Ultrasound in intensive care unit patients: applications, observations, and comparison of two established ultrasound methods

Sonography is the primary imaging modality for a wide variety of medical conditions and is routinely used, primarily in internal medicine, but also in other specialties (e.g., surgery, gynecology, and urology)^(1,2,3,4,5).

In patients in the intensive care unit (ICU), sonography is typically performed in response to specific symptoms and with a targeted question. Common indications include the search for the cause of circulatory arrest, hemodynamic instability, and dyspnea^(6,7,8,9,10). In addition, the placement of central venous catheters and the puncture of pleural effusions or ascites are routinely performed under ultrasound guidance as a standard procedure, which reduces the risk of complications^(11,12).

A study in geriatric patients demonstrated that conventional abdominal ultrasonography, when performed as a standard procedure, provides diagnostically and therapeutically relevant additional information⁽¹³⁾. Whether standard, symptom-independent abdominal ultrasonography is of additional value requires further investigation^(14,15).

Due to the advancement of ultrasound technology, including the development of small portable devices, bedside ultrasound examination is nowadays easily available and complements the physical examination. During the classic physical examination, including auscultation, cardiopulmonary pathologies − such as pericardial effusion, pleural effusion, or reduced systolic pumping capacity of the heart − can often be overlooked. Point-of-care sonography can be used to diagnose such pathologies^(16,17). The European Ultrasound Society (EFSUMB) recommends the use of portable or hand-held ultrasound devices (HHUSD)⁽¹⁸⁾ in specific clinical situations for targeted questions that can be answered “yes” or “no”^(19–20). These include the assessment of free intra-abdominal fluid, pleural or pericardial effusion, aortic aneurysm, urinary retention, hydronephrosis, dilated bile ducts, space-occupying lesions correlating with palpable resistance, spleen size, and large gallbladder stones. In addition, imaging of fluid collections prior to punctures with HHUSD is recommended, as is positional control of urinary bladder catheters when appropriate⁽²¹⁾.

Understanding the performance of portable ultrasound devices would be of interest, since in comparison to high-end US devices they are cheaper and better suited for use in space-limited environments.

The aim of this study was to investigate the usefulness of routinely performed conventional abdominal ultrasonography in ICU patients and to examine whether it provides diagnostically or therapeutically relevant additional information. The consequences of such findings included further imaging or endoscopic examination, respectively, a change in medication or interventional therapeutic measures. Furthermore, the study sought to assess whether there are significant differences between a conventional ultrasound scanner and a portable ultrasound scanner in the detection of pathological findings.

The purpose of this study was to evaluate the utility of conventional abdominal ultrasonography in ICU patients and to determine whether there are significant differences between the HHUSD and HEUS in the detection of pathological findings.

Of the 120 patients investigated, 109 (90.8%) were systematically examined without any specific diagnostic questions. Based on the results of the study presented here, abdominal sonography performed as a standard procedure in ICU patients appears justified, as it yielded diagnostically relevant findings in 13/120 (10.8%) patients and therapeutically relevant findings in 38/120 (31.7%). In addition to findings that directly led to a change in intensive care management (e.g., dilatation of the vena cava), the standard sonographic examination also revealed prognostically relevant findings that may influence decisions regarding escalation or limitation of therapy in intensive care settings. For example, the detection of a metastasized tumor with an unfavorable prognosis may be decisive for determining a limitation of intensive care measures in accordance with the patient’s wishes (e.g., refraining from resuscitation in case of cardiovascular arrest)^(24,25). Of course, the patient’s comorbidities, general condition, and the severity of the intensive care disease are also important factors.

The number of therapeutically relevant findings obtained in this study is consistent with the data in the available literature. In the study by Schacherer et al.⁽¹²⁾, a total of 400 patients in an internal medicine or surgical intensive care unit underwent abdominal ultrasonography. In 116/400 (29.0%) patients, sonography was performed as a screening procedure without any specific diagnostic question. In 79/400 (19.8%) patients, a therapeutically relevant finding was detected. Lichtenstein et al.⁽²⁶⁾ reported therapeutically relevant findings in 33/150 (22.0%) patients in the ICU by performing abdominal ultrasonography as a standard procedure.

Further diagnostic workup was undertaken in the following cases: 3/120 patients (2.5%) with focal renal lesions, 3/120 (2.5%) with focal liver lesions, 1/120 (0.8%) with an echoic splenic lesion, 1/120 (0.8%) with a solid pancreatic mass, 1/120 (0.8%) with a cystic pancreatic lesion, 2/120 (1.7%) with prostatic enlargement, and 2/120 (1.7%) with urinary retention. In three cases, further workup revealed a malignancy requiring treatment that might have been missed without the routine use of ultrasonography. Focal organ lesions are often detected as incidental findings on imaging (e.g., sonography or computed tomography). Kelly et al.⁽²⁷⁾ examined incidental findings noted on computed tomography in 1155 patients presenting to the emergency department with abdominal complaints. Among the 700 incidental findings, 24 were ultimately diagnosed as malignancies. Of the 24 patients with malignancy, six had localized tumor disease that was potentially curable.

Among the therapeutically relevant findings, dilatation of the vena cava was the most frequent (Fig. 1). This led to a change in volume management in 21 patients. In intensive care medicine, the diameter and respiratory-related caliber variation of the vena cava are specifically determined in hemodynamically unstable patients to assess volume status⁽²⁸⁾. In addition, 11/120 (9.2%) patients with urinary retention received a transurethral bladder catheter and 6/120 (5.0%) patients with large pleural effusions underwent pleural puncture.

Fig. 1.

Sonographic image of a large left-sided pleural effusion captured with the Youkey Q7. The patient received therapeutic pleural drainage

In the present study, the diagnostic accuracy of portable ultrasound devices with respect to all abdominal pathologies identified with the HEUS was 78.1%, which is within an acceptable range. In their work on geriatric patients, Fröhlich et al.⁽¹³⁾ demonstrated a higher sensitivity of 89.5% using the HHUSD. Wastl et al. ^(29,30) investigated the utility of the HHUSD in the emergency medical setting in patients who required abdominal ultrasonography for various reasons in a blinded study. They were able to reliably visualize gallbladder stones (sensitivity 83.3%, specificity 89.5%), gallbladder sludge (sensitivity 100%, specificity 96.9%), signs of ileus (sensitivity 87.5%, specificity 60.0%), ascites (sensitivity 88.9%, specificity 93.1%), and pleural effusions (sensitivity 85.7%, specificity 100%) compared with the HEUS using a portable ultrasound device.

Among the false-negative findings, four were diagnostically significant: two lesions of the kidney, one lesion of the liver, and one case of urinary stasis kidney. Further workup resulted in the diagnosis of two renal parenchymal humps and a hemangioma; with regard to the urinary stasis kidney, an outpatient urological evaluation was recommended after CT showed no evidence of urolithiasis or urogenital tumor. No therapeutically relevant findings were missed with the HHUSD. In the present study, the HEUS and HHUSD showed very good agreement in demonstrating increased echogenicity of liver tissue (κ = 0.83) and ascites (κ = 0.83), and good agreement in identifying a dilated vena cava (κ = 0.77) and urinary retention (κ = 0.79). Other authors also demonstrated that certain clinical questions can be reliably answered with HHUSD^(13,31–33). In their study, Dalen et al.⁽³³⁾ reviewed the accuracy of a portable ultrasound device in determining the diameter of the vena cava compared with a high-resolution device. The examination with the portable device was performed by nurses who had received prior training, while the examination with the high-resolution device was conducted by cardiologists. This showed good agreement between the HHUSD and HEUS. In contrast, Wastl et al.⁽²⁹⁾ did not find a strong correlation between the diameters of the vena cava determined with the HEUS and HHUSD. Moreover, due to the low specificity of the HHUSD in assessing respiratory variability of the vena cava, the authors concluded that the HHUSD is not suitable for checking volume status. Kameda et al.⁽³¹⁾ examined the kidneys of 100 patients for the presence of urinary retention using both HEUS and HHUSD. The examination with the portable device was sufficiently sensitive enough to reliably exclude urinary retention. In studies of trauma patients, the sensitivity of portable ultrasound devices in detecting free intraperitoneal fluid was investigated^(34,35). The authors found a sensitivity range of 77% to 88.9%. According to Kirkpatrick et al.⁽³⁴⁾, in 3.8% of patients an injury requiring intervention was missed that was not associated with free intraperitoneal fluid. They concluded that HHUSD examinations cannot replace computed tomography as the gold standard.

Only 33/52 (63.5%) focal intra-abdominal lesions were detected with the Youkey Q7 (Fig. 2). With the exception of the pancreas, there were significant differences between the HEUS and HHUSD in the detection of focal organ lesions. Although further analysis of the false-negative diagnostic findings did not reveal evidence of malignancy, abdominal ultrasonography with HEUS cannot be replaced by HHUSD for the search of focal intra-abdominal lesions. In contrast to our results, Barreiros et al.⁽³²⁾ visualized 162/167 (97.0%) focal lesions using HHUSD compared with HEUS as the gold standard.

Fig. 2.

Sonographic image of a vena cava dilated to 27 mm obtained using the Youkey Q7. The patient’s diuretic therapy was intensified

In detecting thoracic pathology, HHUSD showed a sensitivity of 84.6% compared with HEUS (Fig. 3). Among the false-negative findings, none were diagnostically or therapeutically significant. HEUS and HHUSD showed very good agreement in detecting pericardial effusion (κ = 0.92) as well as right (κ = 0.90) and left pleural effusion (κ = 0.94). HHUSDs are also useful for visualizing pericardial and pleural effusion in emergency medical settings^(29,30). In addition, Wastl et al.⁽³⁰⁾ showed that HHUSD is not inferior to HEUS in detecting reduced ejection fraction, wall motion abnormalities, and right heart strain. Further studies proved that pericardial and pleural effusions can be reliably diagnosed using HHUSD^(36–38). In the study by Graven et al.⁽³⁸⁾, the examinations were performed by inexperienced nurses who had completed a training period under the supervision of an experienced cardiologist before the start of the study.

Fig 3.

Sonographic image of a right-sided renal cyst visualized with the Youkey Q7

With regard to the questions recommended by the EFSUMB that can be answered with HHUSD⁽¹⁹⁾, our findings show that the portable ultrasound device is suitable for answering the following: the presence of pleural effusion (sensitivity: right 86.2% and left 90.9%, specificity: right 100% and left 97.8%), pericardial effusion (sensitivity 85.7% and specificity 97.4%) and urinary retention (sensitivity and specificity 100%). Sensitivity for aortic aneurysm detection was 100%, but only one case was diagnosed. In contrast, HHUSD is not suitable for the detection of gallbladder stones (sensitivity 75.0%, specificity 98.2%), dilated bile ducts (sensitivity 50.0%, specificity 99.2%), or hydronephrosis (sensitivity 50.0%, specificity 100%). Sensitivity for detecting free intra-abdominal fluid was only 72.7%, but all cases involved non-puncture-worthy fluid collections. For larger amounts of ascites, some of which required puncture, the portable ultrasound machine had a sensitivity of 95.8% in the study by Keil-Rios et al.⁽³⁹⁾.

As a secondary criterion of the study, the duration of the investigation was determined for the HHUSD and HEUS in 46/120 patients. The average time was 3.18 minutes longer with the HHUSD. Similarly, in the work of Stock et al.⁽⁴⁰⁾, the time was longer on average with the HHUSD. However, the total examination time, which also took into account the transfer time of the device and start-up duration, was shorter with the HHUSD. Fischer et al. ⁽⁴¹⁾ compared the examination time of HHUSD and portable HEUS in the context of bedside ultrasound. The examination time with the portable ultrasound unit was significantly shorter at 15 ± 3 minutes (HEUS: 22 ± 4 minutes). The time advantage resulted from a shorter duration for start-up and transport of the ultrasound unit. The pure sonication time was not significantly different between the two devices.

This study has several limitations. It was designed to evaluate the benefit of routinely performed, symptom-independent abdominal ultrasonography in ICU patients. In the course of the study, 11 of 120 patients (corresponding to 9.2%) were examined with a targeted question due to gastrointestinal complaints or abnormal laboratory values, potentially influencing the results of the examination.

The study was conducted in a monocentric manner at an internal medicine intensive care unit in a hospital in central Germany. External validity is limited due to the specific internal medicine patient population, as well as the demographic and ethnic composition of the rural catchment area. Thus, the results cannot be directly generalized to intensive care patients in other hospitals. Further multicenter studies are needed for this purpose.

The study design is also a limiting factor. During patient recruitment, some selection is likely due to the dual role of the recruiter and investigator. Because patients were examined by only one investigator, no statement can be made regarding interobserver variability.

The poorer detection rate of thoracoabdominal pathologies in this study, compared with the above-mentioned comparative studies, can be attributed mainly to the examiner’s limited experience. An experienced examiner might have detected a greater number of pathological findings with the HHUSD.

Within the study, the differences in detection rates between the two modalities can also be explained by the better spatial resolution of the HEUS, which makes it easier to identify patterns in B-mode imaging, especially for novices. The results suggest a better detection rate for pathologies that require high resolution for accurate detection (e.g., DHC enlargement, focal lesions of parenchymal organs in the abdomen). Conversely, there is strong agreement between the HEUS and HHUSD in the identification of conditions that are easy to recognize even with lower resolution (e.g., urinary retention, dilated vena cava). As an important prerequisite, image quality was comparable in both modalities, with slightly better performance in HEUS examinations.

The study did not provide sufficient evidence of a time advantage associated with the use of portable ultrasound devices. This is primarily due to the study design and the documentation of the study time in only about 40% of cases. To assess the potential benefit of portable ultrasound devices in the intensive care setting, time and cost efficiency are important parameters in addition to diagnostic yield. This should be further investigated in future studies.

Since the present study was conducted in 2019, it is possible that technical advancements in HHUSD may lead to an underestimation of its current potential. While HEUS has also seen improvements, the rate of advancement is likely not as substantial.

Both examinations were performed by the same examiner with limited experience and under suboptimal examination conditions, which reflects typical real-world circumstances in an ICU, especially for the HHUSD. Using this strategy likely enhanced comparability, as using different investigators with varying skill levels could have introduced additional variability.

The investigator was a resident without specialist training, which possibly reflects again the real-world situation in an ICU. If an experienced investigator had performed the examinations, both machines would not have been comparable.

The aim of this study was to assess whether HHUSD findings could be improved by HEUS, thus allowing to estimate in real-world situations if HEUS is necessary after HHUSD in an ICU or emergency unit. In daily practice, one would not evaluate performing HHUSD after HEUS. If HEUS and HHUSD were regarded as equivalent methods, randomizing their sequence would be appropriate.

No definitive conclusions can be drawn from this study about the prognostic relevance of symptom-independent sonography in patients in the intensive care unit. Further prospective studies with a control group without sonography, as well as a follow-up period, are necessary to provide more robust data in this regard.

Based on the results of the study presented here, standard ultrasound examination in ICU patients appears justified, as diagnostic findings were detected in 13/120 (10.8%) and therapeutically relevant findings in 38/120 (31.7%) patients. Dilatation of the vena cava was the most common therapeutically relevant finding, which could also be reliably detected with the HHUSD. Routine abdominal ultrasonography detected pathological findings that would have been missed if only symptom-based focused sonography was performed.

With the HHUSD, only 33/52 (63.5%) focal intra-abdominal lesions were detected. Among the false-negative findings, four were diagnostically significant: one lesion of the liver, two lesions of the kidney, and one case of urinary stasis kidney. No therapeutically relevant findings were missed with the HHUSD. The use of HHUSDs is appropriate for the clarification of the following yes or no questions: dilatation of the vena cava, presence of urinary retention, prostatic enlargement, pleural or pericardial effusion, and signs of ileus. Contrary to the recommendations of the EFSUMB⁽¹⁹⁾, based on the present findings, the question of dilated bile ducts, gallbladder stones, or hydronephrosis cannot be answered reliably enough with HHUSDs. Furthermore, HHUSDs are not appropriate for the detection of focal lesions. Although no significant difference was found between the HEUS and HHUSD in detecting focal pancreatic lesions, HHUSDs should not be used for addressing this question because of the small number of pancreatic lesions detected. Thus, HEUS examinations cannot be replaced completely by HHUSDs; however, if HEUS is not available, HHUSD is a viable − though not equivalent − alternative. The presence of symptoms could lead to the decision whether HEUS is necessary, as outlined in Tab. 1.

The advantage of HHUSD concerning space requirement and quick availability is currently partially tempered by problems concerning documentation and examination settings.

Routine, symptom-independent abdominal ultrasonography provided diagnostic and therapeutically relevant findings, as well as prognostically relevant additional information. In the case of incurable metastatic disease, for example, escalations of intensive care treatment (e.g., resuscitation or invasive ventilation) should be critically considered. Beyond a patient’s general condition and the severity of the primary illness, these additional sonographic insights provide a valuable foundation for determining appropriate therapy limitations. Based on the findings of this study, it is to be concluded that patients in an internal medicine intensive care unit should receive timely abdominal ultrasonography regardless of the presence of symptoms in order to make diagnostic, therapeutic, and prognostic decisions. Abdominal ultrasonography can also be performed with HHUSDs if the general time pressure of an intensive care unit makes it necessary.