Here, we present a protocol to allow providers to perform focused cardiac ultrasound (FoCUS) in the clinical environment. We describe methods of transducer manipulation, review common pitfalls of transducer movements, and suggest tips to optimize phased array transducer use.
Focused cardiac ultrasound (FoCUS) is a limited, clinician-performed application of echocardiography to add real-time information to patient care. These bedside exams are problem oriented, rapidly and repeatedly performed, and largely qualitative in nature. Competency in FoCUS includes mastery of the stereotactic and psychomotor skills required for transducer manipulation and image acquisition. Competency also requires the ability to optimize the setup, troubleshoot image acquisition, and understand the sonographic limitations because of complex clinical environments and patient pathology. This article presents concepts for successful, high-quality two-dimensional (B-mode) image acquisition in FoCUS.
Concepts of high-quality image acquisition can be applied to all established sonographic windows of the FoCUS exam: the parasternal long-axis (PLAX), parasternal short-axis (PSAX), apical four chamber (A4C), subcostal fourchamber (SC4C), and the inferior vena cava (IVC). The apical five-chamber (A5C) and subcostal short-axis (SCSA) views are mentioned, but are not discussed in-depth. A pragmatic figure illustrating the movements of the phased array transducer is also provided to serve as a cognitive aid during FoCUS image acquisition.
Focused cardiac ultrasound (FoCUS) is a limited, clinician-performed application of echocardiography that provides immediate anatomic, physiologic, and functional information to patient care. These exams, consisting of five classic views, are problem oriented, performed in real time at the bedside, and do not replace comprehensive echocardiography exams1,2. Given the focused nature of these exams, they are often repeatedly performed when clinical status changes or serial monitoring is required. It is important to have standardized training and obtain adequate images of all five views, when possible, as some views may provide limited information depending on the individual patient and pathology.
The use of FoCUS is rapidly expanding. Many clinical landscapes, such as perioperative anesthesiology, critical care and emergency medicine1,2,3, now routinely employ FoCUS. Inpatient medical wards and outpatient clinical care settings are also adopting this tool to enhance clinical practice4,5,6. As a result, several societal bodies, such as the American Society of Echocardiography, the Society of Critical Care Medicine, and the American College of Emergency Physicians, have published guidelines and recommendations for FoCUS competency and scope of practice7,8,9. While these guidelines and recommendations are not codified, much of the content is consistent and influences FoCUS training curricula10.
Beyond didactics and image interpretation, competency in FoCUS includes mastery of stereotactic and psychomotor skill sets. Stereotactic skill refers to the accurate positioning of ultrasound transducers on the body, based on three-dimensional anatomic features. Psychomotor skill describes the relationship between cognitive function and physical movement that influences coordination, dexterity, and manipulation. Expanding knowledge and awareness about these skills supports FoCUS trainee development.
This article presents concepts for high-quality image acquisition in FoCUS, with both pragmatic considerations and attention to stereotactic and psychomotor skill sets. Specifically, it discusses optimal patient positioning, transducer manipulation, and suggests tips to optimize phased array transducer use. Finally, it examines image optimization for 2-dimensional (B-mode or 2-D mode) and motion modes (M-mode).
This material is the authors' original work, which has not been previously published elsewhere. The protocol described is for clinical use and not research purposes. De-identified images were obtained from a volunteer model in a non-clinical environment. The authors did not seek a formal "Not Regulated" determination from the IRB in accordance with institutional policy, as the activity falls outside of the Common Rule and FDA definitions of human subject research.
1. The transducer
2. Patient positioning
3. Transducer manipulation
4. 2-D image optimization
5. Motion mode (M-mode)
6. Parasternal long axis (PLAX)
NOTE: The PLAX refers to obtaining an image that is along the long axis of the heart (Figure 2).
7. Parasternal short axis (PSAX; Figure 3)
8. Apical four chamber view (A4C; Figure 4)
NOTE: Images in patients with chronic obstructive pulmonary disease (COPD), and otherwise inflamed thoracic cavities, are obtained more medially, and images in patients with left ventricular hypertrophy (LVH) or heart failure with reduced ejection fraction (HFrEF) have their view more lateral.
9. Subcostal four chamber view (SC4C; Figure 5)
10. Inferior vena cava (IVC; Figure 6)
Representative images obtained from the focused cardiac ultrasound protocol presented above are presented in Figure 2, Figure 3, Figure 4, Figure 5, and Figure 6, demonstrating the feasibility of the technique described. These images were captured with the phased array 5-1 MHz transducer. The parasternal long axis (PLAX) image obtained from protocol section 7 is displayed in Figure 2. The parasternal short axis (PSAX) image obtained from protocol section 8 is displayed in Figure 3. The apical four chamber (A4C) image obtained from protocol section 9 is displayed in Figure 4. The subcostal four chamber (SC4C) image obtained from protocol section 10 is displayed in Figure 5. The inferior vena cava (IVC) image obtained from protocol section 11 is displayed in Figure 6. The representative images were obtained from a volunteer model in a non-clinical environment, who was not undergoing clinical care at the time the images were obtained.
Term | Why | Transducer Movement | ||||
Slide | Looking for the best sonographic window, following a structure, or moving to a different region of the body | Move the entire transducer in a specific direction without rotation or changes in transducer angle, orientation, or compression. Some literature specifies that sliding is movement along the long axis of the transducer while sweeping is movement along the short axis. | ||||
Tilt | This allows for visualization of multiple cross-sectional images of various cardiac structures | Change the angle of the transducer, in the short axis, relative to the patient in a side-to-side fashion. | ||||
Rotate | Most commonly used to switch between the long and short axis – in FoCUS this can be used to go from parasternal long axis to parasternal short axis. | Turn the transducer in a clockwise or counterclockwise direction relative to its central axis. The position and angle between the transducer and patient is maintained. | ||||
Rock | Rocking allows the provider to center the area of interest, often referred to as in-plane motion | Change the angle of the transducer in the long axis relative to the patient. |
Table 1: Transducer manipulation.
Figure 1: Phased array transducer manipulation/movement (sliding, tilting, rotating, rocking).
Figure 2: Focused cardiac ultrasound parasternal long axis image.
Figure 3: Focused cardiac ultrasound parasternal short axis image.
Figure 4: Focused cardiac ultrasound apical four chamber image.
Figure 5: Focused cardiac ultrasound subcostal four chamber image.
Figure 6: Focused cardiac ultrasound inferior vena cava image.
The aim of this publication is to provide practical recommendations and best practices to achieve optimal FoCUS images in challenging clinical environments. Formal ultrasound seminars, clinical experience, and observations of learners during hands-on teaching have given insight into pitfalls and less optimal tendencies. As a result, many factors that influence the stereotactic and psychomotor skills have become apparent. Although this material is described in relation to FoCUS exams, many of the principles can be applied to other point of care ultrasound exams and ultrasound transducer types. In addition to impacting learners, instructors can incorporate these concepts into their teaching material and methodology.
There are many basic principles of ultrasonography that must be considered to acquire optimal images. Appropriate transducer selection is critical for optimal image acquisition. The phased array transducer, a 4-12 MHz transducer that penetrates deep into the thoracic space, should be used for the FoCUS exam. Use of the phased array transducer requires delicate and fine adjustments via the hand to optimize an image. Learners often overcompensate adjustments by rapidly moving the hand or transducer. One must appreciate that transducer movements at the skin are small but associated with longer arc length movements imposed on deeper anatomical structures.
To develop expertise in FoCUS, providers should practice with both hands to develop ambidexterity, and practice with transducers from various vendors to refine their cognitive skills for transducer manipulation. Depending on the vendor and device specification, ultrasound transducers vary in form factor, overall weight, weight distribution, heat generation, and connectivity (cord vs. cordless). This can impact the user experience, such as an increased need for a coupling agent, the cadence of transducer movement between windows, and fine image adjustments. With the development of capacitive micromachined ultrasound transducers, a universal transducer may have a form factor distinct from traditional phased array transducers, that provide users with the desired frequency range setting.
Patient positioning facilitates optimal imaging in patients with initially challenging images. The FoCUS exam is typically performed in the supine position, however the PLAX, PSAX, and A4C can be further optimized by instructing the patient to extend their left arm above their head and lie on their left side. Extensive breast soft tissue, previous thoracic operations, and devices can further inhibit optimal image acquisition. If patient comfort and ability allow, the patient can manipulate their breast, or the non-dominant hand of the scanner can be used to displace the breast tissue. Patients who have had a mastectomy or thoracotomy may have pain with transducer application and bandages or devices that interfere. Breast implants may be encountered, and are visualized as large hypoechoic spaces on imaging. Imaging through bandages and around devices often results in off-axis images, artifact, or void images, and is not recommended. Alternative imaging modalities should be considered.
Ultrasound machine positioning allows for maximal ease and ability to acquire optimal images. By placing the stand-alone upright ultrasound machine on the same side of the patient as the provider, the provider can scan with one hand while performing knobology for image optimization with the other hand. A right-handed provider generally stands on the right side of the patient, with the ultrasound machine on the same side, so that they can scan with their right hand while manipulating the settings with their left hand. A left-handed provider generally stands on the left side of the patient, with the ultrasound machine on the same side, so that they can scan with their left hand while manipulating the settings on the ultrasound machine with their right hand. Providers should become facile with transducer manipulation using both hands, as the clinical environment may dictate the available space.
To fully utilize the imaging abilities of the ultrasound machine, providers must be able to effectively optimize image depth, gain, and focus in real time. Depth determines how deep the ultrasound beams penetrate, and is dependent on the transducer frequency. Depth is a function that is adjusted with a button on the ultrasound machine being used, and is in a different position on each machine. Only the amount of depth necessary to see the structure of interest should be used. Inadequate depth fails to capture the desired structures. Excess depth reduces the frame rate and thus image quality. Reducing the image depth and width improves frame rate. Quantifiable measurements of depth are present along the right side of the screen, and can be used as an estimate for the depth or size of structures. The starting depth is provided for each view, but the optimal depth varies from patient to patient depending on body habitus and anatomical variation.
The gain optimizes the brightness of the image; it increases or decreases the amplitude of the returning ultrasound signals, which affects the brightness of what is visualized on the screen (brightness mode, or B-mode). Under-gained and over-gained are terms used to describe images that are too dark and bright, respectively. Under-gained images reduce the ability to visualize relevant structures, whereas over-gained images potentiate artifacts. All ultrasound machines can adjust (increase or decrease) the gain of the entire image uniformly, while some allow the gain at different depths to be adjusted individually, termed time gain compensation (TGC). The gain can be adjusted on the machine via a turn knob, button, or lever, depending on the machine manufacturer.
TGC allows the gain to be adjusted individually at different depths. This is most frequently accomplished through a column of knobs that can be adjusted from side-to-side. The top rows of TGC knobs adjust the regions of the image with less depth (the near field), while the bottom rows of knobs adjust the regions with the greatest depth (the far field). Some machines simplify the available knobs to "near field" and "far field" to allow for the adjustment of the top (shallowest half) and bottom (deepest half) of the image, respectively. TGC is adjusted on each machine differently, depending on how the manufacturer set up the knobs. It can be a set of levers corresponding to the depth of the field, or a set of three slides for "near", "middle", and "far" field.
The focus, otherwise known as the focal zone, concentrates the ultrasound waves at a specific depth, and is the location along the ultrasound beam that maximizes the lateral resolution. The focal point setting adjusts the focal zone (frequently superimposed on the depth marking) to be aligned at the depth corresponding with the image of interest. The focal point or focal zone is labeled on each machine, and is able to be adjusted up or down by the provider performing the scan.
The progression of FoCUS sonographic windows (sections 8-12) is consistent with the American Society of Echocardiography exam sequence11, and when time permits, following this sequence consistently is recommended. A standard exam sequence ensures unsuspected findings are not missed and builds a repertoire of consistency in exam content and build competency. Furthermore, serial exams for comparison can be performed before and after an intervention, such as a fluid bolus or initiation of vasoactive medications, to assess for intervention effect12.
Additional ultrasound modalities, such as color doppler and pulse wave (PW) doppler, augment the clinical information provided by FoCUS. In color doppler, red indicates the flow of blood toward the probe, while blue indicates flow away from the probe. An example of this application is when color-flow doppler is applied to the mitral valve in the A4C views. A blue-colored jet of flow going from the left ventricle to the left atrium during ventricular systole indicates mitral valve regurgitation. A useful application of PW doppler is to quickly estimate cardiac output. This is done by obtaining the A5C view by first obtaining the A4C view and tilting the probe slightly cephalad, until the aortic valve (AV) and left ventricular outflow tract (LVOT) appear. The PW doppler is then applied, and the doppler gate (two horizontal lines) positioned approximately 1 cm above the AV within the LVOT, before activating the PW doppler. Tracing the systolic waveform begets the LVOT velocity time integral (VTI). An LVOT VTI of less than 18 cm suggests low cardiac output.
Competency in FoCUS image acquisition requires appropriate training and quality assurance. Clinicians should complete a minimum portfolio under the supervision of a mentor. as recommended by various societal bodies13,14. The stereotactic and psychomotor aspects of FoCUS require repetition, time, and experience to achieve mastery. The experience should include the performance of exams on patients with varying body habitus in a diversity of clinical settings.
There are some clinical scenarios in which limitations cannot be overcome. A skilled provider recognizes situations in which FoCUS should not be performed and pursues alternative investigations, such as transesophageal echocardiography or formal comprehensive transthoracic echocardiogram. Adequate images cannot be obtained in patients who have an open chest or have diffuse subcutaneous emphysema affecting the chest wall. Indiscriminate use of FoCUS may lead to further unnecessary testing, unnecessary interventions resulting from false positive findings, or inadequate workup of false negative findings2. FoCUS should not be used for the identification of subtle abnormalities. Although transducers that are used for FoCUS have become more compact and portable, these devices do not possess the complex image enhancement, artifact reduction abilities, and higher resolution capabilities of state-of-the-art instruments used in formal echocardiography15. Diagnosis of complex and unusual cardiac pathologies is outside the scope of FoCUS. Quantification of regurgitant or stenotic valvular lesion severity should not be performed using FoCUS alone. Instead, FoCUS should be used to detect significant deviations from normal, and are usually reported as "present" or "absent"15.
Although FoCUS has been well established within the cardiology community for decades, its use is now virtually ubiquitous in emergency medicine and critical care, and is expanding into other care settings16. As ultrasound technology improves, and devices become more portable, FoCUS is becoming an important tool for both diagnosis and guiding management of cardiac disease. Over time, competency in FoCUS can be achieved through a structured and consistent approach to exam sequence, use of appropriate terminology, and the development of stereotactic and psychomotor skills.
FoCUS is a limited, problem oriented application of echocardiography which is rapidly expanding in the clinical environment. Competency in FoCUS includes mastery of the stereotactic and psychomotor skills required for transducer manipulation and image acquisition. Competency also requires the ability to optimize the setup, troubleshoot image acquisition, and understand the sonographic limitations due to complex clinical environments and patient pathology. We describe methods of transducer manipulation, review common pitfalls of transducer movements, and suggest tips to optimize phased array transducer use.
The authors have nothing to disclose.
We would like to thank the University of Michigan Department of Anesthesia, Max Harry Weil Institute for Critical Care Research and Innovation, and Katelyn Murphy for their administrative and graphic design support.
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