title: Pressure Monitoring of Intraneural an Perineural Injections Into the Median, Radial, and Ulnar Nerves; Lessons From a Cadaveric Study.
abstract: BACKGROUND
  Nerve damage after regional anesthesia has been of great concern to anesthetists. Various modalities have been suggested to recognize and prevent its incidence. An understudied area is the measurement of intraneural pressure during peripheral nerve blockade. Previous investigations have produced contradicting results with only one study being conducted on human cadavers.
  
  
  OBJECTIVE
  The purpose of this investigation was to systematically record intraneural and perineural injection pressures on the median, ulnar, and radial nerves exclusively as a primary outcome.
  
  
  METHODS
  Ultrasonography-guided injections of 1 mL of 0.9% NaCl over ten seconds were performed on phenol glycerine embalmed cadaveric median, ulnar, and radial nerves. A total of 60 injections were performed, 30 intraneural and 30 perineural injections. The injections pressure was measured using a controlled disc stimulation device. Anatomic dissection was used to confirm needle placement.
  
  
  RESULTS
  Intraneural needle placement produced significantly greater pressures than perineural injections did. The mean generated pressures in median, radial, and ulnar nerves were respectively 29.4 ± 9.3, 27.3 ± 8.5, and 17.9 ± 7.0 pound per square inch (psi) (1 psi = 51.7 mmHg) for the intraneural injections and respectively 7.2 ± 2.5, 8.3 ± 2.5, and 6.7 ± 1.8 psi for perineural injections. Additionally the intraneural injection pressures of the ulnar nerve were lower than those of the median and radial nerves.
  
  
  CONCLUSIONS
  Obtained results demonstrate significant differences between intraneural and perineural injection pressures in the median, ulnar, and radial nerves. Intraneural injection pressures show low specificity but high sensitivity suggesting that pressure monitoring might be a valuable tool in improving the safety and efficacy of peripheral nerve blockade in regional anesthesia. Peripheral nerves "pressure mapping" hypothetically might show difference amongst various nerves depending on anatomic location, histologic structure, and ultrasonographic appearance.
authors.affiliation: Department of Anaesthesia and Chronic Pain Service, St Georges Hospital, London, United Kingdom.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Krol
authors.affiliation: St George's University of London, London, United Kingdom.
authors.forename: Matthew
authors.initials: M
authors.lastname: Szarko
authors.affiliation: St George's University of London, London, United Kingdom.
authors.forename: Arber
authors.initials: A
authors.lastname: Vala
authors.affiliation: Department of Anaesthesia Critical Care and Pain Management, School of Medicine, University of Valencia, General University Hospital, Valencia, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: De Andres
keywords: Injections; Pressure; Radial Nerves