A descriptive prospective, cross-sectional study was performed in the ED at Odense University Hospital, Svendborg, Denmark, which has approximately 29,000 visits per year of which around 4100 are triaged as high-acuity patients upon arrival.
Acute admissions in Denmark are to public hospitals via emergency call or referred to by the general practitioner. Selected patients bypass the ED and are transported directly to an expert department (e.g. with signs of acute myocardial infarction, pregnancy or trauma to head, thorax or column).
Initial diagnostic tests ordered for patients admitted to the ED are in general based on symptoms and signs and include blood sample analyses, ECG, microbiological analyses and imaging (e.g. X-ray, CT, MR). Ultrasonography examinations are mainly performed by summoned specialists and are not an integrated part of the initial examination of ED patients [14].
The inclusion took place from December 2013 to March 2016. Included patients constituted a convenience sample; consequently, inclusion only took place immediately after the patients’ arrival to the ED. The investigators were blinded to the patients’ medical history and only aware of the patients’ direct cause of admittance upon inclusion. Patients were included after informed consent by the investigators if they were: (1) acutely admitted to the ED, (2) ≥ 18 years, (3) upon primary assessment they presented with a high-acuity score or systolic blood pressure < 100 mmHg. A high-acuity score was defined as the two highest levels of acuity in our ED triage system based on the patients’ initial clinical scores (e.g. saturation, respiratory rate, heart rate) (Additional file 1: Appendix S1). Exclusion criteria were patients with mental disability or patients unable to sign informed consent.
The included patients constituted a mixture of both surgical and medical etiology with symptoms and signs of various diseases (e.g. respiratory problems, cerebral thrombosis or hip fracture). The investigators performed the wbf-us blinded to the EP and only in his absence. The wbf-us was performed with a Philips CX 50 ultrasound machine (Philips, USA) and consisted of wbf-us of the lungs (Flus), the heart (Fcu), the abdomen (Faus) and the deep veins of the legs (Lcu). The wbf-us was always performed in the same sequence commenced by Flus then Fcu, Faus and Lcu and only aborted or paused on demand of the patient (e.g. due to pain or nausea) or in case of urgent treatment or supplemental analysis (e.g. scans, blood samples). The wbf-us was not completed if not resumed within 1 h and the investigation time was defined as the time spent on the actual ultrasound examination. The time used at wbf-us examination time was measured from the first to the last gaze with the ultrasonography probe. Interruptions were not included.
Wbf-us diagnoses were assessed according to predefined diagnostic criteria (Additional file 2: Appendix S2) and performed according to the following predefined f-us protocols.
Focused lung ultrasonography (Flus): performed with a L12-5 linear array transducer (Philips) (12–5 MHz) or a C5-1 curved array transducer (Philips) (5–1 MHz) using a modification of the principles described by Lichtenstein, Volpicelli and colleagues as described by Laursen et al. [15,16,17]. We looked for pneumothorax, interstitial syndrome and pleural effusion.
Focused cardiac ultrasonography (Fcu): performed with a S5-1 sector transducer (Philips) (5–1 MHz) using the focus assessed transthoracic echocardiography (Fate) protocol [18]. We looked for reduced ejection fraction (EF) and pericardial effusion.
Focused abdominal ultrasonography (Faus): performed with a C5-1 broadband curved array transducer (Philips) (5–1 MHz) using the three abdominal windows from the RUSH protocol and including a transverse and oblique window of the abdominal aorta [7]. We looked for free abdominal fluid and abdominal aorta aneurism.
Limited compression ultrasonography (Lcu): performed with a L12-5 linear array transducer (Philips) (12–5 MHz) or C5-1 curved array transducer (Philips) (5–1 MHz) according to the American College of Emergency Medicine’s imaging criteria compendium [19]. We looked for signs of a deep-vein thrombosis (DVT).
The investigators (ER and MR) had varying experience in wbf-us. Prior to inclusion MR performed: focused lung ultrasonography (Flus) > 80, Focused assessment with transthoracic echocardiography (Fate) > 50, focused assessment with sonography in trauma (Faus) > 40, limited compression ultrasonography (Lcu) > 50. Of these, 25 of each scanning area were supervised and evaluated during a period of f-us certification according to the national guidelines [13]. ER had no prior f-us skills and received an e-learn course of the wbf-us protocol including an oral presentation and hands on training followed by 5–10 supervised examinations until she was capable of performing the wbf-us protocol with an image quality sufficient for diagnostic evaluation (Additional file 2: Appendix S2).
A video clip from each window of the wbf-us examination (e.g. one respiratory cycle from each Flus window, 6 s of the heart from each Fcu projection) was saved to an external hard disc for later expert evaluations. With the exception of wbf-us findings of acute life-threatening conditions all wbf-us results were kept blinded from patients and EPs.
All wbf-us clips were finally assessed by expert physicians with European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) for ultrasonography level 2–3 from specialties of respiratory medicine (Flus), cardiology (Fcu) and radiology (Faus, Lcu). The expert sonographers evaluated the investigators’ wbf-us examinations and assessed the final diagnoses blinded to the investigators’ interpretations and the EPs clinical evaluations.
All results from the wbf-us were compared to gold standard, which was defined as the final diagnoses assessed by blinded clinical audit of the medical record.
The blinded audit was performed according to predefined diagnostic criteria by two auditors who, independently of each other and blinded to all wbf-us clips and the interpretations of these, set the final diagnoses. In case of any discrepancy, a third auditor made the final decision (Additional file 3: Appendix S3).
Analyses
Data were reported as proportions with a 95% confidence interval (CI) based at binominal distribution. Diagnostic performances were established using sensitivity, specificity, positive and negative predictive values (PPV, NPV), their 95% CI and Fleiss kappa coefficients (K) using the results from the blinded medical record audit as gold standard.
Descriptive statistics, describing medical history, medication and vital parameters upon admission were performed. Data analysis was conducted using Stata version 14.0 (Stata Corporation LP®, Texas, USA).
The main analyses were performed by the ‘intention to treat’ principle. Missing data in the basic characteristics were handled by simple imputation: we kept patients with no or incomplete wbf-us in the study. Any cases of image quality inadequate for evaluation were handled as follows: (a) handled as non-pathologic in the analysis of total wbf-us diagnoses, (b) left out in the analysis of diagnostic accuracy and inter-observer agreement.
Ethics
Patients were included after informed consent. Any wbf-us that revealed signs of a predefined acute life-threatening condition was immediately non-blinded to the EP in charge (e.g. pericardial effusion, ejection fraction ≤ 45%, pulmonary edema, massive pleural effusion, pneumothorax, pulmonary emboli or deep-vein thrombosis (DVT). Subsequently, it was up to the clinician to assess whether further action should be taken. The study was undertaken in accordance with the Helsinki Declaration and approved by the Committee on Biomedical Research Ethics for the Region of Southern Denmark (ID S-20130047) and the Danish Data Protection Agency (ID 13/12076).