Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов

alive your patients for gold standard testing and treatment. POCUS and FAST save lives!

References

      1 Bahner DP, Blickendorf JM, Bockbrader M, et al. 2016. Language of transducer manipulation. J Ultrasound Med 34:183–188.

      2 Evans DH, McDicken WN, Skidmore R, Woodcock JP. 1989. Doppler Ultrasound: Physics, Instrumentation, and Clinical Applications. Chichester: Wiley.

      3 Filly RA. Ultrasound: the stethoscope of the future, alas. Radiology 167:400.

      4 Nyland TG, Mattoon JS, Herrgesell EJ, et al. 2002. Physical principles, instrumentation, and safety of diagnostic ultrasound. In: Small Animal Diagnostic Ultrasound, 2nd edition, edited by Nyland TG, Mattoon JS. Philadelphia: WB Saunders, pp 1–18.

      5 Pozniak MA, Zagzebski JA, Scanlan KA. 1992. Spectral and color Doppler artifacts. Radiographics 12:35–44.

      6 Rozycki GS, Pennington SD, Feliciano DV, et al. 2001. Surgeon‐performed ultrasound in the critical care setting: its use as an extension of the physical examination to detect pleural effusion. J Trauma 50:636–642.

Chapter Five POCUS: Top Ultrasound Mistakes During Global FAST

      Gregory R. Lisciandro

Introduction

      Having trained close to 1000 veterinarians from around the world in Global FAST, AFAST, TFAST, and Vet BLUE, we have come up with our top list for image acquisition and interpretation mistakes made during Global FAST that will help synthesize the previous three excellent chapters by Dr Fulton. Whichever machine you work with, you must understand its software, how it interprets artifacts, and what its strengths and weaknesses are to gain full confidence in its imaging potential. You also need to know how to optimize image acquisition by taking advantage of external patient features and the role your hands should play. This takes time, repetition, and critical thinking during image acquisition and a sonographer who dares to use the different buttons and controls on the machine.

      We strive to perform the entire Global FAST using the abdominal preset with the same curvilinear (microconvex) probe for the abdomen and thorax, including heart and lung. However, in time the sonographer may come to prefer different presets (cardiac, small parts) and probes (phased‐array, linear), depending on the structure(s) of interest, the stability of the patient and the clinical questions being addressed. However, the curvilinear (microconvex) probe is absolutely acceptable for the entire Global FAST examination.

       What POCUS Top Mistakes Can Do

       Make the sonographer aware of the most common mistakes which occur during Global FAST image acquisition.

       Make the sonographer aware of the most common air and fluid‐associated artifacts and where they commonly occur during Global FAST.

       By raising awareness of these mistakes during Global FAST, the sonographer will carry over these principles to other ultrasound studies.

       What POCUS Top Mistakes Cannot Do

       Cannot replace proper ultrasound training and experience.

       Indications

       For all sonographers performing Global FAST for a basic understanding of how to optimize image acquisition and avoid mistaking artifacts for abnormalities.

       Objectives

       Provide a basic understanding of Global FAST ultrasound image acquisition to help accelerate the learning process.

       Provide a practical approach for image optimization and artifact identification as they pertain to the standardized examination of Global FAST and its 15 acoustic windows, and to help make your ultrasound interpretation more accurate.

Image Acquisition Mistakes

       Not Recognizing Air Trapping

Ultrasound does not transmit through air. Air reflects your ultrasound beam from its path from the probe head to your areas of interest. Optimizing image quality relies on eliminating the phenomenon of “air trapping,” especially the air trapped between the probe head and its contact with the patient’s skin (Figures 5.1 and 5.2). Air trapping is potentially more problematic when not clipping hair, and hair is rarely clipped for Global FAST, AFAST (abdomen), TFAST (pleural cavity, heart, and lung), and Vet BLUE (lung). So be sure to part the hair, part the hair, part the hair! Parting the hair gets the probe in direct opposition to skin and the best image is optimized with the probe head directly on skin, with no hair in between, and with ample acoustic coupling medium. So what do we recommend?

       70% isopropyl alcohol helps strip out air and lipids from hair follicles and is used for that reason. We use 70% isopropyl alcohol unless electrical defibrillation is anticipated (it’s a burn/fire hazard in the presence of electrical current and 100% oxygen) followed by alcohol‐based hand sanitizer, a brilliant trick of the trade given to me several years ago by the Mississippi State radiologist Dr Jennifer Gambino. Note that saline and water, although more gentle, lack the aforementioned properties of 70% isopropyl alcohol.Figure 5.1. Wet and part the hair. In (A) the area is wetted without parting the hair. By doing so, the image will not be optimized because of all the air trapping (see Figure 5.2). In (B) the wetted hair is parted to optimize the coupling of the probe head directly to skin to produce the best image in unshaved patients.Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

       Alcohol‐based hand sanitizer is an excellent coupling medium and has advantages over both 70% isopropyl alcohol and commercially available acoustic coupling gel.Figure 5.2. Air trapping. In (A) the probe head is placed on a wetted mat of fur in which air is trapped between the hairs. Air trapping attenuates the beam by its reflection and scattering of echoes (blue arrows) off the small pockets of air (white circles). In (B) the hair is parted and thus the probe head is coupled directly to the skin for best image acquisition in an unshaved patient. Note all the beam is transmitted with no reflection or scatter of echoes (blue arrows).Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

       Alcohol‐based hand sanitizer when compared to 70% isopropyl alcohol is not as noxious on skin or indirectly by its fumes. The coldness associated with isopropyl alcohol is not only objectionable to your patient, but also contributes to their cooling (hypothermia) which may be detrimental for a critical patient. The fumes are also problematic for patients placed in closed environments such as an oxygen cage. My personal experience is that our patients associate the coldness with the anticipation of something painful if they have had previous blood draws and catheter placements. Try smaller volumes of 70% isopropyl alcohol and larger amounts of alcohol‐based hand sanitizer.

       When compared to acoustic coupling gel, alcohol‐based hand sanitizer not only wipes off your patient more readily than the gooey consistency of commercially available gel but also evaporates off the hair and skin. The final benefit is that your hands are clean after scanning!

      Pitfall: Placing the probe on a wetted mat of hair leads to marked air trapping and