Mastering the technique of inferior vena cava ultrasound from transhepatic view in intensive care unit: A practical approach to the ultrasound technique,tips,and pitfalls

Abstract

Background:

Bedside ultrasound of inferior vena cava is used by clinician sonographers in intensive care units. Its data can impact clinical decision-making. Subcostal view is a standard view for this issue. A significant proportion of the intensive care unit patients have very difficult approach to this view. In these patients, an alternative view is a transhepatic view, feasible in nearly every intensive care unit patient. Limited data on the ultrasound technique exist in literature.

Aim:

In this review, we discuss in detail the technical aspects of the inferior vena cava ultrasound technique assessed from the transhepatic view, ultrasound tips, and pitfalls.

Methods:

A search was performed using PubMed, Google Scholar, EMBASE, and Scopus databases with the terms “inferior vena cava ultrasound,” “transhepatic view,” “right mid-axillary view,” “right lateral intercostal view,” “ultrasound technique,” “inferior vena cava pitfalls,” and inferior vena cava ultrasound tips,” “intensive care unit.” The latest articles were reviewed and this review was written using the most current information.

Discussion:

A standardised ultrasound approach from mid-axillary line provides optimal image acquisition. When there are difficulties finding inferior vena cava or in obesity alternative approaches should be used. Potential pitfalls during acquisition are: misidentifying the inferior vena cava; technical issues in inferior vena cava measurements; utility of the inferior vena cava data in isolation.

Conclusion:

Mastering the ultrasound technique from the transhepatic view offers clinicians the opportunity to perform inferior vena cava ultrasound, even in the most challenging patients. Awareness of potential pitfalls and knowledge how to avoid them is important to intensive care unit clinicians to avoid wrong decisions at the bedside.

Keywords

Transhepatic view inferior vena cava ultrasound ultrasound technique ultrasound tips ultrasound pitfalls intensive care unit bedside ultrasound

Introduction

Inferior vena cava (IVC) is the largest vein in the body, situated in retroperitoneum to the right of aorta within abdominal cavity. The IVC passes posterior to liver and is joined by hepatic veins before it enters thoracic cavity, and then drains into right atrium. Its intrathoracic course is very short. The IVC consists of four segments: hepatic, suprarenal, renal, and infrarenal.¹

Ultrasound is highly successful in demonstrating the upper abdominal portion of the IVC. The IVC ultrasound can be done by a treating clinician sonographer at the patient’s bedside in intensive care units (ICUs). Although the IVC imaging is usually neglected during a standard transthoracic echocardiography, it is widely used as a part of point-of-care ultrasound (POCUS) and critical care echocardiography in the ICUs.^2–5 Bedside IVC ultrasound is one of the recommended parts of the POCUS examination.³ The IVC ultrasound is practiced by a wide range of specialties, such as cardiologists,^6,7 intensivists,^5,8 anesthesiologists,⁴ and nephrologists.⁹ Although each specialty uses IVC ultrasound data in slightly different ways, mostly is used for rapid assessment of intravascular volume status and fluid responsiveness.^3,10

The data from the IVC ultrasound can impact clinical decision-making in the ICU.^3,10 It is clinically important in the ICU, especially in three scenarios: first, for assessing volume status and fluid responsiveness;^1,3,11 second, for estimation of central venous pressure;¹⁰ and last, as a bedside rapid diagnostic tool (in excluding pericardial tamponade,^11,12 identifying heart failure patients,^13,14 venous congestion,¹⁵ visualisation of IVC thrombus¹⁶ (Figures 1 and 2, Supplemental videos 1 and 2)). In the last few years, IVC ultrasound is used for vascular procedural guidance.^7,17

Subcostal (SC) IVC view is the gold-standard ultrasound view to evaluate the IVC, preferred by echocardiographers and POCUS sonographers.^2,3,5 However, ICU patients, especially those with recent abdominal or cardiac surgery, often have factors that make the standard SC view inaccessible or a challenge to obtain. Obesity, highly prevalent among the ICU patients, is another obstacle. These limitations may be overcome by using an alternative ultrasound view. Such alternative view is a transhepatic (TH) IVC view, recommended by the guidelines from American Society of Echocardiography,² the ICU ultrasound protocols.^15,18 For many years, this has been valued as a “rescue view” in the ICU.^3,19,20

Because of the limitations of the standard SC view, the alternative TH view is becoming increasingly important in the ICU. It is clinically valuable for two reasons. First, it is an excellent view to visualise and to assess the IVC especially if the SC view is difficult to obtain³ and due to other advantages over the SC view. Second, it is an extremely useful view in the field of vascular access.^6,7,17 It is more preferable view than the SC view in ultrasound guidance of bedside procedures in the ICU (such as intra-aortic balloon pump insertion (IABP), extracorporeal membrane oxygenation (ECMO) cannulation,^6,7 and femoral vein catheter tip location).¹⁷

However, the IVC ultrasound remains highly operator-dependent.^11,21 There are challenges that the sonographer may encounter during acquisition and interpretation of the IVC images assessed from the TH view. Sometimes, it can be a challenge to find the IVC or to find a good view of the IVC.

In this educational review, we discuss the ultrasound acquisition technique of the IVC from the TH view in detail. We provide tips in finding IVC and in acquiring good images of IVC from a technical point. In addition, we discuss ultrasound pitfalls and how to avoid them.

Methods

We did a literature search on databases PubMed, Google Scholar, EMBASE, and Scopus using the terms “inferior vena cava ultrasound,” “transhepatic view,” “right mid-axillary view,” “right lateral intercostal view,” “ultrasound technique,” “inferior vena cava pitfalls,” and inferior vena cava ultrasound tips,” “intensive care unit.” The references of the included articles were also searched when considered relevant by the authors. The selection strategy was restricted to articles focusing on the use of IVC assessment among adult ICU patients. No restriction filters were used with regard to language.

Ultrasound IVC visualisation

IVC ultrasound is relatively simple technique, non-invasive, cheap, easy to learn, immediately available, quick to perform at the patient’s bedside, repeatable, and applicable in a wide range of patients.¹

IVC image acquisition and technical steps

In adults, standardised IVC ultrasound is performed with low frequency (2–5 MHz) probes, which ensures better visualisation of deep structures. Typically, phased-array probe (frequency of 2.0–4.0 MHz) or sometimes curvilinear probe (frequency of 3.5–5.0 MHz) is used. Use of cardiac or abdominal settings varies by preferences of the sonographer, but both are acceptable. Although the American Society of Echocardiography guidelines recommend left lateral position for imaging the IVC,² the patients in ICU are often assessed in the semi-recumbent or supine position.^9,22 In our institution, we do the study in the same patient’s position at the time of the scan, in order to avoid time-consuming repositioning of the patient. Most sonographers prefer to stand to the patient’s right, holding the probe with their right hand, while controlling US machine with their left hand. Standing to the patient’s right may not always be possible, so it’s practical for the sonographers to learn to be flexible. Ultrasound gel should be used generously. Inadequate use of gel limits the view. The sonographers should hold the probe close to its head, anchoring with their fourth or fifth finger. This avoids unintentional movement with the probe. Appropriate pressure on the probe should be applied to maintain good contact with the patient’s skin. The sonographer’s hand holding the probe should rest on the patient’s body or the patient’s bed to avoid moving out of the ultrasound view. All these maneuvers provide stability of the ultrasound image²³ (Table 1).

Table 1.

Summary of IVC scanning tips.

IVC scanning tips	Comments
Stabilise the ultrasound image to have accurate measurements.²³	The sonographer’s hand resting on the patient’s belly or bed steadies the ultrasound image. The probe should not be moved after a good image is found.
Always scan the IVC in two axes (longitudinal and transverse).¹	Scanning in both axes gives much more information, than scanning in one. Like all vessels, the IVC is most accurately measured in its transverse axis.
Set the depth very deeply, then adjust as needed^2,22	Obese patients have deeper vessels and require an increased depth.
Set colour Doppler scale <50 cm/s^2,22	Low flow venous velocities (of the IVC) are detected on a low color scale.
Obese patients require special scanning adjustments^24,25	Sonographers should apply excessive force to the probe to decrease the depth of adipose tissue to penetrate through. Scanning with a lower frequency (2.5-MHz) probe Scanning from the alternative approaches. Scanning with a different ultrasound machine may sometimes provide better image quality.

IVC = inferior vena cava.

Inadequate SC IVC views in the ICU

Approximately 20% of the ICU patients have inadequate SC views.^11,13,26 The SC view may be inaccessible in number of conditions, such as postoperative dressings, wounds, abdominal distention,³ third trimester pregnancy,^12,17 percutaneous gastrostomy, ascites,¹⁷ and patient’s discomfort or suboptimal position.^3,22,27 Post-cardiac surgery patients have mediastinal drainage tubes in place,⁸ which can interfere with the sonographer’s view (Figure 3). Some patients with abdominal pain or tenderness do not tolerate any pressure with the probe in the subcostal region. Distention of colon and stomach by gas or enteral nutrition will hinder the SC view. Gastric or bowel gas interferes with ultrasound transmission.^13,17 Obesity is another obstacle for the SC view. Ultrasound waves are attenuated by adipose tissue, so the image quality is poor.³

TH IVC view in the ICU

This view has several names, TH view,^26–29 right mid-axillary view,^3,22 right lateral IVC view,^2,22,30 right lateral intercostal view,²⁰ right upper quadrant view,¹² also known as “rescue view” in the ICU.^3,8,19,20 The TH view allows visualisation of the suprarenal and the hepatic segment of the IVC.¹⁷ From the TH view, there are three image views on which can be visualised the IVC: longitudinal axis (Figure 1), transverse axis (Figures 2 and 4), and double-barrel view (Figure 5). The double-barrel view provides simultaneous coronal (longitudinal) visualisation of the IVC and abdominal aorta, parallel to each other. This view resembles the longitudinal section of a double-barreled rifle.⁸

The TH view provides high-quality images equal as the SC view,¹² feasible in almost all ICU patients.^12,26,28 The TH view has several advantages over the SC view. First, it is feasible in patients with inaccessible SC view.^3,12,26,28 Second, it avoids artifactual IVC compression with the ultrasound probe, which can lead to wrong impression of collapsed IVC (“iatrogenic flat IVC”).³¹ From the TH approach, compression of the IVC with the probe is not allowed because of the ribs. Contrarily, from the SC approach, excessive pressure with the probe may compress the anterior wall of the IVC. This produces a shift of the IVC posterior wall and falsely low anterior–posterior IVC diameter.^12,31 The probe pressure needed to compress the IVC from the SC approach may vary from one patient to another, but it is more pronounced in pediatric patients than in adults due to thinner abdominal wall. In mechanically ventilated patients and morbidly obese adult patients, it is hard to get good interpretable ultrasound images, therefore greater pressure is applied on the probe.³¹ This manoeuver with the probe may lead to artefactual IVC collapse, which can be erroneously interpreted as a respiratory collapse of the IVC. This is a common pitfall.^9,31 In contrast, the IVC respiratory collapse visualised from the TH view (in absence of intraabdominal hypertension)³² is a very reliable finding.³³

In the ICU, the TH view is more preferred view than the SC view for bedside intraprocedural ultrasound procedures due to feasibility in almost all patients. In the cardiac ICU, the TH “double-barrel” view provides excellent coronal images of the abdominal aorta and the IVC together, within the same image. It serves as a good view to confirm the position of devices (ECMO cannulas, IABP, and Impella devices)^6,7 and location of femoral venous catheter tip.¹⁷

Ultrasound technique of the TH IVC view

The IVC ultrasound technique from the TH approach is easy to learn, although it requires an experience in ultrasound to get a quality view of the IVC.¹² Through hepatic window, the IVC is evaluated between the ribs. Liver parenchyma is a perfect acoustic window for imaging of major abdominal vessels. The main challenge is trying to navigate the probe between the ribs. This is more easily done with the cardiac probe. Small footprint fits between the ribs. Useful tip is to place the patient’s right arm behind the head or to outstretch laterally, in that way opens up the lateral trunk rib spaces.

This technique is briefly described in the guidelines from American Society of Echocardiography in the section on alternative views.² Standard approach is a scan from a right mid-axillary line (Figure 6(a)). The probe is placed on the right mid-axillary line, around 10th or 11th intercostal space, (or slightly inferior to the xiphoid, if it is difficult to see the ribs) with the orientation marker pointed toward patient’s head. It is the same position as Morrison’s pouch view in Focused Assessment with Sonography for Trauma (FAST) exam.^2,18,29 From this point, it should be identified the liver and right kidney with Morison’s pouch in between them, the diaphragm and the spine. The spine serves as internal landmark. Prominent acoustic shadowing is a sign of the spine. IVC lies just anterior to the spine. So, it is useful tip to visualise aiming just anterior to the spine.²² As the probe is slid cranially, with slight anterior angulation, the IVC comes into view. The probe should be moved up and down to obtain the best longitudinal view of the IVC. The IVC is visualised running adjacent to the liver and crossing the diaphragm. Aorta is often seen parallel and posterior to the IVC.^12,22,26 From here, IVC should be followed with the probe until entrance to the right atrium is reached.²⁷ To acquire transverse-axis of the IVC, the probe should be rotated 90° from the longitudinal-axis view.²

In order to gain optimal image quality, some optimisations from a technical standpoint should be done (Table 1). The focus should be aligned along the sector at the region of interest. Scanning should be started deeply, often 20–25 cm (depending on the patient’s body size) and afterward adjusted to allow complete visualisation of the IVC. Colour scale in the abdominal and cardiac settings is set at different values. In cardiac settings, the typical scale is 50 to 60 cm/s. To detect flow in lower velocity areas, such as the IVC, it needs to be lowered below 50 cm/s and colour gain adjusted to have good colour fill in the IVC.^2,22

Challenges finding the IVC from the TH view

Rule of a thumb is to scan the IVC in any place it is found, since it can be surprisingly tricky to find it in some patients. Although finding the IVC from the right mid-axillary line approach is usually very easy, sometimes it may be a challenge. Positioning the patient into a left lateral decubitus can also be used to optimise this view, as recommended position for scanning by the guidelines.²

Seldom there are technical obstacles for scanning from TH view, such as fatty, fibrotic liver (which does not transmit ultrasound beam well),³⁴ morbid obesity, or a very large chest.²² Obese patients should be scanned with a lower frequency (2.5 MHz) probe^24,25 since this frequency results in deeper ultrasound penetration (Table 1). Also, in these difficult cases, an alternative scanning approach can be used.^25,35,36 Scanning the IVC from closer distance to the probe has better performance of the scan.²⁵ The IVC may be visualised in the place between the right mid-axillary and anterior-axillary line³⁵ (Figure 6(b)) or the place between the anterior-axillary and mid-clavicular line.³⁶ (Figure 6(c)). Midclavicular line usually passes through the nipple. For the first alternative approach, the probe should be placed approximately at 9th–10th intercostal space in the anterior-axillary line with medial upward angulation.³⁵ For the second alternative approach, the probe should be placed in 7th intercostal space. For both approaches, the marker should be pointed to the patient’s head. Some sonographers use these approaches for IVC visualisation during vascular procedural guidance.³⁶ When the transverse-axis of IVC is difficult to be obtained from the mid-axillary line, it should be tried from these two approaches (Figures 2 and 4).

IVC assessment techniques

Techniques of IVC assessment can be quantitative (IVC metrics) and qualitive (visual assessment).

Quantitative assessment

Measurements of the IVC are taken manually on B-mode and M-mode using caliper, video clips, and still images.^2,37 Recorded 10-second video clips should be stored digitally for later review. The following IVC parameters are measured: maximum (max), minimum (min) diameter, collapsibility index in spontaneously breathing patients,^26,38 and distensibility index (in mechanically ventilated patients).^29,39,40 According to the guidelines from the American Society of Echocardiography,⁴¹ the IVC measurements should be done 2–3 cm caudal to the IVC-right atrial junction or distal to the hepatic vein. This is recommended for both views (the SC view and the TH view).^9,20,41 The IVC diameters are recorded over several respiratory cycles with spontaneous respiration or mechanical ventilation.⁹ Min and max diameters are determined visually and measured on a still image on B-mode. Using cine loop option should be identified the best min and max diameter and then should be measured at the same location and the same respiratory cycle. M-mode measurements can be used when good alignment with the IVC is obtained. The max and min diameters are measured during the expiratory and inspiratory phases on the same respiratory cycle.²⁶ Sweep speed should be low enough to measure at least one full respiratory cycle.^9,20 We suggest the sweep velocity to be of 25–50 mm/s (depending on the respiratory rate), in order to include at least three respiratory cycles. Measurements can be done in the longitudinal axis. Measurements in the transverse axis are also accurate. When transverse axis is used for measurements, the sonographer should avoid the image of IVC with insertion of the hepatic veins, in order to have accurate measurements. This image deforms the shape of the IVC and may lead to an erroneous impression of the its shape and size.

Overall IVC diameter normally is between 1.5 and 2.5 cm according to 2010 American Society of Echocardiography guidelines.⁴¹ Small IVC is when max. diameter <1 cm. When IVC >2.5 cm, it is considered dilated. Sniff is used for the assessment of respiratory collapsibility. Normally collapses >50% with inspiration of sniff.⁴¹ Many ICU patients cannot perform sniff test which can accentuate IVC collapse. For consistency, in these patients, we calculate IVC index. In real clinical practice, the IVC metrics (the size and respiratory variability of IVC) are most useful at extremes. In practice, the following terminologies are used: “flat,” “virtual,” and “fat.”³ The IVC is “flat” when IVC max ⩽1 cm, with significant collapse throughout the respiratory cycle,^3,9 or when the IVC is so small that it cannot be seen (“virtual” IVC),⁴² then the patient probably needs fluids. The IVC is “fat” when the IVC max >2.5 cm, with minimal collapsibility, suggesting that is possibly present intravascular volume overload.^9,42,43

The IVC indices are calculated by determined formulas by using max and min diameters. The IVC collapsibility index is calculated with the following formula: (IVC max – IVC min)/IVC max). It is reported as a percentage.^9,10,13,26 In spontaneously breathing patients, the IVC collapsibility index for identifying fluid responders has optimal cut-off ranges between 25% and 50%, according to the different studies.^38,44,45 In patients breathing spontaneously, the IVC will collapse on inspiration, while in patients on positive-pressure mechanical ventilation, the IVC will distend. Therefore, the IVC distensibility index is recommended in patients on positive-pressure mechanical ventilation, instead of the collapsibility index. The IVC distensibility index is calculated as the ratio of (IVC max – IVC min)/IVC min) and expressed as a percentage.^39,40 In mechanically ventilated patients, the best cut-off value to identify fluid responders is the IVC distensibility index >18%.⁴⁰

Qualitive assessment

Visual estimation consists of visual appearance of gross IVC size, shape and collapse. The IVC shape is assessed on transverse axis. Circular shape is associated with hypervolemia, semicircular with normal findings, and pancake shape with hypovolemia. The visual (eyeballing) estimation of the IVC metrics should be done by experienced sonographers who have already been practiced in manually measurements. It is equally reliable to traditional (B-mode, M-mode) measurements and it is done more rapidly.³⁷ In practice, busy sonographers usually do gross visual estimate of the IVC collapsibility index (>50% vs <50%). According to one study,⁴⁴ the performance of the IVC collapsibility index was highly depended on the sonographer’s experience. The cut-off value of the IVC index was significantly better performed by an expert than by novice sonographer (ROC = 0.82 vs ROC = 0.69; p = 0.006).

The IVC metrics for assessment volume status and volume responsiveness in the ICU have been widely studied for the SC view.^38,44,45 Studies on the TH view are limited.^29,40 There are some differences in the IVC metrics between both views that should be taken in account by the sonographers. First, there are differences in the min and max diameters, related to the oval shape of the IVC. From the SC view, the measurement of the IVC is close to its minimum (anteroposterior) diameter, while from the TH view, it is closer to its maximum (latero-lateral) diameter.²⁷ Therefore, when scanned from the TH view, from the longitudinal axis, the IVC looks “fuller” than it really is. When the IVC max diameter is used for the assessment of volume status, it will overestimate the patient’s volume status, with impression of patient being volume overload, while he is not. The IVC is most accurately measured in its transverse plane, when scanned from the TH approach (this is not so important for the SC approach). When the IVC is scanned from the TH view, it should always be assessed in two planes (longitudinal and transverse axes).³³ Kulkarni et al.²⁹ found discordance in the IVC diameters among the SC and the TH views, while the value of IVC index was not significantly different. So, they suggest the IVC index to be used in determining the volume status, instead of the IVC max diameter, as more reliable parameter, when the assessment is done via the TH approach. The collapsibility of the IVC is a very reliable finding from the TH view.³³ But, in the assessment of the IVC respiratory variation should always be taken in account intra-abdominal pressure,³² intrathoracic pressure variations,³⁹ and right ventricular function.⁴⁶ Further discussion on this topic is beyond the scope of this review.

IVC ultrasound pitfalls

Pitfalls are often present and inevitable. A pitfall is a possible danger or problem that is not obvious at first glance during imaging. POCUS sonographers should have awareness of several potential pitfalls, related to image acquisition and/or interpretation (Table 2). It is important for the novice sonographers to pay attention to these pitfalls while practicing ultrasound and to learn how to avoid them, since their findings can potentially affect clinical decision in the ICU.

Table 2.

Summary of IVC pitfalls.

IVC pitfalls while scanning	How to avoid
Misidentification with aorta	Scan both vessels in one image
Technical issues with the IVC measurements (wrong angels of the measurement on longitudinal axis, M-mode sonography).	Scanning line should be perpendicular to the IVC wall. M-mode sonography should be used only after B-mode analysis of the IVC size and variability.
Pulsatile IVC misinterprated as respiratory variation	Looking for presence of severe tricuspid regurgitation.
Pulsatile IVC mimicking aorta	Pulsed-wave Doppler ultrasound of aorta and IVC will distinguish both vessels.
Interpretation of the IVC data in isolation	The IVC data must be interpreted in the clinical context along with other ultrasound data.

IVC = inferior vena cava.

Failure to properly identify the IVC

The most common pitfall is mistaking the aorta for the IVC.^11,47 Both vessels run parallel to each other, in direct proximity, similarly sized, so they can be easily mistaken for one another. To avoid this, several tips may be of help. The best tip is to visualise both vessels at the same image¹¹ on the double-barrel view. The IVC is adjacent to the liver, while the aorta is parallel to it, in the far field of the image. Another clue is to visualise both IVC landmarks: right atrium–IVC junction and hepatic vein–IVC junction.⁴⁸ Identifying their position could be of help. The IVC is touching the liver, while the aorta is away from the liver, running more posteriorly, positioned just in front of the vertebral column.⁴⁷ Variations in the size with respiration are usually seen in the IVC, while in the aorta there are no changes. The IVC is non-pulsatile, while the aorta is pulsatile structure. But this is not a good tip, since the IVC is often pulsatile due to transmitted cardiac pulsations.⁴⁸ On a transverse view, the IVC is thin-walled, teardrop-shaped, while the aorta is thick-walled, circular-shaped.⁴⁹ Finally, spectral pulsed wave and colour Doppler can be used. Spectral Doppler pattern can identify both vessels. The aorta has a “spiky” triphasic pattern with high flow velocities, while the IVC has more of a “M-pattern” with low flow velocities.⁴⁸ Colour-flow Doppler may be used to confirm characteristic arterial flow in the aorta.⁴⁹ This pitfall is especially likely to occur in severely hypovolemic patients where it is easy to overlook a totally collapsed IVC (virtual IVC). In this case, totally collapsed IVC occurs in conjunction with a totally collapsed hepatic veins. Misidentifying the aorta as IVC can erroneously give the impression of no respiratory variation of the IVC.⁹

Misinterpretation of the IVC pulsation as respiratory variation

The IVC can be very pulsatile in severe tricuspid regurgitation. On M-mode, systolic dilation and diastolic collapse of the IVC in a pulsatile manner can be seen. This mimics respiratory variation on M-mode. To avoid this, variation of the IVC diameter should be correlated with respiratory cycle and not with the cardiac pulse. Very pulsatile IVC mimics aorta.⁵⁰ Pulsed-wave Doppler ultrasound of the aorta and the IVC will distinguish both vessels.

Technical issues with the IVC measurements (off-axis measurements)

The longitudinal axis view of the IVC is susceptible to “cylinder effect” when the measurement is made off-axis. This generates an oblique view of the vessel, resulting in a falsely smaller diameter. This leads to an incorrect interpretation during follow-up examinations, particularly when different operators are performing the study. To avoid this, the measurement should be as perpendicular as possible to the IVC walls to yield an accurate measurement (fine rotation of the probe helps to capture the true diameter of IVC). Another tip is to evaluate in transverse axis as well. Transverse axis overcomes the cylinder effect.^9,13

The M-mode measurement is prone to false measurements, when M-mode line is not perfectly perpendicular to the long axis of the vessel. Wrong angle of measurement will cause the IVC diameter to be overestimated and this may underestimate the IVC collapsibility index, leading to a conclusion that the IVC is “fuller.” Even experienced sonographers can get the angles wrong. To avoid this, sonographers should be sure that the M cursor is perfectly perpendicular to the long axis of the vessel.^1,5,13 M-mode sonography is better to be used after B-mode analysis of the IVC size and variability.

Blind faith in the IVC metrics

Sonographers should be caution about using the IVC metrics in isolation to make clinical decisions. The IVC ultrasound is a data point and should be never use in isolation. Blind faith in the IVC metrics, as well as in any test, can do more damage than good. Even when properly imaged, the IVC metrics should always be incorporated into clinical context. When the IVC metrics do not fit the clinical presentation, the IVC study should be re-evaluated. When there are discrepancies of the IVC metrics and clinical presentation, then the IVC findings should be ignored, and the patients should be treated as they did not have the IVC study. Other ultrasound data (cardiac, lung, venous congestion, and other) should all be corroborated with the IVC findings, along with the clinical context, in order to avoid diagnostic errors.¹²

Clinical implication

The TH view is highly valuable view in the ICU, as for some patients it is the only available “rescue view” for the IVC assessment. Recent studies are exploring the use of artificial intelligence (incorporated into the ultrasound systems) for automation or semi-automation of the IVC analysis.^1,21,43 These new methods are utilised through deep learning applications.²¹ The goal is to overcome operator dependency and to eliminate analysis errors done by novice or less experienced sonographer.⁴³ However, they are still under development. They lack speediness to be used in routine practice in the ICU.²¹ Often, the IVC happens to be accidentally lost from imaging plane and then the whole procedure has to be repeated from the beginning.^21,43 Also, they are highly costly and rarely available on the ultrasound machines. Furthermore, these new ultrasound technologies are still dependent on the sonographer’s skills in acquiring IVC images with quality. In these platforms, the sonographer has to obtain transverse view of the IVC and the deep learning application is doing all the rest.⁴³ This approach is new and needs to be validated in further larger studies. Currently, in routine practice in the ICU, the IVC assessment is mostly performed by qualitive visual assessment and by manually performed IVC metrics. Mastering the technical skill to obtain good images of the IVC is equally vital for standard manual assessment approach and for the newly developed automised platforms approach.

What actually is missing in the literature is a practical approach to the ultrasound technique of the IVC assessment from the TH view in the ICU. Therefore, we have tried to overcome this issue, we gathered all available data from the published literature, plus, in combination with shared author’s ultrasound experience. Some of the tips shared herein are based on the authors’ practical experience, who use IVC ultrasound in their daily practice.

IVC ultrasound limitations from the TH view

Requirement for advanced sonographic skills and experience

Ultrasound is an operator-dependent technique and is heavily dependent on the sonographer’s skills and experience.^11,21,37,38 Although learning curve is short,¹³ as in any examination, training and gaining experience through practice are essential.

Poor visualisation of the IVC due to the patient’s factors

It is a challenge to visualise the IVC in patients with fatty liver and fibrotic/cirrhotic liver due to increased acoustic attenuation of the liver parenchyma which produces poor-quality images.³⁴ In patients with morbid obesity, the large amount of subcutaneous fat tissue does not transmit ultrasound beam well. In these cases, radiology imaging may be superior to ultrasound.^13,34

Conclusion

In the ICU, the SC IVC view is limited by many factors and can be difficult to obtain. Therefore, the alternative TH view is becoming increasingly important for the clinician sonographers, since it is feasible in almost all patients. The IVC ultrasound is highly dependent on the sonographer’s skills. Finding a good IVC view is equally vital as for the manual assessment approach and for the automised platforms approach. The sonographers should be aware of the many potential pitfalls and able to avoid them. In the hands of a skilled sonographer, the IVC ultrasound, combined with other data, allows the intensivist to confidently make important bedside clinical decisions in the ICU.

Footnotes

Contributors

Marija Kotevska Angjushev: Substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; drafting the article or revising it critically for important, intellectual content; final approval of the version to be published.

Darko Angjushev: Drafting the article or revising it critically for important, intellectual content; final approval of the version to be published.

Ana Djordjevic Dikic: Drafting the article or revising it critically for important intellectual content; final approval of the version to be published.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethics approval

Not applicable.

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Not applicable.

Permission obtained in writing from patient or any person whose photo is included for publishing their photographs and images

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Confirm that you are aware that permission from a previous publisher for reproducing any previously published material will be required should your article be accepted for publication and that you will be responsible for obtaining that permission

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ORCID iDs

Marija Kotevska Angjushev

Darko Angjushev

Supplemental material

Supplemental material for this article is available online.

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