Abstract
Introduction
It has been shown that general intensive care nurses are able to perform an examination of the deep venous system of the lower extremities for the diagnosis of proximal deep vein thrombosis (DVT) using a compression ultrasound test with a high degree of reliability. (Skulec et al. in Eur J Intern Med 76:130–131, 2020) Another challenge for the use of vascular point-of-care ultrasound in intensive care is the diagnosis of central venous catheter-related thrombosis. It is a common problem that is often underdiagnosed. Due to the simplicity of the examination and the possible link with nursing care of inserted central venous catheters, this may be another potential diagnostic competency for critical care nurses.
Methodology
Before the start of the study, each nurse participating in the study completed a two-hour training in duplex ultrasonography and examined 5 patients under supervision. Then patients in the intensive care unit (ICU) included in the study, underwent a duplex ultrasound performed by a nurse. Within 24 h, the examination was repeated by the ICU doctor. In the case of catheter insertion into the internal jugular vein (VJI) or the subclavian vein (VSC), the jugular vein, subclavian vein, and axillary vein (VA) were examined bilaterally. When the catheter was inserted into the femoral vein (VF), the patients were subjected to a duplex ultrasound of the femoral vein and the popliteal vein (VP) of both lower limbs. The examination results of each patient were blinded until both tests were performed. Calculations were used to evaluate the reliability of the test.
Result
A total of 160 patients aged 62.9 ± 12.3 years were included. In our sample, the prevalence of CRT was found to be 41%. The overall sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of examinations performed by general intensive care nurses were 90.8%, 97.1%, 91.8%, 96.8%, and 95.5%, respectively.
Conclusion
The results of our study suggest that general ICU nurses are able to perform inpatient CRT duplex ultrasound with excellent specificity but only moderate sensitivity after a short, predefined training.
Keywords: Duplex ultrasonography (DUS), Catheter thrombosis (CRT), General nurse
Introduction
Central venous catheter-related thrombosis (CRT) is a typical complication associated with inserted central venous catheter. It is defined as the occurrence of a thrombus in a vein with an indwelling catheter. Any inserted catheter represents a risk factor for the development of thrombosis. Traditionally, the incidence of CRT is reported in a broad range of 3–70% [6]. This heterogeneity is mainly due to different CRT definitions, different methods for diagnosing CRT and different target population evaluated in the studies [2, 5, 6, 16]. In critically ill patients, CRT is usually asymptomatic and usually manifests only as central venous catheter dysfunction [2, 7]. The first choice diagnostic method for finding CRT is duplex ultrasound (DUS) It is a simple, inexpensive and non-invasive examination. It can be performed at the bedside with the sensitivity and specificity more than 90% [2, 3]. It has previously been shown that general intensive care nurses are able to perform the examination of deep vein thrombosis using a compression ultrasound test with a high degree of reliability [11]. Due to the simplicity of the examination and the possible link with nursing care of inserted central venous catheters, DUS for CRT may be another potential diagnostic competency for critical care nurses. Therefore, we conducted a prospective observational study to compare the diagnostic reliability of DUS in the diagnosis of CRT performed by general nurses in the ICU setting with the examination performed by an intensive care physician experienced in DUS.
Methodology
We conducted a single centre prospective observational clinical study of adult patients hospitalized in the ICU. The study was approved by the Ethics Committee of Krajska zdravotni a.s., Masaryk Hospital (reference code 258/40). The study was conducted in accordance with the Declaration of Helsinki and good clinical practice. Informed consent was not required as this was a non-invasive observational clinical trial. The study has been preregistered and assigned by trial registration number NCT03924583.
All patients included in this study were hospitalized in the intensive care unit of the Department of Anesthesiology, Perioperative and Intensive Medicine, Masaryk Hospital in Ústí nad Labem, Czech Republic. They were included from November 2019 to March 2020. The inclusion criteria were a patient older than 18 years, hospitalized in the ICU, a central venous catheter (CVC) in the upper or lower vena cava basin inserted for more than 48 h. Exclusion criteria were as follows: age under 18 years, local finding preventing examination (e.g., subcutaneous emphysema).
The reference examinations were performed by 3 intensivists, experienced in point-of-care ultrasonographic vascular examination, each with of more than 100 DUS examinations prior to the beginning of the study. The study examinations were performed by 3 general intensive care nurses, without previous experience with DUS examination. Before the beginning of the study, each of them completed 2 h of practical examination training and then performed 5 separate examinations under supervision.
Protocol and intervention
Patients meeting the inclusion and exclusion criteria were included to the study. Thromboprophylactic measures were practiced in all patients according to the latest guidelines. The general intensive care nurse performed a duplex ultrasound examination of patient's entire vena cava basin, where the CVC was inserted. In the case of a CVC in vena jugularis interna or vena subclavia, an examination of the jugular, subclavian and axillary vein bilaterally was performed. In case of insertion of the CVC in femoral vein, the investigator performed a DUS examination of the femoral and popliteal vein bilaterally. All findings were recorded into the written protocol. Not later than 24 h from this investigation, an intensive care physician performed the reference examination to the same extent and recorded the findings in the separate protocol. The results of both DUS examinations were blinded until the complete examination was performed. Only in the case of a positive finding, the attending physician was immediately informed by the nurse and the patient was treated according to the recent guidelines. In all enrolled patients, basic demographic data, medical history and the data characterizing their current critical illness were recorded from standard medical records.
Duplex ultrasound examination
All examinations were performed with a Vivid S6 ultrasound machine (GE Healthcare, Chicago, Illinois, USA) using a high-frequency linear probe. The probe was set to a frequency of 5.0–7.0 MHz and a viewing depth of 4 cm. Each vessel was examined using duplex ultrasonography—a compression test was performed in B-mode followed by Doppler flow imaging. During the compression test, such pressure was applied that caused complete collapse of the vein or partial compression of the adjacent artery. The sequence of compressions was done in centimeter intervals. Subsequently, the Color doppler mode was activated and the blood flow was examined in both transverse and longitudinal views. The examination was classified as negative in the case of total compressibility of the vein without visible intraluminal thrombosis and with blood flow evident throughout the vessel cross-section. If the vein was only partially compressible or not compressible, a dropout was noted in Doppler imaging or a thrombus was visualized, the examination was classified as positive. All positive findings were recorded and archived.
At the beginning of the examination, the patients were placed to the supine position. Depending on the place of CVC insertion, the scope of the examination was determined, i.e., the upper or lower basin of the caval vein (see above). When examining vv. jugulares, the patient's face was turned away from the examination site, the chin was pointing upwards, the vessel was examined from the processus mastoideus to the clavicle. The probe was placed perpendicular to the vessel. Vv. subclaviae were examined subclavicularly, in the lateral third of its course, with the probe placed longitudinally with the vessel. Vv. axillares in longitudinal view with the probe in the axillary fossa. In the case of inferior vena cava basin, vv. femorales were examined from the inguinal ligament to a distance of 15 cm. Vv. popliteae then after positioning the limb into external hip rotation and knee flexion, with the probe transversally inserted into the popliteal fossa.
Objectives of the study
The primary objective of this study was to compare the diagnostic reliability of DUS in the diagnosis of CRT performed by general nurses in the ICU setting with the examination performed by an intensive care physician experienced in DUS.
Statistical analysis
A sample size of 160 patients was calculated for the study based on evidence from the literature and historical data from our ICU. Mean values ± SD or percentages were calculated as necessary. Differences between three means were compared by one-way ANOVA test. Differences between the proportions were calculated using χ2 Pearsons test. Diagnostic accuracy of DUS performed by nurse and physician was expressed as sensitivity, specificity, positive and negative likehood ratio, positive and negative predictive value, accuracy and kappa measure of agreement. The post-test probability of having and not having the target disorder in the case of positive or negative result of DUS was calculated. Confidence intervals for sensitivity, specificity and accuracy were calculated as Clopper-Pearson confidence intervals. Confidence intervals for the likelihood ratios were calculated using the Log method [1]. Confidence intervals for the predictive values were calculated as the standard logit confidence intervals [8]. Data were analysed using Microsoft Excel 2016 (Microsoft, Redmond, WA, USA) and JMP 3.2 statistical software (SAS Institute, Cary, NC, USA). A p value of < 0.05 was considered statistically significant.
Results
A total of 160 patients in the age range of 22 to 89 years were included in the study. We performed a total of 177 examinations. Up to 17 patients had 2 catheters inserted, one central venous catheter for fluid and drugs administration, the other was high-flow hemodialysis catheter. As much as 165 catheters were inserted in the superior vena cava basin (SVC basin), of which 101 (57%) in the jugular vein, 64 (36.1%) in the subclavian vein and 12 in the inferior vena cava basin (IVC basin), all in the v. femoralis. A central venous catheter (CVC) was inserted in 155 (87.5%) patients, a hemodialysis catheter (HD) was introduced in 22 (12.4%) patients, 17 (9.6%) patients had 2 catheters inserted. The mean catheter insertion time at the day of examination was 4.5 ± 1.8 days.
Thromboprophylactic measures were used in all patients, of which only mechanical measures were used in 12 (7.5%) of them. In the other 148 (92.5%) patients, pharmacological prophylaxis was performed with enoxaparin. The average dose was 50 ± 26 mg/day. Among other antithrombotic drugs, acetylsalicylic acid was used in 17 patients, heparin in 2 patients, clopidogrel in 3 of them and ticagrelor in one of them.
Table 1 summarizes basic medical history, patients´ characteristics, the data characterizing their critical illness and causes of admissions. Our patient group shows a high severity of critical illness with a SOFA score of 8 ± 5 points associated the risk of ICU mortality up to 20% [4, 13]. More than half of our cohort (65%) required vasopressor support and 82.5% of patients were dependent on mechanical ventilation.
Table 1.
Medical history, clinical characteristics and causes of admission
| Medical history | |
| History of DVT (%) | 8.13 |
| History of PE (%) | 1.25 |
| Coronary artery disease (%) | 28.13 |
| Arterial hypertension (%) | 65.63 |
| Hyperlipidemia (%) | 30.63 |
| Diabetes mellitus (%) | 28.13 |
| Active smoker (%) | 32.5 |
| CHF (%) | 11.88 |
| CRF (%) | 6.25 |
| HD (%) | 4.38 |
| Pulmonary disease (%) | 27.5 |
| Cerebrovascular disease (%) | 5.63 |
| Oncologic disease (%) | 21.25 |
| Endocrinological disease (%) | 13.75 |
| Psychiatric illness (%) | 16.88 |
| Addiction (%) | 7.5 |
| Clinical characteristics | |
| Height (cm ± SD) | 171 ± 8 |
| Weight (kg ± SD) | 84 ± 15.9 |
| Sex (f/m) | 54/106 |
| Age (years ± SD) | 62.9 ± 12.3 |
| Mean arterial pressure (mmHg ± SD) | 83 ± 10 |
| Body temperature (°C ± SD) | 37 ± 0.3 |
| Pulse (beats/min ± SD) | 87 ± 14 |
| SpO2 (% ± SD) | 96 ± 2 |
| SOFA (points ± SD) | 8 ± 5 |
| MV/NIV (%) | 82.5 |
| Vasopressor support (%) | 65 |
| BMI (points ± SD) | 29 ± 5 |
| GCS (points ± SD) | 8 ± 5 |
| Causes of admission | |
| Trauma (%) | 20.63 |
| CPR (%) | 16.25 |
| Medical (%) | 41.25 |
| Surgical (%) | 21.88 |
CRF chronic renal failure, CHF congestive heart failure, HD chronic heamodialysis, MV mechanical ventilation, NIV non-invasive ventilation, SOFA score Sequential Organ Failure Assessment score, RRT renal replacement therapy, GCS Glasgow Coma Scale
The overall prevalence of CRT in our sample was 41%. Total of 83 thrombothic events were identified. In 35 (42.2%) patients unilateral thrombosis associated with ipsilaterally inserted catheter was found, 21 in right jugular vein, 10 in left jugular vein, 3 in right subclavian vein and one in left femoral vein. We were not able to distinguish between thrombosis originated from catheter's fibrin sleeve or vessel’s wall. In 16 (19.3%) patients was identified thrombosis not associated with the catheter. Five of them had right jugular vein thrombosis while the catheter was inserted in the left jugular vein and was thrombus free, as much as five suffered from left jugular vein thrombosis while catheter was inserted in left subclavian vein and in three patients we found right jugular vein thrombosis and the catheter inserted in the left subclavian vein. In 1 patient we determined thrombosis in right jugular vein while catheter was inserted in right subclavian vein, one patient had thrombosis in left jugular vein and catheter was inserted in right jugular vein and 1 patient presented with left femoral vein thrombosis and catheter was inserted in the right femoral vein. Only basin, where the catheter was inserted, was examined, therefore we are not able to compare occurrence of thrombosis in superior and inferior vena cava basins in the same patient. Table 2 summarize occurrence of CRT in individual veins.
Table 2.
Occurrence of CRT in individual locations
| Location | Number of CRT in individual locations | Percentage of all CRT |
|---|---|---|
| Superior vena cava basin | 81 | 97.6% |
| Right internal jugular vein | 46 | 55.4% |
| Left internal jugular vein | 21 | 25.3% |
| Right subclavian vein | 7 | 8.4% |
| Left subclavian vein | 4 | 4.8% |
| Right axillar vein | 3 | 3.6% |
| Left axillar vein | 0 | 0% |
| Inferior vena cava basin | 2 | 2.4% |
| Right femoral vein | 0 | 0% |
| Left femoral vein | 2 | 2.4% |
| Right popliteal vein | 0 | 0% |
| Left popliteal vein | 0 | 0% |
In 16 (19.3%) patients, thrombosis in two different locations was found. In 6 patients both thrombosis were situated on the catheter (jugular vein bilaterally in 4 patients, right jugular and subclavian vein in 2 cases). In 7 patients, one thrombosis was found on catheter (three in right subclavian vein, one in left subclavian vein and three in right jugular vein), the other thrombosis was located in vein without inserted catheter. Three of this secondary thrombosis were found on ipsilaterally, four were situated contralaterally. One patient had both thrombosis in veins without inserted catheter (right jugular vein and left subclavian vein).
The overall sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of examinations performed by general intensive care nurses were 90.8%, 97.1%, 91.8%, 96.8%, and 95.5%, respectively. Table 3 summarizes the reliability of the examination performed by general nurses in individual locations.
Table 3.
Reliability of the nurse-performed examinations in individual locations
| All examined branches of SVC and IVC | All examined branches of SVC | All examined branches of IVC | |
|---|---|---|---|
| Sensitivity (%) | 90.8 | 91.6 | 75 |
| Specificity (%) | 97.1 | 97.2 | 94.8 |
| Positive predictive value (%) | 91.8 | 92.1 | 85 |
| Negative predictive value (%) | 96.8 | 97.1 | 90.7 |
| Accuracy (%) | 95.5 | 95.8 | 89.3 |
| Kappa measure of agreement | 88.3 | 89 | 72.4 |
| Both internal jugular veins | Right internal jugular vein | Left internal jugular vein | |
|---|---|---|---|
| Sensitivity (%) | 89.4 | 90.8 | 87.6 |
| Specificity (%) | 95.1 | 95.1 | 95.1 |
| Positive predictive value (%) | 89.7 | 90.8 | 88.3 |
| Negative predictive value (%) | 94.9 | 95.1 | 94.8 |
| Accuracy (%) | 93.2 | 93.6 | 92.9 |
| Kappa measure of agreement | 84.6 | 86 | 83 |
| Both subclavian veins | Right subclavian vein | Left subclavian vein | |
|---|---|---|---|
| Sensitivity (%) | 96.8 | 86.9 | 93.8 |
| Specificity (%) | 90 | 99.5 | 98 |
| Positive predictive value (%) | 96.7 | 86.9 | 93.4 |
| Negative predictive value (%) | 90.2 | 95.4 | 98.1 |
| Accuracy (%) | 95.1 | 93.2 | 97 |
| Kappa measure of agreement | 86.8 | 82.4 | 91.7 |
| Both axillary veins | Right axillary vein | Left axillary vein | |
|---|---|---|---|
| Sensitivity (%) | 97.1 | 98.2 | 96 |
| Specificity (%) | 99.6 | 99.5 | 99.7 |
| Positive predictive value (%) | 98.5 | 98.2 | 98.8 |
| Negative predictive value (%) | 99.2 | 99.5 | 98.9 |
| Accuracy (%) | 99.1 | 99.2 | 98.9 |
| Kappa measure of agreement | 97.2 | 97.8 | 96.7 |
| Both femoral veins | Right femoral vein | Left femoral vein | |
|---|---|---|---|
| Sensitivity (%) | 90.6 | 68.1 | 93.7 |
| Specificity (%) | 83.3 | 88.6 | 97.5 |
| Positive predictive value (%) | 92.8 | 75 | 93.7 |
| Negative predictive value (%) | 78.9 | 84.7 | 97.5 |
| Accuracy (%) | 88.5 | 81.8 | 96.4 |
| Kappa measure of agreement | 72.8 | 60 | 91.2 |
| Both popliteal veins | Right popliteal vein | Left popliteal vein | |
|---|---|---|---|
| Sensitivity (%) | 70 | 52.6 | 100 |
| Specificity (%) | 96.7 | 93.6 | 100 |
| Positive predictive value (%) | 87.5 | 76.9 | 100 |
| Negative predictive value (%) | 90.7 | 83 | 100 |
| Accuracy (%) | 90 | 81.8 | 100 |
| Kappa measure of agreement | 71.4 | 58.3 | 100 |
Discussion
The main finding of presented study is that general ICU nurses are able to carry out a duplex ultrasound examination for CRT diagnosis after short training with high reliability when compared to an examination by experts.
Venous thrombosis is a typical complication associated with inserted central venous catheter. The main causes are reduction in blood flow through the vein and endothelial damage induced by inserted catheter and/or by the current disease [5, 15]. In the critical care setting, all pathophysiological processes of CRT formation are potentiated by the length of inserted catheter, patient's immobilization and sedation, pharmacological treatment and the presence of inflammatory activity [12]. Several types of CRT can be identified: fibrin catheter coating (fibrin sleeve, thrombus seeding the catheter and pericatheter, mural venous thrombosis near the catheter without contact with the catheter [2, 5, 6]. CRT is a critical concern in healthcare settings. Numerous studies have documented the prevalence and risk factors associated with this complication. The frequency of CRT varies from 2 to 5% in general inpatient population [6], depending on factors such as catheter type, insertion site, and patient population. The prevalence of CRT in intensive care unit is generally higher than in other clinical settings and range from 20 to 40% [6]. The clinical consequences of CRT may not be negligible in critically ill patients.
The risk of pulmonary embolism associated with CRT is low, still present [5, 14]. Catheter dysfunction may require further intervention, the catheter replacement. Swelling and/or pain in the extremity, thrombus infection and catheter sepsis are other potential serious complications.
Several clinical studies have been published demonstrating that intensivists are able to perform DUS with high reliability, with sensitivity of 94.8% and specificity of 96.2% [10].
On the other hand, there is a very limited amount of data on ultrasound in the diagnosis of venous thrombosis performed by general nurses in intensive care. Mumoli et al. [9] evaluated the accuracy of a nurse-performed ultrasound compression test (UCT) for the diagnosis of proximal deep vein thrombosis in outpatients with clinically suspected DVT. Compared to a physician-performed UCT, nurses achieved a sensitivity of 84.4% and a specificity of 97.0%. In 2020, Skulec et al. evaluated the reliability of the UCT performed by the ICU general nurse in critically ill patients, where the nurses achieved a sensitivity of 88.89% and a specificity of 99.06%. This clinical study was conducted at our department and after finding high reliability of general nurse examination in the diagnosis of deep vein thrombosis, we chose to conduct this study as the next step. The duration and method of nurse training were primarily based on long-term local experience. We utilized knowledge gained from previous POCUS training for non-medical healthcare professionals, and most of the study participants were already experienced in performing compression ultrasonography.
There are two main reasons why competence to DUS examination could be delegated to ICU nurses. First, intensive care physician may not always be available for DUS performance, especially if screening of CRT is considered in ICU patients. Second, optimal timing for DUS is during a nursing visit when the protective patch is redressed, and the catheter is exposed to the testing. Nevertheless, this timing may be not optimal for the physicians.
On our best knowledge, there has not been published any study evaluating the diagnostic reliability of duplex ultrasonography performed by general nurses in intensive care patients. In our study, the overall sensitivity and specificity reached 90.8% and 97.1%, respectively. Examination by a nurse in the SVC basin proved to be significantly more reliable than in the IVC basin. The lowest reliability was achieved in the examination of the popliteal vein. This difference may be due to the small number of cases with a catheter inserted in the IVC and specifically for the popliteal veins, the reason for the lower reliability may be the greater difficulty in identifying the popliteal vein and its small diameter. Moreover, Skulec et al. demonstrated that the reliability of the popliteal vein examination was lower than that of the femoral vein (sensitivity 75%, specificity 99,1%). Therefore, it is necessary to devote more time and attention to the training of the examination of the VCI basin and especially the popliteal vein.
Even it was not the objective of our study, we identified the incidence of thrombosis associated with an inserted central venous catheter up to 41%. This is relatively high number compared to other clinical studies, despite excellent compliance with thromboprophylactic measures in our study. We can only speculate that the reasons may be high average age of the patients, the body mass index bordering on obesity and the high SOFA score indicating the severity of the disease in our cohort.
We didn’t find significantly higher risk of CRT depending on the catheter insertion site. The high occurrence of thrombosis in the SVC basin was caused by highest frequency of venous catheter insertion in this location. We found no impact of as the type of a catheter, catheter material, number of entries and length of insertion on the incidence of CRT.
Study limitations
We recognize few limitations of our study. First, even the sample size is large enough to show the difference in the main endpoint, it is not large not enough to describe the learning curve. Second, this is a single-center study and the results may be influenced by local practices of intensive care. Third, the period between the nurse-performed and physician-performed ultrasound was in some cases several hours and we cannot exclude that CRT could arise in the meantime. However, in most of the cases the period was less than one hour.
Conclusion
We conclude that the general critical care nurses in our study were able to perform DUS with high reliability after brief training, which was greater in the SCV basin. Therefore, it seems potentially feasible to delegate nurses with this diagnostic competence.
Acknowledgements
We acknowledge statistical support of Ondrej Bradac, MD, PhD. We also we thank with respect all the patients who participated in the study.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Data Availability
The data that support the findings of this study are available from the corresponding author, Barbora Stadlerová, upon reasonable request.
Declarations
Conflict of interest
None.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author, Barbora Stadlerová, upon reasonable request.