Assessment of sensory block

  • Dermatome assessment

    © Children's Pain Management Service,
    The Royal Children's Hospital, Melbourne

    Rationale

    • The area of skin that is supplied by a single spinal nerve is known as a dermatome.

    • Local anaesthetics work by blocking nerve impulses on sensory, motor and autonomic nerve fibres. The smallest diameter fibres are most sensitive to the effects of local anaesthetics: autonomic fibres will be blocked first then sensory fibres then motor fibres.

    • The sensory fibres respond to pain, temperature, touch and pressure. Since pain and temperature nerve fibres are similarly affected by local anaesthetic drugs, changes in temperature perception indicate the area where the epidural is working.

    • The area of sensory block should be assessed using cold sensation (eg ice) to establish which dermatome levels are covered. Both left and right sides need to be assessed.

    It is important to assess sensory block:

    • To ensure the spinal/epidural/caudal is covering the patient's pain.
    • To ensure the block is not too extensive, which may increase the risk of complications.

    Procedure

    1. Explain procedure and purpose to patient/parent.

    2. Wrap an ice cube in tissue/paper towel leaving part exposed.
      (This is preferable to ice in a rubber glove as many patients at RCH receiving epidurals are in the high-risk group for latex allergies eg patients with CP & Spina Bifida)

    3. Place ice on an area well away from the possible dermatome cover (eg face or forearm) and ask them to tell you how cold it feels to them.

    4. Apply the ice to an area likely to be blocked on the same side of the body and ask the patient "Does this feel the same cold as your face/arm or different?" Patients may report the ice feeling colder, warmer or the same.

    5. Apply the ice to areas above and below this point until it's clear at which level the top and the bottom of the block is.

    6. Repeat the procedure on the opposite side of the body. (Blocks may be uneven or unilateral.)

    7. Document the blocked dermatomes on the observation chart. Record both the upper and lower limits of the block:
      eg T7-L1  L = R  or  R: T7-L1   L: T10-L2

    Assessment in infants or non-verbal patients

    • It is possible to assess dermatome levels on infants and non-verbal patients by carefully observing flinching and facial expression in response to ice on presumed blocked and unblocked dermatomes.
    • Another method to determine the effectiveness of the regional blockade is by observing the patient's response to movement and their response to very gentle palpation of the operative site.

    Perform assessment 4 hourly and at the following times:

    • In the recovery room following surgery
    • On return to the ward/unit from operating suite
    • At commencement of each nursing shift
    • If the patient complains of pain
    • 1 hour after a bolus or increase in infusion rate

    Contact the Children's Pain Management Service if:

    • Epidural block higher than T3
    • No evidence of block
    • Block insufficient to relieve pain

    Adapted from Epidural Assessment Session, Fremantle Hospital Acute Pain Service, Fremantle, WA, Australia

    Devised October 2000, Updated October 2010