Estudio del periodo de latencia de la bupivacaína tras su administración por vía epidural lumbosacra, espinal o epidural tras la punción de la duramadre, y evaluación de la inyección epidural sacrococcígea como alternativa a la lumbosacra en el perro (Canis familiaris L.)

Zusammenfassung

INTRODUCTION Epidural anaesthesia is a popular locoregional anaesthetic techniques in dogs, especially in the lumbosacral space (LS). OBJECTIVES Comparing the bupivacaine onset time when administered via epidural injection at LS and SCO intervertebral spaces, spinal anaesthesia (SPI), and dural puncture epidural (DPE), comparing the cranial spread of different volumes of epidural injectates between the LS and SCO approach, and adaptation and comparison of two advanced methods of identification of the epidural space to the SCO approach. MATERIALS AND METHODS Article 1 Forty-one dogs randomly received one of the following: epidural anaesthesia in the LS or SCO approach, spinal anaesthesia (SPI), or dural puncture epidural (DPE). The presence of the patellar reflex was confirmed before the neuraxial block and every 30 seconds after until it disappeared (Westphal’s sign). The time between the injection and this disappearance was taken as the onset time. Data was analysed using a one-way ANOVA for the trimmed means and the Kaplan-Meier function (p<0.05). Article 2 A total of 13 greyhound cadavers randomly received an epidural injection of diluted contrast in incremental doses via the LS or the SCO approach. After each injection, a computed tomographic scan was performed. The cranial spread of contrast was studied in the transverse images using the most cranial image with 90% (or more) of the epidural space filled with contrast. Data was analysed using the Student’s t-test and a REML (p<0.05). Article 3 Sixty-two dogs requiring epidural anaesthesia were recruited. In all cases the epidural anaesthesia was SCO and the identification of the epidural space was performed randomly using the nerve stimulation technique (NS) or the running-drip method (RUN). In all cases, the success of the epidural injection of LA was determined by the absence of patellar reflex 5 minutes after the injection. Data was analysed using the Mann-Whitney test and the Fisher’s exact test (p<0.05). RESULTS AND DISCUSSION Article 1 The SCO onset time was 3.0 (1.0–5.0) minutes and it was longer than the SPI onset time (0.5 (0.5–0.5) minutes) (p=0.009). The Kaplan-Meier curve showed differences in the onset time between groups when no other factor is controlled. This curve also showed a great overlapping between the DPE and LS groups with the SPI. There was no difference in the number of attempts or the time required to perform the different neuraxial techniques. The time to complete the epidural injections (SCO and LS) tended to be shorter, but there was not a significant difference. Article 2 Twelve dog cadavers were included in the study as one of the cadavers had air in the epidural space and had to be excluded. The groups were similar regarding signalment. There was no difference between groups in cranial spread with any of the volumes of contrast studied (p=0.242), but there was a direct interaction between the volume injected and the cranial spread in vertebral number (p<0.001). Article 3 Both techniques of identification of the SCO epidural space were similar in the number of attempts required, but the RUN was faster to perform than the NS (p=0.0225). The RUN successfully identified the epidural space in 90.3% (74.2%-98.0%), and the NS in 87.1% (70.2%-96.4%). There was no difference in the success rate between techniques (p=1.000). CONCLUSIONS The SCO epidural anaesthesia had the longest onset time. The LS, spinal, and dural puncture epidural had shorter and indistinguishable onset times. There was no difference in the cranial spread between groups, so current guidelines for dosing LS epidural anaesthesia can be used for the SCO approach. The advance techniques (NS and RUN) were easily adapted to the SCO approach, and rapidly and successfully identified that epidural space.