Paravertebral Block Using Low-concentration Lidocaine Hydrochloride and an Alfa-2 Agonist for Ovariohysterectomy in Cats

Abstract

We aimed to identify a technique for performing ultrasound-guided paravertebral block (PVB) and to determine the related isoflurane-sparing effects and potential complications during ovariohysterectomy in cats. Forty-two healthy female cats were used in the study, and we divided the cats into five groups according to five different PVB procedures. Under general anesthesia with isoflurane, paravertebral intermuscular injections of lidocaine hydrochloride (L), dexmedetomidine hydrochloride (D), lidocaine hydrochloride and dexmedetomidine hydrochloride (LD), or lidocaine hydrochloride and medetomidine hydrochloride (LM), were used as PVB. To evaluate the effects of the administration route, we evaluated lidocaine PVB using a femoral intramuscular injection of dexmedetomidine hydrochloride (LDIM) or medetomidine hydrochloride (LMIM). Ultrasound-guided PVB was performed bilaterally in the second to third intervertebral paravertebral space. After each procedure, we recorded time-sequential changes in end-tidal isoflurane concentration (ETISO), heart rate (HR), and blood pressure (BP). Compared with the reference control, ETISO increased by 15% with increasing HR and/or BP, whereas ETISO decreased with decreasing BP (<60 mmHg). Ataxia and urinary incontinence were not detected with any procedure, postoperatively, and no HR- and BP-related complications necessitating immediate treatment occurred. ETISO was significantly lower in the LD group compared with the L group. In particular, the LD group showed continuous decreases in ETISO. No significant difference in ETISO was observed between the L, LM, and LMIM groups. Ultrasound-guided PVB with lidocaine and dexmedetomidine resulted in a significant isoflurane-sparing effect and is a potentially appropriate method for inducing analgesia for feline ovariohysterectomy.