Evaluation of ultrasound-guided pecto-intercostal block in canine cadavers.

OBJECTIVE: To describe the technique for performing an ultrasound-guided pecto-intercostal fascial (PIF) block and compare two volumes of injectate in canine cadavers. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: A total of 11 canine cadavers (11.8 ± 1.9 kg). METHODS: Parasternal ultrasound-guided injections were performed within the PIF plane, between the deep pectoral and external intercostal muscles, at the intercostal space between ribs four and five. Each hemithorax was injected with 0.25 mL kg-1 (treatment low volume, LV) or 0.5 mL kg-1 (treatment high volume, HV) of 1% methylene blue dye. Treatments were randomly assigned to either right or left hemithorax, with each cadaver injected with both treatments, for a total of 22 injections. Anatomical dissections were performed to determine staining of ventral cutaneous branches of intercostal nerves, surrounding nerves and musculature and spread of injectate. The presence or absence of intrathoracic puncture was also noted. RESULTS: The PIF plane was identified and injected in each hemithorax. No significant differences between treatments LV and HV were found for number of ventral cutaneous nerve branches stained or any other analyzed variable. The ventral cutaneous branches of intercostal nerves (T3-T8) were variably stained, and the most commonly stained nerves were T5 (6 and 10), T6 (8 and 9) and T7 (2 and 7) in treatments LV and HV, respectively. Staining outside the immediate parasternal region was noted in both treatments, with greater spread away from the parasternal region in treatment HV. No intrathoracic staining was found. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided PIF injections resulted in staining of ventral cutaneous branches and parasternal musculature; however, the spread observed was inadequate to provide effective analgesia to the sternum. In vivo studies are warranted to investigate this regional anesthetic technique in veterinary patients.

Effect of intracoelomic administration of alfaxalone on the righting reflex and tactile stimulus response of common garter snakes (Thamnophis sirtalis).

OBJECTIVE: To determine the intracoelemic (ICe) dose of alfaxalone required to induce loss of righting reflex (LRR) in garter snakes (Thamnophis sirtalis) and to evaluate the tactile stimulus response in unanesthetized and alfaxalone-anesthetized snakes. ANIMALS: 8 healthy mature garter snakes. PROCEDURES: During the first of 3 phases, snakes received each of 3 doses (10, 20, and 30 mg/kg) of alfaxalone, ICe, with a 2-week washout period between treatments. Times to LRR and return of righting reflex were determined after each dose. During phase 2, unanesthetized snakes underwent tactile stimulation testing with Semmes-Weinstein monofilaments once daily for 3 consecutive days to determine the baseline tactile pressure required to elicit purposeful movement. During phase 3, snakes were anesthetized with alfaxalone (30 mg/kg, ICe), and the tactile pressure required to induce purposeful movement was assessed at predetermined times after LRR. RESULTS: Intracoelomic administration of alfaxalone at doses of 10, 20, and 30 mg/kg induced LRR in 0, 5, and 8 snakes, respectively. For snakes with LRR, median time to LRR following the 30-mg/kg dose (3.8 minutes) was significantly shorter than that following the 20-mg/kg dose (8.3 minutes); median time to return of righting reflex did not differ between the 2 doses. Mean ± SD tactile pressure that resulted in purposeful movement in unanesthetized snakes was 16.9 ± 14.3 g. When snakes were anesthetized, the mean tactile pressure that resulted in purposeful movement was significantly increased from baseline at 10, 20, and 30 minutes after LRR. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested ICe administration of alfaxalone might be effective for anesthetizing garter snakes.

Comparison of the Sedative Effects of Alfaxalone and Butorphanol-Midazolam Administered Intramuscularly in Budgerigars (Melopsittacus undulatus).

Intramuscular (IM) administration of either alfaxalone or butorphanol with midazolam was evaluated for sedation and effects on heart and respiratory rates in budgerigars (Melopsittacus undulatus). Twenty adult budgerigars were randomly assigned to receive 1 of 2 treatments: alfaxalone at 15 mg/kg IM or butorphanol and midazolam at 2.5 mg/kg IM and 1.25 mg/kg IM, respectively. Baseline heart and respiratory rates and sedation score were collected and, after injection, time to initial effects and initial recumbency were recorded. Five minutes after injection, birds were assessed for a righting reflex, and, if absent, response to noxious stimulus was assessed by hemostat clamp on the first digit. Birds then underwent a standardized diagnostic evaluation of radiographs, jugular venipuncture, and physical examination. At the end of the physical examination, a sedation score was assigned, and birds were placed in dorsal recumbency for recovery. Times from injection to initial arousal, final recumbency, standing, and full recovery were recorded. Although time to onset of sedation was the same between groups, alfaxalone produced a shorter (P = .04) and more consistent duration of sedation (mean ± SD: 27.5 ± 5.9 minutes) compared with butorphanol-midazolam (72.0 ± 56.9 minutes). Only 3 of 10 birds receiving butorphanol-midazolam were recumbent by 5 minutes compared with 10 of 10 birds receiving alfaxalone. Radiographs were successfully obtained in 9 of 10 and 7 of 10 birds administered alfaxalone and butorphanol-midazolam, respectively. No adverse effects were observed in any bird. Intramuscular alfaxalone produces safe, effective, and reliable sedation in budgerigars and is a more consistent and shorter duration alternative to intramuscular butorphanol-midazolam.