Make it SIMPLE: enhanced shock management by focused cardiac ultrasound
© The Author(s). 2016
Received: 7 April 2016
Accepted: 12 July 2016
Published: 15 August 2016
Shock is a spectrum of circulatory failure that, if not properly managed, would lead to high mortality. Special diagnostic and treatment strategies are essential to save lives. However, clinical and laboratory findings are always non-specific, resulting in clinical dilemmas.
Focused cardiac ultrasound (FoCUS) has emerged as one of the power tools for clinicians to answer simple clinical questions and guide subsequent management in hypotensive patients. This article will review the development and utility of FoCUS in different types of shock. The sonographic features and ultrasound enhanced management of hypotensive patients by a de novo “SIMPLE” approach will be described. Current evidence on FoCUS will also be reviewed.
Focused cardiac ultrasound provides timely and valuable information for the evaluation of shock. It helps to improve the diagnostic accuracy, narrow the possible differential diagnoses, and guide specific management. SIMPLE is an easy-to-remember mnemonic for non-cardiologists or novice clinical sonographers to apply FoCUS and interpret the specific sonographic findings when evaluating patients in shock.
Shock is a clinical syndrome in which there is inadequate cellular and tissue oxygenation due to circulatory failure . The presentation of shock can vary with different causes of shocks and degrees of physiological abnormalities. Shock can be classified into five different categories according to the underlying pathophysiology, namely hypovolemic shock (due to hemorrhage or intravascular volume depletion), cardiogenic shock (e.g., acute myocardial infarction, myocarditis), obstructive shock (e.g., pulmonary embolism, tension pneumothorax, and cardiac tamponade), and distributive shock (e.g., septic, neurogenic, and anaphylactic), and lastly, shock related to cellular poisoning . One of the cardinal features of shock is hypotension. It can be defined as systolic blood pressure lower than 90 mmHg or more precisely mean arterial pressure lower than 65 mmHg as suggested by the latest international consensus definitions for sepsis and septic shock . It is associated with high mortality and adverse hospital outcomes in non-traumatic patients in the emergency department [4, 5].
In order to save our patients in shock, early diagnosis, and timely targeted therapy is vital. To do so in a timely manner is a challenge as clinical presentation of different types of shock may be similar. Point-of-care ultrasound (PoCUS) performed by clinicians providing direct care to the patients is considered an invaluable clinical tool to facilitate diagnosis-making, to rule out potentially fatal conditions, and to provide guidance to life-saving procedures . Among the different applications of PoCUS, focused cardiac ultrasound (FoCUS) is gaining popularity in emergency care settings. It is considered as one of the core emergency ultrasound applications by the American College of Emergency Physicians and the International Federation for Emergency Medicine [7, 8]. Recently, FoCUS has been integrated into scanning protocols together with focused scans in other regions, e.g., lung, abdomen, and lower limb deep vein system to manage patients in clinically undifferentiated hypotensive state [9–11]. In the following sessions, the SIMPLE approach, the role of FoCUS in the management of shock, and the current evidence for this application will be discussed.
Essentials of FoCUS and SIMPLE approach
The name “focused cardiac ultrasound” (FoCUS) is interchangeable with “focused echocardiography,” “emergency echocardiography,” “bedside limited echocardiography,” “point-of-care cardiac ultrasound,” and “goal-directed echocardiography” . Lately, the term “focused cardiac ultrasound” has been recognized as a more appropriate term to take into account the nature of point-of-care application of ultrasound assessment of cardiac anatomy and physiology, distinct from the formal echocardiographic study done by cardiologists, according to the first international evidence-based recommendations issued by World Interactive Network Focused on Critical UltraSound (WINFOCUS) . FoCUS was first introduced into emergency communities in the 1990s [14, 15]. With the wider availability and miniaturization of ultrasound machines, FoCUS has quickly become standard practice in acute care settings across the globe. In contrast to the conventional comprehensive echocardiography performed in the cardiac laboratory by cardiologists, FoCUS is performed by emergency physicians or intensivists at the bedside. It is essentially a limited evaluation of cardiac function, pericardial space, and intravascular volume in order to answer clinical questions vital to patient management. Contrary to what some may believe, the requirement for the FoCUS is not high. A portable or even pocket-sized handheld ultrasound machine can provide adequate image quality for assessment of left ventricular function, detection of pericardial effusion, and measurement of abdominal aorta size [16–18]. Pocket-sized machines are advantageous in unfavorable environments where full-sized machines will be impractical, e.g., pre-hospital assessment in an ambulance or helicopter .
SIMPLE approach for evaluation of key elements during focused cardiac ultrasound sound (FoCUS) in shock patients
SIMPLE approach in focused cardiac ultrasound
Chamber size and shape, particularly LV and RV size
IVC size and collapsibility
Intimal flaps inside the aorta, suggestive of aortic dissection
Mass in the heart chambers (commonly intramural clots and atrial myxoma)
Myocardium (motion and thickness)
Left ventricular systolic function
Abdominal aorta in the epigastrium
Summary of typical findings in different types/causes of shock by SIMPLE approach
Type of shock
Early: small LVESA
Near normal LVEDA but small LVESA
Dilated RV, small/normal LV
Diastolic collapse of RA and RV; normal LV
Distended <50 % respiratory collapse
Distended and loss of respiratory collapse
Distended and loss of respiratory collapse
Normal when no cardiac tamponade
Paradoxical IVS and D-shaped LV
Hyperdynamic or normal
McConell’s sign, LV hyperdynamic
Diastolic collapse of RA and RV
Normal if coronary ostia not involved
Masses in heart
Intramural thrombi if AF/AMI
Thrombi in RA/RV and IVC
Small amount if inflammatory cause
Moderate to large but can be small if acutely collected
Present if retrograde dissection and echogenic
Present if pneumonia
Present if hemothorax
LV systolic function
Early: normal or hyperdynamic
Normal or hyperdynamic
Normal or hyperdynamic
Abdominal aorta in epigastrium
Aneurysmal if due to AAA rupture
Intimal flap seen
In addition to the five orthodox TTE views, the subcostal region or epigastrium is included in this SIMPLE scanning protocol to assess the size of IVC and abdominal aorta which may be involved in aortic dissection and aneurysmal rupture (Fig. 2). In this approach, a single ultrasound probe is used to look for the causes for hypotension and guide treatment by means of a focused point-of-care ultrasound study. Concerning the sequence of examination, it would be a good habit to start at the parasternal views then move to the apical view and, finally, the subxyphoid/epigastric regions to assess the IVC and the abdominal aorta. However, in some patients with emphysematous lungs, hyperinflation of the chest and morbid obesity, and on mechanical ventilation, only one to two views can be obtained for evaluation. Cardiac function assessment, although limited, may still be possible in these situations through the remaining one to two views. If FoCUS reveals features of hypovolemia (as will be discussed later), a focused assessment with sonography for trauma (FAST) protocol (i.e., SIMPLE + FAST approach) is warranted to look for intra-abdominal bleeding and hemothorax. Although limited when compared to comprehensive echocardiography carried out in the cardiac laboratory, this approach provides valuable information concerning the pathology, heart function, and physiology to differentiate between different types of shock and guide subsequent management.
The size of the RV can give clues to the right heart function. Normally, it should be smaller than the LV and the apex should be formed by LV, not RV (Fig. 1). It is easily visualized in the apical four-chamber view as a triangular-shaped structure. The normal basal diameter of RV should be less than 4 cm . If it is enlarged acutely in the appropriate clinical setting, the diagnosis of acute right heart failure due to massive pulmonary embolism should be suspected. The end-diastole area ratio of RV/LV should be less than 0.6 in the normal heart. A ratio higher than 0.66 would suggest cor pulmonale . When this happens together with a normal RV wall thickness (<5 mm in parasternal long views), then it is very likely that there is acute right heart failure resulting from massive pulmonary embolism.
IVC size and collapsibility
IVC size can be used as a surrogate measurement of preload and volume status and therefore right atrial pressure (RAP). IVC diameter can be used to estimate RA pressure. The American Society of Echocardiography suggested the cutoff value of 2.1 cm . IVC diameter <2.1 cm that collapses >50 % with inspiration would correlate with RA pressure of 3 mmHg (range, 0–5 mm Hg) while an IVC diameter >2.1 cm that collapses <50 % with inspiration suggests high RAP of 15 mm Hg (range, 10–20 mmHg). In patients with hypovolemic shock, the IVC diameter will be expected to be <2.1 cm and collapse >50 % with inspiration. In a recent meta-analysis of data from five studies on the sonographic measurement of the IVC in assessing the fluid status in the emergency department (ED), it was evidenced that the maximum IVC diameter is lower (6.3 mm 95 % CI 6–6.5 mm) in patients with hypovolemia than euvolemia . Resuscitation of hypotensive patients usually involves fluid challenge. IVC diameter may give us some clues. The IVC distensibility index where maximum IVC diameter minus minimal IVC diameter divided by minimal IVC diameter times 100 % was found to be useful in predicting fluid responsiveness using the cutoff of 18 % in mechanically ventilated patients . However, for patients with spontaneous breathing, the value of IVC size was less distinguished in predicting fluid responsiveness. With the cutoff of 40 %, the IVC collapsibility index that is maximum IVC diameter minus minimum IVC diameter divided by maximum IVC diameter times 100 % would only give a sensitivity of 70 %, specificity of 80 %, positive predictive value of 72 %, and negative predictive value of 83 % . In trauma patients with hemorrhage, IVC measurement in addition to FAST is also helpful for managing trauma patients with hypovolemia to guide fluid therapy and shorten the time to operation theater [33, 34].
Intimal flap in aortic dissection
Mass in cardiac chambers: thrombus/myxoma
During systole, different parts of the LV thicken in a coordinated fashion to act as a pump to eject blood out of the heart. According to the European society of Cardiology and American Society of Echocardiography, the LV can be divided into 17 segments and each individual segment can then be graded as normal/hyperkinetic, hypokinetic (reduced thickening), akinetic (absent thickening), or dyskinetic (abnormal thinning and stretching especially in aneurysm) according to their motions during systole [23, 42]. This can give clue to myocardial ischemia/infarct and the culprit coronary vessel involved when the areas of abnormal regional wall motion correspond to the territory supplied by the culprit vessel. With compatible sonographic findings and clinical picture, primary percutaneous intervention will be warranted when myocardial ischemia/infarct is believed to be the cause for cardiogenic shock.
Abnormal thickening of the myocardium (LV posterior wall and interventricular septum thickness >1 cm at end-diastole; RV free wall >5 mm) is suggestive of chronic heart conditions resulting from pressure overload (e.g., hypertensive cardiomyopathy, hypertrophic cardiomyopathy, pulmonary hypertension, and aortic stenosis). Together with gross dilatation of ventricle and atrium, detection of myocardial thickening is considered by the latest international consensus to be an essential part of FoCUS . It can help avoiding misdiagnosing pre-existing heart conditions (e.g., chronic cor pulmonale) as an acute one (e.g., acute massive pulmonary embolism) and avoiding inappropriate treatments (e.g., intravenous fibrinolytic).
Pericardial effusion vs pleural effusion
LV systolic function
Echocardiography or cardiac ultrasound can give an accurate assessment of global function of the left ventricle and guide subsequent treatment (e.g., inotropic support versus fluid therapy). There are several options to assess the LV systolic function sonographically, including fractional shortening (FS) and LV ejection fraction (LVEF).
The normal value should be 25–45 % for adults . If the value falls below <15 %, severe LV systolic dysfunction is present. This measurement is very simple and easy. However, the measurement must be done perpendicular to the axis of the left ventricle, and the ventricle should not be foreshortened. There is also an assumption of no severe dysfunction in other parts of the left ventricle.
In B-mode, the LVEF can be measured by the modified Simpson biplane method. Most modern ultrasound machines have the calculation package pre-installed. The endocardial margins of the LV are traced in systole and diastole from two different views (i.e., two individual planes perpendicular to each other) to calculate the volume change between systole and diastole. The normal LVEF should be >55 %, and <30 % indicates severe left ventricular systolic dysfunction . This is not a simple method compared with the FS, and the endocardial margins have to be traced correctly or under/overestimation of the LVEF may result. In emergency settings, suboptimal images of the LV and inadequate cardiac views would render this method less practical.
Assessment of LVEF by eyeballing appears the most feasible yet reliable method for estimating the LV systolic function. It can be done through assessing the movement and thickening of the LV myocardium, the change in size and shape of the LV chamber as well as the mitral valve anterior leaflet excursion in the cardiac cycle. It was found that the accuracy of eyeballing estimation correlated well with other quantitative methods including Simpson biplane ejection fraction, fractional shortening, wall motion score index, and aortic valve (AV) plane displacement [45, 46]. This advantage is not confined only to the experienced cardiologists. With focused training, the estimation of LV ejection fraction by emergency physicians had a strong agreement with cardiologists [47–49]. Even inexperienced emergency medicine trainees could achieve good agreement on the visual estimation of LV ejection fraction with cardiologists after web-based learning and proctored practical training (K = 0.79, 95 % CI 0.773 to 0.842) . Thus, visual estimation of the LV ejection fraction should form an important part of left heart systolic function assessment in FoCUS, in particular when quantitative measurements are not possible due to poor echogenicity of the heart and limited cardiac views in some patients.
Abdominal aortic at the epigastrium
Evaluation of undifferentiated shock by SIMPLE approach
Massive pulmonary embolism
Septic shock represents a distinctive spectrum of hemodynamic instability. In the early stage, the afterload is reduced and left ventricular dysfunction, although present, is masked by the severely reduced afterload due to sepsis [61, 62]. Thus, FoCUS will find a normal LVEDA but small left ventricular end-systolic area (LVESA) and a hyperdynamic LV. There is a substantial decrease in the size of the LV from diastole to systole in contrast to hypovolemia where the LV size is small throughout the cardiac cycle. The IVC would collapse in this stage with >50 % inspiratory collapse. After the initial phase, myocardial depression occurs in around 60 % septic patients . Once the afterload is restored by vasopressors and fluid therapy, the LV myocardial dysfunction is unmasked. LV would be normal or dilated with myocardial hypocontractility [61–63]. At this stage, the IVC is distended and the respiratory collapsibility is lost similar to the profile in cardiogenic shock. Recognizing these sonographic findings can help clinicians tailoring appropriate treatments to different stages of septic shock.
SIMPLE approach versus other protocols
Summary of current major protocols of point-of-care ultrasound for undifferentiated shock/cardiac arrest
Year of publication
Simplified version of extended FAST
Pleural effusion only
Similar to extended FAST
PLX, PSX, AP4, SXP
Pleural effusion only
Chronic pathologies included
Pediatric patients only
SXP, PLX, PSX, AP4
Integrated into ACLS protocol for cardiac arrest
PLX, PSX, AP4, SXP
Surgical patients; SV and CI included
SXP, PLX, AP4
Pleural effusion only
RUSH-pump, pipe, tank 
PLX, PSX, SXP, AP4
Physiological model of pump, pipe, tank
SXP, PLX. AP4 (any one of them)
Pleural effusion only
Cardiac arrest and peri-arrest state
PLX, PSX, AP4, SXP
Lung scan first approach
PLX, PSX, AP4, SXP
Not specifically mentioned
Mainly lung scan
FAST and RELIABLE 
PLX, PSX, AP4, SXP
Ectopic pregnancy included
Volpicelli et al. 
PLS, SXP, AP4
Similar to RUSH 
Shokoohi et al. 
SXP, PLX, PSX, AP4
PLX, PSX, AP4, AP2, SXP
Easy-to-remember checklist of sonographic findings; intracardiac mass and intimal flap included; can be combined with FAST
In contrast to existing protocols like rapid ultrasound for shock and hypotension (RUSH) , abdominal and cardiac evaluation with sonography in shock (ACES) , undifferentiated hypotension patient (UHP) , Trinity , or focused assessed transthoracic echocardiography (FATE) , every single letter in the SIMPLE approach represents a specific assessment in cardiac ultrasound. This simple mnemonic provides clinicians with a simple and easy-to-remember, yet valuable checklist of sonographic findings to look for when managing patients in shock. Unlike the RUSH protocol, physiology is not emphasized in the SIMPLE approach but systematic interpretation of sonographic findings can help the clinicians narrow down the differential diagnosis of shock and guide initial therapy (e.g., small and kissing LV with flat IVC already warrants fluid resuscitation and hypovolemia is suspected, while dilated and hypokinetic LV would suggest cardiogenic shock and inotropic support is needed). It can also help avoiding complications associated with indiscriminate use of fluid therapy and inotropes.
To my knowledge, this is the first protocol to include two specific findings explicitly: intramural mass and intimate flap so as to improve the diagnostic power of two challenging and lethal conditions, namely massive pulmonary embolism and aortic dissection. Although abdominal assessment is not routinely included in the SIMPLE approach, combination with FAST to look for the source of intra-abdominal bleeding is indicated when FoCUS reveals features of hypovolemia. As most emergency physicians and intensivists have been using FAST scan routinely in trauma assessment, a combination of SIMPLE with FAST (SIMPLE + FAST) would easily be incorporated into their daily practices. SIMPLE + FAST suggests cardiac assessment first before abdominal assessment in order to detect obstructive and cardiogenic shock, in contrast to the FAST + RELIABLE protocol suggested by Liteplo et al. . This allows early specific treatment such as pericardiocentesis and inotropes to correct the circulatory failure and prevent indiscriminative fluid challenge which is detrimental in cardiogenic shock.
Current evidence of FoCUS for evaluation of shock
Among the literature, there is growing evidence demonstrating that FoCUS could improve the diagnostic accuracy and change the clinical management. Although the results of this evidence may not necessarily prove that FoCUS can lead to better patient survival and shorten the hospital stay, it can logically be assumed that with more accurate diagnostic capability for various types of shock, implementation of FoCUS could lead to a better clinical outcome in patients with circulatory failure.
FoCUS is helpful in confirming the correct diagnoses and detecting the etiology of shock. In a randomized trial in 184 patients by Jones et al. in the emergency department, early goal-directed ultrasound at 0 min was found to correctly diagnose the etiology of shock in 80 % of patients compared 50 % of patients in the group only received standard care at the initial 15 min of presentation in the emergency department . This trial can be concluded into two important points. Firstly, it was the first study to prove that early focused ultrasound can allow the emergency physicians to narrow the differential diagnoses of shock. Secondly, it proved that early focused ultrasound at the initial presentation is feasible and can be combined with standard care interventions, e.g., venous access establishment, electrocardiography, blood sample analysis, and chest radiography.
Subsequent trials on protocol-driven ultrasound for diagnosis of shock further confirmed the role of FoCUS to diagnose and differentiate different types of shock in the emergency department. Volpicelli et al. did a prospective study on 108 ED patients in undifferentiated shock by comparing the sonographic diagnosis with the final clinical diagnosis . The ultrasound assessment in this study included FoCUS and IVC assessment, lung scan, abdominal scan for free fluid, and leg scan for deep vein thrombosis. They found a very good concordance between the ultrasound diagnosis and the final clinical diagnosis (k = 0.710). Ghane et al. also found similar finding in a study in 52 ED patients by using RUSH protocol (k = 0.7) . It was also found that ultrasound achieved 100 % sensitivity for hypovolemic and obstructive shock, 91.7 % sensitivity for cardiogenic shock, and 94.6–100 % specificity for all types of shock. However, in distributive and mixed type of shock, the sensitivity was found to be lower only 70–75 %. The same group also found similar results in another study on 77 patients . The common limitation of the above three studies is that ultrasound assessments were done by either radiologist or emergency physicians experienced in PoCUS, and so the results may not be generalizable to other inexperienced clinicians from other specialties.
Apart from correct diagnosis and differentiation of shock, the other major role of FocUS for shock is to tailor the treatment according to the underlying etiology and improve the clinical outcome of patients. In an observational study conducted on 220 patients in intensive care unit, use of FoCUS by hand-held ultrasound device was found to be associated with significantly lower fluid prescription (49 vs 66 mL/kg, p = 0.01) and more dobutamine use (22 vs 12 %, p = 0.01) than the historical control group which was managed in a standard fashion . More importantly, this study found that FoCUS group had better 28-day survival (66 vs 56 %, p = 0.04) and a reduction in acute kidney injury (20 vs 39 %). These findings are supportive of using FoCUS to guide the resuscitation of hypotensive patients. The limitations of this study include no randomization, use of historical control, and a significant number of patients (14 %) with significant valvular pathologies. Another recent study performed in ED also confirmed the impact of FoCUS findings on management plan (in 24.6 % of patients), including the use of intravenous fluid, vasoactive agents, or blood products. This study also found an excellent concordance of protocol-driven ultrasound diagnostic protocol in undifferentiated hypotension with the final diagnosis (k = 0.80). Moreover, ultrasound was also found to influence the diagnostic imaging, consultation, and patient disposition in this study. Again, the limitations are the lack of randomization and use of single ultrasound operator.
Managing patients in profound shock poses a very great challenge to clinicians. Correct diagnosis and timely specific treatment to restore the otherwise jeopardized circulation are vital to the survival of hypotensive patients. Throughout the past 10 years, FoCUS has emerged as one of the important allies of emergency physicians and intensivists to provide crucial answers to challenging clinical conditions. In properly trained hands, FoCUS can provide real-time valuable information on the pathology and physiology of circulation to differentiate between different types of shocks. Through the suggested SIMPLE approach, different types of shocks can be characterized according to 2D ultrasound findings and simple measurements (Table 2). This approach is not only simple and practical but also provides an easy-to-remember checklist of ultrasound findings for clinicians to focus on when managing patients with undifferentiated shock. Integrating SIMPLE approach with FAST scan (i.e., SIMPLE + FAST) can be feasible and particularly helpful in identifying intraperitoneal bleeding and initiating fluid resuscitation in hypovolemic shock. Current evidence supports the role of FoCUS in undifferentiated shock to improve the diagnostic accuracy, narrow the possible differential diagnoses, and guide specific management. More high-quality clinical trials are warranted to further look into the impact of FoCUS on the clinical outcomes, patient survival, and financial implication in future.
AAA, abdominal aortic aneurysm; ACES, abdominal and cardiac evaluation with sonography in shock ; ACLS, advanced cardiac life support; AF, atrial fibrillation; AMI, acute myocardial infarction; AP2, apical two-chamber view; AP4, apical four-chamber view; AV, aortic valve; AVG, atrioventricular groove; BEAT, bedside echocardiographic assessment in trauma/critical care ; BLEEP, bedside limited echocardiography by emergency physician ; CAUSE, cardiac arrest ultrasound exam ; CI, cardiac index; CVP, central venous pressure; DA, descending aorta; ED, emergency department; EGLS, echo-guided life support ; FALLS, fluid administration limited by lung sonography ; FAST, focused assessment with sonography for trauma; FATE, focused assessed transthoracic echocardiography ; FEEL, focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients ; FEER, focused echocardiographic evaluation in resuscitation ; FoCUS, focused cardiac ultrasound; FS, fractional shortening; ICU, intensive care unit; IVC, inferior vena cava; IVS, interventricular septum; LA, left atrium; LV, left ventricle; LVEDA, left ventricle end-diastole area; LVEDD, left ventricle end-diastole diameter; LVEF, left ventricular ejection fraction; LVESA, left ventricular end-systolic area; LVOT, left ventricular outflow tract; PC, pericardium; PcE, pericardial effusion; PLE, pleural effusion; PLX, parasternal long axis view; PoCUS, point-of-care ultrasound; PSX, parasternal short axis view; PW, posterior wall of left ventricle; RA, right atrium; RAP, right atrial pressure; RUSH, rapid ultrasound for shock and hypotension ; RUSH-HIMAP, rapid ultrasound for shock and hypotension-heart, inferior vena cava, Morrison pouch with FAST exam view and hemothorax windows, aorta, and pneumothorax ; RV, right ventricle; RVOT, right ventricular outflow tract; SV, stroke volume; SXP, subxyphoid view; TTE, transthoracic echocardiography; UHP, undifferentiated hypotension patient ; WINFOUCS, World Interactive Network Focused on Critical UltraSound
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The conclusion of this article is drawn from the author’s observation and the available evidence from the literature included already in the reference list.
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The author declares that he has no competing interests in writing up this article.
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