Abdominal POCUS in Critical Care

The secrets of the abdomen

Overview of abdominal point-of-care ultrasound use in the ICU, potential diagnoses and findings common to the critical care patient population.

The use of point-of-care ultrasound (POCUS) in critical care as a diagnostic and monitoring tool is rapidly expanding. While its role in cardiovascular and respiratory assessment is well established (within critical care), abdominal ultrasonography is less so; perhaps because of the myriad of potential diagnoses that can be made and the fact that the abdomen is often less accessible due to gaseous interposition. Regardless of modality, the key difference between radiology department scans and scans performed by intensivists is that the latter are more focused and aim to answer a specific clinical question in the context of a specific clinical situation.

It is without the scope of this article to describe every single (potential) use of abdominal POCUS; the aim is to provide an overview of the potential diagnosis and findings common to the critical care patient population.

Basic B-mode ultrasound

1. Trauma

One of the earliest uses of ultrasound (US) outside of radiology was in the detection of intra-abdominal free fluid (or blood) in the context of trauma. The Focused Assessment with Sonography in Trauma (FAST) scan has been consistently included as part of the Advanced Trauma Life Support (ATLS) course over the latest editions (Royal College of Surgeons 2017). The original FAST scan included assessment of the hepato-renal recess (right upper quadrant a.k.a Morison’s pouch), the spleno-renal recess (left upper quadrant) and the pelvis for the presence of free fluid/blood (Carroll et al. n.d.).This has been expanded to include the subcostal views (pericardial fluid/tamponade), anterior thoracic views (to rule out pneumothorax) and the detection of pleural fluid in the so-called extended FAST or eFAST (123sonography.com n.d.) (Figure 1).

The sensitivity and specificity of FAST for the detection of free intraperitoneal fluid were 64–98% and 86–100%, respectively (Bloom and Gibbons 2018). This range may be explained by differences in the levels of clinical experience and in the reference standards.

2. Abdominal free fluid

Ultrasound allows for the identification of free fluid, quantification of the volume and potentially, the underlying aetiology.

The differential diagnosis of the presence of abdominal free fluid is summarised in Table 1. In the critically ill the main cause for abdominal fluid is in the setting of sepsis, capillary leak and massive fluid resuscitation, as seen in severely burned patients. The aetiology of spontaneous haemoperitoneum can vary, and the causes may be classified as gynaecologic, hepatic, splenic, vascular, or coagulopathic conditions.

US is not sensitive at identifying a focus of extravasation from a vessel or organ (Schmidt et al. 205). Therefore, FAST may be an option for the initial evaluation of a patient to detect haemoperitoneum in non-trauma patients, but it does not replace computed tomography (CT) scanning.

3. Assessment of gastric content

Dysfunctional gastric emptying in critically ill patients can contribute to complications during procedures related to airway management and can result in unsuccessful enteral feeding as well as an increased risk of aspiration (Marik 2001). A 6-hour fasting period (2 hours for clear fluid) has been recommended for patients undergoing elective surgery to reduce the risk of aspiration during anaesthesia (s.n. 2017). In the ICU, gastric emptying is frequently altered and influenced by several factors, including age, diagnosis on admission (Hsu et al. 2011) underlying disease processes (e.g. diabetes, porphyria, shock)(Nguyen et al. 2007), therapeutic interventions (e.g. mechanical ventilation), medications (e.g. opioids, sedatives, neuromuscular blockers, vasopressors) (Nimmo et al. 1975; Steyn et al. 1997), electrolyte and metabolic disturbances and mechanical ventilation (Mutlu et al. 2001).

Epidural anaesthesia, on the contrary, improves gastric emptying and peristalsis. The measure of the antral cross-sectional area (CSA) by US is feasible in most critically ill patients and would allow for direct visualisation of stomach content. On average, a CSA > 15-25 cm2 corresponds to a gastric residual volume (GRV) > 300 mL. The same principle has been studied with regard to assessment of preoperative fasting status amongst surgical patients (Van der Putte and Perlas 2014; Perlas et al. 2009).

Gastric US can also identify other pathologies such as gastric tumours (carcinomas and rarely teratomas), hypertrophic pyloric stenosis and even bezoar related to enteral nutrition.

Normal stomach wall anatomy consists of five layers, referred to as the gut signature:

1. Serosa (hyperechogenic)
2. Muscularis propria (hypoechogenic)
3. Submucosa (hyperechogenic)
4. Muscularis mucosa (hypoechogenic)
5. Mucosa (hyperechogenic)

4. Bowel obstruction

Features of the bowel which can be assessed using US include:

• Wall thickness
• Diameter and intraluminal contents
• Peristalsis
• Vascularity

The diameter of the bowel and its contents may vary according to site, fasting/feeding state and bowel function. In adults, the normal small bowel measures under 30mm in diameter and the normal large bowel under 60 mm in diameter (Reintam Blaser et al. 2012). Dilated loops may show thickened walls (normally up to 3 mm in the small bowel), or thickened valvulae conniventes (normally up to 2mm in the large bowel). The exceptions to this are the duodenal bulb and rectum, which are less than 3 and 4mm in thickness respectively (Lichtenstein et al. 2014).Ultrasound patterns can aid in the differentiation of small from large bowel (Table 2).

Assessment of bowel peristalsis is difficult and subjective, but may provide useful information in several intestinal diseases. Increased small bowel peristalsis has been described in coeliac disease and acute mechanical bowel obstruction (increased to-and-fro motion of the bowel contents) (Hefny et al. 2012). In later phases, one may detect a fluid-filled lumen, thinning and spasm of the bowel wall, evidence of extraluminal fluid and decreased or absent peristalsis.

Types of peristalsis:

• Absent peristalsis
• Present ineffective peristalsis
• Present effective peristalsis
• Augmented peristalsis

5. Viscus perforation

Physiologic air can be seen in the lumen of the bowel as small stars. Larger air bubbles can appear as hyperechoic stripes generating comet tail artefacts (these are rare in the small bowel but frequent in the large bowel), much like a linear view of the lung would look. Air artefacts can emanate from the thoracic cavity and the lung over the liver. Pathological air, however, may produce an enhanced peritoneal stripe sign (EPSS), reverberation artefacts and ring-down artefacts (Figures 2a and 2b) (Hoffmann et al. 2012).

6. Renal dysfunction

International guidelines recommend that all patients who present in acute renal failure undergo an ultrasound examination to ascertain its cause (Kidney Disease: Improving Global Outcomes 2012). Hydronephrosis due to obstructive uropathy is a reasonably straightforward diagnosis to make.

More advanced techniques include the assessment of blood flow within the renal artery and vein using Doppler analysis.

Analysis of the urinary bladder should be performed as well. The bladder can be empty, filled or distended (globus). The position of the bladder catheter balloon can be checked, as well as the presence of hyperechogenic structures (debris, tumour, blood clot etc).

7. Liver and spleen 

Ultrasound of the liver is divided into general US views including anatomic views of the liver, gallbladder and biliary tree. Pathology within these organs e.g. acute liver failure, can result in intensive care admission, but is beyond the scope of this paper.

Advanced modalities

1. Doppler and colour Doppler techniques

Doppler US is used to assess the signal from visceral vessels that supply the gastrointestinal (GI) tract and smaller vessels within the intestinal wall. Although the technique cannot be used to assess capillary flow, it can be used to analyse all the major visceral vessels e.g. renal, hepatic, mesenteric. It has to be noted that normal bowel wall perfusion cannot be demonstrated by colour or power Doppler. The presence of flow in the bowel wall points towards pathologic perfusion (e.g. hyperaemia in actively inflamed segments, as seen in appendicitis).

Commonly used measurements which can be performed include:

• Systolic, diastolic and mean velocities
• Pulsatility index
• Resistance index (peak systolic velocity – end diastolic velocity)/peak systolic velocity
• Blood flow volume

GI tract blood flow

Colour Doppler allows for the assessment of mural flow, the absence of which is a sign of ischaemia. Unfortunately, this finding is only reported in 20–50% of patients with a proven diagnosis of ischaemic colitis (Danse et al. 2000a; Danse et al. 2000b). Doppler US can show stenosis, emboli, and thrombosis in the near visible parts of the coeliac trunk, the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA). In the early phase of bowel ischaemia, US examinations may show SMA occlusion, hyperaemic segments and bowel spasm. Collateral vessels cannot be reliably displayed using ultrasound. Systolic velocities of more than 250–300 cm/s are sensitive indicators of severe mesenteric arterial stenosis (Hamada et al. 2014; Koenig et al. 2011). The spectral analysis of Doppler signals of arteries supplying the GI tract (truncus coeliacus, superior and inferior mesenteric arteries) and the vessels draining the intestine, can be used to estimate bowel perfusion (see below). Assessment in transverse and longitudinal plane should be performed. Low flow states can also be identified by the presence of spontaneous contrast and turbulent flow in the large vessels.

Hepatic blood flow

Portal vein: the normal main portal vein (MPV) is gently undulating with peak systolic velocities ranging between 20 cm/s and 40 cm/s. A low flow velocity of <16 cm/s in addition to a calibre increase in the MPV are diagnostic features of portal hypertension (PH). Further worsening of PH leads to a to-and-fro flow pattern, whereby the nearly stagnant blood column in the portal veins is seen to shift into and out of the liver with the respiratory cycle. In the end stages, stagnation of the blood column can lead to thrombosis or progress to a frank flow reversal or non-forward portal flow (NFPF). This is considered to have grave prognostic significance, indicating severe and irreversible liver failure (Wachsberg et al. 2002).

Hepatic vein: the normal flow is triphasic with two hepatofugal phases related to atrial and ventricular diastole. Fibrotic or inflammatory changes may create a monophasic flow pattern. Early waveform changes in cirrhosis patients include spectral broadening and dampening of the normal, retrograde, pre-systolic wave of the hepatic vein waveform. Later, the normal triphasic waveform pattern may be diminished or replaced with a monophasic pattern. Therefore the monophasic hepatic vein waveform indicates relatively high portal pressures (Ralls 1990).

Hepatic artery: hepatic arterial resistance changes with increasing portal pressure values, but hepatic arterial resistive indices correlate poorly with the severity of cirrhosis and will not be further discussed here.

Renal blood flow

Doppler US can be used to assess renal perfusion. Normal resistive index (RI) is approximately 0.58 ± 0.10 and values >0.70 are considered to be abnormal. A renal Doppler RI may also help in detecting early renal dysfunction or predicting short-term reversibility of acute kidney injury (AKI) in critically ill patients. A recent meta-analysis suggested that RI may be a predictor of persistent AKI in critically ill patients with a pooled sensitivity and specificity of 0.83 (95% CI, 0.77-0.88) and 0.84 (95% CI, 0.79-0.88) (Ninet et al. 2015).

Increased renal resistive index (RRI) has been proven to be an independent predictor of worse cardiovascular and renal outcomes, especially when combined with reduced glomerular filtration rate (GFR), thus providing a useful diagnostic complement to the assessment of renal function in these patients. High RRI has also been correlated with the presence of hypertensive and atherosclerotic organ damage. Values >0.80 have been reported to be predictive of all-cause mortality in chronic kidney disease patients and may indicate impending renal transplant failure in this patient subset (Barozzi et al. 2007; Guinot et al. 2013; Ninet et al. 2015; Schnell et al. 2012).

Gastrointestinal and urinary tract sonography (GUTS) protocol

Gastrointestinal function can be assessed with US, using a combination of anatomical, functional and blood flow evaluation (Schmidt et al. 2005).

1. Function: peristalsis, bowel motility, gastroparesis, small bowel ileus, large bowel paralysis
2. Dimensions: bowel dilatation, bowel obstruction, Ogilvie syndrome, bacterial overgrowth, toxic megacolon, bowel wall oedema, abdominal wall oedema
3. Collections: bowel content (blood, liquid, air, solid), haematoma, gastrointestinal bleeding, ascites
4. Perfusion: bowel ischaemia, hepatosplanchnic perfusion, shock state (spontaneous contrast), renal resistive index, abdominal perfusion pressure (APP) = mean arterial pressure (MAP)-intraabdominal pressure (IAP)

This approach is summarised by the GUTS (Gastrointestinal and Urinary Tract Sonography) protocol (Figure 3). The structured and stepwise approach may lead to improved practical management of adult ICU patients with acute gastrointestinal injury (AGI), as graded by the European Consensus Definitions (Reintam Blaser et al. 2012). Such a management strategy has not been shown to improve patient outcome, however.

The European Consensus Definition of AGI suggests a graded severity score:

1. AGI grade I represents a self-limiting condition with increased risk of developing GI dysfunction or failure
2. AGI grade II (GI dysfunction) represents a condition requiring interventions to restore GI function
3. AGI grade III (GI failure) represents a condition when GI function cannot be restored with interventions
4. AGI grade IV represents a dramatically manifesting GI failure, which is immediately life-threatening (e.g. abdominal compartment syndrome with organ dysfunction) (Reintam Blaser et al. 2012).

Future works

Contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) involves the use of contrast agents containing gas-filled microbubbles administered intravenously, producing an image with greater contrast and/or highlighting more vascular areas. Although reasonably well established in radiology, and more recently cardiology departments, its use in intensive care is in its infancy. Unlike CT contrast agents, CEUS appears safe for patients with renal dysfunction and the modality itself remains free of radiation exposure to patients. Possible use within critical care includes enhanced echocardiography and in blunt abdominal trauma to assess solid-organ injuries (Dietrich 2017).

 
Doppler analysis as a marker of fluid status and venous congestion

As mentioned, Doppler analysis of the vasculature of specific abdominal organs allows for assessment of its perfusion. Some early work showed that this modality could also be used as a marker of systemic vascular congestion (Lewis et al. 1989).

Conclusion

 This paper summarises the multiple uses of abdominal US on the ICU and highlights future work and development. It must be remembered however that despite the myriad of potential diagnosis, utilisation and interpretation of such techniques requires training and experience.

Acknowledgements and conflicts of interest 

Jonny Wilkinson is a member of the International Fluid Academy (IFA) faculty. Manu Malbrain is founding President of WSACS (The Abdominal Compartment Society) and current Treasurer, he is also member of the medical advisory Board of Getinge (former Pulsion Medical Systems) and Serenno medical, and consults for ConvaTec, Acelity, Spiegelberg and Holtech Medical. He is co-founder and member of the executive committee of the International Fluid Academy (IFA). 

Adrian Wong is a member of the executive committee of the IFA.

Abbreviations 

FAST Focused Assessment with Sonography in Trauma 

GI gastrointestinal 

POCUS point-of-care ultrasound 

US ultrasound

Pediatric EDs using more ultrasound, MRI instead of CT

By Erik L. Ridley, AuntMinnie staff writer

August 3, 2020 -- Although pediatric emergency departments (EDs) performed fewer CT exams between 2009 and 2018, their utilization of advanced imaging increased overall due to expanded use of MRI and ultrasound exams, according to research published online August 3 in JAMA Pediatrics

A research team led by Dr. Jennifer Marin of UPMC Children's Hospital of Pittsburgh assessed the change in CT, ultrasound, and MRI rates in over 26 million ED visits archived in the Pediatric Health Information System administrative database from January 1, 2009, to December 31, 2018.

They found that the proportion of pediatric ED encounters that resulted in a CT exam decreased amid expanded use of ultrasound and MRI. But there was also considerable variation in utilization between practices.

"The magnitude of the decrease in CT use varied by site and was associated, in part, with the use of alternative advanced imaging modalities for certain diagnoses, most notably ultrasonography for abdominal conditions," they wrote. "Future efforts appear to be needed to standardize imaging approaches and evaluate the effect of the changing

landscape of advanced imaging on patient-level outcomes."

Change in use of advanced imaging in pediatric ED
	2009	2018
At least one advanced imaging study	6.4%	8.7%
CT	3.9%	2.9%
Ultrasound	2.5%	5.8%
MRI	0.3%	0.6%

*All differences were statistically significant (p < 0.001, p = 0.001, p < 0.001, and p < 0.001, respectively).

Delving further into the data, the researchers found that most of the decrease in CT occurred in eight all patient-refined diagnosis-related groups (APR-DRGs), led by concussion (-23%), appendectomy (-14.9%), ventricular shunt procedures (-13.3%), and migraine and other headaches (-12.4%). Declines in CT use also occurred in other disorders of the nervous system (-10.1%); abdominal pain (-6.1%); other ear, nose, mouth, throat, and cranial or facial diagnoses (-5.9%); and seizure (-5.3%).

The researchers also found that strategies to reduce abdominal CT use by performing ultrasound first for evaluating abdominal pain may be associated with the higher use of ultrasound for that application.

"Interestingly, the increase in the use of ultrasonography for these conditions was greater than the decrease in the use of CT," they wrote. "Therefore, a proportion of these ultrasonographic examinations likely represent overuse of a typically widely available and nonradiating imaging tool."

In other findings, the researchers observed wide variation among EDs in the use of ultrasound for appendectomy (median 57.5%), as well as MRI (median 15.8%) and CT (median 69.5%) for ventricular shunt procedures.

In terms of outcomes, the researchers found that hospitalization and three-day ED revisits decreased during the study period. However, the ED length of stay did not change.

While it's encouraging that lower utilization of CT avoided radiation exposure in nearly 28,000 fewer kids, the increase in the number of children receiving at least one form of advanced imaging was less encouraging from a healthcare value perspective, according to an accompanying editorial by Dr. Alan Schroeder and Dr. Alan Imler of Stanford University in Palo Alto, CA.

Although outcomes appeared to have improved somewhat during the study period, other secular trends -- such as heightened public awareness of concussions -- might also explain those outcomes, wrote Schroeder and Imler. Increased imaging among patients who were ultimately hospitalized also further suggests that the more imaging is not associated with reduced hospitalization. 

USPSTF advises against carotid artery stenosis screening

By Theresa Pablos, AuntMinnie staff writer

August 5, 2020 -- The U.S. Preventive Services Task Force (USPSTF) is poised to once again recommend against screening for asymptomatic carotid artery stenosis. The task force reaffirmed its D rating in a draft recommendation statement published on August 4.

The USPSTF last weighed in on the topic in 2014, concluding with moderate certainty that the harms of screening for carotid artery stenosis in the general population outweighed the benefits. In its new draft recommendation statement, the agency reaffirmed that position, stating there was not enough new evidence to change its previous recommendation against screening with either carotid duplex ultrasound, CT angiography, or MR angiography.

"The USPSTF found no new substantial evidence that could change its recommendation and therefore reaffirms its recommendation," the task force wrote.

In theory, screening the general population for stenosis could lead to early detection of narrowed blood vessels, thus enabling medical professionals to conduct potentially life-saving interventions, such as carotid endarterectomy (CEA) and carotid artery stenting (CAS). But the USPSTF concluded that the evidence it reviewed didn't readily support that hypothesis.

The task force has consistently found limited evidence in favor of asymptomatic carotid artery stenosis screening, especially when compared with other medical therapies, such as statins and antihypertensive agents. And the evidence has been particularly lacking since the USPSTF's last review in 2014.

USPSTF draft recommendation rationale for asymptomatic carotid artery stenosis
Detection	Ultrasonography has reasonable sensitivity and specificity for detecting clinically relevant carotid artery stenosis, but it also yields many false-positive results in the general population.
	Scanning the neck for carotid bruits has poor accuracy for clinically relevant carotid artery stenosis.
Benefits	Direct evidence does not indicate that screening for asymptomatic carotid artery stenosis can improve stroke, mortality, or other adverse health outcomes.
	Carotid endarterectomy (CEA) or carotid artery angioplasty and stenting (CAS) provides little or no benefit for improving stroke, myocardial infarction, mortality, or other adverse outcomes compared with current medical therapy.
Harms	While direct evidence does not show that screening for asymptomatic carotid artery stenosis can cause harm, there are known harms with confirmatory testing and interventions.
	Direct evidence supports that treating asymptomatic patients with CEA or CAS could cause harms, including stroke or death.
	Harms related to screening and treating asymptomatic carotid artery stenosis have small-to-moderate magnitude.

After searching the scientific literature, USPSTF investigators found no recent eligible studies that directly investigated the benefits or harms of asymptomatic carotid artery stenosis screening. The two studies that were conducted on the topic in the past six years were both prematurely terminated and produced mixed results.

When looking at the benefits and harms of CEA or CAS, the authors found an additional two national datasets and three surgical registries that met their inclusion criteria. Rates of 30-day postoperative stroke or death after CEA ranged from 1.4% to 3.5% depending on the registry or database. Similarly, 30-day stroke or death after CAS ranged from 2.6% to 5.1%.

Based on the evidence -- or lack thereof -- the investigators concluded there wasn't enough new information to change the D rating for asymptomatic carotid artery stenosis screening. However, they pointed out that two clinical trials are currently underway, which may shed light on the topic in the future.

"There were few new trials, all with methodologic concerns, examining the important question of the comparative effectiveness and harms of revascularization plus best medical treatment compared with best medical treatment alone," they wrote. "The ongoing CREST-2 and ECST-2 trials will be the largest trials to address this issue."

The draft recommendation is available for public comment through August 31. After the comment period has ended, the task force will publish its final recommendation.

COVID-19 pandemic driving increase in ultrasound use

By Theresa Pablos, AuntMinnie staff writer

August 3, 2020 -- The COVID-19 pandemic is driving an increase in the use of lung ultrasonography among physicians in Italy, according to the results of a small survey published in the Journal of Ultrasound in Medicine.

More physicians said they're using ultrasound equipment now than before the pandemic, and experienced physicians are performing more lung ultrasound scans than ever before. The findings support anecdotal evidence that COVID-19 has increased interest in ultrasound, including among clinicians with no prior ultrasound experience.

"Thanks to online resources, many operators could e-learn and apply the technique," wrote the authors, Dr. Allessandro Zanforlin and Dr. Francesco Tursi, who are both members of the Italian thoracic ultrasound academy behind the survey (July 16, 2020, Journal of Ultrasound in Medicine).

The informal, one-week-long survey was conducted by Italian ultrasound society Academia di Ecografia Thoracia after the group noticed its membership spiked from 1,700 members in February to 4,000 members in May. The academy promoted its survey on social media and received 123 responses.

Survey respondents worked in a variety of settings, including on COVID-19 floors (34%), in intensive care units (31%), and in the emergency department (20%). The majority said they used lung ultrasound to monitor pneumonia (63%) and screen for COVID-19 (60%).

A total of 14% of respondents started using lung ultrasound exclusively because of the COVID-19 pandemic. Among these respondents, 81% said they learned how to perform lung ultrasound scans by following video tutorials or participating in webinars. The remaining 19% of respondents gained experience through expert mentoring or local courses.

As the number of patients with COVID-19 surged at hospitals in Italy, so too did the number of lung ultrasound exams. Respondents said the number of daily chest scans increased from an average of three per day before the pandemic to seven per day during the outbreak. For so-called "expert operators" with at least five years of lung ultrasound experience, the number of exams rose from five per day to nine per day.

The majority of respondents also said their lung ultrasound exams had increased in quality (58%) and accuracy (66%) during the pandemic. These percentages were even higher for participants who took an online course or webinar, with 83% of these respondents saying their exams increased in both quality and accuracy.

One factor driving the increase in lung ultrasound exams could be the availability of additional equipment thanks to donations and emergency purchase approvals. More than half of respondents said they acquired new ultrasound equipment during the pandemic, namely portable wheeled systems (37%) or handheld/wireless systems (19%).

The survey adds to the evidence that ultrasound is becoming an invaluable tool for care teams, especially those in Italy, who are treating patients with the novel coronavirus. However, the increase in skilled operators and new equipment may mean the modality will remain prominent for lung imaging even after the pandemic is over.

"What we are learning from this pandemic is the importance of [lung ultrasound] in the diagnosis, evaluations, and monitoring of pneumonia, which, in the hands of many physicians ... could improve the quality of the treatment of respiratory patients," the authors concluded.

US correlates with COVID-19 severity, duration

By Theresa Pablos, AuntMinnie staff writer

July 28, 2020 -- Findings on lung ultrasound scans were correlated with COVID-19 severity and duration in a study published on July 23 in the American Journal of Roentgenology. In particular, pulmonary consolidations distinguished between patients with moderate and severe forms of the novel coronavirus disease

The study included dozens of patients who were consecutively treated for COVID-19 at a Chinese hospital in March. The findings may aid physicians in managing patients with moderate-to-severe COVID-19, the authors noted.

"Our results indicate that lung [ultrasound] findings can be used to reflect both the infection duration and disease severity," wrote the authors, led by Dr. Yao Zhang from Ditan Hospital in Beijing.

Zhang and colleagues enrolled 28 patients consecutively hospitalized for COVID-19 at their institution between March 1 and March 30. The patients all tested positive for the novel coronavirus on a nasopharyngeal test and underwent a bedside lung ultrasound scan in a sitting, supine, and decubitus position.

Every patient in the study had B-lines on their ultrasound scans, which indicate areas of increased interstitial fluids and decreased alveolar air. Another two-thirds of patients had pulmonary consolidation, and 61% had a thickened pleural line. Only one patient had a pleural effusion.

Pulmonary consolidation occurred significantly more often in patients with severe or critical COVID-19 than patients with moderate disease, the authors found. Almost 87% of patients with severe or critical disease had pulmonary consolidation on ultrasound, compared with just 46% of patients with moderate COVID-19.

(A) Lung ultrasound image obtained with a convex probe. The outer arrows show confluent B-lines. The middle arrowheads point to a thickened pleural line. (B) Lung ultrasound image obtained with a linear probe. The arrow points to a B-line. The star denotes a patchy pulmonary consolidation. (C) Chest CT image showing reticular and interlobular septal thickening and patchy, focal opacities associated with architectural distortion. Image courtesy of the American Journal of Roentgenology.

Furthermore, patients with a thickened pleural line had experienced a longer infection period than those without a thickened pleural line. Patients with fewer than 20 days between the day they first noticed COVID-19 symptoms and the day of their ultrasound scan were significantly less likely to have a thickened pleural line than those with a difference of 20 days or more.

The study findings add to the growing body of research demonstrating that severity on lung ultrasound scans can predict worse outcomes and even mortality for patients with COVID-19. The authors emphasized that ultrasound also has unique benefits over other imaging modalities, including CT, for treating patients with the novel coronavirus.

"[Ultrasound] is repeatable in critically ill patients, which ensures that monitoring of the severity of the disease and the effects of therapies can be easily carried out," they wrote. "This capability is particularly important in situations in which chest CT is not available, such as in isolation wards and [intensive care units]."

The authors cautioned that their study focused on a small number of patients and did not evaluate how ultrasound findings might have changed over time. They hope future studies will continue to study the use of lung ultrasound for COVID-19, particularly how lung ultrasound scoring systems might improve COVID-19 assessment and treatment.

"Lung [ultrasound] was highly sensitive for detecting abnormalities in patients with COVID-19, and B-lines, a thickened pleural line, and pulmonary consolidation were the most commonly observed features," the authors concluded.