LOCAL ANESTHETIC NERVE BLOCKS and ANALGESIA. Carolyn Cartwright, RVT, VTS (Anesthesia/Analgesia)

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1 LOCAL ANESTHETIC NERVE BLOCKS and ANALGESIA Carolyn Cartwright, RVT, VTS (Anesthesia/Analgesia) Effective approach for optimum pain management requires a practical multimodal anesthesia and analgesia protocol. The goal is to provide the best pain management for the individual patient and achievable for all members of the veterinary team for optimal patient outcomes. We should all strive to be patient advocates, particularly when managing pain. Managing patient pain is part of the Standard of Care, according to the AAHA regulations. The veterinary team needs to be proactive in assessment and application for patient pain management. There are numerous approaches for patient management with a large variety of pain assessment and treatment protocols. Knowledge of the physiology of pain, pharmacology of analgesics and thorough patient evaluation are essential for optimal patient outcomes. Anesthetic allows for surgical, medical or diagnostic procedures for humanitarian reasons. Historically the view was a Triad of anesthesia consisting of narcosis, muscle relaxation and analgesia. Currently, the fourth dimension added is spinal reflex suppression, and is referenced as balanced anesthesia or multimodal anesthesia. Anesthetic drugs have progressed over recent years, although they still fall short of ideal. Consequently, careful pre-anesthetic assessment of patients before sedation and anesthesia is essential to identify any physiological, pathological or drug-related factors that may complicate anesthetic management. Patient evaluation, special considerations such as proposed procedures, history, breed, drugs, equipment, facility available and the veterinary team member s skill level should be taken into consideration when developing a patient protocol and selecting particular techniques. NB: This lecture will focus on local anesthesia/analgesia protocols and techniques. The afternoon wetlab will concentrate on applied local block techniques. Some examples of drugs used to achieve balanced anesthesia are: 1. Analgesia 2. Narcosis - Opiods can be used for premedication, added intra-operatively and for postoperative pain management - NSAIDS can be used pre or postoperatively ( caution with preoperative administration due to low perfusion if hypotension occurs) - Local anesthetics For protocols on the patient awake, sedated or under general anesthesia, and in combination with other anesthetic techniques. Can be added intra or post-operatively. - Isoflurane - Thiopental - propofol

2 3. Muscle relaxation and reflex suppression - Isoflurane - thiopental How do we determine what protocol and when to add analgesics? Patient Management requires - We need to assess if the procedure is: Painful how invasive is the procedure who is performing the procedure and time required is the patient already injured or diseased would the patient benefit from the other effects of analgesics, ex: Sedation - Patient assessment - Providing non-pharmacological comfort and care - Differentiating pain from stress - Appropriate analgesia/sedation - Administering medications and performing analgesic techniques - Monitoring and treating drug effects - Assessing patients pre, intra and post- operatively - Optimal Communication with veterinary team and clients - Maintain Medical record and controlled substance records Recognition and Assessment of the patient pain level is key to optimal pain management - Pain assessment on the awake patient: Pain assessment can be Objective or Subjective data, and can be affected by the assessors skill level and experience - Objective is observation of the autonomic nervous system, endocrine responses and behavior cardiovascular/respiratory response, muscle guarding, movement, food and water intake Objective data is measured either directly or remotely, by assessing with hands on, telemetry, video or force plate for example. - Subjective Pain Scoring may be affected by the following factors; Temperament Vocalization Posture Locomotion level of sedation behavioral changes

3 There are many pain-scoring systems, from simple to complex. - Simple Descriptive Scale - Visual Analogue Scale - Numerical Rating Scale - Multifactorial Pain Scale Pain assessment on the anesthetized patient requires understanding the responses to nociceptive stimulation under anesthesia. - Generally noxious stimulation causes a stress response - True pain is only experienced by conscious animals - Stress triggers the sympathetic nervous system resulting in increased blood pressure, heart rate, muscle tone and respiratory rate and decreased depth of anesthesia resulting in awakening Can we safely combine analgesics? The answer is yes as long as understand the pharmacology and side effects of the drugs chosen, and be aware of how drugs interact. This combination can create a more powerful way to control pain. Each drug has the potential to act at a different location within the body, pending combination and route administered, ex: Lidocaine is administered for cardiovascular, GI or local anesthetic effects. LOCAL ANESTHETICS Local anesthesia is the use of chemical agent on sensory neurons to disrupt nerve impulse transmission, results in temporary loss of sensation. - Local anesthetics can be used on patients that are: - Conscious - Sedated - Under general anesthetic - used in combination with other anesthetic techniques - use intra-operatively or post-operatively - Local anesthetics do not affect the brain, therefore no sedation effects (Caution is used when administering local anesthesia for head blocks) - Local anesthetics can have toxic effects - Always pre calculate the toxic dose, the toxic dose is IV and for local blocks we are administering a depot injection, so well under safe dosage - Local anesthetics have rapid absorption, are generally administered in vascular areas and blood flow to the area is a major rate limiting step. This is why epinephrine, a vasoconstrictor, is used commonly with lidocaine How do we determine when to use local analgesics and which technique and drug is indicated? - Is the procedure painful? - How invasive is the procedure? - Who is performing the procedure?

4 - Is the animal already injured / diseased? - Would the animal benefit from the other effects of analgesics? Ex: Sedation Reasons to use Locals; - Perform procedures on conscious animals - Aids in pain control in traumatized patients E.g. Eye examination - Analgesia during general anesthesia Amount of general anesthetic can be lower Avoids excessively deep planes of anesthesia Commonly used Local Anesthetics: Lidocaine - Commonly used for short duration or infusion - Toxic effects: Sedation, convulsions (Tx: Diazepam) - Duration of effect is 1 2 hours with epinephrine, and about 1 hour with lidocaine neat - Toxic doses: Canine 22 mg/kg IV, Feline 11 mg/kg IV - Maximum safe doses: Canine 10 mg/kg, Feline 6 mg/kg Mepivacaine (Carbocaine) - Indicated to use when longer duration of action is needed - Duration of effect is hours - Toxic dose: 20 mg/kg Bupivacaine (Marcaine) - Commonly used for longest duration - Duration of effect 2 + hours - Toxic dose: 4 mg/kg IV - Maximum safe dose: 2 mg/kg - Toxicity: Cardiac arrhythmias (TX: bretyllium) Levobupivacaine Ropivacaine (Naropin) - Duration of effect about 2 hours - Toxic dose: 5 mg/kg - Maximum safe dose: 3 mg/kg Strict aseptic technique should be adhered to when administering any local blocks.

5 Surface and Infiltration Anesthesia - Simply infiltrate the tissue/region required to block - Ideal for small mass excision and diagnostics - As a technique, use the previous wheal (bleb) to pass needle to next part of block - Avoid infected tissue - Care with epinephrine in extremities - Splash Blocks - Use lidocaine or bupivacaine - Place on incision prior to closing skin and after closure of body wall - Reduces incisional pain - Volume used depends on toxic dose and size of site - Wound Infiltration Catheter aka: Wound Soaker Catheters - Can administer as intermittent or continuous rate infusion (CRI) - intermittent bupivacaine every 6-8 hours - CRI lidocaine 0.03 mg/kg/min, can dilute solution to deliver 3-5 ml/hr - Works well for very invasive surgery such as limb amputation - Can provide poste-op analgesia for 2-3 days - Can be placed prior to surgery - Commercial kits are available (Mila) - Mucosal Analgesia - Surface : - Lidocaine spray often used for endotracheal intubation in cats - Metered dose is 10mg! - Can use catheter and vial lidocaine - Ointments and gels - Lidocaine gel commonly used to assist with: - Urinary catheter - Nasal catheter (O 2 ) - Eutectic Mixture of Local Anesthetic (EMLA) - Lidocaine and prilocaine - Surface analgesia for catheterization - Low toxicity - MethHb from prilocaine - Care in use in cats

6 - Lidocaine Patch - 5 % Lidocaine - Local effect - Placed either side of wound/ incision - Currently unavailable in Canada - For further information for the use of these patches, refer to Weil & Ko. Compendium, April 2007 pp Nerve blocks (the application of the nerve blocks will be covered in the afternoon wetlab sessions) - Use of a nerve stimulator with an insulated needle will increase accurate deposition of local anesthetic around the nerve bundles. The use of Ultrasonography to assist nerve location is becoming more popular in veterinary medicine. - Nerve Blocks of the Head used for Dental, Aural and Ophthalmic Procedures Canine Feline - Infra-orbital - Mandibular - Mental - Auricular - Limb Blocks

7 3 Point Hindlimb block - For thoracotomies and chest pain

8 Epidurals

9 Common events - Blood or CSF through needle - Entered venous sinus or spinal area - Back out slightly - Try again - Resort to systemic analgesics

10 - Striking bone; Either: - Dorsal spinal column - Not in space, walk off - Once placed Inside surface spinal canal Okay to inject Before Finishing Anesthetic - Consider repeat dose opioids - Anti-emetic at vomiting centre - Low dose triggers chemoreceptor trigger zone - Usually don t observe vomiting when post-op opioids are given - Consider keeping patient on infusions - Long anesthetic may consider repeat local epidural or blocks - Need to watch for side effects - Dysphoria - Cardiac arrhythmias Post-surgery during recovery - Continue powerful analgesics first 24 hours - Top-up IV hydromorphone, morphine intermittently or CRIs and can use fentanyl patches - Can continue any intra-operative infusions - Morphine can produce dysphoria after 24 hours - Morphine-3-glucuronide - Usually decrease ketamine infusion to 0.3mg/kg/hr - Dysphoria possible - May add NSAID at this point Postoperative Period - Carprofen, Meloxicam, Onsior - Monitor for pain - Use pain assessment charts - RVTs very skilled at being in tune to patient needs - Repeat opioids as necessary - Change infusion rates as necessary - Review analgesic approach - Ice packs - Good nursing care Continuing Analgesics - May be able to move onto less powerful opioids - Tramadol (efficacy?) - Buprenorphine (contraindicated if using Fentanyl patch) - Butorphanol (contraindicated if using Fentanyl patch)

11 - Meperidine (short acting) In Summary - Choose powerful analgesics for invasive surgery - Use several drugs and techniques wisely - Good multimodal regimes vs polypharmacy - Ensure plasma concentrations are maintained - Monitor for pain (use score sheets) - Adjust analgesic regime as necessary - Gradually wean off powerful drugs as healing occurs The benefits of local anesthetics as part of your patient pain management are: - Lower anesthetic agents used - Lower intensive monitoring post-op, monitor vitals & pain but not dealing with uncomfortable patient through the night - Quicker recovery time - Greater patient comfort & care - Local anesthetics are economical