Ultrasound is an elegant method which provides insight into the patient. Focused cardiac ultrasound (FoCUS) includes a basic approach to the heart and inferior vena cava (IVC) by ultrasound. By only using the eye-balling method attending physicians can obtain important information for a better understanding of a patient’s pathophysiology. Obtained data can be used immediately and integrated together with other clinical data, which helps physicians in their decision-making process.
Key words: focused cardiac ultrasound, point of care ultrasound, physicians performed ultrasound, hemodynamic monitoring, shock, cardiac arrest
Ultrasound is a bedside available, elegant method that literally provides insight into the patient. Echocardiography has been available in medicine for more than half a century and has been developed to an exact and reproducible method which provides precise information about heart function. To master this method requires systematic education and a lot of experience in the field. A comprehensive echocardiographic exam requires significant time to be performed.
In the hands of an attending emergency or ICU physician, unable to conduct a comprehensive echocardiography, ultrasound can still be a helpful tool.
Focused cardiac ultrasound (FoCUS)
By only using a simple eye-balling method, without any measurements, an ultrasound exam lasting for several seconds may provide useful data for better recognition and understanding of the clinical problem and may become a useful addition to a classical physical examination. Occasionally the obtained data are lifesaving.
At the basic level the learning curve is steep. Brief visual impression about heart morphology and function, together with the assessment of filling status represented by dimensions of inferior vena cava (IVC), which are quickly achieved by ultrasound, provides essential data for understanding the main problems of impaired haemodynamics. Recommendations on focused cardiac ultrasound (FoCUS) released by the International Liaison Committee in 2014 are based on a well-documented level of evidence. (1)
When the ultrasound examination is performed by an attending physician the obtained data can be immediately used for the clinical decision-making process. Some clinical questions raised at the bedside can be answered by ultrasound and can make the clinical picture clearer. Ultrasound provides insight into the most important elements of the circulatory system, so a lot of useful information about a patient’s hemodynamics can be achieved at the patient’s admission and during follow up, when the response to the treatment is to be assessed.
In the most critical of situations the timeframe is narrow and an attending physician must often count only on his own judgment. However, the more critical the patient’s condition is, usually the pathophysiologic derangements are more severe and the ultrasound findings are more obvious. Consciousness about the limitations of the method and the critical opinion of the personal level of expertise is essential to judge the reliability of the ultrasound obtained data in a particular situation. Clinicians are accustomed to dealing with data with a questionable level of reliability. The clinical picture is a mosaic. In this picture some pixels are clear, some are less clear, and some are missing. Sometimes even blurred pixels can help in the recognition of the contour, particularly if there are several of them. Many clinical variables are expressed as numbers. In a clinician’s mind those numbers are translated into categories such as “normal findings” or “mild”, “moderate” or “severe impairment”, taking into account the possibility of measurement error and multifactorial influence on the variable values. Borders between categories are never sharp. The eye-balling method, in the estimation of heart function, filling status etc. skips the numbers, but provides categories directly available for clinical opinion making process.
Usually there are several main questions related to the heart’s performance: What is the left ventricle size and contractility? Is there significant pericardial effusion? Are there signs of right ventricular overload? What is the inferior vena cava diameter and how it is changing by breathing?
By estimating the left ventricular size and contractility in a patient with shock, the contribution of pump failure in the aetiology of shock can be assumed. If there is dilatation of the left ventricle and wall excursions are small, it is suggestive of cardiogenic shock. A hyperdynamic heart is usually found in hypovolemic shock. In such cases the left ventricular cavity can be almost empty at the end of systole. Similar findings of a hyperdynamic heart can be found in patients with septic shock due to absolute and/or relative hypovolemia. If present, septic cardiomyopathy can modify this pattern.
In the case of cardiac tamponade, an anechoic layer around the heart can be seen as well as a collapse of the heart chambers during diastole, particularly the right atrium and right ventricle. The patient’s clinical condition together with visible signs of collapsed chambers will dictate immediate need for a pericardiocentesis. Ultrasound aid during pericardiocentesis is a standard of care.
Right ventricular dilatation with the interventricular septum shifted toward the left ventricle is suggestive of right ventricular overload. Acute right ventricular overload is often caused by pulmonary embolism. A dilated IVC, signs of venous thrombosis and exclusion of the excess of extravascular lung water supports this diagnosis.
It was shown that the IVC diameter and its narrowing during inspiration in spontaneously breathing patients correlates well with central venous pressure (CVP), particularly if the central venous pressure is low. (2-6) A narrow IVC with marked reduction of the anteroposterior diameter during inspirium implicates hypovolemia. A dilated IVC with little or no oscillations in diameter according to the breathing is suggestive of hypervolemia or other causes of elevated central venous pressure, such as right ventricular failure, pulmonary embolism, cardiac tamponade etc.
Despite the fact that measurements are simple and seem very exact, errors are possible due to the oval cross section and its nonparallel walls. When measurements are performed in M-mode, movements caused by diaphragm motion result in the fact that measurements in inspirium and expirium are not performed on the same segment of the IVC. All of this can produce some errors. Physicians experienced in ultrasound can estimate the volume status just by simple visual impression of the IVC during several breathing cycles, without any measurements, processing automatically other variables, such as breathing pattern and right heart function, which can influence their interpretation.
When there is a question about adequacy of volume administration, FALLS protocol can be applicable in patients with initially “dry” lungs and not impaired right ventricular function. (7) By frequent monitoring of the lungs, volume administration can be limited by the first appearance of lung B lines. At that moment lung interstitium starts to contain more extravascular lung water. Lung function is still not impaired and maximal left ventricular output can be expected because left ventricle preload is at the optimal point of the Frank-Starling curve. Further volume administration can worsen lung function due to lung congestion.
Ultrasound in cardiac arrest
In the case of cardiac arrest, ultrasound can be helpful in monitoring the heart function, recognising and treating some potentially reversible causes of arrest (cardiac tamponade, pneumothorax, hypovolemia, pulmonary embolism, etc) and is an aid while performing procedures, like endotracheal intubation, venous access, pericardiocentesis, pneumothorax or liquidothorax drainage, abscess drainage etc. (8-13) In such circumstances it is of utmost importance not to interrupt the recommended algorithm of advanced life support. The correct time to use ultrasound for a brief look is when chest compressions are stopped to check for cardiac action. Protocols such as FEER, RUSH, and SESAME are designed for the inclusion of point of care ultrasound to facilitate resuscitation of cardiac arrest victims. (14-17) One of the first ultrasound protocols used in emergency medicine, FAST protocol, designed to detect internal bleeding in pericardial, pleural or abdominal space in traumatized victims with the aim to facilitate surgical operation, if positive indirectly suggests the need for hemodynamic support by fluid administration and transfusions. (18)
More than eye-balling
In addition to the eye-balling method, some echocardiographic applications that require measurements are of particular interest for intensivists, such as MAPSE, TAPSE and measurements of cardiac output. (19, 20)
Measurements of systolic movements of mitral (MAPSE) or tricuspid (TAPSE) annulus ring along longitudinal plane by using apical four-chamber view can additionally support the left ventricle or right ventricle impairment. MAPSE < 8 mm implies reduced left ventricle ejection fraction, while TAPSE < 16 implies impaired right ventricular function.
By measuring the diameter of the left ventricular outflow tract and calculating the average speed of blood passing through during systole, the stroke volume can be calculated, which if multiplied by the heart rate (if it is regular) corresponds to cardiac output. For such analysis ultrasound devices should have pulsed wave Doppler and software for calculating the velocity time integral. The learning curve is steep and measurements are not so time consuming. Measurements of the effects of fluid challenge or passive leg rising on cardiac output can help in assessing fluid responsiveness. (21)
Ultrasound as an extension of physical examination
An ultrasound exam can be performed by following protocols designed for different clinical scenarios, or they can be performed as a “whole body” exam, complementary to the classic physical examination, which can provide additional insight into the morphology and function of important organs and organ systems accessible by ultrasound, paying more attention to details relevant in the particular clinical scenario.
FoCUS is usually just a part of a protocol or part of a brief, orientational, bed-side, physician performed “whole body” ultrasound exam. Other ultrasound findings, particularly information about lungs, when integrated together with FoCUS and with other available clinical data can provide a clearer picture about the patient’s condition. (22- 24, 7) Understanding ultrasound as a holistic discipline, which enables visual insight into the patient, satisfies clinicians who care about the “whole” patient. This approach can have implications on more appropriate immediate treatment and/or more directed eventual additional diagnostic investigations and consultations.
PoCUS works, particularly if it is integrated with other clinical variables including also other data obtained by ultrasound which are out of the PoCUS range.
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