Venous excess ultrasound: A mini-review and practical guide for its application in critically ill patients

Table 1 The essential ultrasonography formulae relevant to venous excess ultrasound

Formula	Relevance
λ = c/f. λ is the wavelength, c stands for the sound velocity in the tissue, and f is the frequency[8,11,12]	The equation illustrates the inverse relationship between frequency and wavelength. The lower frequency corresponds to longer wavelengths, which allow them to penetrate deeper into the tissues as longer wavelengths reduce scattering and absorption. However, longer wavelengths lead to reduced spatial resolution, thereby diminishing the ability to distinguish between two objects. Thus, lower-frequency probes have better penetration but lower resolution images, while higher-frequency probes have the opposite characteristics
Doppler shift = (2 × f) × (V/c) × cos θ. f is ultrasound frequency, V stands for blood flow velocity, c for speed of sound in the tissue, and θ for insonation angle	The Doppler shift is directly proportional to blood flow velocity, and aliasing tends to happen when the Doppler shift surpasses the Nyquist limit[12,13]. Besides, this formula illustrates the importance of the insonation angle in the PW study. Adjusting PW's insonation angle to zero, or at least less than 60 degrees, is ideal as it maximizes the Doppler shift at zero degrees (cos 0 = 1), whereas at 90 degrees (cos 90 = 0), there is essentially no Doppler shift
Nyquist limit = PRF/2. PRF stands for pulse repetition frequency	PRF is the rate at which the ultrasound system emits pulses of sound waves and receives their echoes. It is also known as the sampling rate, measured in hertz (Hz), and typically ranges from 1000 to 5000 Hz in clinical settings
PRF = 1/pulse duration. PRF stands for pulse repetition frequency. Pulse duration is the period between pulses	According to the inverse proportional relationship, the lower the PRF, the longer the pulse duration. Prolonging the pulse duration allowed for deeper transmission and improved sensitivity to low-velocity flow. But the trade-off features of lower PRF will include lowering the Nyquist limit and increasing the chances of aliasing, where the Doppler signal falsely creates an appearance of the flow reversing or oscillating in the opposite direction[12,13]

PRF: Pulse repetition frequency.

Table 2 Summary of the studies relevant to utility of venous excess ultrasound in various clinical settings

Ref.	Study objectives	Clinical outcomes
Andrei et al[53], 2023	Prospective observational study to describe prevalence of venous congestion based on VExUS grading in general ICU patients, and its association with AKI injury and 28-day mortality	Low prevalence of severe venous congestion (16% and 6% of VExUS grades 2 and 3 respectively), which did not change over the study period. No significant association between admission VExUS scores and AKI (P = 0.136) or 28-day mortality (P = 0.594)
Beaubien-Souligny et al[7], 2020	To develop a prototypical VExUS grading system and to validate the model in predicting post cardiac surgery related AKI	Severe congestion (Grade 3) defined by the VExUS C grading system was the most strongly associated with AKI (HR = 3.69, 95%CI: 1.65–8.24, P = 0.001)
Bhardwaj et al[52], 2020	Prospective cohort study on the correlation between serial VExUS score and AKI in patients with cardiorenal syndrome	Resolution of AKI showed significant correlation with improvement in VExUS grade (P = 0.003). There was significant association between changes in VExUS grade and fluid balance (P = 0.006)
Landi et al[54], 2024	Prospective, observational study to determine if venous congestion (using VExUS grading) predicts heart failure related hospitalization and mortality in patients admitted to the emergency department, with acute decompensated heart failure	In patients with a VExUS grade of 3, the probability of both readmission and mortality was significantly greater compared to those with lower grades
Longino et al[49], 2024	Prospective cohort study to assess the diagnostic accuracy of VExUS grade for elevated intracardiac pressure	AUC values for VExUS as predictor of right atrial pressure > 10 mmHg was 0.9 (95%CI: 0.83-0.97), and significantly greater than inferior vena cava diameter or inferior vena cava collapsibility index
Rihl et al[51], 2023	To determine whether VExUS score can be used to guide decongestion in ICU patients with severe AKI, and whether the modification of the score is associated with an increase in the number of RRT-free days in 28 days	Patients with higher VExUS grades (> 1) used more diuretics. Patients who reduced the VExUS grade in 48 hours had more RRT-free days at Day 28 (28.0; 8.0-28.0) than patients who did not reduce VExUS grade (15.0; 3.0-27.5), P = 0.012
Rola et al[32], 2021	Case series on the use of VExUS in identifying pathophysiology and guiding clinical management	Case 1 Continuous drainage of ascites was performed until 12 L was removed. Intravenous frusemide was restarted at a higher dose until a net balance of negative 1000 mL per 8-hour shift was achieved. Case 2 A planned surgical cholecystectomy was cancelled as ultrasound results showed venous congestion instead of cholecystitis. Patient was discharged home with frusemide and an outpatient cardiology review. Case 3 A patient with preexisting pulmonary hypertension received high-dose intravenous frusemide until a net balance of negative 1200 mL per 24 hour was achieved, followed by dose titration to achieve a negative balance of 3200 mL per 24 hours. Dobutamine was further decreased to 3 mcg/kg/min. Case 4 A patient with severe venous congestion and hyperkalemia was treated with intravenous frusemide 200 mg and thereafter hemodialysis was started as there was no diuretic response. A repeat VExUS scan showed improvement in venous congestion, and the patient produced 800 mL of urine. Further diuresis with intravenous frusemide infusion 200 mg/day and spironolactone 50 mg twice a day was given, and a negative fluid balance of 15.5 L was achieved. Case 5 Patient underwent ultrafiltration, and 5 L of fluid was removed within 24 hours. Over the next 48 hours, lactate normalized, and vasopressor requirements improved. VExUS showed refractory shock was related to volume overload and RV dysfunction
Viana-Rojas et al[48], 2023	Prospective, single-center study to evaluate the association between venous congestion assessed with VExUS and the incidence of AKI in patients with acute coronary syndrome	As the degree of VExUS increased, a higher proportion of patients developed AKI: VExUS = 0 (10.8%), VExUS = 1 (23.8%), VExUS = 2 (75.0%), and VExUS = 3 (100%; P < 0.001). A significant association between VExUS ≥ 1 and AKI was found (odds ratio: 6.75, 95%CI: 2.21–23.7, P = 0.001)
Wong et al[50], 2024	Single-center, observational study to evaluate the utility of VExUS to access volume status, in relation to patient’s weight and fluid removal during dialysis	Patients with normal VExUS grades and elevated VExUS grades had no difference in starting weight, dry weight, or fluid removal. Patients with VExUS grades > 1 had more fluid removed than those with VExUS grade 0. All patients with VExUS grades > 1 had impaired right ventricular systolic function

VExUS: Venous excess ultrasound; AKI: Acute kidney injury; ICU: Intensive care unit; HR: Hazard ratio.

Table 3 Hypothetical clinical scenarios where the application of venous excess ultrasound in clinical medicine is possible

Clinical scenario	Clinical application of VExUS
Cardiomyopathy cases such as ischemic cardiomyopathy, septic cardiomyopathy, dengue cardiomyopathy etc.	By detecting the presence of venous congestion via the VExUS grading system, it helps the clinician to decide when to cease fluid therapy. Conversely, when no venous congestion is detected using VExUS, clinicians may be guided to cease diuretic therapy
End stage renal failure	By detecting the presence of venous congestion via the VExUS grading system, it helps the clinician to optimize the adequacy of fluid removal via dialysis
Cases required large amount of fluid resuscitation such as diabetic ketoacidosis, hyperosmolar hyperglycemic state etc.	By detecting the presence of venous congestion via the VExUS grading system, it helps the clinician to detect the threshold to cease the fluid resuscitation
Acute pulmonary oedema secondary to cardiomyopathy, hypoalbuminemia, hypertensive emergency, acute renal failure, acute liver failure etc.	By detecting the absence of venous congestion via the VExUS grading system, it helps the clinician to detect the threshold to cease the diuretic therapy

VExUS: Venous excess ultrasound.