Use of pressure waves to confirm the correct placement of epidural needles in dogs

Epidural Volume of Injectate Using a Dose Regimen Based on Occipito-Coccygeal Spinal Length (OCL): Randomized Clinical Study Comparing Different Ropivacaine Concentrations, with or without Morphine, in Bitches Undergoing Total Unilateral Mastectomy

A prospective, randomized clinical trial was designed to compare four epidural treatments in dogs undergoing total unilateral mastectomy. The epidural volume of injectate was based on the individual occipito-coccygeal length (OCL) aiming to reach the first thoracic vertebra (T1). The first ten dogs were allocated in a control group (C) and did not receive epidural treatment. Subsequently, forty dogs were randomly allocated in four groups of ten: epidural ropivacaine 0.5% (R0.5%); morphine 0.1 mg kg−1 plus ropivacaine 0.5% (MR0.5%); morphine 0.1 mg kg−1 plus ropivacaine 0.35% (MR0.35%); morphine 0.1 mg kg−1 plus ropivacaine 0.25% (MR0.25%). Intraoperatively, isoflurane requirement (1.3% vs. <1.1% FE’Iso) and fentanyl requirement (9.8 vs. <1.1 µg kg−1 h−1) were significantly higher in C group compared to all epidural groups. Postoperatively, methadone requirement was higher (1.8 mg kg−1 vs. <0.8 mg kg−1) for C group compared to all epidural treatment groups. The ability to walk and to urinate returned 4 h earlier in MR0.35% and MR0.25%. The mean epidural volume of ropivacaine, using a dose regimen based on OCL, to reach T1 was about 0.15 mL cm−1. The addition of morphine further reduced the methadone requirement, without affecting urinary and motor functions.

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

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.

What is the evidence? The issue of verifying correct needle position during epidural anaesthesia in dogs

OBJECTIVES

To review the methods for verifying the needle position while performing epidural anaesthesia in dogs, and to discuss the advantages, disadvantages, usefulness and reliability of each technique in the experimental and clinical research setting.

DATABASES USED

PubMed, Scopus, Google Scholar and the Basel University Library online catalogues; the latter, which was provided by the University of Berne, were used as databases. The results were filtered manually based on the titles and abstracts in order to narrow the field.

CONCLUSIONS

Besides some drawbacks, including the potential side effects of contrast medium injection, which may limit its routine use in clinical patients, epidurography should still be regarded as one of the most reliable techniques to verify needle position in dogs. Ultrasonography, electrical nerve stimulation, loss of resistance and the hanging drop technique are regarded as less invasive than epidurography and, for this reason, their use may be more applicable to clinical patients. However, these methods have been described in only a few published reports, all of which involved a limited number of dogs. Finally, the detection of epidural pressure waves has been investigated more extensively in dogs, and the findings of these studies suggest that this technique may be used to verify epidural needle placement for experimental and clinical research, on condition that all the negative subjects are excluded from the study.

Clinical Practice of Epidural Puncture in Dogs and Cats Assisted by a Commercial Acoustic Puncture Assist Device-Epidural Locator: Preliminary Results

The objective of this study was to compare an Acoustic Puncture Assist Device-Epidural Locator (APAD-EL) with the "pop sensation" (POP) and "lack of resistance" (LOR) commonly used to confirm penetration of the ligamentum flavum and to ensure correct epidural placement in dogs and cats. We recruited 38 dogs and cats undergoing surgery and receiving epidural analgesia. Two anesthetists performed epidural puncture using the POP and LOR signs. Simultaneously, APAD-EL was used to collect visual and acoustic confirmation during advancement and placement of the needle tip for post hoc evaluation. A positive APAD-EL sign consists of a sudden pressure drop at the needle tip visible on a display and a concomitant pitch change of an acoustic signal. Failure to record a sudden pressure drop is considered a negative APAD sign. Descriptive statistics were used. In 32 patients with positive POP and LOR, the APAD was also positive. In one patient, POP was positive with a negative LOR and APAD result. Five patients had negative POP but positive LOR. Four patients had APAD positive and one (a dog) APAD negative. The study results showed that the APAD-EL information supports the subjective signs of correct needle placement suggested by positive POP and LOR experienced by trained anesthetists. The technique can be useful to assist difficult epidural puncture and as a training and teaching tool.

Limitations of the use of pressure waves to verify correct epidural needle position in dogs

The use of pressure waves to confirm the correct position of the epidural needle has been described in several domestic species and proposed as a valid alternative to standard methods, namely, control radiographic exam and fluoroscopy. The object of this retrospective clinical study was to evaluate the sensitivity of the epidural pressure waves as a test to verify the correct needle placement in the epidural space in dogs, in order to determine whether this technique could be useful not only in the clinical setting but also when certain knowledge of needle's tip position is required, for instance when performing clinical research focusing on epidural anaesthesia. Of the 54 client-owned dogs undergoing elective surgeries and enrolled in this retrospective study, only 45% showed epidural pressure waves before and after epidural injection. Twenty-six percent of the animals showed epidural pressure waves only after the injection, whereas 29% of the dogs showed epidural pressure waves neither before nor after injection and were defined as false negatives. Our results show that the epidural pressure wave technique to verify epidural needle position lacks sensitivity, resulting in many false negatives. As a consequence, the applicability of this technique is limited to situations in which precise, exact knowledge of the needle's tip position is not mandatory.

Pressure profile in the caudal extradural space of standing horses before and after extradural drug administration

The objectives of this study were to measure the pressure in the caudal extradural space of standing horses and to evaluate the usefulness of pressure waves to identify correct needle placement. Caudal extradural pressure was measured in 12 healthy horses. The pressure and any extradural pressure waves were recorded for 3min after puncture, for 1min after testing for lack of resistance (LOR), and for 10min after lidocaine injection. Successful extradural drug administration was confirmed in all horses. The median extradural pressure findings after puncture, after LOR, immediately after injection and 10min after needle placement were -1.60kPa (range -2.27 to 1.33kPa), -0.67kPa (-2.27 to 5.73kPa), 5.00kPa (0.93 to 9.87kPa) and 0.13kPa (-0.67 to 4.53kPa), respectively. Extradural pressure waves were not always present. Extradural space pressure was sub-atmospheric in most horses and extradural injection significantly increased this pressure for up to 10min. Extradural pressure waves had limited usefulness in the confirmation of the correct placement of the needle.