Study design and setting
This is a prospective observational study examining the use of thoracic POCUS in adult patients on the general ward treated by the MET. The Modified Early Warning Score (MEWS) was used to assess the need for MET assistance (figure of MEWS score in Additional file 1).
The study (METUS NL61884.091.17) was approved by the local ethical committee and conducted in a Dutch 750 bed teaching hospital (Rijnstate Hospital, Arnhem) from January 18, 2019 until February 1, 2020. The study was registered at ClinicalTrials.gov. (NCT03214809).
Characteristics of participants
All patients 18 years and older in all regular hospital wards in need of a MET call were included.
Exclusion criteria were:
Acute illness requiring direct lifesaving intervention (e.g., intubation, cardiopulmonary resuscitation).
Glasgow Coma Score < 9 or a decline of the Glasgow Coma Score ≥ 2 as the primary reason for MET attendance.
Patients consent was obtained directly after the MET call; in case of an incapacitated patient, the next of kin was contacted. Deferred consent was also permitted.
MET team staffing
The ICU of Rijnstate Hospital runs a MET since 1996. The MET is staffed by 2 intensive care nurses and 1 ICU resident physician. Board certified intensivists are available within 15 min. The ICU of Rijnstate Hospital uses POCUS since 2009. ICU residents are trained in basic POCUS shortly before ICU rotation. The training program consists of 4 training days in basic cardiac, lung and abdominal ultrasound, POCUS is part of daily care .
Our cardiac POCUS protocol consists of 5 straightforward questions combined with a simple qualitative interpretation. Standard transthoracic windows using only 2D-ultrasound were used .
The following questions were answered:
Is the left ventricle dilated?—yes/no/don’t know. Is the left ventricle function hyperdynamic/normal/moderately decreased/severely decreased/don’t know?
Is the right ventricle dilated?—yes/no/don’t know
Is the right ventricle function normal/abnormal/don’t know?
Is pericardial effusion present?—yes/no/don’t know
Is pericardial tamponade present?—yes/no/don’t know
From the subcostal view the inferior vena cava (IVC) was identified. The IVC was measured and categorized:
Collapsed: < 1.5 cm.
Normal: 1.5–2.5 cm.
Dilated: > 2.5 cm.
Lung ultrasound was used according to the Blue protocol by Lichtenstein  with the following diagnostic profiles:
A-profile: normal lung.
A/A’-profile (one sided): suspect pneumothorax, atelectasis, pleurodesis, pneumonectomy.
B-profile: (both sides) suspect pulmonary edema, acute respiratory distress syndrome (ARDS).
A/B-profile (one sided B-lines): suspect pneumonia.
C-profile (consolidation): suspect pneumonia, atelectasis or compression.
The MET physicians started with cardiac POCUS in case of primary hemodynamic problems and with the Blue protocol of the lungs in case of primary pulmonary problems.
We used a hand held ultrasound device (Philips Lumify® S4-1) connected to an Android tablet attached to the MET cart. The LumifyR S4-1 is a phased array transducer with software for cardiac and lung ultrasound exams.
Eligible patients were included consecutively: in even weeks the POCUS protocol was used (US+), in odd weeks standard care without the use of POCUS (US−) was deployed.
After the initial assessment, a diagnosis was registered by the MET physician.
In the US+ weeks, a second diagnosis was registered after subsequent use of the POCUS protocol. The attending MET physician could decide to use POCUS in the US- weeks after an initial diagnosis was made. This deviation of protocol was registered and, in these cases, also a second diagnosis (after the use of POCUS) was noted.
All diagnoses were recorded in a case research form (CRF).
An experienced intensive care consultant and member of the hospital mortality committee (independent expert) conducted a full chart review (electronical medical record, HIX®) on all enrolled patients to determine a definite diagnosis 2 weeks after inclusion. The independent expert was unaware of the ultrasound findings (recorded in a separate CRF), the initial diagnosis made by the attending MET physician and he had no other role in the study. After evaluation by the independent expert, the MET diagnosis was rated as completely correct or completely incorrect. In case of multiple definite diagnosis made by the independent expert (for instance, acute heart failure and COPD), the MET diagnosis could also be rated partially correct if not all elements of the definite diagnosis were recorded in the CRF.
Diagnostic certainty was scored on a visual analogue scale of 0 (no clue) to 10 (absolute certain). The 10 point VAS scale was used because all other clinical scoring in our hospital is done with the 10 points VAS score (for instance pain). Other scales like the 5-point Likert scale would be novel for our physicians to use thereby possibly clouding the results. Ten point VAS scores have been used in other studies before in certainty assessment . In the US+ weeks the MET physician rated certainty before and after the use of POCUS. In the US− weeks certainty was scored without the use of POCUS and in case of protocol deviation also after the use of POCUS.
We also registered the reason the MET was called, baseline demographics (age, gender, previous medical history, weight and height), clinical and laboratory parameters (heart rate, blood pressure, temperature, serum lactate and white blood cell count) and 28-day mortality.
The MET physicians were asked to rate the quality of the POCUS studies (good, moderate, bad) and were encouraged to capture the POCUS studies for review. Two investigators (FHB and MJB) checked the stored studies.
The primary outcome measure was the percentage of correct diagnoses made by the MET physician in the US+ and US− weeks. The second diagnosis after the use of POCUS in the US+ weeks and the initial diagnosis in the US− weeks without the use of POCUS were compared to the final diagnosis made by the independent expert.
Secondary outcome measures were a change in diagnosis after the use of POCUS in the US+ group and (after protocol deviation) in the US− group, percentage of correct diagnosis in the US− group after the use of POCUS, the change in diagnostic certainty before and after the use of POCUS and 28-day mortality. The MET physician also noted first treatment (intravenous fluids, diuretics, vasopressors/inotropes, anti-coagulants, anti-arrhythmic drugs, vasodilators, morphine/sedatives, intubation or non-invasive ventilation, O2 supply, or other treatments and the need for supervisor attendance).
Descriptive statistics are presented as mean with standard deviation for normally distributed continuous data, median and inter-quartile range (IQR) for skewed continuous variables and as numbers and percentages for dichotomous and categorical variables. Differences between groups (US+ group and US− group) were tested using the Pearson Chi-square test, Fisher exact and Students’ T test. In case of not normally distributed variables, differences between groups were tested using the Mann–Whitney U test. Changes within groups were tested using the Wilcoxon signed rank test and the McNemar–Bowker test. Statistical analysis was done using SPSS® software (version 25). Sample size was estimated to detect an increase in the number of correct diagnosis of 30% (α = 0.05 and β = 0.20). Based on Jones et al.  we estimated that a total of 76 patients should be enrolled (38 patients per group). Because few data exist on the use of POCUS during MET calls we decided to include 100 patients in total.