title: Diabetic neuropathy increases stimulation threshold during popliteal sciatic nerve block.
abstract: BACKGROUND
  Peripheral nerve stimulation is commonly used for nerve localization in regional anaesthesia, but recommended stimulation currents of 0.3-0.5 mA do not reliably produce motor activity in the absence of intraneural needle placement. As this may be particularly true in patients with diabetic neuropathy, we examined the stimulation threshold in patients with and without diabetes.
  
  
  METHODS
  Preoperative evaluation included a neurological exam and electroneurography. During ultrasound-guided popliteal sciatic nerve block, we measured the current required to produce motor activity for the tibial and common peroneal nerve in diabetic and non-diabetic patients. Proximity to the nerve was evaluated post-hoc using ultrasound imaging.
  
  
  RESULTS
  Average stimulation currents did not differ between diabetic (n=55) and non-diabetic patients (n=52). Although the planned number of patients was not reached, the power goal for the mean stimulation current was met. Subjects with diminished pressure perception showed increased thresholds for the common peroneal nerve (median 1.30 vs. 0.57 mA in subjects with normal perception, P=0.042), as did subjects with decreased pain sensation (1.60 vs. 0.50 mA in subjects with normal sensation, P=0.038). Slowed ulnar nerve conduction velocity predicted elevated mean stimulation current (r=-0.35, P=0.002). Finally, 15 diabetic patients required more than 0.5 mA to evoke a motor response, despite intraneural needle placement (n=4), or required currents ≥2 mA despite needle-nerve contact, vs three such patients (1 intraneural, 2 with ≥2 mA) among non-diabetic patients (P=0.003).
  
  
  CONCLUSIONS
  These findings suggest that stimulation thresholds of 0.3-0.5 mA may not reliably determine close needle-nerve contact during popliteal sciatic nerve block, particularly in patients with diabetic neuropathy.
  
  
  BACKGROUND
  NCT01488474.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Heschl
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria.
authors.forename: B
authors.initials: B
authors.lastname: Hallmann
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Zilke
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Gemes
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Schoerghuber
authors.affiliation: Department of Internal Medicine, Medical University of Graz, Auenbruggerplatz 15, Graz 8036, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Auer-Grumbach
authors.affiliation: Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Auenbruggerplatz 2, Graz 8036, Austria.
authors.forename: F
authors.initials: F
authors.lastname: Quehenberger
authors.affiliation: Department of Anaesthesiology, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, Amsterdam 1105AZ, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Lirk
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Hogan
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Auenbruggerplatz 29/I, Graz 8036, Austria marcelrigaud@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Rigaud
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003929:Diabetic Neuropathies / Q000503:physiopathology*; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000187:drug effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D035002:Lower Extremity / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D009431:Neural Conduction / Q000187:drug effects; D019637:Orthopedic Procedures; D058748:Pain Perception / Q000187:drug effects; D010543:Peroneal Nerve / Q000187:drug effects; D012584:Sciatic Nerve / Q000000981:diagnostic imaging; D012684:Sensory Thresholds; D013979:Tibial Nerve / Q000187:drug effects; D018084:Ultrasonography, Interventional
keywords: diabetic neuropathies; nerve block; peroneal nerve; tibial nerve