Evaluation of the effect of ultrasound guidance on the accuracy of intercostal nerve injection: a canine cadaveric study

Physiological variables for the objective detection of nerve block failure in dogs

OBJECTIVE

To identify physiological variables for objectively detecting nociception indicative of intraoperative peripheral nerve block failure.

STUDY DESIGN

A double-blinded randomized clinical study.

ANIMALS

A sample of 14 male (40.8 ± 12 kg; mean ± standard deviation) and 16 female (34.3 ± 11.4 kg) client-owned dogs.

METHODS

Dogs were randomly assigned to one of three groups for psoas compartment and proximal sciatic nerve blocks (0.2 mL kg-1 per site): guided bupivacaine (GBB), or saline (GSB) block or a blind bupivacaine block (BBB). Guided blocks were performed using an ultrasound-peripheral nerve locator combination. Premedication consisted of medetomidine 0.01 mg kg-1 and morphine 0.3 mg kg-1. General anaesthesia was induced with propofol and maintained with isoflurane in oxygen. Receiver operator characteristic curve analysis was used to compare actual values and change in values of physiological variables between GSB and GBB. The Youden index and associated criterion for each physiological variable were used to determine an objective measure for nociception. Fisher's exact t test, McNemar's test and Cohen's kappa statistical analysis were used to determine association, differences and inter-score reliability between the objective and subjective scoring for BBB.

RESULTS

Cardiovascular variables had good discriminating ability to identify a nociceptive response (p < 0.01). The Youden indices for mean (MAP) and diastolic (DAP) arterial pressure were most reliable in detecting nociception. The highest sensitivity was that of ΔMAP (100%) with good agreement between the subjective and objective scores of Δheart rate or systolic arterial pressure (SAP). The use of ΔMAP, ΔSAP, ΔDAP had the best ability in indicating peripheral nerve block failure (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Blood pressure values can detect a response to surgical stimulus in adequately anaesthetized dogs. The use of ΔMAP, ΔSAP or ΔDAP may be considered as objective measures to detect nerve block failure.

Image analysis comparison of nerve staining with food dye, methylene blue or tissue marker

OBJECTIVE

Novel locoregional techniques use dye studies to confirm successful nerve targeting. The goal was to objectively quantify and compare nerve staining characteristics of dye mixtures commonly reported in the literature using image analysis software.

STUDY DESIGN

Prospective, randomized cadaveric study.

METHODS

Thirty-six brachial plexus nerves from unpreserved pig cadavers were randomized into three groups of 12: FD (1:10 mixture of blue food dye and bupivacaine 0.5%), MB (methylene blue 1%) and TM (0.1:10 mixture of blue tissue marker and lidocaine 2%). Nerves were immersed in dye for 1, 15, 30 or 60 minutes (n = 3 each). Images of nerves before immersion (baseline) and at each time point with epineurium intact (superficial staining) and after longitudinal bisection (deep staining) were processed using image analysis software. Color saturation values were divided into quartiles (dark, medium-dark, medium-light or light). Percentage of stained nerve area in each quartile was calculated and compared using two-way anova.

RESULTS

Superficially, at minute 1, dark saturation covered 40% of nerve area in FD versus 19% in MB (p = 0.04) and 0% in TM (p < 0.0001). In bisected nerves, dark and medium-dark saturations occurred only in FD; medium-light saturation comprised anywhere from 4% to 22.5% over time in FD versus <1% at any time in MB (p = 1.000; p = 0.343; p = 0.383; p = 0.262). Deep staining was not found in TM at any point.

CONCLUSION AND CLINICAL RELEVANCE

Food dye rapidly stains superficial and deep nerve layers. Based on these characteristics, investigators can choose the appropriate dye for their study.

Lumbosacral plexus block using a combination of ultrasound-guided lateral pre-iliac and parasacral approaches in cats

OBJECTIVE

To describe an ultrasound-guided lateral pre-iliac (LPI) and parasacral (PS) approach in feline cadavers (phase I) and compare the perioperative analgesic use and complications in cats administered LPI and PS blocks (group PNB) or epidural anesthesia (group EPI) for pelvic limb surgery (phase II).

STUDY DESIGN

Experimental uncontrolled, anatomic and retrospective cohort study.

ANIMALS

A group of eight feline cadavers and 52 medical records.

METHODS

Bilateral LPI and PS approaches with 0.1 mL kg^-1 of dye to stain the femoral and obturator nerves and the lumbosacral trunk, respectively, were performed on each cadaver. Nerve staining effect was evaluated upon dissections (phase I). Perioperative analgesics use, and complication rates were retrospectively compared between groups PNB and EPI (phase II). Continuous data were compared using the Mann-Whitney U test and the prevalence of events with Fisher's exact test. Differences were considered significant when p < 0.05.

RESULTS

Dissections revealed that the LPI approach stained 94% and 75% of the femoral and obturator nerves, respectively. The PS approach stained 100% of the lumbosacral trunks. Cats enrolled in group PNB (n = 23) were administered lower doses of intraoperative opioids than those in group EPI (n = 25) (p = 0.006). Intraoperative rescue analgesia was required in 60% and 17.4% of cats enrolled in groups EPI and PNB, respectively (p = 0.003). Group PNB required more intraoperative anticholinergics than group EPI (p = 0.02). There were no differences in postoperative pain scores, analgesic use and complication rates.

CONCLUSIONS AND CLINICAL RELEVANCE

The ultrasound-guided LPI and PS approach stained the femoral/obturator nerves and the lumbosacral trunk, respectively, in feline cadavers. Furthermore, PNB was associated with lower intraoperative opioid use and similar postoperative pain and analgesic use compared with epidural anesthesia in a cohort of cats undergoing surgery of the pelvic limb.

Development of Enhanced Recovery After Surgery (ERAS) protocols in veterinary medicine through a one-health approach: the role of anesthesia and locoregional techniques

Enhanced Recovery After Surgery (ERAS) is a new and emerging concept in human medicine that involves rethinking the preoperative, intraoperative, and postoperative periods. The ultimate, overarching aim is to improve patient outcome following surgery and, thus, return to a normal daily routine as soon as possible. The development and implementation of locoregional anesthetic techniques in humans is one of the key elements driving these protocols. In veterinary medicine, we are no exception: the rapidly growing interest, development, and refinement of these techniques in our veterinary species is changing the way we think of anesthesia and analgesia. The potential real benefits are yet to be determined, as this concept is implemented into our veterinary hospitals in general, and our surgical patients in particular, in a more systematic and routine way. In this article, we will introduce the reader to the concept of ERAS protocols and the role of regional anesthesia in some common surgical procedures.

A Two-Point Ultrasound-Guided Injection Technique for the Transversus Thoracis Plane Block: A Canine Cadaveric Study

Simple Summary

The transversus thoracis plane block is a locoregional technique recently described in canine cadavers to desensitize the intercostal nerves running through this plane. In canine cadavers, a transverse approach through a single injection point at the fifth intercostal space has been described, although consistent staining of the intercostal nerves was not completely achieved. The objective of this study was twofold: (1) to evaluate if the transverse approach is feasible at the third and sixth intercostal spaces and (2) to compare, by anatomical dissection, the spread of a dye solution and the staining of the intercostal nerves when a low volume (0.5 mL kg⁻¹) or a high volume (1 mL kg⁻¹) was equally divided at a two-point injection in the same hemithorax. Our results showed that the injection of the high-volume dye solution, equally injected at the third and sixth intercostal spaces using the transverse approach, achieved a consistent staining of from T2 to T7 intercostal nerves. This block could achieve adequate desensitization of the ventral chest wall during sternotomy in the dog. Clinical studies in live animals are necessary to confirm the efficacy of this technique.

Abstract

The transversus thoracis plane (TTP) block desensitizes the intercostal nerves that run through this plane, providing analgesia to the ventral thoracic wall. Two canine cadavers were used to assess the feasibility of the transverse approach for the TTP (t-TTP) under ultrasound guidance to inject a solution at the third and sixth intercostal spaces. Eight cadavers were used to compare the spread and number of intercostal nerves that were stained when a low volume (LV) 0.5 mL kg⁻¹ or a high volume (HV) 1 mL kg⁻¹ of a dye-lidocaine solution was injected into the same hemithorax, injecting the volume equally at these intercostal spaces using the transverse approach. Fisher’s exact test and Wilcoxon signed-rank test were used to contrast the spread of the different volume solutions. The injectate spread along the TTP after all injections, dying a median number (range) of 3 (2–5) and 6 (5–6) nerves with LV and HV, respectively (p = 0.011). The two-point injection of HV, using the t-TTP approach, is a feasible technique that provides a consistent staining from T2 to T7 intercostal nerves. The injection of HV instead of LV increases the spread and enhances the number of stained intercostal nerves.

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.

Description of an Ultrasound-Guided Transverse Approach to the Transversus Thoracis Plane Block and Evaluation of Injectate Spread in Canine Cadavers

Simple Summary

In humans, the aim of the transversus thoracis plane block is to desensitise the intercostal nerves running through this plane, providing analgesia to the anterior chest wall. Our objective was twofold: describing an ultrasound-guided transverse approach to the transversus thoracis plane and evaluating the spread of two injectable volumes in canine cadavers. Gross anatomy of the ventral thoracic area and sonoanatomy between the fifth and sixth costal cartilages were described in two dog cadavers. Eight cadavers were used to describe this approach and were subsequently dissected to evaluate the injectate spread and the intercostal nerves staining after low volume (0.5 mL kg⁻¹) and high volume (1 mL kg⁻¹) dye-lidocaine injection. After all injections, the injectable solution was distributed along the transversus thoracis plane, staining a median number (range) of 3 (2–4) and 4 (3–5) nerves with low and high volume, respectively (p = 0.014). The transverse approach to the transversus thoracis plane is a feasible, single injection point technique that provides the staining of several intercostal nerves. The injection of high versus low volume increases the number of stained nerves.

Abstract

Transversus thoracis plane (TTP) block has demonstrated to produce analgesia in humans undergoing median sternotomy. The objectives of the study were to describe an ultrasound-guided transverse approach to the transversus thoracis plane (t-TTP) and to evaluate the spread of two injectable volumes in canine cadavers. Two cadavers were used to describe relevant gross anatomy of the ventral thoracic area and sonoanatomy between the fifth and sixth costal cartilages. Then, eight cadavers were used to describe the ultrasound-guided injection into the TTP and were dissected to evaluate the injectate spread and the intercostal nerves staining with two different dye-lidocaine volumes: low volume (LV) 0.5 mL kg⁻¹ and high volume (HV) 1 mL kg⁻¹. To compare the spread between both volumes the Fisher’s exact test and Wilcoxon signed-rank test were used. The solution spread along the TTP after all injections, staining a median number (range) of 3 (2–4) and 4 (3–5) nerves with LV and HV, respectively (p = 0.014). The injection of HV versus LV increases the number of stained nerves. Ultrasound-guided t-TTP is a feasible technique that provides staining of several intercostal nerves with a single injection site, so it could be useful to provide analgesia to the ventral chest wall.