Point-of-care ultrasound in critically ill patients: Where do we stand?

Abstract

Experience over the last 25 years has shown that point-of-care ultrasound is a very useful tool when used by nonradiologists. Its value will be optimized by understanding its limitations and by adopting a focused binary decision making approach to answer specific questions without going into detailed radiological studies. Point-of-care ultrasound became an extension of the clinical examination. There are extensive efforts trying to design low-cost portable ultrasound systems by changing the transducer design, the transmission and reception circuitry needs, or the beam forming algorithms which may lead to horizontal expansion of the use of reliable non expensive portable ultrasound machines. The successful story of using ultrasound by nonradiologists, the advanced technology, and the refinement of the educational methods will encourage future clinicians to use ultrasound in their domains.

INTRODUCTION

Using ultrasound in life-threatening conditions is one of the successful stories of carrying portable technology to sick patients so as to improve outcome of their management. Despite its clear advantages, there was initial resistance and reluctance to use ultrasound by nonradiologists. Nevertheless, with more experience and knowledge in this area more acute care physicians are using it. The value of ultrasound will be optimized only after understanding its limitations and pitfalls.

POINT-OF-CARE ULTRASOUND

It was unimaginable 100 years ago to be able to draw a picture from sound. Similarly it was written in “The Times” in 1834: “The medical profession was unlikely ever to start using the stethoscope because its beneficial application requires much time and gives a good bit of trouble.” Ultrasound, which is our future stethoscope, has passed through the same story, as the medical community was initially reluctant to use it for diagnosing life-threatening conditions by nonradiologists. Roy Filly wrote an Editorial in Radiology in 1988 entitled “Ultrasound: The stethoscope of the future, Alas” in which he stated: “As we look to the proliferation of US instruments into the hands of untrained physicians, we can only come to the unfortunate realization that diagnostic sonography truly is the next stethoscope: used by many, understood by few.”[1] Experience over the last 25 years has proven the opposite. This was achieved by adopting a focused binary decision making approach to answer specific questions by yes or no. For example: Is there free intraperitoneal fluid in the trauma patient? Yes or no. This approach has simplified the decision making process in critically-ill patients without going into detailed radiological studies.[2] In reality, point-of-care ultrasound became an extension of the clinical examination answering urgent important questions.[3] Furthermore, we have learned that point-of-care ultrasound, when performed by nonradiologists, has become a more physiological study than an anatomical one. This is well demonstrated during the resuscitation of a hypovolemic shocked patient in which a small anteroposterior diameter of the inferior vena cava will gradually increase with successful resuscitation. The value of point-of-care ultrasound in the diagnosis and management of shocked patients using specific protocols is well established. This includes a focused study to look for fluid in the pericardium, pleural and peritoneal cavities, measuring the IVC diameter, and evaluating the heart contractibility.

Point-of-care ultrasound is rapid, accurate, repeatable, nonexpensive, noninvasive and without the risk of radiation. It can be used in both stable and unstable patients. It may also be performed parallel to physical examination, resuscitation and stabilization.[4] Performing repeated ultrasound exams in critical patients is essential and improves its overall sensitivity. Initially negative sonographic exams may become positive during the course of the disease.

Pitfalls of ultrasound can be related to the patient, the operator, or the ultrasound machine . Ultrasound is inaccurate in obese patients due to poor penetration of sonographic waves. Furthermore, it will be difficult to visualize intraabdominal structures in case when there is ileus or subcutaneous surgical emphysema. Furthermore, ultrasound cannot accurately differentiate between blood, urine, bile, ascites or postresuscitation intraperitoneal exudates.[5] The operator should be very familiar with the ultrasound machine, the type of transducers used, how to improve ultrasound gain and how to control its outcome. The operator should be especially knowledgeable of the sonographic artefacts that can mislead him/her. Knowledge of these artefacts may even help in the diagnosis. For example, the presence of the reverberation artefact may help in the diagnosis of the free intraperitoneal air.

The sonographic findings have to be correlated with the clinical picture to make critical decisions and should be used within diagnostic algorithms. If the patient is hemodynamically stable, then CT scan of the abdomen, if indicated, may give more information than ultrasound.[6] Ultrasound will miss quarter of the intra-abdominal injuries in trauma patients when it is the only used diagnostic modality.[7]

Ultrasound results depend on the operator's training and experience. Doctors who use ultrasound in critically-ill patients should pass a credentialing process before using their own ultrasound results for critical decision-making.[2,8] The period of training will be shortened when the operator aims at mastering limited and focused studies.[9]

There are extensive efforts trying to design low-cost portable ultrasound systems by changing the transducer design, the transmission and reception circuitry needs, or the beam forming algorithms.[10] These developments in technology will have a tremendous impact on the cost and utility of portable ultrasound machines. This will be more evident in the per-hospital setting and management of disaster situations, allowing accurate field triage and direction of patient care, in even the most austere of environments.[11] This has been recently well documented in the Wenchuan earthquake in China.[12] Dan et al., treated 3207 patients of whom 37.6% benefitted from sonography. Ultrasound detected trauma-related pathologies in 7% of the patients, had a positive predictive value of 100% and a negative predictive value of 96%.[12]

Furthermore, satellite and mobile wireless transmission of ultrasound images have been successful using hand-held units.[13] For example, ultrasound images have been transmitted from an international space station to the earth.[14] Ultrasound images can be interpreted after transmission using telemedicine without the physical need of the radiologist in the disaster field. Despite the tremendous progress in technology, we have to be cautious that the treating physician should lead the technology and not the opposite. What is feasible may not be indicated. This gives a major task for clinicians to define the indications and limitations of sonography in different settings.

The successful story of using ultrasound by nonradiologists, the advanced technology in ultrasound machines, and the refinement of the educational methods have encouraged more acute care physicians to use ultrasound in their practice. It is amazing how the indications and utilization of ultrasound has expanded during the last three decades. We hope, through this symposium, to promote the use of point-of-care ultrasound by nonradiologists so that sonography, our future stethoscope, will be understood by many and used by many.

CONCLUSION

The horizon of point-of-care ultrasound is expanding dramatically. Knowledge, training, technical skills, critical decision making, and imagination will make point-of-care ultrasound our future stethoscope.