Background and Aims Nerve injury is a rare but well-known complication of regional anaesthesia and may arise from high pressure administration of local anaesthetic directly into nerve fascicles.
Safe injection pressures (< 20psi) 1,2 are subjective to estimate with manual injection, and this task is often delegated to skilled assistants. Pressure-limiting injection devices such as SAFIRA® (Medovate, UK) have been designed to reduce this risk.
This study measures injection pressures deemed ‘safe’ by experts and compares them with that of SAFIRA®.
Methods Following IRB approval and with consent, ten skilled Operating Department Practitioners (ODPs) and ten Anaesthetists were recruited to inject 0.9% Saline at the ‘highest pressure they thought safe’ using a series of syringes (2.5 ml, 5 ml, 10 ml, 20 ml and 50 ml) attached to a Fluke 700GO6® pressure transducer (Fluke Corp, WA, USA). One hundred measurements were recorded.
We then attached the SAFIRA® device (fitted with a 20 ml syringe) to the pressure transducer and measured the machine-limited pressure 100 times for comparison.
Results In 21/100 manual injections, estimated ‘safe’ pressure was exceeded, with the highest measured at 44psi.
Though the data was skewed by a few individuals, 50% of ODPs and 30% of Anaesthetists injected at pressures ≥20psi at least once (at all syringe sizes).
Cut-off pressures from SAFIRA® were consistently below 20psi.
Conclusions Practitioners best estimates of safe manual injection pressure is inaccurate. In contrast, a calibrated and engineered solution such as SAFIRA® does not require subjective user estimation.
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