Ultrasonography in cardiopulmonary emergencies

Abstract

The utilization of ultrasound has rapidly increased over the past few decades due to its ease of use, wider availability of portable machines, broad applicability, non-invasiveness, and real-time imaging. A varied spectrum of clinical conditions such as diverse lung pathologies and various etiologies of acute circulatory failure can be rapidly ascertained using bedside ultrasonography. It has been shown that lung ultrasonography has more sensitivity than chest x-ray in detecting pulmonary congestion in heart failure, subpleural lung consolidation in pneumonia, and characterizing and detecting even minimal pleural effusions. This review gives an overview of the application of ultrasonography in the evaluation of cardiopulmonary failure which is the most commonly encountered clinical entity in the emergency room (ER). The most feasible bedside tests to predict fluid responsiveness are described in this review. Lastly, essential ultrasonographic protocols that are useful for systematic examination of critically ill patients were presented.

INTRODUCTION

Ultrasound has become an essential tool for the evaluation and management of critically ill patients arriving at the emergency room (ER). The goal of using ultrasound in ER is, for rapid and early detection of life-threatening emergencies, interventions using ultrasound, and monitoring therapeutic response. Its main advantage lies, in its non-invasiveness, cost-effectiveness, and rapid and real-time imaging.^[1,2] The steep learning curve and teaching feasibility are potential barriers to learning lung ultrasound. However, structured training programs incorporating ultrasonography in the teaching curriculum can enhance their utilization. The spectrum of clinical conditions that can be diagnosed using ultrasound includes (but are not limited to): pneumothorax, pneumonia especially subpleural in origin, minimal pleural effusion before it is evident in chest X-ray, endo-bronchial intubation, pericardial effusion, cardiac tamponade, regional wall motion abnormality of heart, certain aortic dissections such as Stanford type A. It is also useful for the assessment of fluid status in patients with shock, and a great tool for obtaining venous or arterial vascular access in emergencies.^[1] Critically ill patients often present to ER with cardiopulmonary failure. A screening ultrasound is an invaluable tool for the evaluation of these patients and ascertaining the diagnosis. In this article, we describe the clinical application of ultrasonography as an initial assessment tool in non-traumatic, critically ill adults who presents to ER with cardiopulmonary failure.

For the sake of discussion, the topic is divided into three parts

1. Lung ultrasound
1. Normal scan findings
2. Abnormal findings in pneumothorax, pleural effusion, and pneumonia
2. Ultrasound of heart and inferior vena cava (IVC)
1. Assessment of a hypotensive patient
3. Protocols for systematic examination of a critically ill patient with cardiopulmonary failure
1. BLUE protocol
2. FALLS protocol
3. SESAME protocol

DISCUSSION

I. Lung ultrasound

Since time immemorial ultrasound of the lung was thought to be impossible.^[3] Although André Dénier mentioned the utility of thoracic ultrasound in 1946, only in 1993 did Professor Daniel A. Lichtenstein pioneered this idea and showed the feasibility and utility of the same.^[4,5] Since then, lung ultrasound has become an increasingly useful tool and has gained universal acceptance due to its broad applicability, non-invasiveness, and real-time imaging. While a steep learning curve and teaching feasibilities are the potential barriers to learning ultrasonography, these may be mitigated with a structured training program incorporating ultrasonography in the teaching curriculum.

To maintain uniformity and better reproducibility of lung ultrasound findings; the surface of the chest is divided into three points.^[6]

1. Upper BLUE (bedside lung ultrasound in an emergency) point
2. Lower BLUE point
3. PLAPS (posterior and/or lateral alveolar and/or pleural syndrome) point

Two hands are placed as shown in Figure 1. The ulnar surface of the upper hand lies just below the clavicle, thumbs excluded, and the lower hand placed next to the index finger of the upper hand. The upper BLUE-point corresponds to the middle of the upper hand and the lower BLUE-point to the middle of the lower hand [Figure 1]. The PLAPS-point is identified at the intersection of a horizontal line drawn from the lower BLUE-point and a vertical line at the posterior axillary line.

Figure 1: Upper BLUE point, Lower BLUE point and PLAPS point

Three types of probes are commonly used.^[7]

1. A phased array probe used for cardiac imaging (1–5 MHz) has the advantage of having a smaller footprint and is better suited for imaging between the ribs.
2. A linear array probe (6–13 MHz), is useful for analyzing superficial structures like pleura and its sliding.
3. A curvilinear array probe (2–5 MHz), for abdominal imaging and commonly, used to image deeper structures of the lung.

A micro convex probe was used by the original investigators.^[8] This probe has the advantage of being smaller and flatter which can be easily placed posteriorly in a supine patient. This is a universal probe that allows whole-body screening without switching the probes between the regions of the body thus decreasing cross infections with different probes.^[6,9]

Normal lung scan findings

Normal: In a healthy lung, while breathing, the visceral pleura slides over the parietal pleura, thereby producing a to-and-fro movement called the “lung sliding”. On ultrasound imaging, lung sliding produces a homogenous twinkling, shimmering, sparkling, or glittering movement of the pleural line [Figure 2a, Videos 1 and 2].^[6] While an absent lung sliding is a strong pointer towards the presence of pneumothorax [Video 3], there may be other conditions where an absent sliding can be observed such as in endobronchial intubation, tumors obstructing bronchus, pleural symphysis, ventilator disconnection or apnea.^[10]

Figure 2: (a) The ribs (white arrows) followed by rib shadows are displayed. The pleural line (green arrow), is a horizontal hyperechoic line. Below the pleural line, there are horizontal repetitions of the pleural line that are equally spaced are called the A-lines (red arrows).(b) M-mode, green arrow points to the pleural line. Above the pleural line is a stratified pattern that represents a motionless chest wall (yellow arrow). Below the pleural line, the dynamic moving lung produces a sandy pattern (blue arrow). The whole pattern is a seashore[Figure 2c]

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M-mode is useful to detect the motion of structures over time. It provides an excellent view to ascertain pleural sliding, especially in elderly and chronic obstructive lung disease patients where sliding may be subtle. The M-mode when placed over the pleural line produces two different patterns. The top horizontal “wave” like pattern represents a motionless portion of the chest above the pleural line. The bottom “sandy” or “granular” pattern represents the movement of the lung below the pleura. Putting it together, the overall picture resembles a wave hitting the sand of a shore and is therefore called the ‘seashore sign’ [Figure 2b and c].^[6,9]

A-lines

A-lines are horizontal lines that arise from the pleural line at regular intervals. The distance between the two A-lines equals the distance between skin and pleura. These lines are artifacts produced because of subpleural air that reflects the ultrasound beam. The presence of A-lines with lung sliding is normal [Figure 2a, Video 2].^[11] A-lines in the absence of lung sliding indicate a high probability of pneumothorax and mandate a careful search for a lung point[Video 3].

Lung scan in pathologies

Pneumothorax: A lung scan can be used for rapid diagnosis of life-threatening emergencies like tension pneumothorax, where one can observe a complete absence of lung sliding which is rapidly picked up using an M mode scan. The absence of lung sliding produces a horizontal wave-like pattern throughout the ultrasound window including the portion below the pleural surface, resembling a “Barcode or Stratosphere”, hence the name for the sign[Figure 3a].^[6]Another sign which is more specific to pneumothorax is the identification of the “lung point sign”[Figure 3b and c]. The lung point is a specific spatial point where the visceral and parietal pleura meet each other[Video 4].^[6] Lichtenstein et al.,^[12] have shown that ultrasound has a sensitivity of 95.3% and a specificity of 91.1% for detecting pneumothorax in intensive care unit patients. When an M mode scan is performed at this point one can see an alternating normal (seashore sign) and absent (stratosphere sign) lung sliding. In a supine patient, lung point is usually identified in the anterior region of the chest, second to fourth intercostal space in the mid-clavicular line. Therefore, this is a recommended initial area to scan in a trauma patient when pneumothorax is suspected.^[13,14]

Figure 3: (a) M-mode shows a complete absence of lung sliding represented as horizontal lines throughout the window. This is called a stratosphere sign or barcode sign. This suggests pneumothorax as a possible cause. (b) Lung point sign is a pathognomonic sign of pneumothorax. An alternating pattern of sea-shore and stratosphere signs is due to the placement of the probe exactly at a point where the inspiratory increase in lung volume leads to contact of parietal pleura to the region of lung scan. (c) CT chest shows localization of lung point

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B-lines

Normal: Next common finding on lung scans is the presence of B-lines. These are vertical laser-like hyperechoic lines that arise from the pleural surface, erasing the A-lines, and can be tracked till the bottom of the screen [Figure 4]. These lines are reverberation artifacts and can appear in a normal lung due to the acoustic impedance difference between air and water.

Figure 4: Vertical lines arising from the pleural line (arrowhead) are called the B-lines (arrows) between the two ribs shadows

Pathologies associated with B-lines: Three or more B-lines between two ribs are almost always abnormal and are called lung rockets [Video 5]. This signifies interstitial edema of various etiologies.^[6]

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Common causes of B-lines

1. Cardiogenic pulmonary edema
2. Non-cardiogenic pulmonary edema (re-expansion, negative pressure)
3. Pneumonia
4. Acute respiratory distress syndrome [ARDS]
5. Interstitial lung diseases.

Pleural effusion

Massive pleural effusion is an important cause of respiratory distress. Effusions are anechoic because fluid causes the attenuation of ultrasound waves.^[6] Effusions form between the pleurae, hence, a small effusion can be seen as an anechoic area separating the two pleurae [Figure 5a, Video 6]while a massive effusion is seen as a lung floating in the sea (Jellyfish sign) [Figure 5b, Video 7].

Figure 5: (a) Minute pleural effusion can be seen easily at the PLAPS-point. The visceral and parietal pleura are separated by effusion, lateral boundaries are formed by rib shadows displaying a kind of quad: the quad sign. (b) Massive effusion make the lung collapse and undulate within the pleural effusion displaying a jellyfish sign

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Pneumonia

One of the most common causes of respiratory distress in a patient presenting to ER is pneumonia.^[6]A lung scan can be an invaluable tool to diagnose and demarcate the extent of lung involvement, especially in subpleural consolidation. Early stages are represented by discontinuity of pleural line (shreds) later progressing to consolidation [Figure 6, Video 8]. The later stage of consolidation is termed hepatization as the lung parenchyma looks similar to the liver in echogenicity. The dynamic air bronchogram is the movement of gas bubbles in the bronchi of the consolidated area of the lung is another ultrasonographic sign of pneumonia and can be used to differentiate pneumonia from atelectasis.

Figure 6: (a) Small consolidation, which does not involve the entire lobe. There is a demarcation between the top consolidation and the underlying aerated healthy lung: the fractal sign.(b) Massive consolidation right lower lobe. Non-aerated lung tissue, The pattern looks like a tissue: the tissue sign

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II. Ultrasound of heart and inferior vena cava (IVC)

Assessment of a hypotensive patient

Hypotension is a common presentation in patients arriving at the ER. The most common cause of hypotension is hypovolemia. Hypovolemia can be relative or absolute. Relative hypovolemia is defined as a decrease in effective circulatory volume which occurs in conditions such as systemic inflammatory response syndrome due to systemic vasodilatation. On the other hand, absolute hypovolemia results from a total reduction in circulatory blood volume either due to plasma or blood loss. Septic shock is a classic example where both absolute and relative hypovolemia exists.^[15] Refractory vomiting, diarrheal illness, and hemorrhage can lead to absolute hypovolemia while pancreatitis and burns can result in relative hypovolemia.

Fluid resuscitation is the first and most common therapeutic intervention in these patients and is considered the standard of care. But a major concern is that each patient is different and do not tolerate the same quantity of fluid. This can be best understood by studying the Frank-starling (FS) curves as depicted in Figure 7. Patients have their cardiac activity lying on different points on the FS curve. Infusion of fluids in a patient whose cardiac activity lies on the flat portion of the FS curve can be counterproductive. Therefore, it is important to know the upper limit of resuscitation in each patient. Ultrasound is an invaluable tool in assessing the cardiac loading conditions, that is, working point of the heart on the FS curve, thereby estimating the fluid deficits and titrating fluid therapy. There are two ways to assess the fluid status in a hypovolemic patient. First, to “predict fluid responsiveness” and second to “test for fluid responsiveness”.^[16]

Figure 7: Frank-Starling curve. (a) Flat portion of the curve where preload increase does not translate to a significant increase in the stroke volume (b) Steep portion of the curve where the same increase in left ventricular preload translate into a greater increase in the stroke volume

Predictors of fluid responsiveness

Fluid responsiveness can be predicted using static or dynamic parameters.

Static parameter: This is a parameter measured under a single ventricular loading condition. Some routinely measured static parameters are Inferior vena cava (IVC) diameter, ventricular chamber size, and Doppler indices such as E/A ratio, E/Ea ratio. They are presumed to provide a decent estimate of preload condition of the heart.

IVC diameter and a visual estimate of ventricular chamber size are two simple bedside static parameters that will be discussed here.

• IVC diameter: Although there are uncertainties and controversies about the reliability of IVC diameter in estimating the fluid status, at least the extreme values of central venous pressure (CVP) can be predicted by measuring the size of IVC on a subcoastal window using transthoracic echocardiography.^[17] The first step is to align IVC in a longitudinal axis and then identify the hepatic vein-IVC junction. Measure the IVC diameter 2 cm caudal to this point using M-mode. An IVC diameter <10 mm predicts a positive response to the fluid infusion [Video 9], while a dilated IVC >20 mm indicates a negative response to fluids [Figure 8].^[16] One should note that IVC diameter is a good surrogate of CVP in patients on mechanical ventilation.
• Visual estimate (eyeballing) of the ventricular chamber: Apical four-chamber or parasternal short-axis window can be used to eyeball the left ventricular chamber size. When a ventricle looks hyperkinetic and collapses completely in systole (i.e. ”kissing ventricles”), fluid responsiveness is likely [Figure 9, Videos 10 and 11].^[18]

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Figure 8: IVC in longitudinal view. (a) Thin collapsed IVC – likely fluid responsive. (b) Distended IVC; note the hepatic vein draining in IVC (arrowhead). IVC diameter measured 2 cm caudal to it

Figure 9: Parasternal short-axis view. (a) Left Ventricular (LV) chambers completely emptying at end-systole: Kissing ventricular walls (b) Dilated overfilled LV even at systole, suggests volume overload or severe LV dysfunction

Dynamic parameter: This is a parameter used to determine whether a patient’s cardiac operating point is on the steep or flatter portion of the FS curve. Dynamic parameters are further classified into those measured during mechanical ventilation and those during spontaneous breathing. Some examples of dynamic parameters are IVC distensibility, superior vena cava collapsibility, measuring variations of velocity-time integral (VTI) or stroke volume variation (SVV) or pulse pressure variation (PPV) or end-tidal CO₂ [ETCO₂] with passive leg raise and respiratory variations of VTI, SVV, PPV during controlled mechanical ventilation.

To conclude, a hypotensive patient is most likely a fluid responder if he has A-profile on a lung scan with collapsed IVC and a small hyperkinetic ventricle. Whereas, a hypotensive patient is unlikely a fluid responder if he has B-profile on lung scan with evidently distended IVC and dilated ventricular chambers.

Tests for fluid responsiveness

The second method is the test for fluid responsiveness, which is performed by administrating a fluid bolus and measuring the change in stroke volume or cardiac output. Describing the methods to test fluid responsiveness is beyond the scope of this review, further reading is recommended.^[18]

III. Protocols for systematic examination of a critically ill patient with cardiopulmonary failure

Various protocols have been proposed for a systematic examination of critically ill patients.^[8] Important among those are:

A. BLUE (Bedside Lung Ultrasound in Emergency) protocol for assessment of a patient with respiratory failure

B. FALLS (Fluid Administration Limited by Lung Sonography) protocol for assessment of a patient with acute circulatory failure

C. SESAME (Sequential Emergency Sonography Assessing Mechanism) protocol for assessment of a patient with cardiac arrest.

A.BLUE Protocol^[8]: BLUE protocol is a useful screening algorithm to identify the cause of acute respiratory distress[Figure 10]. It is primarily based on lung scans and venous ultrasound findings. The first step is to look for lung sliding.

Figure 10: BLUE protocol

Identify A and B profiles as described above.

• A’ and B’ represents A and B profiles respectively with abolished lung sliding.
• A’ profile with no lung sliding points towards pneumothorax. However, the identification of lung points is diagnostic [€W 3 and 4]. B’ profile suggests an association with pneumonia.
• C profile represents anterior lung consolidation.
• A profile with no deep vein thrombosis (DVT) and with consolidation at PLAPS point is associated with pneumonia [A-V-PLAPS profile].

B.FALLS Protocol^[8]: FALLS protocol is used in patients with acute circulatory failure. This protocol involves a combination of a lung scan and a simple cardiac ultrasound to arrive at a probable etiology of circulatory failure and also to administer fluids.^[19]

The first step is to rule out obstructive shock (tamponade and pneumothorax). The second step is to screen for B profile (cardiogenic shock). If both the above conditions are excluded (i.e. the presence of A-profile), it suggests the possibility of hypovolemic shock, and fluids may be safely administered. If A-profile turns to B-profile, then distributive/septic shock is the possible etiology of circulatory failure [Figure 11]. This classification follows Weil’s classification of shock.^[20]

Figure 11: FALLS protocol

C.SESAME Protocol^[8]: SESAME protocol is followed in a cardiac arrest to exclude most common causes like tamponade, pneumothorax, intra-peritoneal bleed, and possible pulmonary embolism [Figure 12]. This protocol is designed to look at the sites that are least disruptive to CPR.

Figure 12: SESAME protocol

Briefly, the protocol starts with ruling out pneumothorax. The next step is to screen for DVT in lower limbs (most commonly femoral veins) which is the likely source of pulmonary embolism; if DVT is positive, look for right ventricle size. Then the abdomen is screened to rule out intra-peritoneal bleed; followed by the pericardium to rule out tamponade.^[19]

CONCLUSION

Ultrasound may be considered a 21^st-century modern stethoscope. Most regions of the body can be scanned using ultrasound. Particularly heart, lung, major vessels, and peritoneal cavity are the four most vital regions that can be easily scanned; thereby assisting in establishing the etiology for physiological derailment in cardiopulmonary failure. Furthermore, with the broad applicability, high-cost effectiveness, and sparse side effects, ultrasound has become a favorite tool in the management of critically ill patients in ER.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.