Abdominal ultrasound in the intensive care unit: a 3-year survey on 400 patients
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- Schacherer, D., Klebl, F., Goetz, D. et al. Intensive Care Med (2007) 33: 841. doi:10.1007/s00134-007-0577-3
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This study analyzed 400 ultrasound examinations in the ICU to assess the indications of this imaging modality.
Design and setting
Retrospective analysis on prospectively collected data on 400 patients in a tertiary care hospital.
Patients and participants
The observational, prospective, clinical study examined 400 bedside abdominal ultrasound examinations performed in the ICU, of which 2% were performed emergently, 56% urgently, and 42% electively.
Measurements and results
Environmental conditions impaired the examination slightly in 54%, moderately in 27%, and severely in 4%. Total time per study ranged from 1 to 45 min (median 10). New pathological findings were detected in 31% while 33% confirmed already known pathologies. In 53% there was no therapeutic consequence, in 27% treatment was continued based on the sonographic findings, in 10% an intervention was necessary, in 6% other therapeutic changes followed, and in 4% additional evaluation was deemed necessary. In 80% no other imaging test had to be performed.
Ultrasound studies are deemed sufficient in a large proportion of patients and help to avoid other, more elaborate imaging studies. However, more focused indications for studies may help to improve cost-effectiveness.
The indications for abdominal ultrasound in ICU patients include bedside diagnosis of common disorders of various organs or anatomical sites such as liver, gallbladder, bile ducts, pancreas, kidney, spleen, pleural space, and vessels. In ICU patients presenting with acute abdominal symptoms sonography has shown sensitivity for the final diagnosis of 88.8%, specificity of 76.3%, and accuracy of 83.7% . Use of ultrasonography may be limited by cost and by availability of the equipment and physicians, for each of which factors there is a specific learning curve. The aim of this observational study was to assess the circumstances and the diagnostic and therapeutic impact of ultrasound examinations in the ICU.
Materials and methods
Patients and study design
The study enrolled 400 patients treated either in the medical, surgical, or anesthesiological intensive care unit of the University Hospital Regensburg, Germany, between August 2001 and November 2002 and between August 2004 and February 2005. An observational, prospective, clinical study evaluated the abdominal sonographic examinations of these patients. The study was approved by the ethics committee of the University of Regensburg. A documentation sheet was completed for each examination, including epidemiological data, clinical data (e. g., type of ventilation, treatment with catecholamines, and infection/colonization with multiresistant bacteria), and parameters of the sonographic examination, including patient-related conditions (e. g., adipositas, excessive digestive gas, loss of consciousness or necessity for banding), environment-related conditions (e. g., brightness of the room, space around the patient, noise, isolation), duration of the examination, and quality of the scan as judged by the examiner. Duration of the examination included the scanning time itself, the time needed for transporting and preparing the ultrasound machine, time for positioning the patient, and time for writing the final report. Twenty-eight examiners who had passed an internal qualifying test, and had performed at least 400 abdominal sonographies prior to the study were involved.
One of the following machines were used: Sonoline Sienna (Siemens, Erlangen, Germany), Logiq 400 CL (GE Medical Systems, Wisconsin, USA) or Titan SonoSite (SonoSite, Bothell, USA).
Values are reported as mean, median, SD, minimum and maximum as required, and were calculated using version 12 of SPSS (SPSS for Windows, Chicago, Ill., USA).
Reasons for the examination
Conditions of the sonographic examination
In 248 cases (62.0%), patient-related conditions (e. g., adipositas, digestive gas, bandages) were described as “good” or “slightly impaired”, in 85 (21.3%) as “moderately impaired”, and in 67 (16.8%) as “strongly impaired”. Concerning environment-related limitations (e. g., brightness, shortage of space), most of the examinations were carried out under “slightly impaired” (n = 217, 54.3%) or “moderately impaired” (n = 107, 26.8%) conditions. In only 62 cases (15.5%) were environmental conditions labeled as “good” and in 14 (3.5%) as “strongly impaired”.
Duration of the examination
Examination time ranged from 4 to 75 min (median 18.5). When assessed at 5-min intervals, the examinations most frequently took 11–15 min (n = 126, 31.5%) or 16–20 min (n = 102, 25.5%). The scanning time itself ranged between 1 and 45 min (median 10).
Quality of the examination and its results (Table 1)
Quality of the sonographic examinations and environmental limitations (n = 400)
Quality of the sonographic examination
Limited or poor quality
No answer possible
Patient related limitations of sonography
Good or slightly impaired
Environmental related limitations
Good or slightly impaired
Consequences of the sonographic examination
In 22 cases (5.5%) immediate consequences followed the findings of sonographic examinations: urgent further diagnostic procedures in 6, surgical interventions in 9, and urgent modification of medical therapy in 7. The sonographic examination also affected further treatment in many more cases: in 109 cases (27.3%) findings affirmed the current therapy, in 63 (15.8%) therapeutic changes or interventions were necessary, and in 17 (4.3%) treatment was affected after further diagnostic investigations, surgical assessment, or control scans. In 198 patients (52.8%), the scan had no further impact on treatment, but may have reassured the treating physicians.
In 318 patients (79.5%) sonographic results were deemed sufficient, and no further imaging procedure was necessary. In 28 (7%) sonography described pathological findings with the need of further imaging modalities. In 32 patients (8%) another imaging test was planned at the same time or prior to sonography, and in 3 (0.8%) another imaging test was performed between ordering the sonographic examination and obtaining its results.
When scans with a focused indication were compared to requests for complete abdominal scans, there was no clear difference regarding therapeutic consequences. However, the necessity of further imaging studies differed significantly (p = 0.036, Pearson's χ2 test).
Use of mechanical ventilation has increased in recent years and constitutes a major therapeutic modality in the ICU. As the transfer of the critically ill patient is itself potentially dangerous, sonographic examinations as bedside tests are frequently performed in the ICU. The aim of this study was to analyze sonographic examinations in the ICU in an everyday setting which includes the use of various machines according to availability. Portable ultrasound machines are surprisingly effective in the hands of experienced examiners [2, 3]. The frequency of 55% mechanically ventilated patients in our study population is comparable to data in the literature . Multiresistant bacteria, especially infections/colonizations caused by methicillin-resistant Staphylococcus aureus, are a growing problem leading to prophylactic isolation of patients [5–7]. The performance of imaging modalities with a need for transportation such as computed tomography, magnetic resonance tomography, and angiography is more awkward in these patients.
A limitation of the study is that we may have missed examinations. Some intensivists carry out sonographic studies themselves. We included only patients for whom an abdominal ultrasound was requested from the inter disciplinary Department of Sonography , which is responsible for all abdominal ultrasound examinations in our hospital. The impact of this bias is hard to judge. Diagnostic (and interventional) ultrasound requires training, skill, knowledge, experience, and continued quality assurance. In our study several examiners were involved. All of them had fair sonographic skills. It is possible that extensively trained and highly skilled sonographers would have reached better results, but this was not the question of our study. The inclusion of a broad spectrum of trained examiners more closely resembles the situation in everyday practice. To our knowledge, there is no published report on patient- or environment-related limitations of sonography on the ICU. Surprisingly, patient-related limitations were described as “good” to “moderately impaired” in most patients and as “strongly impaired” in fewer than one-fifth. Regarding environment-related limitations, almost all examination conditions were described as “good” or only “moderately impaired”.
A median duration of 18.5 min for the overall examination and of 10 min for the scan itself seems justifiable considering that there have been few particularly long examinations (e. g., one intervention), and hygienic measures in isolated patients. Fischer et al.  also stated that their median examination time of 16 ± 4 min was affected particularly by the time required for switching on and initializing the ultrasound device and that for positioning at the bedside. Although the conditions for sonography are at least moderately limited in approx. every third ICU patient (mechanical ventilations plays a major role in this context), the quality of our examinations were described as not limited in 50% of patients. In only 1.5% was the question of interest not answered. The direct impact on immediate patient management in our study was comparable to that in a similar study by Lichtenstein et al.  in which ultrasound findings affected the diagnosis and work-up of ICU patients and had a direct impact on the therapeutic plan in 33 of 150 patients (22%). Sonography is certainly not able to diagnose all abdominal pathologies . In our study population four of five patients needed no further abdominal imaging procedures. This proportion seems high, since it means that it had been possible in many cases to avoid other more expensive and potentially more risky imaging examinations.
In summary, the examination conditions for abdominal ultrasound on the ICU are judged surprisingly positive by examiners. Sonography in many cases is sufficient to answer the questions of interest. In about one-half of cases examinations had no effect on further therapeutic decisions but potentially reassured current treatment. Ultrasonography was described as underutilized in the 1980s , and in our opinion it should be more liberally performed in patients admitted to the ICU when there is need for an abdominal imaging modality.