title: Detection of intraneural needle-placement with multiple frequency bioimpedance monitoring: a novel method.
abstract: Electrical impedance measurements have been used to detect intraneural needle placement, but there is still a lack of precision with this method. The purpose of the study was to develop a method for the discrimination of nerve tissue from other tissue types based on multiple frequency impedance measurements. Impedance measurements with 25 different frequencies between 1.26 and 398 kHz were obtained in eight pigs while placing the tip of a stimulation needle within the sciatic nerve and in other tissues. Various impedance variables and measurement frequencies were tested for tissue discrimination. Best tissue discrimination was obtained by using three different impedance parameters with optimal measurement frequencies: Modulus (126 kHz), Phase angle (40 kHz) and the Delta of the phase angle (between 126 and 158 kHz). These variables were combined in a Compound variable C. The area under the curve in a receiver operating characteristic was consecutively increased for the Modulus (78 %), Phase angle (86 %), Delta of the phase angle (94 %), and the Compound variable C (97 %), indicating highest specificity and sensitivity for C. An algorithm based on C was implemented in a real-time feasibility test and used in an additional test animal to demonstrate our new method. Discrimination between nerve tissue and other tissue types was improved by combining several impedance variables at multiple measurement frequencies.
authors.affiliation: Department of Clinical and Biomedical Engineering, Oslo University Hospital Rikshospitalet, Oslo, Norway.
authors.forename: Håvard
authors.initials: H
authors.lastname: Kalvøy
authors.affiliation: Division of Emergencies and Critical Care, Department of Anaesthesiology, Oslo University Hospital Rikshospitalet, Oslo, Norway. sauter@start.no.
authors.forename: Axel R
authors.identifier: http://orcid.org/0000-0003-1415-8143
authors.initials: AR
authors.lastname: Sauter
mesh_terms: D000818:Animals; D003943:Diagnostic Techniques, Neurological; D004599:Electric Stimulation Therapy / Q000379:methods*; D004566:Electrodes; D009339:Needles; D009407:Nerve Block / Q000295:instrumentation / Q000379:methods*; D010992:Plethysmography, Impedance / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results; D012584:Sciatic Nerve / Q000502:physiology*; D012680:Sensitivity and Specificity; D013552:Swine
keywords: Bioimpedance; Monitoring; Needle; Nerve; Nerve stimulation; Regional anaesthesia