This session discusses the most practical local anesthetic blocks and their application in small animal clinical practice. These techniques do not require advanced training in veterinary anesthesia and are cost-effective. The veterinary practitioner only requires a set of needles, syringes and local anesthetics in most cases.

Aseptic techniques are always mandatory. For anesthesia of the oral cavity, chlorhexidine can be used before injection. Doses and concentrations must be always considered/calculated. See proceeding notes on "Basic Concepts on Local Anesthetics").

This session will describe these techniques and highlight anatomical landmarks and potential adverse-effects.

1. Topical Anesthesia

Local anesthetics can be used as topical anesthetics for desensitization of the skin when using a eutectic mixture of local anesthetics (EMLA cream). This cream is used for venipuncture and venous catheterization. Systemic absorption is minimal and analgesia occurs at a local level.

2. Intratesticular Anesthesia

This block blunts stress response to castration, decreases intra- and post-operative pain and prevalence of rescue analgesia.¹ It decreases inhalant anesthetic requirements during surgery. Under general anesthesia and aseptic conditions, a 23-G or 25-G needle is inserted into the testicular parenchyma and approximately 0.25–0.5 ml per testis is injected.

3 and 4. Intraperitoneal and Incisional Analgesia

Incisional anesthesia is accomplished by infiltrating the skin in the surroundings of the surgical field with local anesthetics. For laparotomy, local anesthetics are injected into the subcutaneous tissues along the linea alba, just before final aseptic preparation.

Intraperitoneal anesthesia with bupivacaine produces postoperative analgesia in cats undergoing an ovariohysterectomy;² plasma concentrations of bupivacaine were below toxic levels.³ For ovariohysterectomy, the solution of bupivacaine 0.5% (2 mg/kg) is diluted with an equal volume of saline 0.9% resulting in a final concentration of 0.25%. The final solution is equally divided in three parts and instilled into the peritoneal space, specifically over the right and left ovarian pedicles, and caudal uterus using a 3 ml syringe attached to a 22-G x 1.16'' catheter.

5. Oral Cavity (Dental Blocks)

Dental cleaning/procedures should always be performed under general anesthesia and proper intubation. Mouth-gags are no longer applied for surgical procedures involving the head and oral cavity in cats because they are associated with post-anesthetic blindness.⁴ These techniques require simple and low-cost material such as disposable 1-ml syringes and 25-mm to 30-mm needles. Stainless steel needles can be used but they are relatively costly. Larger needles may cause nerve and vascular damage.

These following blocks can be used for dental procedures including extractions or surgery of the oral cavity such as maxillectomy, mandibulectomy, among others: infraorbital, mental, inferior alveolar (mandibular) and maxillary nerve block.^5,6,7

A small amount of local anesthetic (lidocaine or bupivacaine) is required. In general, volumes may vary between 0.2–0.5 ml unless otherwise indicated. These blocks will reduce intraoperative heart rate and blood pressure, anesthetic requirements and postoperative pain. Importantly, a technique used in dogs cannot be extrapolated to the cat due to some anatomical differences between species.⁵ This lecture discusses these blocks using videos and case examples.

References

1.  Moldal ER, Eriksen T, Kirpensteijn J, et al. Intratesticular and subcutaneous lidocaine alters the intraoperative haemodynamic responses and heart rate variability in male cats undergoing castration. Vet Anaesth Analg. 2013;40:63–73.

2.  Benito J, Monteiro B, Lavoie AM, et al. Analgesic efficacy of intraperitoneal administration of bupivacaine in cats. J Fel Med Surg. 2016; in press.

3.  Benito J, Monteiro BP, Beaudry F, et al. Pharmacokinetics of bupivacaine after intraperitoneal administration to cats undergoing ovariohysterectomy. Am J Vet Res. 2016;77:641–645.

4.  Stevens-Sparks CK, Strain GM. Post-anesthesia deafness in dogs and cats following dental and ear cleaning procedures. Vet Anaesth Analg. 2010;37:347–351.

5.  de Vries M, Putter G. Perioperative anaesthetic care of the cat undergoing dental and oral procedures: key considerations. J Fel Med Surg. 2015;17:23–36.

6.  Aguiar J, Chebroux A, Martinez-Taboada F, et al. Analgesic effects of maxillary and inferior alveolar nerve blocks in cats undergoing dental extractions. J Fel Med Surg. 2015;17:110–116.

7.  Woodward TM. Pain management and regional anesthesia for the dental patient. Top Companion Anim Med. 2008;23:106–114.