Background

As per the Imperial College of Healthcare NHS Trust, about 46% of emergency patients have an urgent need for their volume status to be assessed, and these patients are among the most at risk of death (NIHR Imperial BRC statement, 2014).

In critical care and emergency patients, accurate and reliable estimation of circulating blood volume is crucial to provide a determination of blood loss. Standard methods for measuring blood volume are impractical in many critical care situations owing to the need for specialized equipment and operators, radiation exposure, cost, or time requirements. In the trauma setting, changes in blood volume must be determined urgently and accurately to indicate and properly treat a patient in shock. Clinical evaluation involving assessment of skin color, blood pressure, heart rate, urine output, mental status, and capillary refill is often used. However, these bedside estimations can be inaccurate and unreliable, and there is currently no gold standard for blood volume assessment in the trauma or critical care setting.

Technology Overview

A researcher at the University of Hawaii has developed a fast, precise, and reproducible method to calculate blood volume status in a patient. The methods are suitable to critical care and trauma patients because they combine and adapt equipment that is readily available in urgent and emergent care settings with known techniques to provide results that are superior to current practices. Contrast enhanced ultrasound (CEUS) makes use of contrast agents to enhance the echogenicity of blood, thereby improving its visualization. CEUS imaging has been used by cardiologists for decades to assess perfusion through the intravenous injection of microbubbles. The microbubble contrast agent is acoustically destroyed in the field of view and the resultant acoustic signal is quantified as the vasculature is replenished with contrast. The intensity of the signal is plotted graphically, whereas area under the plateau phase equates to the blood volume in the image window.

Nonlinear contrast agent imaging uses multiple ultrasound pulses in which the amplitude of the pulse is modulated. By performing this type of imaging, the nonlinear response of the microbubbles to ultrasound pulses is utilized. This modality of imaging suppresses the tissue signal while increasing the detection of the contrast agents, providing a much more sensitive imaging technique, thereby essentially eliminating the noise associated with the acquired intensity data.

Power Doppler sonography displays the strength of the Doppler signal in color, rather than the speed and direction information. It has three times the sensitivity of conventional color Doppler for detection of flow and is particularly useful for small vessels and those with low‑velocity flow.

This method combines nonlinear contrast and/or power Doppler imaging with a contrast agent-based destruction/replenishment protocol, to provide a blood volume estimation using minimally invasive procedures. Furthermore, the technique can be fully integrated with current trauma practices, adding only seconds to the current assessment protocols. Following trauma, patients are subject to Focused Assessment with Sonography for Trauma (FAST) or extended FAST (eFAST) to assess the extent of injury. FAST/eFAST exam sites can be used as sites for determining blood volumes by using contrast perfusion curve analyses. While the ultrasound exams are being performed, contrast agent can be injected IV and destruction/replenishment curves performed while imaging each site (with the added benefit of better images due to contrast agent being present). Total blood volume can be determined by adding the sites together.

Moreover, the whole procedure can be implemented using a hand-held ultrasound device and requires only the injection of microbubbles to facilitate the imaging modalities used to quantify circulating blood volume. Hand-held applications will allow the system to be portable adding the additional benefit of field use by EMTs or combat medics.Hand-held devices allow the system to be portable and available for field use by EMTs or combat medics.

Benefits

Minimally invasive
Rapid and simple method for blood volume measurement
Designed for the trauma setting
Streamlined for FAST/eFAST integration
Compatible with current ultrasound equipment
Ideally suited for portable handheld ultrasound devices
Readily adaptable to field sites and combat settings

Applications

Assessment of blood volume
Evaluating trauma related blood loss

Ultrasound Mediated Assessment of Blood Volume

Patents

IP Status

Seeking