Local analgesic techniques for gonadectomy: Focus on testicular block

More than 53 million pet dogs (69% of total US dog population) and approximately 47 million pet cats (80% of total US cat population) had been gonadectomized in the US at the time of the most recent Pet Ownership Survey (2016), according to data from the American Veterinary Medical Association.¹ Surgical pain is most effectively controlled using multimodal analgesia, which should include local anesthetic blockade.^2,3 Advantages of local anesthetics include intraoperative nociception and postoperative pain relief that predictably extends beyond the expected duration of the drug.⁴ In general, local anesthetics are inexpensive and easy to use. Local anesthetic techniques for gonadectomies include peritoneal lavage and testicular block, which are both highly effective and easy to perform. This article focuses on testicular blocks. Intraperitoneal lavage was covered in the July 2022 issue of dvm360®.

Testicular block for castration⁵

Although called a testicular block, local anesthetic injected into the testicle rapidly diffuses to the spermatic cord and associated structures⁶ and provides intraoperative nociception and postoperative pain relief from surgical crushing of the tissue at that site. To perform the block, insert a sterile hypodermic needle (25- to 22-Ga needles of 5/8-1 or 1.5 in, depending on patient size) into the testicular body, with the needle tip directed toward the spermatic cord. After aspiration to ensure the needle tip is not in a blood vessel, inject half the total recommended dose of bupivacaine, ropivacaine, or lidocaine for the species (Table), or the volume that causes the testicle to become slightly more turgid. Stop injecting when either of those 2 endpoints are reached. Expect to inject between 0.1 to 2.0 mL per testicle, depending on dog/cat size. A block of the skin at the incision site should be included with the testicular block. In cats, the incision is generally made directly over the testicle to infiltrate the drug as the needle exits the testicle to block the skin and subcutaneous tissue. In dogs, the incision is generally made at a prescrotal site, and the drug should be injected into the skin and subcutaneous tissue at that site. Testicles that have been injected often appear bruised when visualized during surgery. This is inconsequential, as the testicle is being removed and any pain caused from bruising would be minimal compared with the profound effect of the local anesthetic.

Frequently asked questions

Is there a concern of uptake of the drug into the bloodstream?

The testicular block is widely used in many species, yet a thorough search yielded no safety studies. Safety could potentially be predicted from studies using injection of local anesthetics into other highly vascularized tissue (eg, in the oral cavity). In this light, this block can be considered safe when, as with all drugs, used at the correct dose and using the correct technique (ie, aspirate before injecting).

Which drugs are preferred for this technique?

The longer-duration drugs, bupivacaine and ropivacaine, are generally preferred and have been used for this block (Table). However, some clinicians use only lidocaine because the testicles are highly vascularized, potentially increasing likelihood of systemic drug uptake. There is no evidence that one drug is better/safer than another, so the clinician should use experience and comfort with the drugs to decide which drug to use for this block.

Occasionally, in dogs, the scrotum looks very irritated after the block. Any solutions?

The scrotal irritation is more likely due to clipping and scrubbing at the injection site rather than the small-gauge needle insertion. The scrotum does not require clipping and scrubbing for this technique, just as a vaccination site does not need to be clipped and scrubbed. The worry is further decreased, as the testicle will be removed. Another option is to slide the testicles under the skin up toward the surgical incision site and inject them through the abdominal wall instead of through the scrotum.

How long do I have to wait before starting surgery?

In a study in pigs, maximum lidocaine concentration was achieved at the spermatic cord within 3 minutes of injection.⁶ Bupivacaine and ropivacaine could take slightly longer.

Any special considerations for cats?

No, as with most science, there are fewer publications for cats, but the block is widely used.

Tamara Grubb, DVM, PhD, DACVAA is a board-certified veterinary anesthesiologist with a strong clinical interest and research focus in pain management. She is President-Elect of the International Veterinary Academy of Pain Management (IVAPM), a certified veterinary acupuncturist and a consultant in a private small-animal veterinary practice.

References

1. American Veterinary Medical Association. AVMA Pet Ownership and Demographics Sourcebook. 2017-2018 Edition. American Veterinary Medical Association; 2018.
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6. Ranheim B, Haga HA, Ingebrigtsen K. Distribution of radioactive lidocaine injected into the testes in piglets. J Vet Pharmacol Ther. 2005;28(5):481-3.
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10. Fernandez-Parra R, Zilberstein L, Fontaine C, Adami C. Comparison of intratesticular lidocaine, sacrococcygeal epidural lidocaine and intravenous methadone in cats undergoing castration: a prospective, randomized, investigator-blind clinical trial. Vet Anaesth Analg. 2017;44(2):356-363. doi:10.1016/j.vaa.2016.03.010
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12. Kushnir Y, Toledano N, Cohen L, Bdolah-Abram T, Shilo-Benjamini Y. Intratesticular and incisional line infiltration with ropivacaine for castration in medetomidine-butorphanol-midazolam sedated dogs. Vet Anaesth Analg. 2017;44(2):346-355. doi:10.1016/j.vaa.2016.03.007