Nerve damage can occur after ultrasound-guided peripheral nerve block (PNB). Injection pressure monitoring could improve the safety of PNB. The aim was to analyse parameters affecting pressure measurements during PNB.

The flow characteristics of needles connected to a pressure-sensing device were evaluated. Needles were placed under ultrasound guidance extra or epineurally in nerves/plexus of fresh cadavers. Using three flow rates, 4 mL of saline was injected and plateau pressure was measured. Finally, orthopaedic surgery patients receiving PNB were enrolled for an observational real-time pressure monitoring study. During PNB, periods with pressure > 50 mmHg were noted (high pressure ≥ 750 mmHg). A blinded investigator recorded injection pressure curves and peak pressure.

The needle diameter influenced the injection pressure (β = 66.8; P <  0.0001). Non-echogenic needles increased the injection pressure (β = 82; P =  0.0009) compared with echogenic needles. Cadaver injection pressure was higher for intraneural (255 [122.5–555] mmHg) versus extraneural needle tip location (90 [50–158] mmHg; P < 0001); for high flow (9.6 mL/min; 470 [265; 900] mmHg) versus low flow (1.2 mL/min; 120 [71–250] mmHg) (P <  0.001) and for cervical roots (900 mmHg, intraneurally) compared with nerves (300 mmHg, intraneurally). In 37 patients and 61 procedures, there were 7 [1–18] peaks of injection pressure per procedure. Pressure was noted > 750 mmHg during 13.80% of the procedural time.

Needle diameter, needle tip location, type of nerve/plexus, flow rates, and the anaesthetist can have a significant effect on injection pressure values and monitoring.

Trial registration: ClinicalTrials.gov ID: NCT03430453