CHAPTER 1
Ultrasound Guidance: The Inevitable Evolution of Locoregional Anesthesia

Berit L. Fischer

There's a way to do it better. Find it.

-Thomas Edison

INTRODUCTION

It should come as no surprise that advancements in veterinary medicine often follow those in human medicine, and it is no different with the evolution and use of locoregional anesthesia. This is despite the fact that animals are often used to study and develop new techniques before they are ever used in people. Even Carl Koller, the Austrian ophthalmologist who first used topical cocaine to induce sensory anesthesia of the cornea in a patient for glaucoma surgery in 1884, first experimented with its desensitizing effects on the corneas of dogs and guinea pigs (Calatayud and González 2003).

The interest in, and use of, locoregional techniques has increased significantly. Much of the research up until the mid-1990s focused on the discovery of new drugs (e.g. bupivacaine, ropivacaine, bupivacaine liposome injectable suspension), techniques (e.g. nerve block catheters), and adjuvants (e.g. dexamethasone, clonidine, etc.) that could be used to extend the duration of anesthesia and analgesia provided to patients (Dahl et al. 1988; Eledjam et al. 1991; McGlade et al. 1998). Additionally, methods to assist in nerve location (i.e. paresthesia, electrical nerve stimulation) were sought to provide ways other than anatomic landmarks to target peripheral nerves, and hopefully, improve patient safety and increase success. In 1994, this search culminated in the use of ultrasound guidance when Kapral et al. (1994) published a randomized, controlled trial examining ultrasound-guided brachial plexus blocks in people. A new era in locoregional anesthesia had begun.

ULTRASOUND TECHNOLOGY

A BRIEF HISTORY

The discovery of piezoelectricity by brothers, Jacque and Pierre Curie in 1880, provided the foundation for the development of the modern-day ultrasound transducer. By applying an electric current to quartz crystals, they caused the crystals to vibrate and produce ultrasonic waves. This revolutionary finding became critical to the development of sonar that was used by submarines in World War I, and of ultrasound therapy whereby physicians could use the vibrations that were produced to treat a variety of illnesses (Duck 2021). It was not until 38 years later, in 1928, that Russian physicist SY Sokolov utilized ultrasound for imaging purposes. He invented an ultrasound transducer using a single transmitter and receiver that, when placed on opposite sides of a metal sheet, was able to detect imperfections in the metal and display line images produced from the disruptions in sound wave transmission (Duck 2021).

Ultrasound for medical imaging eventually emerged after several researchers struggled to develop transducers that could work in a hospital setting. In 1956, a predecessor of today's B-mode (i.e. "brightness" mode) ultrasound, the 2-D compound scanner, was developed by obstetrician Ian Donald and engineer Tom Brown to image an unborn fetus (Whittingham 2021) (Figure 1.1). Worldwide advancement of ultrasound technology continued throughout the 1960s and 1970s, culminating in the invention of the linear array transducer that utilized several rows of transducer elements to produce real-time scanning (Whittingham 2021).

USE OF ULTRASOUND FOR LOCOREGIONAL ANESTHESIA

Using ultrasound technology to assist with performing locoregional blockade was first reported by la Grange et al. (1978) who, after identifying the subclavian artery using Doppler ultrasound, performed supraclavicular brachial plexus blocks in 61 patients using anatomy and the presence of paresthesia to determine where to deposit the local anesthetic. It was not until 1994, however, that the use of ultrasound was first described to help guide a stimulating needle toward the target nerve trunks when performing brachial plexus blocks via both axillary and supraclavicular approaches (Kapral et al. 1994).

ULTRASOUND-GUIDED LOCOREGIONAL ANESTHESIA IN VETERINARY SPECIES

As the use of ultrasound guidance in regional anesthesia grew in human medicine, its use slowly started to emerge in the veterinary literature, first with a paper describing the sonographic appearance of canine sciatic nerves in 2007, followed shortly thereafter by a similar study that described the use of ultrasound for evaluation of the canine brachial plexus (Benigni et al. 2007; Guilherme and Benigni 2008).

FIGURE 1.1 Drawing of the 2-D compound scanner, developed through the collaborative efforts of Dr. Ian Donald and Tom Brown.

Source: McNay and Fleming (1999)/with permission of Elsevier.

The first study to describe the use of ultrasound-guided blocks in dogs was accepted for publication in 2009 (Campoy et al. 2010). That study reported using an in-plane needle technique to approach the brachial plexus and the femoral and sciatic nerves in medium- and large-breed dogs. Each approach was followed by deposition of a mixture of lidocaine and methylene blue at the target site, allowing for later identification of nerve staining after euthanasia of the dogs for unrelated purposes. Later that same year, the first efficacy study that documented successful sensory blockade following ultrasound-guided saphenous and sciatic nerve blocks in dogs was submitted for publication by Costa-Farré et al. (2011), and the first description of using ultrasound-guided blocks in cats was published by Haro et al. in 2013. Since then, use of ultrasound guidance for nerve blocks has been reported in a wide range of veterinary species (De Vlamynck et al. 2013; Hughey et al. 2022).

HOW ULTRASOUND GUIDANCE HAS CHANGED LOCOEGIONAL ANESTHESIA

Objective measurement of the impact a new modality or treatment has on an industry, in this case medicine, can be difficult to determine, particularly when it is first being instituted. Fortunately, the impact of ultrasound guidance on regional anesthesia has been established. In 2017, Vlassakov and Kissin (2017) published a study assessing notable advances in regional anesthesia from 1996 through 2015. They evaluated meta-analyses that had been published on a variety of regional anesthesia topics based on their ability to demonstrate measurable clinical benefits. Various topics were analyzed based on their level of academic interest, findings of statistically significant effects, their overall risk of bias, the degree of heterogeneity between the studies within each meta-analysis, and the determination of a minimal clinically important difference (MCID). Of all the topics they analyzed, they concluded that within this 20-year time period, the discovery and development of ultrasound guidance for performing upper and lower limb peripheral nerve blocks was the one of greatest clinical importance.

This has been supported in practice by several studies that compared the use of ultrasound guidance to other methods of nerve location (i.e. electrostimulation, paresthesia, etc.) for performing regional blocks. A compilation of these findings, published by the American Society of Regional Anesthesia and Pain Medicine (ASRA), provided an objective evidence-based assessment of the literature in order to determine if ultrasound guidance produced a positive effect on the performance, efficacy, and/or safety of regional blocks over other methods of nerve location (Neal et al. 2016). As interest has grown, the feasibility of incorporating ultrasound guidance into large-scale operations and its financial impact have also been investigated and addressed through cost-analysis studies (Liu and John 2010; Ehlers et al. 2012).

PERFORMANCE AND EFFICACY

The ASRA determined that when ultrasound guidance was compared to other methods of nerve location for extremity blocks, it was favored based on fewer needle passes, faster block performance, decreased onset time, and greater block success, with high levels of evidence and minimal differences between upper and lower extremities (Neal et al. 2016). Use of ultrasound guidance for neuraxial blocks also demonstrated superior performance when compared to palpation in terms of determining the correct vertebral interface, requiring fewer needle sticks, and the ability to accurately predict the needle insertion depth to the target ahead of time. Less demonstrable evidence was available at the time of that study to fully evaluate the impact of ultrasound guidance on the performance of truncal blocks, with many of the techniques currently being used still in development and/or lacking methods of comparison to other techniques.

SAFETY

When compared to other methods, one of the most notable benefits of incorporating ultrasound guidance into performance of regional anesthesia is a decreased incidence of local anesthetic systemic toxicity (LAST). Barrington and Kluger (2013) published a landmark study that evaluated the incidence of LAST following peripheral nerve blockade using either ultrasound-guided or non-ultrasound-guided techniques in 20021...