Cardiac Point-of-Care Ultrasound: Background, Instrumentation, and Technique

When a Stat Echo is Not Fast Enough

Developed for military triage, POCUS techniques easily translated to use by trauma surgeons and emergency room physicians, exemplified by the development of the Focused Abdominal Sonography for Trauma (FAST) exam in the early 1990s to diagnose traumatic intraperitoneal bleeding. Point-of-care ultrasound (POCUS) capitalizes on the immediacy and utility of ultrasound at the bedside, especially when initial triage and clinical urgency demand action or when findings are intermittent and fleeting.

The immediate clinical value of limited cardiac ultrasound data obtained from POCUS disrupts the standard conventions of the detailed-oriented philosophy and comprehensive format of standard echocardiography. The advent of portable devices ( Fig. 16.1 ) opened new markets for development in emergency, critical care, internal medicine, and family medicine and has created novel terminology distinct from the practice of echocardiography, using descriptors such as “hand-carried” or “handheld” ultrasound, “quick-look” studies, “focused cardiac ultrasound,” and more recently “point-of-care ultrasound.” No term has yet sufficiently distinguished POCUS practice from that of echocardiography because a “stat echo” also can be performed at the “point of care” using the smaller echocardiographs and recording equivalent data.

Pocus: Intents and Purposes

Defining characteristics of current POCUS practice include the imaging of only a few ultrasound findings, performance by the treating physician, and indications to assist in the immediate diagnosis, treatment, triage, or risk stratification of the patient ( Table 16.1 ). With on-the-spot imaging and diagnosis, POCUS will change current standards of imaging and interpretation in ultrasonography. Despite common features in individual specialty use, cardiac POCUS practice is evolving but appears bounded by two distinct imaging philosophies:

• 1.

  A generalized practice, in which POCUS is used routinely whenever a stethoscope is used in ultrasound-augmented physical examination (UAPE) or,

• 2.

  A subspecialized practice as a formal limited echocardiogram directed to answer specific clinical questions that may arise after initial clinical evaluation.

Although real-world POCUS practice often consists of both philosophies to some degree, these two polar boundaries of POCUS have differential impact on medical education, competency requirements, and the approach to medical testing and reimbursement.

POCUS, when practiced to augment the physical examination, is best done by the physician taking care of the patient as a directed search for a simplified ultrasound signs, each a clue to formation of a preliminary diagnosis. The POCUS equivalents of cardiac physical findings improve their detection while allowing the continued use of the same time-honored cardiac physiologic concepts taught in medical school ( Table 16.2 ) . Potential applications are similar to the use of the stethoscope and include initial and frequent reapplications at initial presentation, during subsequent hospital rounds, or in clinic visits. An evidence-based POCUS technique named cardiovascular-limited ultrasound examination (CLUE) has been validated and is a compilation of six easily learned, quick-look ultrasound signs performed within a 2-minute examination ( Fig. 16.2 ). Notably, the CLUE has shown both diagnostic and prognostic value in outpatients and inpatients referred for echocardiography, ^, as well as in patients admitted by hospitalists. The CLUE represents a proof-of-concept POCUS exam—one that improves traditional bedside physical examination techniques for prognostic findings and has been successfully incorporated into the curriculum of an internal medicine residency program in which residents have proven its effectiveness. Any significant abnormality found on bedside examination—whether by ultrasound or auscultation and palpation—can be documented as a part of the physical examination and is taken into consideration for confirmation by formal echocardiographic study or consultation, time permitting. Because clinically relevant ultrasound techniques can be successfully taught in medical school ^, or internal medical residency, ^, ultrasound-augmented physical examination may be a gateway for all physicians to learn POCUS. Ultimately, physicians’ use of UAPE to improve their evaluation and management is an individual assessment of its incremental value in clinical context.

POCUS, when practiced as a form of limited echocardiography, can be differentiated from UAPE in an expert consensus document of the American Society of Echocardiography. In UAPE, the number of views and interpretation are limited to only ultrasound signs suggesting cardiac disease, in contrast to a limited echocardiogram, in which the user is responsible for all diagnoses, primary and incidental, manifest in the limited number of views in the imaging protocol ( Table 16.3 ). Under these terms, the term “limited” refers to the number of views and not the number of diagnoses. Limited echocardiography is a formal medical imaging test requiring imaging standards, study archival, and an all-inclusive interpretation and report. The evolving practice of POCUS is clearly different from the current practice of limited echocardiography because no formal diagnostic medical imaging test has the potential of being applied with such repetition and frequency by multiple physicians on the same patient.

Instrumentation: Form Fits Function

The form of developing POCUS equipment follows its intended function by maximizing portability and simplicity but also for documentation, limited quantitation, and connectivity. By far the most controversial development has been in pocket-sized ultrasound devices, bringing to the forefront issues of device ownership and use in the hospital—as either a personally owned ultrasound stethoscope or a hospital-purchased device with compatibility to archive studies into hospital-based systems. Currently, additional features vary by manufacturer and include color or Spectral Doppler, interchangeable or multifrequency transducers, and varying forms of image storage and transmission. Image setting presets are available to allow quick “boot-ups” for cardiac, abdominal, or obstetrics and gynecology imaging. Color or spectral Doppler gives the user the capability to differentiate an anechoic region such as a cyst as opposed to a vessel and allows a gross visual assessment of flow patterns as arterial or venous. For more advanced users, the presence of color Doppler can also be used to estimate valvular regurgitation and severity. Pulsed-wave spectral Doppler also provides the potential to assess diastolic filling patterns. Battery-life generally provides 1 to 2 hours of continuous imaging, further promoting brief quick-look application and recharging every 1 to 2 days. Remote real-time imaging with “telementoring” has already been reported as a feasible and inexpensive method for health care delivery and training.

Today, portable ultrasound devices have a wide range of cost, from $2000 for a pocket-sized device to $25,000 for a bedside tablet or laptop ultrasound device. No specific payor reimbursement exists for use of any device when used to augment bedside physical examination. However, cost savings to a health care system will be significant by improving diagnostic efficiency in outpatient echo referral, timeliness of triage, and appropriateness of consultation. For inpatients, assuming billing is performed for limited echocardiography and fully overread by a cardiologist, a preliminary reimbursement model (with application on approximately 30%–40% of medical admissions) predicted remuneration capable of funding POCUS equipment purchase and training. ^, Presently, partnerships, call groups, hospital departments, and clinics often share a POCUS device given the limited number of trained users.