Background and Goal of Study: 
Nerve injury is a rare but devastating complication of regional anaesthesia, and is
associated with excessive injection pressures.[1] Injection pressures < 26 kPa indicate perineural needle placement; pressures < 75 kPa include intraneural injections with no neurological sequelae; pressures > 103 kPa are associated with
needle nerve contact.[1,2] We assessed the effect of haptic training with a sealed air-filled 20 mL syringe (which was previously calibrated in gauge pressure (kPa) using Boyle´s law and validated against an industrial precision pressure
transducer)[3] (Fig 1) on injection pressures exerted by volunteers.

Materials and Methods: 
30 volunteers exerted what they considered to be a maximum `safe´ pressure on the syringe in 5 blinded attempts both before and after a 5 minute period of training on the device with feedback. The truncated mean of each group of 5 attempts was taken to exclude outliers, and a 2-tailed paired t-test was performed.

Results and Discussion: 
A significant reduction in individual mean injection pressures occurred after training (t-statistic: 3.148; p = 0.004); and the overall mean pressure for the group decreased from 28.0 kPa to 19.6 kPa (Fig 2). The number of volunteers exerting mean pressures > 75 kPa fell from 1 before training to 0 after training; and the number exerting pressures > 26 kPa fell from 11 before training to 3 after training.

Conclusion(s): 
Training with a simple haptic feedback device significantly reduces injection pressures, and therefore may help prevent nerve injury during regional anaesthesia.

References:
[1] Reg An Pain Med 2004;29(5):417-23
[2] Anesthesiology. 2014;120(5):1246-53
[3] EJA 2015; 32(eSupp 53):94

A pilot study to investigate effects of haptic feedback training on injection pressure during simulated regional anaesthesia