Validation of the Soft Embalmed Thiel Cadaver as a High Fidelity Simulator of Pressure during Targeted Nerve Injection

Introduction: Although administration of regional anaesthesia nerve blocks has increased during the COVID 19 pandemic, training opportunities in regional anaesthesia have reduced. Simulation training may enhance skills, but simulators must be accurate enough for trainees to engage in a realistic way - for example detection of excessive injection pressure. The soft embalmed Thiel cadaver is a lifelike, durable simulator that is used for dedicated practice and mastery learning training in regional anaesthesia. We hypothesised that injection opening pressure in perineural tissue, at epineurium and in subepineurium were similar to opening pressures measured in experimental animals, fresh frozen cadavers, glycol soft-fix cadavers and patients.

Methods: We systematically reviewed historical data, then conducted 3 validation studies delivering a 0.5ml hydrolocation bolus of embalming fluid and recording injection pressure. First, we delivered the bolus at 12ml.min^-1 at epimysium, perineural tissue, epineurium, and in subepineurium at 48 peripheral nerve sites on three cadavers. Second, we delivered the bolus at using three infusion rates: 1ml.min^-1, 6ml.min^-1 and 12ml.min^-1 on epineurium at 70 peripheral nerve sites on five cadavers. Third, we repeated three injections (12ml.min^-1) at 24 epineural sites over the median and sciatic nerves of 3 cadavers.

Results: Mean (95%) injection pressure was greater at epineurium compared to subepineurium [geometric ratio 1.2 (95%CI: 0.9 – 1.6)], P = 0.04; and perineural tissue [geometric ratio 5.1 (95%CI: 3.7 – 7.0)], P < 0.0001. Mean (95%) injection pressure was greater at 12ml.min-1 compared to 1ml.min^-1 [geometric ratio 1.6 (95%CI: 1.2 – 2.1), P = 0.005]. Pressure measurements were similar in study 3 (P > 0.05 for all comparisons).

Discussion: We conclude that the soft embalmed Thiel cadaver is a realistic simulator of injection opening pressure.