LOCAL AND REGIONAL NERVE BLOCKS
Fundamentals of LNBs The only available analgesics that can completely block perioperative pain are local anesthetics, which are administered via various routes, such as wound/tissue infiltration, regional nerve blocks, neuraxial injection (intrathecal, epidural), and injection through catheters (soaker, perineural) (Enomoto et al., 2020). Local anesthetic drugs are unique in that their analgesic effects are produced following local or regional, rather than systemic, administration (Grubb et al., 2020). Due to their ability to profoundly decrease both intraoperative nociception and postoperative pain, local anesthetic drugs are recommended for use in the majority of surgical procedures and traumatic injuries, as outlined in recent veterinary pain management guidelines. Benefits include: ● Decreased likelihood of adverse effects. ● Local anaesthetics prevent the pain (or nociceptive) impulse from reaching the CNS (Grubb et al., 2020). ● Improved anesthetic safety because the inhalant dose, or minimum alveolar concentration (MAC), required to
produce a surgical plane of anaesthesia is decreased in patients receiving local/regional blocks as part of a multimodal analgesic protocol (McNerney, 2023). ● May also play a role in increased survival from cancer, as inhalants appear to suppress cell-mediated immunity and allow proliferation of tumor cells. ● The need for rescue analgesia, including opioids, is decreased with the use of local/regional analgesia. ● Local anesthetics may decrease the incidence of intermediate duration (i.e. several days or a few weeks) and chronic (i.e. months to years to end of life) pain. ● Local anesthetics are inexpensive. Local anesthetics primarily block sodium channels in nerves, which prevents nerve depolarization and propagation of the action potential, thus preventing propagation of the pain stimulus (Grubb et al., 2020). The absorption of local anaesthetics is dependent on the site of injection, rate of injection, dosage, and vasoactivity of the injectate (Taylor et al., 2019). ● Widely available. Mechanism of action
Table 4: Common Local Anesthestics Used for Local and Regional Nerve Blocks in Small Animals Local Anesthetic Onset Of Action Duration Of Action Maximum Safe Dose
Toxic Dose
Lidocaine hydrochloride
Rapid, approximately 1–2 (<5) min Slow (Approximately 2–5 minutes for first onset and 5–10 minutes for full blockade) Slow (Approximately 5–10 minutes)
60–120 min
Dog 10 mg/kg Cat 6 mg/kg
Dogs >20 mg/kg IV Cats 11 mg/kg IV
Bupivacaine hydrochloride (HCl)
4–6 hours for diffusion techniques, potentially 6–8 hours when injected into a dental forame 4–6 hours for diffusion techniques 2–3 hours for soft tissue and 0.5–1 hour for pulp desensitization in dental procedures
Dog/cat 2 mg/kg Dog/cat 4 mg/kg IV
Ropivacaine hydrochloride (HCl) Mepivacaine hydrochloride (HCl)
Dog 2 mg/kg
5 mg/kg IV
Slow (2–5 minutes)
Dog 10 mg/kg
20 mg/kg IV
Additional notes: ● Ropivacaine is structurally similar to bupivacaine but is less cardiotoxic and less likely to cause motor dysfunction. ● Levobupivacaine has properties and dosages very similar to that of bupivacaine but is less cardiotoxic
than bupivacaine in dogs, requiring 27 mg/kg to produce cardiovascular collapse in fentanyl/ midazolam anaesthetized dogs, and may be less likely than bupivacaine to cause motor blockade in dogs. Levobupivacaine has been reported for clinical use in cats (Grubb et al., 2020). sterile 0.9% normal saline or Lactated Ringer's solution to ensure adequate coverage of the infiltration area without reduced efficacy. Precautions: ● Water or other hypotonic solutions may disrupt the liposomes and should not be used. ● BLIS should not be mixed with lidocaine as this can cause significant disruption of the liposomes. ● BLIS should not be administered intravascularly. If accidental intravascular administration occurs, patients should be monitored for adverse cardiovascular (dysrhythmias, hypotension, hypertension) and neurologic (tremors, ataxia.
Bupivacaine liposome-encapsulated injectable suspension (BLIS) (Grubb et al., 2020) This is the newest of the local anesthetics and is approved for veterinary use in the US. In 2016, the US Food and Drug Administration (FDA) approved single-dose infiltration of BLIS (13.3 mg/mL) into the surgical site to provide local postoperative analgesia for cranial crucial ligament surgery in dogs.
Onset of action : Within 2–5 minutes Duration of action : Up to 72 hours
Label-approved dose: 5.3 mg/kg (0.4 ml/kg) total dose in the dog; 5.3 mg/kg per forelimb (0.4 ml/kg per forelimb) for a total dose of 10.6 mg/kg in the cat: *If a larger volume of drug is required to infiltrate the tissue area, according to the prescribing information for dogs, BLIS may be volume expanded 1:1 with
Page 31
Book Code: VFL1526
EliteLearning.com/Veterinarian
Powered by FlippingBook