Subjective feel of injection pressure – are we guessing it right? A cadaver study.
R Sadasivan, UHCW NHS Trust, Coventry, United Kingdom.
Nerve injury remains a serious risk of peripheral nerve blockade. High opening injection pressures (OIP) may indicate direct needle nerve contact and/or intraneural needle placement.
After obtaining institutional ethics committee approval, 50mm nerve block needles were placed in three different locations in a human cadaver: intraneural in the median nerve and extraneural in the radial nerve and interscalene brachial plexus under direct ultrasound visualisation. The needles were placed by the same operator for each participant. The needles remained in situ between participants and needle tip orientation was reconfirmed by ultrasound imaging before each injection. Anaesthetic operation department practitioners injected 1 – 2mls of local anaesthetic at each site using a full 10ml syringe and scored the injection pressures as easy, medium or hard. The participants were blinded to the pressure monitor (B Smart, B Braun) that measured the injection pressure and was recorded by another observer. Actual OIP and perceived pressure were then compared.
Results & Discussion
52% of the injections placed at the median and radial nerve resulted in a OIP of ≥15psi.
64% of the injections placed at the Interscalene brachial plexus resulted in OIP of >15psi.
In total 58% (43) of the injections recorded an OIP of ≥15psi.
Of the 43 injections recorded as ≥15psi, 37% of these (16) were perceived as an “easy” injection by the ODP.