The Skin Wrinkle Test: a Simple Clinical Test of Regional Block Success
Condition: Skin Manifestations
MeSH terms: Skin Manifestations
Study type: Interventional

Summary: 
      Wrinkling of the hands and feet with exposure to moist environments is a commonly observed
      phenomenon. This "stimulated skin wrinkling" (SSW) is the result of direct stimulation of
      digital nerve sympathetic fibers. The resulting effect is a sympathetically mediated
      vasoconstriction with loss of finger pulp volume, overlying skin traction and wrinkling. It
      has been established that multiple disease states of the sympathetic nervous system such as
      diabetic neuropathy, leprosy and nerve injury can lead to impaired SSW of the affected limb.
      While this test has been successfully utilized for over 80 years to assess patients with
      sympathetic pathology, it has never been evaluated as a tool to determine the success of a
      regional nerve block. A regional nerve block is a method of anesthesia that involves
      injecting a local anesthetic around a particular nerve or nerve bundle in order to block the
      sensation of pain from that particular body part.

      This is of particular importance in the paediatric or non verbal population. These patients
      may not be able to reliably confirm the effectiveness of their analgesia. Pediatric
      anesthesiologists often perform these regional blocks on already anesthetized children
      whereas the non-verbal or cognitively impaired population may not be able to verbalize block
      effectiveness.

      This test, if proven effective as a means of determining block success, would be a quick,
      non-invasive and inexpensive method of ensuring adequate intra-operative and post operative
      analgesia for patients. As this is a pilot project focused on establishing the SSW test as an
      effective tool for assessing regional block success on awake volunteers, further studies
      would need to be performed to assess test effectiveness in different clinical situations.
    

Detailed description: 
      We estimated the sample size of four based on the use of a non-parametric analysis, and for
      the purpose to keep the sample of subjects to a minimum. Further that the effect size is
      expected to be a large effect (e.g. as it's a binary response yes/no wrinkling, previous
      experience and literature with the use of the cream for obtaining a pronounced effect of
      wrinkling (4-5) on the PING scale for an individual with normal peripheral nerve response on
      an unblocked digit. By using the non-parametric chi square statistical analysis it does not
      rely on means and standard deviation so it is more sensitive to even small differences beyond
      chance.

      After informed written consent is obtained, volunteers will be subjected to a digital nerve
      block of ring finger of either the left or right hands. The hand to be blocked will be
      randomized using a coin toss. The nerve block will be performed by members of the research
      team with extensive experience in regional blockade. After full sterile preparation, 3 cc's
      of 2% plain lidocaine will be used to perform the digital nerve block. Five minutes after the
      performance of the block, the affected digit will be tested by both light touch and
      temperature to confirm block success. Ring fingers of both hands of the volunteer will then
      be wrapped in an occlusive dressing after 1mL (millilitre) of EMLA (Eutectic Mixture of Local
      Anesthetic) cream is applied to the pad of each finger. Photos of the blocked finger as well
      as the corresponding unblocked finger of the opposite hand will be taken with tangential
      lighting at 0, 10, 20 and 30 minutes from the time of exposure to EMLA cream. The EMLA cream
      and occlusive dressings will be removed for each photo then reapplied after the photo is
      completed. Photos will then be evaluated by two members of the research team blinded as to
      the finger blocked in each volunteer. Evaluators reviewing the photos of individual fingers
      will be asked to grade the degree of wrinkling on a scale from 0 to 4 described by Ping Ng et
      al (a previously established scale to assess stimulated skin wrinkling).

      Clinical Care Measures To ensure safety of the study participants, digital nerve blocks will
      be performed by anesthesiologists or anesthesiology residents with experience in performing
      these blocks and under strict aseptic conditions. A limited amount of lidocaine is utilized
      to ensure adequate block but minimize duration of block as well as risks of toxicity. The
      study participants will be fully monitored with continuous 3 lead ECG, NIBP (non-invasive
      blood pressure) measurements every 5 minutes and continuous pulse oximetry for 120 minutes
      period after the analysis. The participants will be attended by at least one physician for
      this entire period. A follow up telephone call will be performed 24 hours after the
      performance of the digital nerve block to assess for complications.
    

Intervention name(s): Stimulated skin wrinkling test; Digital Nerve Block
Intervention type(s): Diagnostic Test; Procedure
Intervention description(s): Stimulated skin wrinkling induced by the application of EMLA (eutectic mixture of local anesthetic) cream to the finger pads of blocked and unblocked fingers of study volunteers (test applied to both study arms); A digital nerve block is performed by injecting a total of 3 millilitres of 2% Lidocaine at the base of the ring finger of randomized hand of the volunteer. The effect of the block is confirmed clinically before proceeding with the study data collection. Please see the description for more details on the procedure
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Blinded control trial assessing aquagenic skin wrinkling after digital nerve blockade in healthy volunteers. Digital nerve blocks to be performed on the left or right ring fingers of volunteers (to be randomized with coin toss) with the unblocked finger of each volunteer acting as its own control
Masking: Single (Outcomes Assessor)
Primary purpose: Diagnostic