Role of Ultrasound in Different Types of Shock
Samir Abdelrahman El-Sebaey Talkhan1, Sanaa Farag Mahmoud2, Mayada Ahmed Ibrahim3,Karim Gouda Mostafa Elaidy4
1Professor of Anesthesia and Intensive care and pain management, Faculty of Medicine – Ain shams University, Egypt
2Lecturer of Anesthesia and Intensive care and pain management,Faculty of Medicine – Ain shams University, Egypt
3Lecturer of Anesthesia and Intensive care and pain management, Faculty of Medicine – Ain shams University, Egypt
4M.B.B.Ch, Zagazig University.Egypt
Corresponding Author Name: Karim Gouda Mostafa Elaidy Email: [email protected]
Abstract
Background: Shock is defined as a situation where oxygen transport is inadequate to meet the body's oxygen demand. Clinical ultrasonography as a diagnostic modality that provides clinically significant data not obtained by inspection, palpation, auscultation, or other components of the physical examination. It is a distinct clinical modality not an adjunct to or extension of the physical examination.The (ACEP) and the Council of Emergency Medicine Residency Directors (CORD) have formally endorsed bedside ultrasound by the Emergency Physicians (EP`s) for multiple applications. This technology is ideal for the care of the critical patient in shock and the most recent (ACEP) guidelines further delineate a new category of resuscitative ultrasound. This study aimed to discuss role of using ultrasound in critical care of shock patients and how it helps intensive care doctors to take the right decision for management. METHODOLOGY: Relevant citations were extracted from Pubmed, Google scholar, Clinical key, Scopus, Med-line, Embase and Cochrane to identify role of using ultrasound in critical care of shock patients and how it helps intensive care doctors to take the right decision for management. Conclusion: General and cardiac ultrasound can be easily performed at the bedside by physicians working in the intensive care unit (ICU) and may provide accurate information with diagnostic and therapeutic relevance.Furthermore, ultrasound is relatively inexpensive and does not utilizeionizing radiation. Critical care physicians began to apply ultrasound technology to other non- procedural clinical problems in the ICU, such as the emergency diagnosis of pericardial tamponade and pneumothorax. The availability of clinician ultrasonography has revolutionized the bedside approach to patients in shock. New-onset shock is a medical emergency requiring prompt and definitive therapy. The availability of many protocols to use ultrasound in different types of shock made the ultrasound easy to use and accurate to reach final diagnosis of shock and early start definitive therapy.
Key words: ultrasound- critical care- shock.
Introduction:
Shock isdefined as a situation where oxygen transport is inadequate to meet the body's oxygen demand. An understanding of the mechanism(s) of reduced cardiac output, a determinant of oxygen transport, is crucial in order to initiate appropriate therapy to manage shock (Denault et al., 2014).
Shock is a hemodynamic situation that aggravates the vital prognosis of every patient regardless of the underlying pathology. It has been well documented that the speed at which hemodynamics is restored to standard values significantly decreases the mortality and
morbidity in these patients. Initially described in traumatology, then in every type of shock, the contribution of ultrasonography performed at the bedside by the physician in charge allows for a significant shortening of the diagnostic procedure and thus an earlier start for a goal-directed treatment (Métrailler-Mermoud et al., 2014).
Care of the patient with shock can be one of the most challengingissues in emergency medicine and critical care. Even the most seasonedclinician, standing at the bedside of the patient in extremis, can be unclear about the cause of shock and the optimal initial therapeutic approach. Traditional physical examination techniques can be misleading due to the complex physiology of shock (Jones et al., 2004).
General and cardiac ultrasound can be easily performed at the bedside by physicians working in the intensive care unit (ICU) and may provide accurate information with diagnostic and therapeutic relevance.Furthermore, ultrasound is relatively inexpensive and does not utilize ionizing radiation. (Bouhemad et al., 2007).
The American College of Emergency Physicians (ACEP) defines clinical ultrasonography as a diagnostic modality that provides clinically significant data not obtained by inspection, palpation, auscultation, or other components of the physical examination. It is a distinct clinical modality not an adjunct to or extension of the physical examination.The (ACEP) and the Council of Emergency Medicine Residency Directors (CORD) have formally endorsed bedside ultrasound by the Emergency Physicians (EP`s) for multiple applications.This technology is ideal for the care of the critical patient in shock and the most recent (ACEP) guidelines further delineate a new category of resuscitative ultrasound.
(Phillips et al., 2012).
This study aimed to discuss role of using ultrasound in critical care of shock patients and how it helps intensive care doctors to take the right decision for management.
METHODOLOGY
Relevant citations were extracted from Pubmed, Google scholar, Clinical key, Scopus, Med- line, Embase and Cochrane to identify role of using ultrasound in critical care of shock patients and how it helps intensive care doctors to take the right decision for management.
Physical Principles of Ultrasound
Ultrasound (US) waves are a form of sound waves. US wave frequencies exceed the upper limit of audible human hearing. Medical US frequencies are in the range of 1-20 MHz. Each US wave is characterized by a specific frequency and wavelength, which are inversely related. The higher the frequency, the lower the wavelength is. Frequency is the number of cycles per second and is measured in Hertz (Harsha, 2014).
Wavelength is the distance between two consecutive, similar positions in the pressure wave.
It is determined by the frequency of the wave, and the speed of propagation in the medium it is passing through. Actually the speed of sound is different based on the tissues through which it propagates: air-330 m/s, water-1525 m/s, bone 3000 m/s, fat 1450 m/s, muscle-1600 m/s and blood-1560 m/s.However it is averaged as approximately 1540 m/s for the entire body and is referred to as propagation velocity or acoustic velocity (Harsha, 2014).
Ultrasound Transducer
The US waves are produced by piezoelectric effect, which was discovered by Curie brothers in 1880. It involves the generation of an electrical charge, by a piezoelectric material, when subjected to mechanical stress and the reverse piezoelectric effect involves such an electrical charge being converted to mechanical vibration. In the available US machines the transducer holding the piezoelectric material acts both as a generator and receiver of such signals. US used in medical imaging is referred to as B-mode (2D), meaning brightness mode display.
This means the brightness of the pixel on the image is a representation of the strength of reflection (Lawrence, 2007).
Ultrasound Equipments
Medical US utilizes a transducer attached to a display monitor which also holds the operating console. A transducer (also known as probe) contains a damping material, piezoelectric crystals, a matching layer and a protective layer. Each crystal is isolated and hence transmits its own US wave. The damping layer, present just behind the crystals acts to reduce their resonance so that they are sensitive to the returning signal. The matching layer in front acts to reduce the impedance mismatch and is covered by a protective layer (Lawrence, 2007).
There are several types of transducers and it is necessary to choose the right one for the procedure. Based on the frequency range, commonly 2 types of transducers are used for medical procedures. Some others give 3 varieties, based on the range: High- (8-12 MHz), medium- (6-10 MHz), and low- (2-5 MHz). The smaller one with a straight contact surface is called a linear array transducer due to the linear arrangement of crystals. It also produces high frequency waves in the range of 8-12 MHz. Its penetration, and hence resolution is usually good for structures within 3-4 cm. The larger one with a curved contact surface is called a curved array or curvilinear transducer because of the curved arrangement of crystals. It creates a wedge shaped US beam and produces a much broader view with the image of deeper structures being wider than the footprint of the probe. It is used to visualize deeper structures beyond 4 cm (Brull et al., 2010).
Interaction of Sound and Media Attenuation
Definition The decrease in intensity, power and amplitude of a sound wave as it travels. The farther US travels, the more attenuation occurs.
In soft tissueAttenuation of sound is:
1) Directly related to distance traveled, and
2) Directly related to frequency. This is why we are able to image deeper with lower frequency ultrasound.
Three Components
1. Absorption (sound energy converted into heat energy) 2. Scattering
3. Reflection Media
• Air: much more attenuation than in soft tissue
• Bone: more than soft tissue, absorption & reflection
• Lung: more than soft tissue, due to scattering
• Water: much less than soft tissue
- Air >> Bone & Lung > Soft Tissue >> Water.
(Sidney, 2011) Reflection
- Definition: Sound returning towards the transducer that is disorganized and random.
Reflection occurs when the boundary has irregularities that are approximately the same size as the sound's wave length. It occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer (Sidney, 2011).
Specular Reflection: Reflections from a very smooth reflector (mirror) are specular.
Specular reflections also occur when the wavelength is much smaller than the irregularities in the boundary (Sidney, 2011).
Scattering
- Definition: If the boundary between two media has irregularities (with a size similar to or a bit smaller than the pulse's wavelength), then the wave may be chaotically redirected in all directions. Rayleigh Scattering If a reflector is much smaller than the wavelength of sound, the sound is uniformly diverted in all directions. Higher frequency sound undergoes
more Rayleigh scattering. A red blood cell is a Rayleigh scatter. Rayleigh scattering is proportional to frequency (Sidney, 2011).
Refraction
- Definition: Refraction is transmission with a bend.
Occurs when two conditions are met:
1. Oblique incidence.
2. Different propagation speeds (Sidney, 2011)
Understanding the controls and improving the image quality
A good use of US guidance can only be made when one understands how to operate the equipment and also how to modify the variables to get the best possible image. The following section gives an understanding of these elements (Harsha, 2014).
Resolution
It describes the ability to separately identify to individual structures Types of Resolution:
Axial Resolution The ability to distinguish two structures that are close to each other front to back, parallel to, or along the beam‟s main axis higher frequencies and superficial structures give better axial resolution (Sidney, 2011).
Lateral Resolution
- Definition: the minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes (Sidney, 2011).
GAIN
This simply refers to the strength of the signal. The brightness of the image is proportional to the strength of the signal received by the transducer. A highly reflective structure sends back proportionately more sound signals causing whiter shadow-hyperechogenic, where as less denser and less reflective structures send back less signals to the transducer causing blacker shadow-hypoechogenic. Increasing the gain increases the signal strength and brightness in general. This may not be optimal as even the background structures (noise) are also increased. The optimal gain necessary for visualization might be different from what is set as auto-gain and might need individual adjustments. Such well adjusted image is referred to as contrast resolution. Increasing the gain can also affect lateral resolution (Brull et al., 2010).
FOCUS
The sound waves converge to a point called focal zone and then diverge. The divergence of these waves beyond the focal zone can allow for missed information in a horizontal plane. To minimize this loss, it is important to set the focal zone at the same level as the target of interest. It is achieved usually by a dial setting and is observed on the monitor as a small arrow on either side of the screen (Lawrence, 2007).
Time gain compensation
As the name suggests there is an increase in gain (signal strength) which is restricted to a set field of depth. Attenuation increases with increasing depth. To compensate for this time gain compensation (TGC) allows for stepwise increase in gain which can be adjusted for a particular depth. It is suggested that time gain attenuation (TGA) adjustments are made less frequently than gain adjustments, which is not usually optimal (Sites et al., 2007).
Frequency
Waves of higher frequency are more attenuated. One should choose a higher frequency probe for superficial structures, and low frequency probe for deeper structures (Harsha, 2014).
CONTROLLING ULTRASOUND WAVES
There are different methods that control the way ultrasound waves are emitted from the ultrasound transducers. Emission of ultrasound waves can be either interrupted or continuous.
Interrupted emission of ultrasound waves generates brightness (B) mode images while continuous emission generates Doppler mode. Imaging one line over time is called the moving mode (M Mode). Changing the frequency of ultrasound waves will control the penetration and resolution of the images. The higher the frequency, the better is the resolution, however the depth of penetration decreases. The opposite will happen when using lower frequency transducers. Longer distances and higher frequencies result in greater attenuation (Peter et al., 2011).
This implies that for obese patients and deep structures, probes of low frequencies should be used while probes of high frequency should be used for superficial structures. The received ultrasound signal can be amplified by increasing the gain. Decreased gain yields a black image and details are masked, while increased gain yields a whiter image. Time gain compensation will change the gain factor so that equally reflective structures will be displayed with the same brightness regardless of their depth (Peter et al., 2011).
Ultrasound waves are emitted perpendicular to the surface of the transducer. It is possible to widen the deep sonographic field by bending the surface of the transducer (convex array transducer). Waves will be parallel to each other when the probe surface is flat (linear array transducer). Linear array transducers usually have high frequencies (10-12 MHz), less penetration, and excellent resolution. The ultrasound images obtained by a linear array transducer will be rectangular in shape while those obtained by a convex array transducer will be wider with increased depth. Reducing the surface of the transducer and using fan shaped sectors will enable the examiner to visualize thoracic structure between the ribs (Whittingham, 2007).
Artifacts associated with US imaging
The image produced on the monitor is a 2 dimensional image obtained from converting mechanical energy into electrical signals. The actual conversion of signals into images involves several assumptions on the part of equipment‟s software. These give rise to artifacts:
could be a distortion in the image brightness, duplication, absence of echoes, etc. It is difficult to avoid them altogether and hence must be able to distinguish them. Commonly understood artifacts are described below:
Acoustic shadowing
This happens when a superficial structure has greater attenuation coefficient than the structures deep to it. Due to this the underlying structure appears less echogenic than normal.
This is typically seen under a bone as a black shadow (Kremkau and Taylor, 1986).
Posterior acoustic enhancement
This is almost the opposite of shadowing. Due to the presence of a less attenuating structure superficially, the region behind that structure produces stronger echoes than the surrounding structures (Sites et al., 2007).
Reverberation
It is the multiple representation of the same structure at different depths of display. It is usually caused by a specular reflector such as a needle. It reflects a strong signal back to the tranducer, some of which is again reflected back to cause a repeat of the shadow at a different depth, because of the time delay involved. The lumen and the walls of a hollow needle can also give rise to reverberation artifacts due to differences in the time of reflected wave and appear as multiple but similar shadows. They also give rise to comet tail shadows (Thickman et al., 1983).
Mirror image
It is a type of reverberation artifact, commonly produced due to a significant mismatch in the acoustic impedance between 2 adjacent structures such as air-bone, soft tissue-lung etc.
Interestingly this artifact appears in all modes including Doppler (Harsha, 2014).
Refraction
This is also called as bayonet effect. This appears as a subtle bend in the length of the needle due to refraction. (Gray et al.,2005).
Classification and Types of Shock Introduction:
Shock is an abnormal physiologic state in which there is an inability to deliver adequate oxygen to meet the metabolic needs of the body. At the cellular level, impairment of oxygen delivery leads to ischemia, a transition from aerobic to anaerobic metabolism, lactic acidosis, and ultimately organ dysfunction and failure. If interventions are not made in a timely, aggressive manner, individual organ failure will progress to multisystem organ failure and eventual death (Watson et al., 2003).
Classification of shock:
Hypovolemic
Hypovolemic shock is the most common type of shock and is caused by insufficient circulating volume. Its primary cause is hemorrhage (internal and/or external), or loss of fluid from the circulation. Vomiting and diarrhea are the most common cause in children. With other causes including burns, environmental exposure and excess urine loss due to diabetic ketoacidosis and diabetes insipidus (Judith et al., 2010).
Cardiogenic
Cardiogenic shock is caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large myocardial infarction. Other causes of cardiogenic shock include dysrhythmias, cardiomyopathy, myocarditis, congestive heart failure (CHF), or cardiac valve problems (Judith et al., 2010).
Obstructive
Obstructive shock is due to obstruction of blood flow outside of the heart. Several conditions can result in this form of shock.
● Cardiac tamponade: in which fluid in the pericardium prevents inflow of blood into the heart (venous return). Constrictive pericarditis, in which the pericardium shrinks and hardens, is similar in presentation.
● Tension pneumothorax: Through increased intrathoracic pressure, blood flow to the heart is prevented (venous return).
● Pulmonary embolism is the result of a thromboembolic incident in the blood vessels of the lungs and hinders the return of blood to the heart.
● Aortic stenosis: hinders circulation by obstructing the ventricular outflow tract (Judith et al., 2010).
Distributive
Distributive shock is due to impaired utilization of oxygen and thus production of energy by the cell. Examples of this form of shock are:
● Septic shock is the most common cause of distributive shock, Caused by an overwhelming systemic infection resulting in vasodilation leading to hypotension. Septic shock also includes some elements of cardiogenic shock. In 1992, the American College of Chest Physician and Society of Critical Care Medicine (ACCP/SCCM) Consensus Conference Committee defined septic shock: ". . .sepsis-induced hypotension (systolic blood pressure < 90 mmHg or a reduction of 40 mmHg from baseline) despite adequate fluid resuscitation along with the presence of perfusion abnormalities that may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status. Patients who are
receiving inotropic or vasopressor agents may have a normalized blood pressure at the time that perfusion abnormalities are identified."
● Anaphylactic shock Caused by a severe anaphylactic reaction to an allergen, antigen, drug or foreign protein causing the release of histamine which causes widespread vasodilation, leading to hypotension and increased capillary permeability.
● Neurogenic shock caused by high spinal injuries. The classic symptoms include a slow heart rate due to loss of cardiac sympathetic tone and warm skin due to dilation of the peripheral blood vessels. (This term can be confused with spinal shock which is a recoverable loss of function of the spinal cord after injury). (Judith et al., 2010).
● Hypovolemic Shock
Hypovolemic shock occurs as a result of decreased circulating blood volume, most commonly from acute hemorrhage. It may also be the result of fluid sequestration within the abdominal viscera or peritoneal cavity. The severity of hypovolemic shock depends not only on the volume deficit loss, the time frame within which the fluid is lost, but also on the age and pre injury health status of the individual. Clinically, hypovolemic shock is classified as mild, moderate, or severe, depending on the whole blood volume loss (Bongard and Sue, 2002).
● Cardiogenic Shock
Cardiogenic shock (CS) resulting from abnormalities of myocardial structure and function, impairment of mechanical function of the heart, or arrhythmia. Most commonly, cardiogenic shock is due to an acute myocardial infarction, particularly involving the anterior wall.
However, establishing the diagnosis of cardiogenic shock and determining its aetiology is not always easy. Techniques of invasive haemodynamic monitoring, measurements of specific biomarkers, and noninvasive bedside echo-cardiography may be helpful. The effectiveness of shock management depends on the ability to institute appropriate therapy rapidly and to remove the underlying aetiologic factor(s) (Filipiak et al., 2014).
Obstructive Shock
Obstructive shock was described as involving obstruction to flow in the cardiovascular circuit and characterized by impairment of diastolic filling or excessive afterload. The consequent obstruction of blood flow into or out of the heart causes a decrease in cardiac output, and hence inadequate oxygen delivery, which is manifested by the classic signs and symptoms of the shock state. (Yarmus and Feller-Kopman, 2012).
Distributive Shock Septic shock
Sepsis is a life threatening condition that is associated with a systemic inflammatory response to a microbial infection. Sepsis is the most common cause of mortality in the intensive care unit with a fatality rate that can rise to 80% for those developing multiple organ failure. The progression of an exaggerated systemic inflammatory response is thought to be responsible for the eventual development of septic shock (Goldenberg et al., 2011).
Although immune activation is clearly evident, recent evidence suggests that the immune response may not be the direct mediator of the pathologic process that leads to septic shock.
Studies conducted to define the circulating leukocyte transcriptome have revealed that there is no qualitative difference in the immune genetic response when comparing burn or blunt trauma patients with complicated or uncomplicated outcomes. In other words, severely injured patients who die from their injuries have the same immune genetic response as patients who recover; the only difference being the duration and intensity of systemic inflammation (Xiao et al., 2011).
Table (1): Diagnostic criteria for sepsis
⮚ Systemic inflammatory response syndrome (two or more of the following):
- Temperature > 38oC or < 36 oC.
- Heart rate > 90 beats per minute.
- Respiratory rate > 20 breaths per minute or PaCO2< 32 mmHg.
- White blood cell count > 12000/cu mm or < 4000/cu mm or >
10% bands.
⮚ Sepsis:
- SIRS with an infectious source.
⮚ Severe sepsis:
- Sepsis with associated hypoperfusion, hypotension or organ dysfunction.
⮚ Septic shock:
- Systolic blood pressure < 90 mmHg or reduction of ≥ 40 mm Hg from baseline despite adequate fluid resuscitation along with perfusion abnormalities
(Elizabeth et al., 2014).
Anaphylactic shock
It is generally believed, that during anaphylactic shock, the observed myocardial damage and ventricular dysfunction is the result of depression of cardiac output due to coronary hypo- perfusion from systemic vasodilation, leakage of plasma and volume loss due to increased vascular permeability, and reduced venous return. It has been reported that during anaphylactic shock circulating blood volume may decrease by as much as 35% within 10 min due to transfer of intravascular fluid to extra-vascular space. Furthermore, severe vasodilation resistant to epinephrine and responding only to other potent vasoconstrictors has been also reported (Schummer et al., 2004).
The diagnosis of anaphylaxis is based primarily on clinical signs and symptoms, as well as a detailed description of the acute episode, including antecedent activities and events.
Diagnostic criteria for anaphylaxis were published by a multidisciplinary group of experts in 2005 and 2006. A diagnosis of anaphylaxis is highly likely when any one of the criteria listed in the Table is fulfilled (Harold et al., 2011).
Table (2): Clinical criteria for diagnosing anaphylaxis
Anaphylaxis highly likely when any 1 of the following 3 criteria is fulfilled following exposure to an allergen:
1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (e.g. generalized hives, pruritus or flushing, swollen lips- to:
a. Respiratory compromise (e.g. dyspnea, wheeze, bronchospasm, stridor, reduced PEF, hypxemia).
b. Reduced BP or associated symptoms of end-organ dysfunction (e.g. hypotonia [collapse], syncope, syncope, incontinence)
2 or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours):
a. Involvement of the skin-mucosal tissue (e.g. generalized hives, itch-flush, swollen lips-tongue-uvula)
b. Respiratory compromise (e.g. dyspnea, wheeze-bronchospasm,
stridor, reduced PEF, hypoxemia)
c. Reduced BP or associated symptoms (e.g. hypotonia [collapse], syncope, incontinence)
d. Persistent gastrointestinal symptoms (e.g. painful abdominal cramps, vomiting)
3 Reduced BP after exposure to a known allergen for that patient (minutes to several hours):
a. Infants and children: Low systolic BP (age-specific) or greater than 30% decrease in systolic BP
b. Adults: Systolic BP of less than 90mmHg or greater than 30%
from that person‟s baseline
(Harold et al., 2011).
Uses of Ultrasound in Management of Shock Patients
Over the past decade, critical care ultrasound has gained its place in the monitoring tools. A greater understanding of lung, abdominal, and vascular ultrasound plus easier access to portable machines have revolutionized the bedside assessment of ICU patients. Because ultrasound is not only a diagnostic test, but can also be seen as a component of the physical exam, it has the potential to become the stethoscope of the 21st century. Critical care ultrasound is a combination of simple protocols (Daniel et al., 2014).
The availability of clinician ultrasonography has revolutionized the bedside approach to patients in shock. New-onset shock is a medical emergency requiring prompt and definitive therapy. The differential diagnosis is broad, and every entity on the differential diagnosis is life-threatening and requires specific therapy, Time is the essence and, for patients in extremis, even minutes may count. Clinician echocardiography provides a fast and safe window into the physiology of shocked patients. Although not every patient can be imaged with ultrasonography, in most patients it assists in the categorization of the type of shock (Perera et al., 2014).
Who should perform bedside ultrasonography?
In the past, echocardiography was performed solely by trained technologists and interpreted by cardiologists. Although a formal echocardiogram is the most complete and definitive approach, it is frequently unavailable and has an associated time delay. Shock is a true medical emergency and the so-called golden hour of intervention does not wait for an official echocardiogram. Based on the necessity of immediate information and advances in ultrasonography technology, clinician echocardiography has grown into a well-accepted practice (Razi et al., 2011).
In this case ultrasonography is performed at the bedside by the treating clinician, which eliminates delays in imaging acquisition and interpretation and also allows the treating physician to appreciate the quality of information being obtained. It has been shown that acquiring skills in basic echocardiography is achievable, with performance at answering simple questions approaching that of formal echocardiography (Razi et al., 2011).
Shock ultrasound protocol
The RUSH exam (Rapid Ultrasound in Shock):
Given the advantages of early integration of bedside ultrasound into the diagnostic workup of the patient in shock, this protocol outlines an easily learned and quickly performed 3-step shock ultrasound protocol. This new ultrasound protocol is termed the RUSH exam. This protocol involves a 3-part bedside physiologic assessment simplified as:
Step 1: The pump Step 2: The tank
Step 3: The pipes
RUSH protocol Step one (evaluation of pump):
Imaging of the heart usually involves 4 views. The traditional views of the heart for bedside echocardiography are the parasternal long- and short-axis views, the sub-xiphoid view, and the apical 4-chamber view. The parasternal views are taken with the probe positioned just left of the sternum at inter-costal space 3 or 4. The sub-xiphoid 4-chamber view is obtained with the probe aimed up toward the left shoulder from a position just below the sub-xiphoid tip of the sternum The apical 4-chamber view of the heart is best evaluated by turning the patient into a left lateral decubitus position and placing the probe just below the nipple line at the point of maximal impulse of the heart. It is important to know all 4 views of the heart, as some views may not be well seen in individual patients, and an alternative view may be needed to answer the clinical question at hand (Labovitz et al.,2010).
.
Fig (1): Rapid ultrasound in shock Step 1. Evaluation of the pump (Perera et al., 2014).
“Squeeze of the pump”: determination of global left ventricular function
The first step in the RUSH protocol is to evaluate the heart for contractility of the left ventricle. This assessment will give a determination of “how strong the pump is.” The examination focuses on evaluating motion of the left ventricular endocardial walls, as judged by a visual calculation of the percentage change from diastole to systole. Whereas in the past echo-cardiographers used radionuclide imaging to determine ejection fraction, published studies have demonstrated that visual determination of contractility is roughly equivalent.Other types of shock can be evaluated by knowing the strength of the left ventricle during systole. Strong ventricular contractility (often termed hyperdynamic, because of the strength of contractions of the left ventricle in addition to a rapid heart rate) is often seen in early sepsis and in hypovolemic shock. In severe hypovolemic conditions, the heart is often small in size with complete obliteration of the ventricular cavity during systole. Bedside echocardiography also allows for repeated evaluation of the patient‟s heart, looking for changes in contractility over time, especially in the situation when there is an acute deterioration in the patient‟s status. For example, later in the course of sepsis there may be a decrease in contractility of the left ventricle due to myocardial depression (Jones et al., 2005).
The next step is to search for the presence of a pericardial effusion, which may be a cause of the patient‟s hemodynamic instability. The heart should be imaged in the planes described here, with close attention to the presence of fluid, usually appearing as a dark or anechoic area, within the pericardial space. Small effusions may be seen as a thin stripe inside the pericardial space, whereas larger effusions tend to wrap circumferentially around the heart.
Isolated small anterior anechoic areas on the parasternal long-axis view often represent a pericardial fat pad, as free flowing pericardial effusions will tend to layer posteriorly and
inferiorly with gravity. Fresh fluid or blood tends to have a darker or anechoic appearance, whereas clotted blood or exudates may have a lighter or more echogenic look (Shabetai, 2004).
Once a pericardial effusion is identified, the next step is to evaluate the heart for signs of tamponade. Thinking of the heart as a dual chamber in- line pump, the left side of the heart is under considerably more pressure, due to the high systemic pressures against which it must pump. The right side of the heart is under relatively less pressure, due to the lower pressure within the pulmonary vascular circuit. Thus, most echo-cardiographers define tamponade as compression of the right side of the heart. High pressure within the pericardial sac keeps the chamber from fully expanding during the relaxation phase of the cardiac cycle and thus is best recognized during diastole (Spodick, 2003).
Fig (2) : Sub-xiphoid view: cardiac tamponade (Perera et al., 2014).
Fig (3): Parasternal long-axis view: large pericardial effusion (Perera et al., 2014).
“Strain of the pump”: assessment of right ventricular strain
Any condition that causes pressure to suddenly increase within the pulmonary vascular circuit will result in acute dilation of the right heart in an effort to maintain forward flow into the pulmonary artery. The classic cause of acute right heart strain is a large central pulmonary
embolus. Due to the sudden obstruction of the pulmonary outflow tract by a large pulmonary embolus, the compensatory mechanism of acute right ventricular dilation can be viewed on bedside echocardiography. This process will be manifested by a right ventricular chamber with dimensions equivalent to, or larger than, the adjacent left ventricle (Madan and Schwartz, 2004).
The sensitivity of the finding of right heart dilation to diagnose a pulmonary embolus is moderate, but the specificity and positive predictive value of this finding are high in the correct clinical scenario, especially if hypotension is present. The finding of acute right heart strain due to a pulmonary embolus correlates with a poorer prognosis. This finding, in the setting of suspected pulmonary embolus, suggests the need for immediate evaluation and treatment of thrombo-embolism. The EP should also proceed directly to evaluation of the leg veins for a DVT. (Becattini and Agnelli, 2007).
Fig (4): Parasternal long-axis view: right ventricular strain (Perrera et al., 2014).
RUSH Protocol Step 2: Evaluation of the Tank
“Fullness of the tank”: evaluation of the inferior cava and jugular veins for size and collapse with inspiration
The next step for the clinician using the RUSH protocol in the hypotensive patient is to evaluate the effective intravascular volume as well as to look for areas where the intravascular volume might be compromised. An estimate of the intravascular volume can be determined non invasively by looking initially at the IVC. An effective means of accurately locating and assessing the IVC is to begin with the probe placed in the standard 4-chamber sub-xiphoid position from the epigastric position, first identifying the right atrium. The probe is then rotated inferiorly toward the spine, examining for the confluence of the IVC with right atrium. The IVC should then be followed inferiorly as it passes through the liver, specifically looking for the confluence of the three hepatic veins with the IVC. Current recommendations for the measurement of the IVC are at the point just inferior to the confluence with the hepatic veins, at a point approximately 2 cm from the junction of right atrium and IVC (Jardin and Veillard-Baron, 2006).
Fig (5): RUSH step 2. Evaluation of the tank. IVC exam, inferior vena cava; FAST views (Focused assessment Sonography in Trauma), right upper quadrant, left upper quadrant and supra-pubic; lung exam, pneumothorax and pulmonary edema (Perrera et al., 2014).
Examining the IVC in an oval appearance from the short axis potentially allows the vessel to be more accurately measured, as it avoids a falsely lower measurement by slicing to the side of the vessel, a pitfall known as the cylinder effect. The IVC can also be evaluated in the long axis plane to further confirm the accuracy of vessel measurements. For this view, the probe is turned from a 4-chamber sub-xiphoid orientation into a 2-chamber sub-xiphoid configuration, with the probe now in a vertical orientation and the indicator oriented anteriorly. The aorta will often come first into view from this plane as a thicker walled and pulsatile structure, located deeper to the IVC. Moving the probe toward the patient‟s right side will then bring the IVC into view. While the IVC may have pulsations, due to its proximity to the aorta, it will often be compressible with direct pressure. Color Doppler ultrasound will also further discriminate the arterial pulsations of the aorta from the phasic movement of blood associated with respirations in the IVC (Jardin and Veillard-Baron, 2006).
There is correlation between the size and percentage change of the IVC with respiratory variation to central venous pressure (CVP) using an indwelling catheter. A smaller caliber IVC (<2 cm diameter) with an inspiratory collapse greater than 50% roughly correlates to a CVP of less than 10 cm of water. This phenomenon may be observed in hypovolemic and distributive shock states. A larger sized IVC (>2 cm diameter) that collapses less than 50%
with inspiration correlates to a CVP of more than 10 cm of water. This phenomenon may be seen in cardiogenic and obstructive shock states (Rudski et al., 2010).
Fig (6): Inferior vena cava sniff test: low cardiac filling pressures (Perrera et al., 2014).
New guidelines by the American Society of Echocardiography support this general use of evaluation of IVC size and collapsibility in assessment of CVP, but suggest more specific ranges for the pressure measurements. The recommendations are that an IVC diameter less than 2.1 cm that collapses greater than 50% with sniff correlates to a normal CVP pressure of
3 mm Hg (range 0-5 mm Hg), while a larger IVC greater than 2.1 cm that collapses less than 50% with sniff suggests a high CVP pressures of 15 mm Hg (range 10-20 mm Hg). In scenarios in which the IVC diameter and collapse do not fit this paradigm, an intermediate value of 8 mm Hg (range 5-10 mm) may be used (Rudski et al., 2010).
“Leakiness of the tank”: FAST exam and pleural fluid assessment (Focused assessment sonography for trauma)
Once a patient‟s intravascular volume status has been determined, the next step in assessing the tank is to look for “abnormal leakiness of the tank.” Leakiness of the tank refers to 1 of 3 things leading to hemodynamic compromise: internal blood loss, fluid extravasation, or other pathologic fluid collections. In traumatic conditions, the clinician must quickly determine whether hemo-peritoneum or hemo-thorax is present, as a result of a “hole in the tank,”
leading to hypovolemic shock. (Perrara et al., 2014).
The peritoneal cavity can be readily evaluated with bedside ultrasound for the presence of an abnormal fluid collection in both trauma and non- trauma states. This assessment is accomplished with the FAST exam. This examination consists of an inspection of the potential spaces in the right and left upper abdominal quadrants and in the pelvis. Specific views include the space between the liver and kidney (hepato-renal space or Morison pouch), the area around the spleen (peri-splenic space), and the area around and behind the bladder (recto-vesicular/recto-vaginal space or pouch of Douglas). A dark or anechoic area in any of these 3 potential spaces represents free intra-peritoneal fluid. These 3 areas represent the most common places for free fluid to collect, and correspond to the most dependent areas of the peritoneal cavity in the supine patient. Because the FAST exam relies on free fluid settling into these dependent areas, the patient‟s position should be taken into account while interpreting the examination (Von Kuenssberg et al., 2003).
Fig (7): Right upper quadrant/hepatorenal view: free fluid (Perrera et al., 2014).
Ultrasound can also assist in evaluating the thoracic cavity for free fluid (pleural effusion or hemo-thorax) in an examination known as the extended FAST, or E-FAST. This evaluation is easily accomplished by including views of the thoracic cavity with the FAST examination. In both the hepato-renal and peri-splenic views, the diaphragms appear as bright or hyper-echoic lines immediately above, or cephalad to, the liver and spleen respectively (McEwan and Thompson, 2007).
Aiming the probe above the diaphragm will allow for identification of a thoracic fluid collection. If fluid is found, movement of the probe 1 or 2 intercostal spaces cephalad provides a better view of the thoracic cavity, allowing quantification of the fluid present. In
the normal supra- diaphragmatic view, there are no dark areas of fluid in the thoracic cavity, and the lung can often be visualized as a moving structure. In the presence of an effusion or hemo-thorax, the normally visualized lung above the diaphragm is replaced with a dark, or
anechoic, space (McEwan
and Thompson, 2007).
Fig (8) :Left upper quadrant: pleural effusion (Perrera et al.,2014).
“Tank compromise”: pneumothorax
Although chest radiography reveals characteristic findings in tension pneumothorax, therapy should not be delayed while awaiting radiographic studies. With bedside ultrasound, the diagnosis of tension pneumothorax can be accomplished within seconds. Pneumothorax detection with ultrasound relies on the fact that free air (pneumothorax) is lighter than normal aerated lung tissue, and thus will accumulate in the nondependent areas of the thoracic cavity.
Therefore, in a supine patient a pneumothorax will be found anteriorly, while in an upright patient a pneumothorax will be found superiorly at the lung apex (Slater et al., 2006).
To assess for pneumothorax with ultrasound, the patient should be positioned in a supine position, or even more optimally, with the head of the bed slightly elevated. By looking at the patient from a lateral orientation, one can assess the most anterior portion of the chest cavity.
Subsequent positioning of a high frequency linear array probe at this highest point on the thorax, usually found in the mid-clavicular line at approximately the second through fourth intercostal positions, allows identification of the pleural line. This line appears as an echogenic horizontal line located approximately half a centimeter deep to the ribs. The pleural line consists of both the visceral and parietal pleura closely apposed to one another. In the normal lung, the visceral and parietal pleura can be seen to slide against each other, with a glistening or shimmering appearance, as the patient breathes. The presence of this lung sliding excludes a pneumothorax. Another sonographic finding seen in normal lung, but absent in pneumothorax, is the comet tail artifact. Comet tail artifact is a form of reverberation echo that arises from irregularity of the lung surface. This phenomenon appears as a vertical echoic line originating from the pleural line and ex- tending down into the lung tissue. The presence of comet tail artifact rules out a pneumothorax. The combination of a lack of lung sliding and absent comet tail artifacts strongly suggests pneumothorax (Blaivas and Tsung, 2008).
RUSH Protocol: Step 3-Evaluation of the pipes “Rupture of the pipes”: aortic aneurysm and dissection
The next step in the RUSH exam is to examine the „Pipes‟ looking first at arterial side of circulatory system and then at the venous side. Vascular catastrophes, such as ruptured abdominal aortic aneurysms (AAA) and aortic dissections, are life-threatening causes of hypotension. The survival of such patients may often be measured in minutes, and the ability to quickly diagnose these diseases is crucial (Dent et al.,2007).
Fig (9): RUSH step 3. Evaluation of the pipes (Perrera et al., 2014).
A complete ultrasound examination of the abdominal aorta involves imaging from the epigastrium down to the iliac bifurcation using a phased-array or curvilinear transducer.
Aiming the transducer posteriorly in a transverse orientation in the epigastric area, the abdominal aorta can be visualized as a circular vessel seen immediately anterior to the vertebral body and to the left of the paired IVC.Application of steady pressure to the transducer to displace bowel gas, while sliding the probe inferiorly from a position just below the xiphoid process down to the umbilicus, allows for visualization of the entire abdominal aorta. The aorta should also be imaged in the longitudinal orientation for completion.
Measurements should be obtained in the short axis, measuring the maximal diameter of the aorta from outer wall to outer wall, and should include any thrombus present in the vessel. A measurement of greater than 3 cm is abnormal and defines an abdominal aortic aneurysm.
(Holliday et al.,2008).
Fig (10): Short-axis view: large abdominal aortic aneurysm (Perrea et al., 2014).
Another crucial part of “the pipes” protocol is evaluation for an aortic dissection. The sensitivity of transthoracic echocardiography to detect aortic dissection is poor (approximately 65% according to one study), and is limited compared with CT, MRI, or trans-esophageal echocardiography. Despite this, bedside ultrasound has been used to detect aortic dissections and has helped many patients. Sonographic findings suggestive of the diagnosis include the presence of aortic root dilation and an aortic intimal flap. The parasternal long-axis view of the heart permits an evaluation of the proximal aortic root, and a measurement of more than 3.8 cm is considered abnormal. An echogenic intimal flap may be recognized within the dilated root or anywhere along the course of the thoracic or abdominal aorta. The suprasternal view allows imaging of the aortic arch and should be performed in high-suspicion scenarios by placing the phased-array transducer within the suprasternal notch and aiming caudally and anteriorly (Perkins et al., 2010).
Fig (11): Short-axis view: aortic dissection (Perrea et al., 2014).
“Clogging of the pipes”: venous thromboembolism Bedside ultrasound for DVT
In the patient in whom a thromboembolic event is suspected as a cause of shock, assessment of the venous side of “the pipes.” Should be done. As the majority of pulmonary emboli originate from lower extremity deep venous thrombosis DVT, the examination is concentrated on a limited compression evaluation of the leg veins. Simple compression ultrasonography, which uses a high frequency linear probe to apply direct pressure to the vein, has a good overall sensitivity for detection of DVT of the leg (Blaivas and Tsung, 2008).
An acute blood clot forms a mass in the lumen of the vein, and the pathognomonic finding of DVT will be incomplete compression of the anterior and posterior walls of the vein. In contrast, a normal vein will completely collapse. However, most proximal DVTs can be detected by a limited compression examination of the leg that can be rapidly per- formed by focusing on 2 major areas. The proximal femoral vein just below the inguinal ligament is evaluated first, beginning at the common femoral vein, found below the inguinal ligament.
Scanning should continue down the vein through the confluence with the saphenous vein to the bifurcation of the vessel into the deep and superficial femoral veins. The second area of evaluation is the popliteal fossa. The popliteal vein, the continuation of the superficial femoral vein, can be examined from high in the popliteal fossa down to trifurcation into the calf veins (Bernardi et al., 2008).
The BLUE protocol (Bedside Lung Ultrasound in Emergency):
The Blue protocol approach:
In the BLUE protocol, the three standardized examination points are the upper BLUE point, the lower BLUE point, and the PLAPS point (postero-lateral alveolar or pleural syndromes).
The BLUE protocol uses the seven principles of LUCI. In brief, these are 1) A simple technique, and the simplest machine is the most suitable.
2) In the thorax, air and water are mixed, generating specific ultrasound signs, signatures and artifacts.
3) The lung is the most voluminous organ, but adapted points for analysis, the BLUE points allow for standardized scanning.
4) All signs and artifacts start from the pleural line, a basic landmark.
5) The artifacts, usually considered as annoying limitations of ultrasound, are of specific interest.
6) The lung is a vital organ that moves, therefore dynamic analysis is crucial with lung sliding being the basic dynamic sign of normality.
7) All acute, life-threatening disorders are superficially located around the pleural line, creating a window for LUCI.
(Lichtenstein and Mezière,2011).
The BLUE protocol is easy, if the user agrees to follow each simple step. The BLUE protocol uses the 7th principle to identify and describe ten signs allowing the diagnosis of the six most frequently seen acute diseases (not the most easy to diagnose) by creating eight profiles yielding an overall 90.5% accuracy. The pleural line generates the bat sign, a permanent landmark indicating the parietal pleura. Lung sliding and the A-line define the normal lung surface. They indicate gas movement and sliding of the parietal and visceral pleura with to-and-fro movements. M-mode helps to understand this movement and results in the seashore sign. The quad sign and the sinusoid sign are standardized signs allowing the diagnosis of a pleural effusion, regardless of its volume or echogenicity. The probe is applied at the PLAPS point, a posterior area accessible in the supine position. The boundaries of the collection are regular, and a quadri-angular surface can be drawn (the quad sign). The sinusoid sign is drawn by the visceral pleura moving towards the pleural line during inspiration.. (Meziere and Lichtenstein, 2008).
Fig (12): Ultrasound scan of the anterior intercostal space:‟(Daniel et al.,2014).
Fig (13): Examination of pleural effusions: quad and sinusoid sign; A- ultrasound examination of pleural effusion at the PLAPS point. Below the pleural line, a regular line roughly parallel to the pleural line can be seen: the lung line, indicating the visceral pleura (arrows); B- the visceral pleura (lung line), together with the parietal pleura (pleural line) and the shadow of the ribs, form a kind of quadrant: the quad sign; C-M-mode shows movement of the lung line or visceral pleura (white arrows) towards the pleural line or parietal pleura (black arrows) on inspiration, creating the sinusoid sign compatible with free pleural effusion.
Quantitative data: this effusion found at the PLAPS point has an expiratory thickness of roughly 13 mm, i.e. an expectedly small volume. A 15-mm distance is the minimum required for safe diagnostic or therapeutic puncture (Daniel et al., 2014).
The shred (or fractal) sign and the tissue-like signs are used for diagnosis of lung consolidation. The shred sign corresponds to non-trans-lobar consolidations, with an irregular border between aerated and consolidated lung regions. The tissue sign is seen in trans-lobar consolidation as it looks like liver parenchyma. Lung rockets are a sign of interstitial syndrome with 93% accuracy. The B-line is always a comet-tail artifact, arising from the pleural line and coinciding with lung-sliding. B-lines are almost always long, well-defined, laser-like, and hyper-echogenic, erasing A-lines.A rocket sign consists of three or more B- lines between two ribs. Abolished lung sliding and exclusive A-lines are a basic sign of pneumothorax, with 95% sensitivity and 100% negative predictive value. In a case of pneumothorax, a motionless pleural line can be observed in M-mode generating the stratosphere. Visualization of the lung point allows the ruling in of pneumothorax (Volpicelli et al., 2008).
Fig (14): Lung consolidation: shred, fractal and tissue-like sign; A-a massive consolidation (probe at the PLAPS point) of the whole left lower lobe. No aerated lung tissue is present, and no fractal sign can be generated. The lower border is at the level of the mediastinal line (arrows). The pattern is tissue-like, similar to the spleen (S). The thickness of this image is roughly 10 cm, a value incompatible with a pleural effusion. Quantitative data: the 10-cm depth would correspond to a volume of roughly 1 L; B -partial right middle lobe
consolidation. This generates a shredded, fractal boundary between the consolidation and the underlying aerated lung (arrows). This is the quite specific shred (or fractal) sign as opposed to the regular lung line in a case of pleural effusion. This anterior consolidation generates the C-profile in the BLUE protocol. Quantitative data: the thickness at the right image is 5.5 cm, corresponding to a 165-mL consolidation, roughly. Adapted from „Lung ultrasound in the critically ill‟ (Daniel et al., 2014).
Fig (15): Interstitial syndrome: lung-rockets; A -presence of four or five B-lines, called lung rockets (here septal rockets correlating with thickened sub-pleural interlobular septa), suggestive for lung oedema; B -presence of twice as many B-lines, called ground-glass rockets. Suggestive for severe pulmonary oedema (with ground glass areas on CT); C -Z- lines for comparison. These „parasites‟ are ill-defined, short, and do not erase A-lines (arrows). Adapted from „Lung ultrasound in the critically ill‟ (Daniel et al., 2014).
Fig (16): Pneumothorax: stratosphere sign; A -pleural line with A-lines, indicating gas below the pleural line. Although not visible on the left image, lung sliding was totally absent; B -on M-mode, the abolition of lung sliding is visible through the stratosphere sign (which replaces the seashore sign) and indicates total absence of motion. This suggests pneumothorax as a possible cause. Arrows indicate location of the pleural line. The combination of abolished lung sliding with A-lines, at the anterior chest wall, is the A‟-profile of the BLUE protocol (as opposed to the A-profile, where lung sliding is present, ruling out pneumothorax).
Adapted from „Lung ultrasound in the critically ill‟ (Daniel et al., 2014).
The BLUE protocol defines eight profiles, correlated with six diseases seen in 97% of the patients admitted to the ICU. A consolidation is not a diagnosis, but, incorporated into a specific profile, it contributes to making the correct diagnosis (not necessarily pneumonia).
The A, A’, B, B’, A/B and C-profiles can all be identified at the anterior chest wall in supine patients (Chavez et al., 2014).
The A-profile defines a normal lung surface. Associated with a deep venous thrombosis, it makes the diagnosis of pulmonary embolism with 99% specificity. In combination with the absence of DVT and the presence of a postero-lateral alveolar and/or pleural syndrome (called PLAPS), it highly suggests the diagnosis of pneumonia (specificity 96%). In a case of absence of DVT and PLAPS, this profile is called the nude profile which correlates with severe asthma or COPD (specificity 97%) (Chavez et al., 2014).
The A’-profile, defined as abolished lung sliding with exclusive A-lines, is suggestive of pneumothorax, and makes mandatory the detection of a lung point, a specific sign of pneumothorax. The lung point shows, at the area of inspiratory contact of the lung with the
wall, sudden changes, from an A‟-profile to lungs sliding or lung rockets (Chavez et al., 2014).
The B-profile associates anterior lung sliding with anterior lung rockets, and highly suggests acute cardiovascular pulmonary oedema (specificity 95%).
The B’-profile combines abolished lung sliding with lung rockets, and is also correlated with pneumonia (specificity 100%).
The A/B-profile, i.e. unilateral lung rockets, suggests pneumonia (specificity 100%).
The C-profile defines anterior lung consolidations (from large parenchymal volumes to a simple thickened, irregular pleural line) and again suggests pneumonia (specificity 99%) (Chavez et al., 2014).
Each of these profiles is supported by the pathophysiology. Each profile can be assessed in less (some times much less) than three minutes, making the BLUE protocol a really fast protocol. A recent meta-analysis confirmed the usefulness of lung ultrasound and concluded that, when conducted by highly-skilled sonographers, ultrasound performs well for the diagnosis of pneumonia. General practitioners and emergency medicine physicians should be encouraged to learn LUCI since it appears to be an established diagnostic tool in the hands of experienced physicians (Koeze et al., 2012).
There are of course limitations, such as the presence of pulmonary embolism without DVT.
In bedside lung ultrasound, the operator should be aware and interpret double lung point, septate pneumothorax and hydro-point. The conventional diagnostic protocol of bedside lung ultrasound for pneumothorax should be occasionally adapted to such complex cases (Boero et al., 2013).
One feature of holistic ultrasound is its ability to combine examination of lung and heart. This is referred to as emergency cardiac sonography that combines some elements of the BLUE protocol for the management of acute circulatory failure. This is not „echo‟ (an expert field for cardiologists), nor is it „ultrasound‟, a term too redolent of the radiological world. The FALLS protocol uses the potential of lung ultrasound for the early demonstration of fluid overload at an infra-clinical level. The FALLS protocol is based on Weil and Shubin‟s classification, considering firstly obstructive shock, followed by cardiogenic, hypovolemic and finally distributive shock. The decision tree is illustrated in (Lichtenstein, 2012).
The FALLS protocol searches sequentially for:
1) Substantial pericardial fluid.
2) A dilated right ventricle.
3) An A‟-profile. Obstructive shock is reasonably ruled out in a case of absence of tamponade, pulmonary embolism, or pneumothorax.
4) The B-profile is sought. In its absence, a cardiogenic shock from left origin (i.e. the vast majority) is, by definition, ruled out.
(Daniel et al., 2014).
Table (3) : Classification of shock using ultrasonography findings
Conclusion:General and cardiac ultrasound can be easily performed at the bedside by physicians working in the intensive care unit (ICU) and mayprovide accurate information with diagnostic and therapeutic relevance.Furthermore, ultrasound is relatively inexpensive and does not utilize ionizing radiation.Critical care physicians began to apply ultrasound technology to other non-procedural clinical problems in the ICU, such as the emergency diagnosis of pericardial tamponade and pneumothorax.The availability of clinician ultrasonography has revolutionized the bedside approach to patients in shock. New-onset shock is a medical emergency requiring prompt and definitive therapy.The availability of many protocols to use ultrasound in different types of shock made the ultrasound easy to use and accurate to reach final diagnosis of shock and early start definitive therapy.
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