Cardiovascular and respiratory effects of lumbosacral epidural bupivacaine in isoflurane-anesthetized dogs: The effects of two volumes of 0.25% solution.

Raquel Sartori Gonçalves Dias,Maria Alice Kuster De Albuquerque Gress,João Henrique Neves Soares,Pablo E Otero,Fabio Otero Ascoli,Marcela Lemos Machado,Douglas Dos Santos E Castro

doi:10.1371/journal.pone.0195867

Raquel Sartori Gonçalves Dias, Maria Alice Kuster De Albuquerque Gress + Show 5 more

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https://doi.org/10.1371/journal.pone.0195867

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Abstract

The purpose of this study was to compare cardiovascular and respiratory effects of two volumes of bupivacaine 0.25% (0.2 mL kg-1—treatment BUP02—and 0.4 mL kg-1 –treatment BUP04) administered epidurally at the lumbosacral intervertebral space in dogs anesthetized with isoflurane. This experimental prospective randomized crossover design trial used six mixed breed adult dogs, four neutered males and two spayed females. Each dog was anesthetized on three different occasions: the first for isoflurane minimum alveolar concentration (MAC) measurement, and the following two assigned treatments (BUP02 or BUP04). On the two treatment days, anesthesia was induced and maintained with isoflurane at 1.3 MAC during the experiments. Cardiovascular and respiratory measurements were recorded before (T0) and 5, 15, 30, 60 and 90 minutes after the epidural administration of bupivacaine. Comparisons between and within groups were performed by a mixed-model ANOVA and Friedman’s test when appropriate followed by Bonferroni post-hoc test or Dunnet’s test to compare time points within each treatment with T0 (p < 0.05). Mean arterial pressure decreased significantly from 15 to 90 minutes after the administration of BUP02 and from 5 to 60 minutes in BUP04, with lower values in BUP04 than in BUP02 lasting up to 30 minutes after bupivacaine administration. No significant changes in cardiac output and systemic vascular resistance were observed in either treatment. Hypoventilation was only detected in BUP04. Hemoglobin concentration and arterial oxygen content decreased after both treatment of bupivacaine with no significant decrease in oxygen delivery. Two dogs in BUP04 developed Horner’s syndrome. The epidural administration of 0.4 mL.kg-1 of bupivacaine to dogs in sternal recumbency anesthetized with isoflurane 1.3 MAC caused more cardiovascular and respiratory depression than 0.2 mL.kg-1.

Highlights

Epidural anesthesia has been widely used as an adjuvant anesthetic technique in dogs due to its perioperative analgesia [1], reduction of general anesthetics requirements [2, 3], muscle relaxation, and attenuation of the stress response to surgery [4, 5]
There was a significant difference observed between groups for mean arterial pressure (MAP) (p = 0.0046), pulmonary artery pressure (PAP) (p = 0.0006), VT (p = 0.00147), V_E (p = 0.0165), PaCO2 (p = 0.0318), and HCO3- (p = 0.0318)
There were 5 main findings of the present study of dogs anesthetized with 1.3 minimum alveolar concentration (MAC) of isoflurane and bupivacaine 0.25% epidural administration of 0.2 or 0.4 mL kg-1: 1) A volume-dependent decrease in MAP; 2) occurrence of hypotension was higher in BUP04 than bupivacaine 0.25%: 0.2 mL kg-1 (BUP02); 3) hypoventilation was observed during the initial 15 minutes with BUP04, which was associated with a decrease in VT, fR and in V_E; 4) CaO2 decreased in both treatments mainly because of a decrease in hemoglobin concentration; and 5) the Horner’s syndrome observed in two dogs of BUP04 indicated that the administration of 0.4 mL kg-1 can reach high thoracic levels of blockade (T1—T2—T3)

Summary

Introduction

Epidural anesthesia has been widely used as an adjuvant anesthetic technique in dogs due to its perioperative analgesia [1], reduction of general anesthetics requirements [2, 3], muscle relaxation, and attenuation of the stress response to surgery [4, 5]. The lumbosacral space is the most common site for epidural anesthesia in dogs, and bupivacaine is one of the most commonly used local anesthetic for this technique [8]. Despite the benefits mentioned above, adverse cardiovascular and respiratory effects can be associated with the use of epidural administration of anesthetics [3, 9,10,11,12,13]. This is due to the blocking effect on motor and autonomic neurons. These effects can vary in duration and intensity depending on volume and concentration of the anesthetic that is used [13, 14]

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