Indications for bedside ultrasonography in the critically ill adult patient

INTRODUCTION — Portable bedside ultrasonography is being increasingly used by clinicians in patients who are critically ill [1,2]. Critical care ultrasonography (CCUS) is most commonly used in the emergency department and the intensive care unit. It can also be used in the operating room and postoperative care unit when evaluating patients who become acutely ill in the hospital. CCUS is commonly divided into four separate elements: thoracic (lung and pleural), abdominopelvic, vascular, and cardiac (basic and advanced).

This section will review the clinical utility of these four separate elements of CCUS. Details regarding bedside ultrasonography for trauma patients, thoracic ultrasonography in non-critically ill patients, and transcranial ultrasonography in stroke patients are discussed separately. (See "Emergency ultrasound in adults with abdominal and thoracic trauma" and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Imaging of pleural effusions in adults" and "Ultrasound-guided thoracentesis" and "Neuroimaging of acute stroke", section on 'Ultrasound methods'.)

TERMINOLOGY AND DEFINITION — Critical care ultrasonography (CCUS) refers to the use of ultrasonography in patients who are critically ill. Multiple terms are used to describe various elements of CCUS. These include terms that refer to the bedside application of ultrasonography (eg, point-of-care ultrasonography [POCUS]), and terms that refer to the organs imaged with ultrasonography including multiorgan ultrasonography, thoracic ultrasonography (TUS; lung, pleural, and/or heart), lung ultrasonography (LUS), abdominopelvic ultrasonography, vascular ultrasonography, and cardiac ultrasonography (basic and advanced critical care echocardiography [CCE]).

Protocols that describe the use of CCUS in critically ill patients who present with shock or trauma have been described including rapid ultrasound in shock (RUSH), abdominal and cardiac evaluation with sonography in shock (ACES), focused assessment with sonography for trauma (FAST), and focused cardiac ultrasound (FOCUS). These protocols are discussed separately. (See "Emergency ultrasound in adults with abdominal and thoracic trauma", section on 'Focused Assessment with Sonography for Trauma'.)

A widely accepted definition of the elements of CCUS that are required for competence has been published and constitutes a reasonable definition of the scope of practice of CCUS [1].

CHOOSING CONSULTATIVE OR CRITICAL CARE ULTRASONOGRAPHY — For critical care ultrasonography (CCUS), the critical care clinician is directly responsible for all aspects of image acquisition and interpretation, and integration of the results into the management plan at the point of care. This differs from standard ultrasonography performed by the consultative radiology and cardiology services where there is a delay in these processes. The choice between using consultative ultrasonography or CCUS is dependent upon the available equipment, expertise, and the indication for the examination.

●Consultative ultrasonography – In critically ill patients, consultative radiology- or cardiology-performed ultrasonography is typically done at the bedside or in a radiology suite using large expensive machines; it is usually performed by skilled technicians and later interpreted by radiologists or cardiologists with ultrasonography expertise. Thus, consultative ultrasonography assessment is useful for hemodynamically stable patients with complex disorders that require high level of expertise at image acquisition and interpretation (eg, detailed assessment of the hepatobiliary system, obstetric/gynecologic applications, testicular disease, detailed assessment of valvular heart disease). Another major indication for consultative ultrasonography is when the critical care clinician identifies an abnormality beyond their level of expertise to assess (eg, splenic lesions, complex renal or hepatic cysts).

●Critical care ultrasonography – CCUS uses portable equipment that is compact and relatively inexpensive. Image acquisition and interpretation are performed by the intensivist at the bedside, so the imaging results can be immediately actionable and integrated into a comprehensive management plan. CCUS is typically best suited for patients with imminently life-threatening processes, to categorize shock and respiratory failure, to check for coexisting diagnoses and complications of therapy, and to track the evolution of the critical illness by serial examinations.

Although useful as a standalone bedside tool, CCUS should not eliminate the need for standard imaging tools, particularly when CCUS is not helpful or when confirmation of a diagnosis is important or complex (eg, mitral valve rupture, complicated pneumothorax). When appropriately used, CCUS can reduce the use of other imaging modalities such as chest CT, chest radiography, and pulmonary artery catheter use [3]. In many scenarios, it is best used as a complimentary diagnostic tool to standard pathways. In support of this concept, point of care ultrasonography (POCUS) has been shown to be of value in the evaluation of acute dyspnea in the emergency department and inpatient hospital setting. One meta-analysis of 49 studies reported that the inclusion of POCUS (namely thoracic, cardiac, and vascular US), led to more correct diagnoses in patients with acute dyspnea than standard diagnostic pathways [4]. Specifically, POCUS improved the sensitivities of standard diagnostic testing for the detection of heart failure (88 percent), pneumonia, pneumothorax, pleural effusion, and pulmonary embolism (two to three studies; 78 to 95 percent versus 50 to 64 percent). In-hospital mortality and length of stay were not impacted by POCUS.

THORACIC ULTRASONOGRAPHY — Thoracic ultrasonography (TUS; lung and pleural), is a key component of critical care ultrasonography (CCUS) and for the purposes of this topic does not include cardiac ultrasonography. In critically ill patients, TUS can be used to evaluate patients with dyspnea due to acute cardiopulmonary respiratory failure, pleural effusion, and pneumothorax [5], the details of which are discussed below. (See 'Evaluation of the etiology of cardiopulmonary failure' below and 'Evaluation and treatment of pleural effusion' below and 'Evaluation for pneumothorax' below and 'Investigational' below.)

An algorithmic approach to evaluation of acute respiratory failure that recommends examination of three well defined points on the thorax (anterior, lateral, and posterolateral) bilaterally (the BLUE protocol) [6,7]. Based upon the ultrasonography findings derived from these examination points, the etiology of the respiratory failure may be identified in a high proportion of cases. This algorithm is distinguished by its simplicity and ease of use but other protocols exist with no study demonstrating superiority of one over the other.

Additional techniques used to obtain lung and pleural ultrasonography images, the advantages and disadvantages of TUS compared with traditional radiographic imaging of the lung (chest radiography and computed tomography [CT]), and the value of emergency ultrasonography in adults with thoracic trauma, a probes used for imaging are discussed separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Emergency ultrasound in adults with abdominal and thoracic trauma".)

Evaluation of the etiology of cardiopulmonary failure — Data from observational studies suggest that TUS in critically ill patients can identify abnormalities associated with acute cardiopulmonary failure:

●Presence or absence of pneumothorax – Pneumothorax is suggested by the absence of lung sliding and or lung pulse, and verified by the presence of a lung point, the details of which are discussed separately [8-10]. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Clinical presentation and diagnosis of pneumothorax", section on 'Diagnostic imaging'.)

●Normal aeration pattern versus alveolar/interstitial abnormality – An A-line pattern with lung sliding indicates a normal aeration pattern [11]. The presence of multiple B-lines indicates an alveolar or interstitial abnormality [12]. Profuse bilateral B-lines with smooth pleural morphology are characteristic of cardiogenic pulmonary edema; whereas focal B-lines with irregular pleural morphology are characteristic of a primary lung injury process such as acute respiratory distress syndrome (ARDS) or pneumonia [13]. In a systematic review of three studies of patients with suspected ventilator-associated pneumonia (VAP), although lung ultrasonography was more useful for ruling out pneumonia, useful signs of VAP included subpleural consolidations and dynamic air bronchograms [14]. In another systematic review of 25 studies, lung ultrasonography had a sensitivity of 0.82 and specificity of 0.94 for consolidation, 0.90 and 0.93 for heart failure, and 0.78 and 0.94 for acute exacerbations of pneumonia [15]. In patients with ARDS, lung ultrasound compared favorably with chest CT (diagnostic sensitivity ranged from 82 to 92 percent), and performed best when abnormal findings reached the pleural surface [16]. In another study of 67 patients, a nine-point bedside ultrasonography protocol outperformed routine chest radiography in the evaluation of intubated patients with acute respiratory failure [17]. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax".)

●Pleural effusion – An effusion is suggested by an anechoic area surrounded by typical anatomic boundaries, the details of which are described separately [18]. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax".)

From a diagnostic perspective, TUS compares well with CT and may be superior to chest radiography when performed by experienced operators. As examples:

●In a prospective study of 32 patients with acute respiratory distress syndrome (ARDS), the diagnostic accuracy of bedside chest radiography and TUS was compared with that of thoracic computed tomography as the gold standard [19]. TUS was superior to chest radiography for the diagnosis of pleural effusion (93 versus 47 percent), alveolar consolidation (97 versus 75 percent), and alveolar-interstitial syndrome (95 versus 55 percent).

●In a prospective study of 42 mechanically ventilated patients, the sensitivity and specificity of TUS was reported as 100 and 78 percent for consolidation, 94 and 93 percent for interstitial syndromes, 75 and 93 percent for pneumothorax, and 100 and 100 percent for pleural effusion [20]. In contrast, the sensitivity of chest radiography in the same population was significantly lower: 38 and 89 percent for consolidation, 46 and 80 percent for interstitial syndrome, 0 and 99 percent for pneumothorax, and 65 and 81 percent for pleural effusion. However, this study is flawed, likely due to the small numbers, since in practice the sensitivity of chest radiography compared with CT is not likely to be zero.

●In a study of 404 patients who presented to the emergency department (ED) with acute dyspnea, the performance of TUS was similar to chest radiography for the identification of pulmonary edema, pneumothorax, and consolidation and was superior for the identification of pleural effusion [21].

●In a review of 16 studies, the sensitivity of ultrasound for the diagnosis of pneumonia ranged from 57 to 100 percent with no alteration of sensitivity in critically ill versus non-critically ill subgroups [22].

●In a prospective study of 177 patients who underwent chest radiograph and lung ultrasound, lung ultrasound detected 90 percent of postoperative pulmonary complications compared with 61 percent with chest radiograph imaging [23]. Postoperative complications were also detected earlier.

TUS may be associated with reduced imaging time and a reduction in the number of imaging studies used during care [3,21,24]. As examples:

●In a study of 404 ED patients with acute dyspnea, ultrasound interpretation was completed during the scan at bedside (ie, within minutes), while the average time between a chest radiograph request and its final interpretation was 1 hour and 35 minutes [21]. Similarly, in another prospective cohort study of over 2000 ED patients with acute dyspnea, the time to formulate a diagnosis was lower in patients in whom point of care ultrasonography was used when compared with standard ED care (24 versus 186 minutes) [25].

●In another retrospective chart review that compared use of imaging studies in two intensive care units (ICUs; one used all CCUS elements and the other used ultrasonography for vascular access only), multiorgan ultrasonography (thoracic, cardiac, lung, abdominal, vascular) reduced the number of chest radiographs performed per patient (0.04 versus 0.10) and chest CTs (0.05 versus 0.17), as well as other imaging studies performed per patient [3].

Evaluation and treatment of pleural effusion — TUS can easily identify and quantify the size of an effusion at the bedside. In addition, the use of ultrasonography-guidance is becoming commonplace for guidance of thoracentesis and other pleural access procedures, because of the considerable inaccuracy of the physical examination and chest radiograph in selecting a safe site for needle or catheter insertion. TUS reduces the complications associated with thoracentesis, and in particular, allows safe thoracentesis in patients on mechanical ventilatory support [26], an important consideration given that visceral pleural laceration may result in a tension pneumothorax in this population. A detailed discussion of the indications and contraindications of ultrasonography guided pleural access procedures is presented separately. (See "Ultrasound-guided thoracentesis".)

Few data describe its value in critically ill patients. However, one study suggested that free-flowing effusions can be readily identified and quantified by residents after a focused training session [27].

Evaluation for pneumothorax — Portable ultrasonography is used to detect pneumothorax in several situations, such as after pleural or vascular access procedures, in the evaluation of patients with chest trauma, and following chest tube placement to assess resolution of a pneumothorax. Data indicate that TUS may be superior to standard chest radiography for detection of pneumothorax [28-39]. TUS may also be used to guide timing of chest tube removal following treatment of a pneumothorax [40]. Data to support these applications are presented separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Clinical presentation and diagnosis of pneumothorax", section on 'Pleural ultrasonography'.)

Investigational — Single-center observational studies describe several investigational applications of TUS that have not been validated in larger studies. These include the following:

●Titration of positive end-expiratory pressure (PEEP) in ARDS – Lung recruitment in response to increasing levels of PEEP may be followed by imaging the aeration pattern with lung ultrasonography (LUS) at various levels of PEEP [41]. (See "Acute respiratory distress syndrome: Ventilator management strategies for adults", section on 'Recruitment maneuvers'.)

●Weaning Failure – Weaning failure may be predicted by the pattern of lung aeration with bedside LUS that occurs during a spontaneous breathing trial [42]. Ultrasound can also be used to evaluate diaphragm function in patients who are ready to wean, although its ability to predict successful extubation is variable [43]. (See "Initial weaning strategy in mechanically ventilated adults".)

●Resolution of ventilator associated pneumonia – The resolution of ventilator associated pneumonia may be tracked with ultrasonography [44,45].

●Diagnosis of pulmonary embolism – In the evaluation of hemodynamically stable patients with suspected peripheral pulmonary embolism, lung ultrasonography can identify peripheral wedge-shaped abnormalities or alternate etiologies (eg, alveolar consolidation) [46,47]. (See "Clinical presentation, evaluation, and diagnosis of the nonpregnant adult with suspected acute pulmonary embolism", section on 'Investigational'.)

●Assessment of pulmonary artery occlusion pressure (PAOP) – TUS that includes analysis of A- and B-lines correlates with the PAOP and may distinguish patients with cardiogenic pulmonary edema (elevated PAOP) from those with acute lung injury (normal PAOP) [13,48]. (See "Acute respiratory distress syndrome: Clinical features, diagnosis, and complications in adults", section on 'Initial diagnostic evaluation'.)

●Predicting the development of ARDS after blunt chest trauma – The quantification of lung contusion identified by LUS in one study predicted the occurrence of ARDS [49].

ABDOMINOPELVIC ULTRASONOGRAPHY — Abdominopelvic ultrasonography is an integral component of critical care ultrasonography (CCUS) [1,50]. CCUS of the abdomen and pelvis most commonly evaluates patients for a possible source of sepsis and for acute undifferentiated abdominal pain. This includes patients suspected of having gallstones or acute cholecystitis, urinary tract obstruction, free fluid suggestive of vessel rupture or abscess, or free air suggestive of a ruptured viscus or gas-producing organism, all of which are discussed in this topic (see 'Detection of abdominal free fluid' below and 'Detection of abdominal free air' below). The value of emergency abdominal ultrasound in adults with abdominal trauma (focused assessment with sonography for trauma [FAST]) is described separately. (See "Emergency ultrasound in adults with abdominal and thoracic trauma".)

Critically ill patients are generally in the supine position for abdominal ultrasonography examinations. Focused areas to scan include the hepatorenal recess (Morison's pouch), splenorenal recess, right upper quadrant, left upper quadrant, left paracolic gutter, right paracolic gutter, and suprapubic area with attention to the bladder, rectovesicular, and rectouterine areas. Either a phased-array (1 to 5 MHz) or a curvilinear (1 to 3 MHz) probe can be used for abdominal scanning. (See "Transabdominal ultrasonography of the small and large intestine", section on 'Technical considerations'.)

Detection of gallbladder disease — Ultrasonography is a valuable modality for the evaluation of right upper quadrant abdominal pain suspicious for symptomatic gallstones and acute cholecystitis. Examination of the common bile duct (CBD) requires a higher level of scanning expertise than is typically achieved with CCUS.

Certain maneuvers can help optimize gallbladder visualization; however, it may be limited in the intensive care unit (ICU) when patients are not able to follow commands or are mechanically ventilated. These maneuvers include holding a deep breath to descend the gallbladder below the costal margin and placing the patient in a left lateral decubitus position to move any gas-containing bowel away from the gallbladder.

Studies that support value of CCUS for the evaluation of gallbladder disease in critically ill patients include the following:

●Gallstones – Several studies of bedside CCUS report that the sensitivity and specificity for the diagnosis of symptomatic cholelithiasis is 90 percent when performed by nonradiologists (mostly emergency department physicians) [51-55]. (See "Choledocholithiasis: Clinical manifestations, diagnosis, and management", section on 'Transabdominal ultrasound'.)

●Acute cholecystitis – In a retrospective study of 666 cases of acute cholecystitis and 111 cases of choledocholithiasis, few cases of cholecystitis were missed on bedside CCUS when the following findings were present: gallstones, gallbladder wall thickening, pericholecystic fluid, positive sonographic Murphy's sign, and cholestatic liver function testing abnormalities [56]. The prevalence of isolated CBD dilation was less than 1 percent, suggesting that of the CBD measurement is not critical in this setting to detect clinically significant disease of the gallbladder. (See "Acute calculous cholecystitis: Clinical features and diagnosis", section on 'Ultrasonography'.)

Detection of urinary tract obstruction — Renal failure is a common feature of critical illness. The differential diagnosis of renal failure includes urinary tract obstruction. Although much less common than other causes of renal failure in the critically ill patient, it is mandatory to consider obstructive uropathy in the differential; given that it is an eminently treatable cause. The examination of the kidneys for hydronephrosis and bladder for distension can be performed rapidly at the bedside with CCUS.

●Detection of hydronephrosis – Hydronephrosis results in a dilated pelvicaliceal junction that is evident with renal CCUS (image 1). The sensitivity and specificity of comprehensive renal ultrasonography for the detection of hydronephrosis and the grading system that can be applied clinically to hydronephrosis is discussed separately. (See "Clinical manifestations and diagnosis of urinary tract obstruction (UTO) and hydronephrosis", section on 'High suspicion for UTO: Diagnostic testing'.)

Several studies in patients with abdominal pain from suspected obstructive hydronephrosis report that renal CCUS may be of value [57-60]. In one prospective observational study of 104 patients in the emergency department suspected as having renal colic, bedside ultrasonography had an overall sensitivity and specificity of 88 and 85 percent, respectively for the detection of hydronephrosis [58].

Although many of the causes of hydronephrosis including obstructive stones (parenchymal, uteropelvic, and ureterovesicular), tumors, lymphadenopathy, abdominal aortic aneurysm, and pregnancy can be appreciated with ultrasonography, consultative ultrasonography or other advanced imaging modalities are often needed for full evaluation. Similarly, although renal cysts and complex renal masses can be readily visualized with CCUS, they warrant further investigation and expert consultation.

●Detection of bladder distension – A qualitative assessment of bladder distension is performed by noting the location of the bladder dome to the umbilicus. When the bladder dome extends at least halfway to the umbilicus, the majority of patients will have urinary retention. This finding should prompt a renal CCUS evaluation to assess for hydronephrosis. (See "Acute urinary retention", section on 'Prompt diagnosis of retention'.)

Bladder volume that correlates with catheterized volume can be calculated by the following formula [61,62]:

The width and length is measured in a transverse plane and the height in a sagittal plane.

Although not absolute, bladder volumes greater than 600 mL are concerning for bladder outlet obstruction [63]. Case reports indicate that bladder ultrasonography can detect a range of abnormalities associated with urinary retention including bladder masses, enterovesical fistulae, and bladder rupture [60,64-68]. Bladder masses may appear as irregular, echogenic projections from the bladder wall or as localized bladder wall thickening. Although the bladder wall thickness varies with the degree of filling, the wall thickness is normally between 3 to 6 mm. In addition to malignancy, the differential of bladder masses includes diverticula, bladder wall thickening due to chronic cystitis, foreign bodies, stones, and blood clots. If the bladder mass disappears with irrigation, the cause of the bladder mass was likely due to a blood clot.

Detection of abdominal aorta aneurysm rupture — The value to CCUS in the diagnosis of a ruptured aortic aneurysm is discussed separately. (See 'Abdominal aortic syndromes' below and "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging symptomatic patients'.)

Detection of abdominal free fluid — CCUS may be used for the assessment of free fluid to support the presence of blood due to trauma or ruptured abdominal aortic aneurysm, similar to that described for the FAST examination. The right and left upper quadrant is scanned with attention to the hepatorenal and splenorenal recess, as well as the right and left paracolic gutters, and the rectouterine (pouch of Douglas) and rectovesicular pouch. Noncomplicated collections of fluid often appear as an anechoic collection. With complexity, fluid collections may appear as a complex nonseptated collection, a homogenous complex collection, and/or a septated collection. The presence of blood may give the appearance of an ultrasound "hematocrit sign" (an anechoic layer interfaced with an increased echogenic dependent layer due the gravitational effects on blood). Details regarding the role of FAST and ultrasonographic appearance of fluid in patients with trauma are discussed separately. (See "Emergency ultrasound in adults with abdominal and thoracic trauma", section on 'Intraperitoneal free fluid'.)

Commonly, free fluid from ascites due to a medical cause such as cirrhosis may also be detected by CCUS and, if indicated, may guide paracentesis.

Detection of abdominal free air — Although not a well-established modality for imaging abdominal free air, several studies have reported that abdominal free air can be identified using ultrasonography [69]. For the sonographic examination for abdominal free air, high frequency linear probes and curved array transducers (2.6 to 5 MHz range), are preferred to better visualize the peritoneal layer and associated free air (movie 1). The patient should be positioned at an incline of 10 to 20 degrees or placed in the semi-left lateral decubitus position to maximize the detection of air.

Ultrasonography can be used to detect the following types of abdominal free air:

●Pneumoperitoneum – The identification of free intraperitoneal air is found most consistently over the ventral aspect of the liver when the patient is supine or in a semi-left lateral decubitus position (also known as the enhanced peritoneal stripe sign [EPSS]) [70,71]. EPSS consists of a superficial single or double echogenic line that denotes the interface of the abdominal wall with the peritoneal surface. With more free air, multiple layers of air bubbles create reverberation artifacts referred to as "Comet tails" and "ring-downs." Another reverberation artifact seen in pneumoperitoneum is called A-lines. When echogenic lines run parallel to the peritoneal stripe, this is termed "A-lines." The identification of abdominal organs, such as liver and bowel structures, rules out pneumoperitoneum at the site of the probe position, as air blocks transmission of ultrasonography. The detection of pneumoperitoneum has a reported sensitivity and specificity ranging from 85 to 100 percent and 99 to 100 percent respectively [70-78].

●Pneumoretroperitoneum – This is a rare complication of trauma, cancer, infection, or invasive procedures. The typical ultrasonography findings include air around the right kidney creating a "veiling" appearance, air ventral to the aorta and inferior vena cava creating the appearance of a vanishing vessel, and air collections around the retroperitoneal duodenum, pancreatic head, and posterior to the gallbladder [79-82]. In contrast to free intraperitoneal air, shifting of gas does not occur with positional changes in the patient.

●Intraluminal free air – Air within lumens of non-bowel structures can be observed within the biliary system, gallbladder, bladder, vascular structures, and pancreatic ducts. The interpretation of these findings depends upon the clinical context, with iatrogenic manipulation, trauma, and infection being the typical causes. Air in the portal venous system is associated with significant morbidity and mortality and is often the result of bowel necrosis.

●Intraparenchymal free air – Intraparenchymal free air refers to the identification of gas within an organ (eg, liver, kidney). This most commonly occurs in the setting of infection with abscess formation but can also be due to trauma and neoplasms. The identification of emphysematous pyelonephritis can be made with ultrasonography, and when found, emergency nephrectomy is often indicated.

VASCULAR ULTRASONOGRAPHY — The vascular system is an essential area of critical care ultrasonography (CCUS) application. Key components of this area are focused on the evaluation of the following:

●Deep venous thrombosis (DVT) in the upper and lower extremity

●Venous access for central and peripheral vein catheter placement

●Arterial access for catheter placement

●Abdominal aortic syndromes

Detection of deep venous thrombosis — DVT of the upper and lower extremity is a common cause of morbidity and mortality in critically ill patients. Ultrasonography identifies thrombus as noncompressibility of the imaged vein. The value of compression ultrasonography in the diagnosis of upper and lower extremity DVT is discussed separately. (See "Clinical presentation and diagnosis of the nonpregnant adult with suspected deep vein thrombosis of the lower extremity", section on 'Diagnostic ultrasonography suspected first DVT' and "Overview of thoracic central venous obstruction".)

A high frequency (5 to 10 MHz) linear transducer is used for the assessment of DVT. Compression ultrasonography is performed in a transverse orientation since error can be introduced when the transducer is oriented in a longitudinal axis. A firm, rapid compression with the probe should be used with minimal to no distortion to the corresponding artery. Compressible veins are considered patent and without thrombus while noncompressible veins are diagnostic of thrombus. If a thrombus is visible within the vein, the compression component of the examination is not required and may be rarely associated with dislodgement of the thrombus.

●Lower extremity – For the lower extremity, the patient should be in the supine position in order to image the femoral veins. As the critically ill patient cannot usually assume a prone position, the popliteal vein is examined by flexing the knee with outward rotation of the hip and placement of the linear probe in the popliteal fossa. A compression exam with the ultrasound probe begins in the groin at the proximal common femoral vein. Compressibility of the vein is assessed at the following five sites:

•The proximal common femoral artery and vein

•The junction of the saphenous vein and the common femoral vein

•The bifurcation of the common femoral artery and deep femoral artery

•The bifurcation of the common femoral vein into the superficial and deep femoral vein

•The popliteal vein

Some examiners extend the examination to include the superficial femoral vein. Whether this increases the yield compared to the standard five point examination is debatable. Extending the examination adds very little time to the test.

In a retrospective chart review, multiorgan ultrasonography (thoracic, cardiac, lung, abdominal, vascular) reduced the number of radiology-service-performed DVT studies per patient (0.02 versus 0.2) [3]. In another study, bedside ultrasonography had a sensitivity and specificity of 86 and 93 percent, respectively, compared with standard compression ultrasonography; in addition standard compression ultrasonography was associated with a 14 hour time delay [83].

●Upper extremity – For the upper extremity, the patient should be supine with the arm externally rotated and abducted 90 degrees from the chest. The patient's head is rotated to the contralateral side and elevated above the extremity to avoid external compression of the distal subclavian vein between the first rib and clavicle. The target vein is imaged in a transverse plane in multiple sites with a similar compression technique to that described for the lower extremity.

Central venous access — The use of ultrasonography guidance is commonplace for placement of central venous catheters. Several studies have shown reduced complications, mainly arterial puncture and pneumothorax with ultrasonography-guidance. Further details are provided separately. (See "Basic principles of ultrasound-guided venous access" and "Central venous access in adults: General principles" and "Central venous catheters for acute and chronic hemodialysis access and their management".)

Peripheral venous and arterial access — Most peripheral venous catheters do not require ultrasonography-guidance for successful placement. However, ultrasonography is preferred for the placement of a peripherally inserted central venous catheter (PICC line) for patients with veins that are not readily visualized. Similar to central venous access, pre-procedural scanning and understanding the anatomy of the upper and lower extremity venous system is required for the success of PICC line placement. (See "Peripheral venous access in adults", section on 'Role of ultrasound guidance'.)

Ultrasonography guidance for arterial guided catheters also improves success and reduces complication rates, the details of which are provided separately. (See "Arterial blood gases", section on 'Technical challenges' and "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation", section on 'Use of ultrasound guidance'.)

Abdominal aortic syndromes — Abdominal aortic syndromes, including ruptured abdominal aortic aneurysms (AAA) and dissection are identified with ultrasonography assessment. In hemodynamically unstable patients, ultrasound is the imaging modality of first choice for the diagnosis of a ruptured AAA. Expected findings include an enlarged aorta with or without a fluid collection in the abdomen. In the emergency department, several studies report high sensitivity (97.5 to 100 percent) and specificity (94.1 to 100 percent) for AAA detection using bedside ultrasonography compared with computed tomography (CT) and magnetic resonance imaging [84-87]. Similarly, the ultrasonography detection of abdominal aorta dissection has comparable sensitivity when compared to CT. Detailed discussion of ultrasonography for the diagnosis of AAA and aortic dissection is provided separately. (See 'Abdominopelvic ultrasonography' above and "Emergency ultrasound in adults with abdominal and thoracic trauma" and "Clinical features and diagnosis of acute aortic dissection", section on 'Diagnosis' and "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging symptomatic patients'.)

BASIC CRITICAL CARE ECHOCARDIOGRAPHY — Critical care echocardiography (CCE) can be classified as basic and advanced. Basic CCE, which is discussed in this topic, utilizes a limited number of standard echocardiographic views which include the parasternal long axis, parasternal short axis, apical four chamber, subcostal long axis, and inferior vena cava long axis views. The technical aspects of consultative transthoracic echo is discussed separately. (See "Emergency ultrasound in adults with abdominal and thoracic trauma" and "Transthoracic echocardiography: Normal cardiac anatomy and tomographic views".)

Patient-specific factors such as obesity, heavy musculature, surgical dressings, and chest drains may limit image acquisition. On occasion, image quality will not be adequate for clinical purposes. In this case, transesophageal echocardiography may be indicated, although requiring a higher level of training. Independent of patient specific factors, the examiner may have difficulty in obtaining an effective scanning position due to equipment that surrounds the patient or the patient may be difficult to position for optimal image acquisition. (See "Transesophageal echocardiography: Indications, complications, and normal views".)

The basic CCE examination does not include Doppler measurements of cardiac pressures or flows, or other standard views used for a full echocardiography examination. Competence in basic CCE includes training in when to call for a complete examination that needs to be performed by a clinician who is fully trained in advanced critical care echocardiography including transesophageal echocardiography.

Limited cardiac ultrasound is not a replacement for routine echocardiography. A meta-analysis of nine studies that compared focused cardiac ultrasound (FoCUS)-assisted clinical assessment with clinical assessment alone reported that while FoCUS examination of the left ventricle and mitral valve was more sensitive than clinical assessment alone (84 versus 43 percent), its specificity was similar (89 versus 81 percent) [88].

Evaluation of shock — Basic CCE is useful for evaluating patients with undifferentiated shock (algorithm 1) [89]. Basic CCE is most often used in combination with thoracic, abdominal, and/or vascular elements of critical care ultrasonography (CCUS). In published protocols that promote multiorgan ultrasonography in patients with shock (eg, rapid ultrasound in shock [RUSH] or abdominal and cardiac evaluation with sonography in shock [ACES]) [90-92], the heart is typically examined first, followed by ultrasound of the chest and abdomen and major blood vessels; however, other protocols such as focused cardiac ultrasound (FOCUS) examine the heart only [93]. Details regarding point of care ultrasonography in shock are provided separately. (See "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock".)

In brief, in patients with undifferentiated shock, multiorgan CCUS that includes basic CCE is useful for the following:

●Classification of shock – CCE helps to categorize shock into hypovolemic, obstructive, cardiogenic, or distributive shock. This guides the intensivist in establishing initial management strategy with volume resuscitation, vasopressors, inotropes, and/or mechanical circulatory support. (See "Definition, classification, etiology, and pathophysiology of shock in adults" and "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock".)

●Identification of life-threatening cardiac causes of shock – These include pericardial tamponade, acute cor pulmonale, hyperdynamic left ventricle (LV) with outflow obstruction due to hypovolemia and inappropriate use of inotropes, LV outflow obstruction following aortic valve replacement surgery, catastrophic left sided valve failure, very severe LV dysfunction, or acute RV dysfunction. (See "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock".)

●Tracking evolution of disease and response to therapy using serial CCE examinations.

Data supporting the use of CCE is mostly derived in studies in the emergency department and intensive care unit setting. These studies demonstrate that a multiorgan scanning approach that includes basic CCE is useful to narrow the differential diagnosis, to confirm a clinically suspected diagnosis, to prompt changes in management, and/or to detect a complication from a therapeutic procedure. There is no study that has examined any effect on mortality. These data are described separately. (See "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock".)

Evaluation of acute cardiopulmonary failure — CCE alone may also be useful for the diagnosis of cardiogenic pulmonary edema [94,95]. A meta-analysis of seven prospective cohort studies reported that in patients who present to the emergency department with a moderate to high pretest probability of acute pulmonary edema, bedside CCE showing B-lines had a sensitivity and specificity of 94 and 92 percent, respectively [94].

The addition of CCE to other elements of CCUS improves the diagnostic ability of ultrasonography for evaluation of acute respiratory failure. In a prospective study of 136 patients with acute respiratory failure, adding CCE to thoracic ultrasonography (TUS) improved diagnostic accuracy for cardiogenic pulmonary edema, pulmonary embolism, and pneumonia, when compared with TUS alone [96].

The use of CCE as part of a multiorgan assessment strategy may decrease the use of comprehensive echocardiography assessments. In a retrospective chart review, multiorgan ultrasonography (thoracic, cardiac, lung, abdominal, vascular) reduced the number of consultative echocardiography studies per patient (0.07 versus 0.18) [3].

Cardiopulmonary resuscitation — In patients undergoing cardiopulmonary resuscitation, bedside CCE has been used during pulse checks in order identify potentially reversible causes of cardiac arrest such as pericardial tamponade, profound hypovolemia, or thrombus in transit with acute cor pulmonale [97]. Alternatively, the finding of absent cardiac contractility following a reasonable period of cardiopulmonary resuscitation (CPR) indicates limited probability for return of spontaneous circulation [98,99]. (See "Advanced cardiac life support (ACLS) in adults".)

Investigational — Use of CCE has been described for patients undergoing extracorporeal membrane oxygenation for cannula placement, to follow hemodynamics and to identify those that can be weaned [100-102].

TRAINING AND COMPETENCE — Acquiring the necessary skills for performing critical care thoracic, abdominal, and vascular ultrasonography depends upon an understanding of normal and abnormal ultrasonography anatomy to avoid image misinterpretation. In addition, the clinician should understand the indications as well as limitations of critical care ultrasonography (CCUS). One standard definition of competence is available that is supplemented by an expert consensus statement on training in CCUS [1,50]. One study reported that a three-day course resulted in improved CCUS skills but further studies are needed to determine whether such courses will translate into effective clinical practice [103].

Noncardiologists can achieve competence in basic critical care echocardiography (CCE) with appropriate training [104-117]. The use of basic CCE is supported by the American College of Chest Physicians (ACCP), European Society of Intensive Care Medicine, American Society of Echocardiography, and an international committee on focused cardiac ultrasound [1,50,93,118,119]. Although requirements for training in basic CCE have not been standardized, a typical training sequence includes a didactic component for mastery of the cognitive base of CCE, hands-on training initially with normal human subjects followed by scanning of patients under the supervision of a capable instructor, and review of a comprehensive image set representative of a wide range of normal and abnormal findings. As a guide, one report indicates that a 12-hour learning program blending didactics, interactive clinical cases, and tutored hands-on sessions is a sufficient training period for basic CCE [120].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Use of point-of-care echocardiography and ultrasonography as a monitor for therapeutic intervention in critically ill patients".)

SUMMARY AND RECOMMENDATIONS

●Definition – Critical care ultrasonography (CCUS) refers to the use of ultrasonography in patients who are critically ill. Compared with consultative ultrasonography, CCUS is a bedside tool that can be rapidly performed and interpreted simultaneously by the operator, usually an intensivist or emergency department physician, prompting a diagnosis, a procedure, and/or a therapy. The most common four elements of CCUS are thoracic, abdominal, vascular, and cardiac. (See 'Introduction' above and 'Terminology and definition' above.)

●Consultative versus bedside ultrasonography – Choosing consultative radiology- or cardiology-performed ultrasonography or CCUS is dependent upon available equipment and skill as well as the indication. While consultative ultrasonography assessment is useful for hemodynamically stable patients with complex disorders that require skilled expertise, CCUS is typically best suited for patients with imminently life-threatening processes, in whom the result will determine the administration of a specific or life-saving therapy. (See 'Choosing consultative or critical care ultrasonography' above.)

●Thoracic ultrasonography – Thoracic ultrasonography (TUS) includes ultrasonography of both the lung and the pleural space. In the critically ill patient, TUS can be used to evaluate patients with acute cardiopulmonary respiratory failure, pleural effusion, and pneumothorax. (See 'Thoracic ultrasonography' above and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Ultrasound-guided thoracentesis".)

●Abdominopelvic ultrasonography – Abdominopelvic CCUS is useful for the evaluation of a possible source of sepsis and acute undifferentiated abdominal pain. This includes patients suspected as having gallstones or acute cholecystitis, urinary tract obstruction, free fluid suggestive of vessel rupture or abscess, or free air suggestive of a ruptured viscus or gas-producing organism. Emergency abdominopelvic ultrasonography is useful in the evaluation of patients suspected as having contusion or bleeding from abdominal trauma. (See 'Abdominopelvic ultrasonography' above and "Emergency ultrasound in adults with abdominal and thoracic trauma", section on 'Abdominal examination'.)

●Vascular ultrasonography – Vascular CCUS includes the evaluation of upper and lower extremities for deep venous thrombosis (DVT), imaging of central and peripheral veins and arteries for catheter placement, and evaluation of the aorta for rupture or dissection. (See 'Vascular ultrasonography' above and "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Diagnosis' and "Basic principles of ultrasound-guided venous access" and "Clinical presentation and diagnosis of the nonpregnant adult with suspected deep vein thrombosis of the lower extremity", section on 'Diagnostic ultrasonography suspected first DVT'.)

●Echocardiography – Critical care echocardiography (CCE) can be classified as basic or advanced. Basic CCE, which is discussed in this topic, is useful in the evaluation of patients with undifferentiated shock or acute cardiopulmonary failure; occasionally it can be used to identify potentially reversible etiologies of cardiopulmonary resuscitation. (See 'Basic critical care echocardiography' above.)

●Competency – Acquiring the necessary skills for performing CCUS depends upon an understanding of normal and abnormal ultrasonography anatomy to avoid image misinterpretation as well as a knowledge of the indications and limitations of CCUS. (See 'Training and competence' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Peter Doelken, MD, FCCP, who contributed to earlier versions of this topic review.