’s HospitalBrisbane, 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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