ULTRASONOGRAPHY IN CRITICALLY ILL PATIENTSTITLE PAGEList and order of authors:Dr Sameer Gulati, MD FACP FIACM FIMSA, Associate Professor, Department of Medicine, VMMC and Safdarjung Hospital, New Delhi – 110029.Dr Bhupendra Gupta MD FICP FIACM, Professor of Medicine, North DMC Medical College & Hindu Rao Hospital Delhi. Formerly, Prof & Head of Department of Medicine, VMMC & Safdarjung Hospital New Delhi. ULTRASONOGRAPHY IN CRITICALLY ILL PATIENTS1. INTRODUCTIONUltrasonography (USG) is being increasingly used in intensive care units (ICU) for assessment and monitoring of critically ill patients. USG based algorithms have been devised to facilitate simple, swift and efficient management of respiratory and circulatory failure. USG facilitated cardiopulmonary resuscitation is being increasingly promoted because of its ability to save precious lives. Besides, more and more intensivists are getting trained to do interventions with aid of USG so as to minimize the associated complications. The pleura, heart, veins and abdomen can be assessed and monitored to resolve respiratory and circulatory failure. The objective of the present review is to sensitize the reader to the application of USG as a diagnostic modality in critically ill patients. 2. EQUIPMENTThe ultrasound (US) machines in the ICU should be compact and light enough to facilitate multiple transports for bedside evaluations. A simple low cost grayscale machine, without doppler facilities, and with immediate start up time is adequate to meet the requirements of critical care imaging. It is important that the selected machine can undergo multiple decontamination procedures so as to stop transmission of nosocomial infections. This may be facilitated by an accompanying waterproof keyboard. The machine should be equipped with a small convex array probe (3-5 MHz, generally available on multipurpose ultrasound machines) which should be easily placed on intercostal spaces. A high frequency linear transducer (5-10 MHz) is required for doing the compression USG to locate lower extremity deep vein thrombosis. Whereas, the optic nerve is typically evaluated with a high frequency linear probe (7-15 MHz ) with a smaller footprint probe matching the eye socket size. 3. PROCEDURE: LUNG ULTRASONOGRAPHYAny acute disease of the lung may reduce aeration pattern or may disturb the pleura, which in turn will generate diagnostic patterns on USG. The lung US may be done over the entire chest by applying the probe longitudinally over the intercostal spaces and by moving it transversely in defined standardized areas. The chest is divided into three parts (anterior, lateral and posterior) and each part is further divided into two zones. The dorsal segments of upper lobes cannot be scanned by ultrasound as they are hidden behind the scapula. The complete assessment of these six zones may take 15 minutes. Since, intensivists need to conduct a focussed examination in a much shorter period, Lichtenstein proposed a BLUE protocol utilizing only three points (upper BLUE, lower BLUE and the PLAPS points) on each chest. The lung is located by placing two hands over the anterior chest, upper hand touching the clavicle. The upper BLUE point is at the middle of the upper hand and the lower BLUE point is at the middle of the lower palm. The PLAPS point is located by the intersection of a horizontal line at the level of the lower BLUE point and a vertical line at the posterior axillary line. Such a three point assessment may cut down the duration of examination to three minutes. The distinct sonographic lung patterns have been enumerated in table 2. Table 1: Important signs (all signs arising from pleural line) in Lung ultrasonography.1Pleural lineHorizontal hyperechoic line sliding half a centimeter below the rib line in adults resulting from the movement of the visceral pleura against the parietal pleura during the respiratory cycle. 2Bat signAcoustic shadows of two ribs and the sliding pleural line in between resemble a flying bat. 3Merlin spaceAn area in between the acoustic shadows of two adjacent ribs. 4A LineHorizontal repetition artefacts of the pleural line indicating air/gas (physiological or free). 5Lung slidingTo and fro movement at the pleural line indicating that the pleural line includes the visceral pleura. 6Lung pulseHeart beats are identified at the pleural line because of a non inflating lung. This is used to distinguish atelectasis from pneumonia. 7B LineAn artifact, due to coexistence of elements with a major acoustic impedance gradient such as fluid and air, with 7 features – hydroaeric comet tail artifact, arising from the pleural line, hyperechoic, well defined, spreading up indefinitely, erasing A lines and moving with lung sliding. Multiple B lines 7 mm apart are caused by thickened interlobular septa characterizing interstitial edema. In contrast, B lines 3 mm or less apart are caused by ground glass areas characterizing alveolar edema. 8Seashore sign(M Mode)A stratified pattern above and a sandy pattern below the pleural line indicating lung movement at the chest wall. 9Stratosphere sign(M Mode)A standardized stratified pattern below and above the pleural line indicating pneumothorax. 10Lung pointAt a precise location, in patients with A’ profile, lung signs such as transient B lines and lung sliding suddenly appear with respiration. This location is called as lung point, which is pathognomonic of pneumothorax. 11Dynamic air bronchogramInspiratory centrifugal movement of hyperechoic air in branching echogenic structures of the consolidated lung, which is seen in alveolar consolidation. Table 2: Different profiles in lung ultrasonography and their diagnostic significance.1A ProfileAnterior lung sliding with A linesNormal lungs. If associated with evidence of LEDVT, then A profile may be seen in pulmonary embolism.2A’ ProfileA profile with abolished lung slidingPneumothorax (with lung point), cardiopulmonary arrest, one lung intubation, esophageal intubation, chronic adherences/fibrosis3B ProfileAnterior lung sliding with lung rockets (B lines)Interstitial syndrome – hemodynamic pulmonary edema4B’ ProfileB profile with abolished lung sliding Interstitial syndrome – pneumonia, ARDS5C ProfileIndicates anterior lung consolidation regardless of size and number. A thickened irregular pleural line. Shred or fractal sign: shredded or fractal boundary between the consolidation and the underlying aerated lung. Non translobar alveolar consolidation*In contrast, translobar consolidations identified with help of tissue like sign (looks like liver).6A/B ProfileHalf A profile at one lung, a half B profile at anotherUnilateral diffuse or focal interstitial syndrome 7PLAPS Profile(PosteroLateral Alveolar and/or Pleural Syndrome)This is sought for after detection of an A profile (a pattern compatible with pulmonary embolism) and a free venous network (a pattern making the diagnosis of embolism less likely). The profile combining A profile, free veins, and PLAPS is called A-V-PLAPS profile. Pleural effusion – lung line moves toward the pleural line on inspiration which is observed as the “sinusoid sign” in M Mode. The pleural and the lung line are bounded by the shadows of the ribs forming a kind of a quad, thus generating the “quad sign”. 8Nude ProfileA profile with no DVT and no PLAPSAsthma or COPD4. PROCEDURE: COMPRESSION ULTRASONOGRAPHY FOR DEEP VEIN THROMBOSISA two point compression ultrasonography (common femoral region and the popliteal fossa) has been found to be equivalent to the whole leg color doppler ultrasonography in diagnosis of proximal lower extremity deep vein thrombosis (LEDVT). Although very few additional LEDVT may be picked up by scanning the rest of the entire venous system, few intensivists carry out compression ultrasonography (CUS) of the entire proximal venous system from the common femoral vein to the trifurcation of the popliteal vein with 2 cm increments. The procedure is done by using B mode with a high frequency (5-10 MHz) linear transducer. The operator should have a working knowledge of the lower extremity venous anatomy. The patient should be in supine position with thigh externally rotated and knee flexed at 45 degree angle. To begin with, the common femoral artery is located running laterally to the common femoral vein (CFV). A compression maneuver is done at this point, in the transverse plane, with the probe held perpendicularly and with marker to the patient’s right. Complete compression of the vein with minimal deformation of the adjacent artery is indicative of absence of thrombosis. On the other hand, non compressibility with pressure enough to deform the adjacent artery and/or the presence of echogenic substance in the lumen of the venous vessels are diagnostic of venous thrombosis. Most of the acute thrombi are hypoechoic, which makes their visualization difficult. However, if a thrombus is visualized then a compression maneuver should not be done as it may dislodge the thrombus. Longitudinal scanning may help in confirming the intraluminal echogenic thrombus. The great saphenous vein (GSV) joins the CFV in vicinity of the inguinal ligament. Compression maneuver is done again at the junction of GSV and the CFV. The CFV split into profunda femoris vein and the superficial femoral vein (SFV) approximately 2 cm proximal from the inguinal ligament. The superficial femoral artery usually lies anterior to the SFV and the profunda femoris moves deep between the muscles. The SFV is followed downwards into the Hunter’s Canal/Adductor canal where it becomes the popliteal vein. The compression may be difficult as the SFV nears the adductor canal. The popliteal vein is examined at the popliteal fossa where it is easily compressed. Here, the vein usually lies anterior to the artery. The compression maneuver is continued until the trifurcation into the calf veins caudally. The same procedure may be repeated for the second leg. 5. PROCEDURE: BEDSIDE OCULAR ULTRASOUNDBedside eye ultrasound evaluation is done with the patient supine (head of bed at 0 degree) and the eyelid closed without any clenching. The eye may be covered with a tegaderm and a good amount of gel is applied over it to function as an acoustic stand off. A high frequency linear probe is ideal for an ophthalmic evaluation. The depth and the gain should be appropriately set to visualize all the structures of the globe with the posterior chamber visualized as a hypoechoic structure. Eye is evaluated both in transverse and longitudinal planes. The hemispherical lens is seen as the most anterior structure of the eye. The hemispherical anterior chamber is separated from the posterior chamber by the hyperechoic ciliary body and iris. The posterior chamber is anechoic in younger subjects with vitreous opacities appearing in older patients. The normal retina is not distinguishable from other choroidal layers. The optic nerve is visualized centrally just posterior to the eye as a hypoechoic linear structure extending posteriorly. The nerve and its sheath appear hypoechoic and hyperechoic respectively. The intensivists are particularly interested to measure optic nerve sheath diameter (ONSD), as a surrogate for intracranial pressure (ICP), in patients with suspected intracranial process in a critical care unit. The ONSD expands with increased ICP as it is transmitted to the subarachnoid space surrounding the optic nerve. The measurement of ONSD is done 3 mm behind the posterior globe along an axis perpendicular to the optic nerve and sheath. The normal ONSD is < 5 mm. If it is measured to be > than 6 mm then it signifies an increased ICP. Measurements between 5 and 6 mm require clinical correlation. 6. PROCEDURE: FOCUSSED ECHOCARDIOGRAPHYThe purpose of goal directed echocardiography is to immediately identify life threatening causes of hemodynamic failure, to categorize shock in order to plan initial management strategy and to identify any other coexisting diagnosis. Table 3: Basic echocardiographic viewsVIEWPROBE PLACEMENTSTRUCTURES SEENApical Obtained by placing the probe at the site of apex beat with the probe marker directed towards the left axilla. A four chamber view including the atria, ventricles, the interventricular and the interatrial septa are seen by moving the probe along the intercostal space. Apical 5 chamber Obtained by gradually tilting the probe upwards from the apical four chamber position. Includes the proximal segment of ascending thoracic aorta, left ventricular outflow tract (LVOT) and the aortic valve. PLAX*#Obtained by positioning the probes on the second or third intercostal spaces close to the left sternal border with the probe marker pointing towards the right shoulder. Tilting the patient to the left lateral position improves the view. Right ventricle, left ventricle, mitral valve, left atrium, descending aorta, aortic valve, aortic root, pericardium, right ventricular inflow and outflow tracts. Parasternal short axis#To obtain this view the probe is rotated clockwise through about 90° from the PLAX position to point the probe marker towards the head. Tilting the patient to the left lateral position improves the view. The short axis view between the apex and the base of the heart is made at three levels – mitral valve – fish mouth view of mitral valve, left ventricular walls and right ventricle.mid papillary – papillary muscles, left ventricular wall and right ventricular wall.aortic level – aortic valve, pulmonic valve, tricuspid valve and right atrium. SubcostalTo acquire this view, the probe is placed to the right of the xiphoid notch with the probe marker pointing towards the left hip. Pushing down with gentle pressure would enable the ultrasound beam to travel under the sternum and the rib cage to view the heart. In some patients this may be the only available echo window. Four cardiac chambers, right ventricular outflow tract, aorta and vena cava.Inferior vena cavaBegin in the subcostal 4 chamber view and then rotate the transducer counterclockwise 90 degree angling towards the liver. The IVC will be seen in the long axis. The measurements may be made by utilizing M mode. *PLAX=Parasternal long axis view#Parasternal views: In mechanically ventilated patients, the expanding lung may obscure views. If appropriate, reducing the inspiratory pressures and positive end expiratory pressure level for a brief period might improve visualization. The focussed echocardiography may be utilized by the intensivist for the following purposes – Assessment of right and left ventricular function”Eyeball” estimates of the LV function is made by experienced observers which is comparable to quantitative measures such as ejection fraction. Frequent echocardiographic evaluations may be done to monitor the efficacy of therapeutic interventions. The right ventricular (RV) function may also be assessed visually. The RV:LV ratio is utilized to estimate RV dilatation. The normal ratio is < 0.6. Dilatation is considered moderate if it is 0.6-1.0 and critical if more than 1. The interventricular septum is shifted towards the left in presence of RV overload (eg. ARDS, acute pulmonary embolism or high ventilation pressures). The LV loses its circular shape on the parasternal short axis view and assumes a "D" shape in these circumstances. B. Diagnosis of pulmonary embolismRight ventricular dilatation and dysfunction in presence of a positive CUS for LEDVT is highly suggestive of pulmonary embolism. The pattern of RV dysfunction involving mid septum with apical sparing is quite distinct for acute pulmonary embolism. C. Diagnosis of pericardial effusionPericardial effusion is revealed as an echo free space around the heart. Cardiac tamponade is identified by observing diastolic collapse of the right atrium (RA) and RV. RA collapse lasting for more than one third of the RR interval is suggestive of hemodynamically significant pericardial effusion. The real time echocardiography may also help in draining a hemodynamically significant pericardial effusion. D. Assessment of hypovolemia Assessment of hypovolemia and volume responsiveness is achieved by determining the size of inferior vena cava (IVC) along with its variability with respiration. An IVC diameter of 2 cm or more in a spontaneously breathing patient is suggestive of raised right sided pressures. The IVC diameter is usually larger if the patient is on mechanical ventilation. A respiration variation of IVC diameter of more than 12% predicts an increase in cardiac output with volume expansion. Besides, systolic obliteration of the LV cavity at the level of papillary muscle on the PLAX view ("kissing sign") is suggestive of hypovolemia. E. Echocardiography during cardiopulmonary resuscitation Focussed echocardiography may help to determine the reversible causes of arrest and to detect mechanical activity of the heart during cardiopulmonary resuscitation in presence of absent pulse. This modality can pick up causes such as hypovolemia, cardiac tamponade, PE, coronary artery disease, aortic dissection and pneumothorax. Identification of the correct cause may help in determining the best intervention to save a patient. The USG evaluation is carried out through the subcostal window during brief periods of pulse checks during the cardiopulmonary resuscitation. F. Assessment of a hypotensive patient A systematic USG approach can help the intensivist in determining the cause of hemodynamic instability. The cardiac tamponade and LV systolic dysfunction are ruled out systematically by utilizing appropriate windows. Dilatation of the RA and RV may indicate acute massive PE. A hyperdynamic LV with approximation of papillary muscles on the PLAX view may be noticed in presence of hypovolemia. The IVC diameter and its variation with respiration must be determined to assess volume status. Finally, the presence or absence of B profile on lung ultrasound may help in determining the appropriateness of a fluid challenge. 7. PROCEDURE: SCREENING ABDOMINAL ULTRASONOGRAPHYA screening abdominal USG may be done by the intensivists to identify intra abdominal fluid and examination of the aorta in a hypotensive patient. Examination of aorta in its entire course, with special attention to aorta below renal arteries, is essential to rule out aneurysm. It is scanned right through the epigastrium to the bifurcation of the iliac arteries. The transducer is aimed posteriorly in a transverse orientation. Abdominal aorta is imaged as a circular vessel anterior to the vertebral body and to the left of the inferior vena cava. Evaluation should be done in short axis plane measuring the maximal diameter of the aorta from the outer wall to outer wall. An abdominal aortic aneurysm (AAA) is diagnosed if vessel diameter exceeds 3 cm. Presence of echogenic thrombus or an intimal flap with differential doppler flow suggestive of aortic dissection should also be ruled out. A longitudinal assessment of the aorta will complete the examination. US evaluation is not a good modality to rule out aortic dissection. Still it has been utilized to diagnose aortic dissection in certain settings. Screening for aortic dissection should include transthoracic echocardiography to look for signs of aortic root dilatation, aortic intimal flap, aortic regurgitation and/or pericardial effusion. 8. ULTRASONOGRAPHY IN TRAUMAThe focussed assessment with sonography in trauma (FAST) examination helps in rapidly identifying intra abdominal source of bleeding and has replaced peritoneal lavage for this purpose. An initial negative FAST may be repeated in appropriate clinical settings. A positive examination in presence of hemorrhagic shock may call for urgent operative management. The extended FAST examination, which is employed in patients with thoracic trauma, includes the subcostal evaluation of the heart along with the anterior and lateral chest sonogram. Such an examination may pick up pericardial tamponade, pneumothorax and/or hemothorax. Although computed tomography remains the primary imaging tool for evaluation of trauma patient, the point of care US is the best initial modality for the emergency evaluation of abdominal and thoracic trauma since it provides rapid identification of life-threatening injuries. 9. ADVANTAGES AND LIMITATIONSCritical care sonography has found widespread acceptance because of certain advantages. It is a bedside modality which may be done rapidly to help in making a diagnosis or to follow up patients after therapeutic interventions. The patients do not need to be transferred out of the ICU for the procedure and there is no exposure to ionizing radiation. Significantly, the inter and intra observer variability is small (<5%). The goal directed USG also has its limitations. It is limited in scope and requires formal training to acquire necessary knowledge and skills in image acquisition and image interpretation. Fortunately the learning curve for acquiring these skills is short except those required for diagnosing pneumothorax. It may be difficult to conduct an USG evaluation in obese patients, in patients with subcutaneous emphysema or large thoracic dressings. To conclude, point of care US should complement clinical examination of the critically ill patients. It may be utilized to make swift diagnosis of life threatening emergencies so that appropriate interventions may be carried out immediately to save lives. More and more intensivists should undergo training to utilize US to its maximum potential. REFERENCESLichtenstein DA. BLUE-protocol and FALLS-protocol: two applications of lung ultrasound in the critically ill. Chest.2015 Jun;147(6):1659-70.Lichtenstein DA. Lung ultrasound in the critically ill. Ann Intensive Care. 2014 Jan 9;4(1):1.Bouhemad B, Zhang M, Lu Q et al. Clinical Review: Bedside lung ultrasound in critical care practice. Crit Care. 2007;11(1):205.Karim A, Arora VK. 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