The Evolution of Ultrasound in Critical Care

The Evolution of Ultrasound in Critical Care

Introduction

In today’s medical critical care unit, point-of-care ultrasonography (POCUS) has become a standard of treatment (ICU). POCUS’s position in the medical ICU has expanded sequentially during the last three decades, according to a superficial chronologic assessment (Figure 1).

We feel this demonstrates the evolution of POCUS from a procedural aid to a diagnostic asset included in a comprehensive physical examination. However, we believe that, with recent advances in machine learning and the sophistication of POCUS technologies, POCUS will continue to evolve into a hemodynamic monitoring tool, providing clinicians with cross-sectional measurements that can be trended and used during ICU management in the same way that traditional vital data can.

Chronologic Survey

With the development of smaller, faster, and more-portable real-time ultrasound (US) devices during the last 2 decades, emergency medicine adopted POCUS early in routine care, embracing it as a quicker and accurate management tool in trauma and shock. As evidence of POCUS use in shock and trauma in emergency medicine solidified, medical intensivists also adopted bedside US as a diagnostic tool in shock, with the goal of quickly capturing life-threatening abnormalities. This relatively qualitative approach gave rise to protocolized US assessments summarized by mnemonics such as RUSH (rapid ultrasound in shock,) FAST (fast assessment in shock and trauma), and ACES (abdominal and cardiac evaluation with US in shock).

The popularity of POCUS as a clinical decision support tool in acute care settings has grown. For example, POCUS training is now widely encouraged in both internal and critical care medicine training programs. Broad use of thoracic, abdominal, and vascular US over time has given intensivists confidence when using POCUS for the diagnosis of nuanced conditions. POCUS has been recognized as an important tool in guiding shock management, especially given its ability to quickly and repeatedly provide semiquantitative hemodynamic information such as a change in the left ventricular (LV) ejection fraction, right ventricular size and function, estimation of central venous pressures, and information about third spacing of fluids.

Furthermore, the proficiency with which POCUS provides dynamic parameters of fluid responsiveness such as cardiac output, the LV outflow tract velocity time integral (VTI), inferior vena cava distensibility, and corrected flow time variability has revealed a promising fund of predictive metrics.

Point-of-Care US as a Monitoring Tool

The transition to precise and fully quantitative US has been slowed by high interoperator variability, which can affect the interpretation of US-derived data; for example, capturing and interpreting US images is heavily influenced by training and experience. Accordingly, early methods of artificial intelligence (AI) in POCUS such as autocapture of the LV outflow tract VTI,16 inferior vena cava distensibility,17 and pulmonary B-lines18 have been deployed (Figure 2, A & B).

Ostensibly, acquiring, retaining, and sharing US data that are augmented by AI will mitigate interoperator variability and afford safer clinical practice. Building AI requires large databases of US images with both normal and pathologic findings and finally, AI advancements are not infallible. For instance, VTI measurements can be flawed secondary to image quality or specific pathologic conditions similarly, vena cava variation may be affected by the patient’s condition, leading to erroneous conclusions. In addition to AI, the development of smaller, attachable US transducers, capable of monitoring hemodynamics across time, heralds a new and exciting era whereby POCUS is used as a monitoring device among other applications (Figure 3).

Conclusions

Ultrasound in the ICU will continue to expand and evolve. Although new technology often begins with great excitement, some of this initial enthusiasm must be tempered. Point-of-care US as a decision-making tool during shock resuscitation is still nascent—further research and experience will shape its future and reveal its reliability and limitations. Crucially, POCUS must remain a tool that enhances management based firmly on Bayesian principles. The onus is on the operators to remember that POCUS remains an “extended stethoscope” and, potentially, a supplemental monitor with which the clinician triangulates all available data.

Source:  Barjaktarevic I, Kenny JS, Berlin D, Cannesson M. The Evolution of Ultrasound in Critical Care: From Procedural Guidance to Hemodynamic Monitor. J Ultrasound Med. 2021;40(2):401-405. doi:10.1002/jum.15403