Ultrasound in Anesthesia

By Jordan Phillips, MSIV, University of Oklahoma College of Medicine

Ultrasound is an imaging modality that has a wide range of use in many different specialties. Becoming familiar with the mechanism, uses and technique of ultrasound is a very useful skill for medical students as they navigate the different rotations of the third and fourth year. Even in the preclinical years, many human anatomy courses are now integrating ultrasound into the curriculum and encouraging the students to begin manipulating a probe and identifying structures on ultrasound images. Throughout the years, ultrasound continues to find new places to prove itself useful to anesthesiologists. The first step in approaching ultrasound is to understand the mechanism of how it works.

First discovered for imaging use in the 1930s, ultrasound is a high frequency sound far above a human’s ability to hear. The images produced using ultrasound are referred to as sonograms. The ultrasound machine produces the sound waves through a piezoelectric transducer encased in a plastic housing. The transducer is made up of an array of very thin crystals. The short electric pulses send from the machine to the crystals causes them to vibrate at the desired frequency. The sound waves travel through the skin and then contact tissues of varying densities. The same crystals that produced the original sound are also able to detect the sound waves being reflected off the tissues and recreate an image in real time on the screen. The image is created based upon the time it takes the wave to return and the strength of the echo. This image can be used to identify structures, make a diagnosis, or even guide placement of different medical devices and medications in real time.

For years anesthesiologists have done many of their regional pain management and line placements as blind procedures. These procedures are accomplished with a keen understanding of the anatomy in mind. Some procedures, such as different regional anesthetic blocks, are performed with nerve stimulators that help guide the physician by producing twitches that indicate what nerve the probe is near. The local anesthetic can then be injected into this area to produce a regional anesthesia of different areas of the body for pain management or surgical procedures. Central lines and arterial lines have also been historically performed blind with palpation and anatomy guided needle insertion. With a good understanding of anatomy, these blind procedures are generally safe and effective, but are not without their complications. Ultrasound provides the ability to perform any number of nerve injections and catheter placements with real-time image guidance, creating a safer environment that reduces complications of these needle insertion procedures. It also allows physicians to access regions of the body that were previously too risky to perform blind such as with transabdominal blocks and adductor canal blocks.

Along with needle placement procedures, ultrasound technology has afforded anesthesiologists the ability to intraoperatively improve patient care with transthoracic echocardiograms (TTE) and transesophageal echocardiograms (TEE). The cardiovascular system is a critical management area intraoperatively, and TEE allows physicians to monitor the heart structure and function live during high risk surgery. It can also be used to make life-saving intraoperative diagnoses and help guide proper management.

Ultrasound imaging technology has had a profound impact on the field of anesthesiology and will continue to have an important role in future practice. It has the advantages providing images in real-time, portability, low cost and reduced radiation exposure. In the hands of a skilled operator, ultrasound can improve patient care and reduce procedural complications. As medical students, the more exposure we can get to this imaging modality the better!