5. IVC, VENOUS CONGESTION & FLUID RESPONSIVENESS

5.1 IVC

Spontaneous breathing

IVC <1.5 cm with collapse >50%: collapsed or small; low CVP; possible hypovolaemia. [1]

IVC 1.5–2.5 cm with collapse 20–50%: normal or intermediate; indeterminate; correlate clinically. [1]

IVC >2.1 cm with collapse <50%: formal elevated RAP estimate; standard formal echo RAP ≈15–20 mmHg. [1]

IVC >2.5 cm with collapse <50%: plethoric or marked POCUS finding; avoid empiric fluids. [1]

IVC >2.5 cm with collapse <20%: clearly plethoric; high suspicion of volume overload or impaired RV filling. [1]

IVC >3.0 cm with minimal collapse: markedly plethoric; late warning; possible iatrogenic congestion. [1]

IVC >3.5 cm: marked plethora in some protocols; not a universal formal RAP cutoff. [1]

Collapsibility index, spontaneous breathing: Formula: (Dmax − Dmin)/Dmax × 100. [1]

50%: low CVP. 20–50%: indeterminate. <20%: high CVP. [1] For fluid responsiveness, a collapsibility threshold of ≈40–41% or greater suggests fluid responsiveness. [1,2] Reported specificity ≈80–97%. [1,2] High collapsibility increases the likelihood of responsiveness but does not guarantee it; low collapsibility reduces the likelihood but does not absolutely exclude it. [1]

Technique for spontaneous breathing: Measure during quiet spontaneous tidal breathing. Dmax at end-expiration; Dmin during inspiration. If a quiet tidal inspiration does not elicit a clear Dmin, a brief controlled sniff may be used. Do not use sustained maximal inspiratory strain or Valsalva-like effort. In fully mechanically ventilated patients without spontaneous breathing activity, IVC collapsibility is not the appropriate index; use IVC distensibility or mean-based variability instead. [1]

Integration with diameter Fluid responsiveness is more likely when the IVC is relatively small, commonly <2.1 cm, with collapse >50%, suggesting lower RAP. Fluid unresponsiveness is more likely when the IVC is relatively plethoric, commonly >2.1 cm, with collapse <50%. Very low collapsibility, <10–12%, is particularly indicative of fluid unresponsiveness. Published thresholds for spontaneous-breathing IVC variability are not uniform and have ranged ≈8–50% depending on population, ventilatory conditions, and technique. Diagnostic accuracy in spontaneously breathing patients is less robust than in fully ventilated patients; integrate with other dynamic and static haemodynamic assessments. [1,2]

Mechanical ventilation

Do not use inspiratory collapse for RAP. [1]

IVC distensibility, Dmin-based: (Dmax − Dmin)/Dmin × 100. [1]

Common general controlled-ventilation threshold: 15% or greater. [1] Validation-specific range: ≈12–21%. [1] An 18% threshold remains appropriate in selected fully ventilated septic shock protocols; it is a validation-specific operating point, not the only standard. [1,2]

Validity: tidal volume ≥8 mL/kg, stable ventilator settings, no spontaneous effort. [1]

Invalidity: high PEEP, low tidal volume, spontaneous effort, RV dysfunction, intra-abdominal hypertension. [1]

IVC variability, mean-based: (Dmax − Dmin)/[(Dmax + Dmin)/2] × 100.

Common threshold: 12%. [1] Same validity/invalidity conditions as Dmin-based distensibility. [1] A 15% value labelled “distensibility” refers to the Dmin formula and is a common operational threshold. Do not interchange 15% Dmin-based distensibility, 18% septic-shock-specific distensibility, and 12% mean-based variability. [1,2]

Formula warning: Collapsibility index, Dmin-based distensibility index, and mean-based variability are not interchangeable. State which formula was used. Do not mix thresholds from different formulas. [1,2]

Pitfall:

Using IVC collapsibility in mechanical ventilation without caution.

5.2 VExUS — Venous Excess Ultrasound

VExUS integrates four bedside ultrasound sites. Each site is scored 0 or 1. [3]

Sites

IVC: normal diameter with expected respiratory variation vs plethoric/dilated IVC with reduced respiratory variation. [3]

Hepatic vein: systolic predominance vs S/D <1, diastolic attenuation or reversal, or atrial reversal. [3]

Portal vein: continuous antegrade flow vs increased pulsatility, attenuated or reversed diastolic flow. Abnormal portal pulsatility is commonly defined as pulsatility fraction >50%. [3]

Intrarenal vein: continuous antegrade diastolic flow vs loss, attenuation, or reversal of diastolic flow. [3] Exact portal and intrarenal Doppler thresholds can vary by protocol; state institutional algorithm.

Conventional VExUS grading

Grade 0: IVC normal and all venous Doppler normal. No systemic venous congestion. [3]

Grade 1: isolated IVC abnormality; hepatic, portal, and intrarenal Doppler normal. At risk for venous congestion. [3]

Grade 2: exactly one venous Doppler abnormality. IVC may be normal or abnormal. Possible congestion. [3]

Grade 3: two or more venous Doppler abnormalities. IVC may be normal or abnormal. Probable congestion. [3]

Examples

Plethoric IVC only: VExUS 1.

Normal IVC + abnormal hepatic vein only: VExUS 2.

Abnormal IVC + abnormal hepatic vein only: VExUS 2 (only one venous Doppler site abnormal).

Abnormal hepatic vein + abnormal intrarenal vein: VExUS 3.

All four sites abnormal: VExUS 3. [3]

If an institution uses an additive 0–4 point system, state this explicitly; it is not identical to conventional categorical VExUS grading.

Interpretive caveats

VExUS is a likelihood scale, not a linear severity scale. [3] Grade 2 should be interpreted cautiously as possible congestion with higher false-positive susceptibility; a single venous Doppler abnormality may be influenced by non-congestive factors.

Grade 2 is not equivalent to Grade 3. [3]

VExUS is not a simple volume-status score. It reflects the interaction of venous return and cardiac function. [3] The same VExUS grade can arise from elevated RAP, RV failure, elevated PVR, LV filling-pressure elevation, high intra-abdominal pressure, pericardial constraint, mechanical ventilation, arrhythmia, or altered venous capacitance. [3,4]

Important confounders: spontaneous vs mechanical ventilation, PEEP and tidal volume, atrial fibrillation/other arrhythmias, significant tricuspid regurgitation, RV systolic/diastolic dysfunction, LV diastolic dysfunction, pericardial effusion/tamponade, elevated intra-abdominal pressure, hepatic/renal parenchymal disease, probe positioning, respiratory timing. [3,4]

In sepsis and mixed ICU populations, VExUS–outcome associations are less consistent than in some cardiac surgery cohorts. [3]

Lung ultrasound score and VExUS answer different questions; discordant patterns are clinically meaningful. [3] (see S4.1)

5.3 Fluid responsiveness — dynamic indices

IVC collapsibility

Patient state: spontaneous breathing.

Key threshold: ≈40–41% or greater. Reported specificity: ≈80–97%.

Validity: quiet respiration, good window. Invalidity: PEEP, arrhythmia, RV failure, pericardial disease. [1,2]

IVC distensibility, Dmin-based

Patient state: controlled mechanical ventilation, no spontaneous effort.

Key threshold: commonly 15% or greater; validation-specific range 12–21%; 18% in selected septic shock protocols.

Validity: tidal volume ≥8 mL/kg, stable settings, no spontaneous effort. Invalidity: high PEEP, low tidal volume, spontaneous effort, RV dysfunction, intra-abdominal hypertension. [1,2]

LVOT VTI or peak aortic velocity respiratory variation

Patient state: controlled mechanical ventilation.

Key statistic: sensitivity ≈79% reported in mechanical ventilation circulatory failure.

Validity: no arrhythmia, stable haemodynamics. Invalidity: atrial fibrillation, spontaneous breathing, poor compliance, low tidal volume, RV failure. [5]

Passive leg raising with LVOT VTI or stroke volume

Any patient state, especially when IVC assumptions are not met.

Positive response: 10–15% or greater increase in stroke volume, cardiac output, or LVOT VTI. A 10–15% response is associated with excellent predictive performance.

Validity: supine position, legs raised ≈45°, maintained 30–60 s. Invalidity/caution: lower limb fracture, DVT, pelvic or hip injury, severe oedema. [1,2]

SVC collapsibility

TEE-based, not standard POCUS.

Threshold: >39% in septic shock; specificity ≈84% in mechanical ventilation circulatory failure.

Validity: TEE available. Limitation: limited TTE access. [5]

Formula warning

Percent variation = 100 × (max − min)/[(max + min)/2].

Distensibility index = 100 × (Dmax − Dmin)/Dmin.

Collapsibility index = 100 × (Dmax − Dmin)/Dmax.

These are not interchangeable. State the formula. Do not apply a threshold from one formula to a value calculated with another. [1,2]

5.4 Multimodal low-output/hypovolaemia pattern — sepsis

Aortic VTI <16 cm plus mitral E <67 cm/s plus SVC collapsibility >39% is highly suggestive of hypovolaemia or fluid responsiveness in septic shock. [5]

5.5 Fluid tolerance — harm-limiting markers

New or increasing B-lines: developing interstitial oedema; reduced fluid tolerance. (see S4.1) VExUS grade 2–3: systemic venous congestion; limited capacity for further volume. [3] IVC >2.5 cm plus poor collapse: plethoric; avoid empiric fluids. [1] E/A shift from <1 to >2 during resuscitation: approaching preload ceiling; further fluid of limited benefit. (see S3.5.1) Replacement of A-lines by B-lines is a practical bedside stop signal for further fluid unless the clinical question changes. (see S4.1) Responsiveness is not tolerance. A patient may be fluid responsive and have limited fluid tolerance. [2,3]

5.6 Passive leg raising — practical points

Reversible autotransfusion ≈300 mL. [1,2] Positive response: 10–15% or greater increase in stroke volume or LVOT VTI. [1,2] The response is transient; interpret in context. Cautions: lower limb DVT, hip or pelvic fracture, severe oedema, intra-abdominal hypertension. [6] PLR is a preload test, not a fluid bolus. [1]

5.7 Pitfalls

  1. Using IVC collapsibility in mechanical ventilation without caution.

  2. IVC diameter is a number, not a diagnosis.

  3. Collapsibility index is less reliable in mechanical ventilation.

  4. Plethoric IVC in heart failure is expected; in a young patient with sudden dyspnoea and leg swelling, consider PE.

  5. Collapsible IVC in sepsis does not guarantee fluid responsiveness.

  6. VExUS grade 2 is possible congestion, not definitively severe congestion.

  7. VExUS reflects venous return plus cardiac interaction, not simple fluid overload.

  8. VExUS is affected by COPD, PEEP, mechanical ventilation, obesity, tamponade, and CVC.

  9. Formula-specific thresholds: do not mix.

  10. IVC greater than 2.1 cm with collapse less than 50% is the formal elevated-RAP criterion.

  11. IVC greater than 3.5 cm is not a universal formal RAP cutoff.

  12. Using 18% as the only standard Dmin-based distensibility cutoff; the common general threshold is 15%, with 18% as a septic-shock-specific operating point.

  13. Interchanging Dmin-based distensibility with mean-based variability.

  14. Applying Valsalva-like effort for IVC collapsibility measurement.

  15. Using a linear probe as the standard transducer for adult subcostal IVC assessment.

  16. Ignoring PEEP, spontaneous effort, low tidal volume, RV failure, intra-abdominal hypertension, and arrhythmia.

References

  1. Monnet X, et al. ESICM guidelines on circulatory shock and hemodynamic monitoring: 2025 update. Intensive Care Med. 2025;51(11):1971-2012. doi:10.1007/s00134-025-08137-z.

  2. Huard K, Deschamps J, Couture EJ, et al. Venous congestion in critical care: combining VExUS, lung ultrasound, and echocardiography. Ann Intensive Car. 2026;16:100127. doi:10.1016/j.aicoj.2026.100127.

  3. Malbrain MLNG, et al. Fluid management in sepsis. In: Malbrain MLNG, Wong A, Nasa P, Ghosh S, eds. Rational Use of Intravenous Fluids in Critically Ill Patients. Cham: Springer; 2024. doi:10.1007/978-3-031-42205-8.

  4. Mekontso Dessap A, AlShamsi F, Belletti A, et al. European Society of Intensive Care Medicine (ESICM) 2025 clinical practice guideline on fluid therapy in adult critically ill patients: part 2 — the volume of resuscitation fluids. Intensive Care Med. 2025;51(3):461-477. doi:10.1007/s00134-025-07840-1.

  5. Chen L, Hong L, Ma A, et al. Intraoperative venous congestion rather than hypotension is associated with acute adverse kidney events after cardiac surgery: a retrospective cohort study. Br J Anaesth. 2022;128(5):785-795. doi:10.1016/j.bja.2022.01.032.

  6. Beurton A, Teboul JL, Girotto V, et al. Intra-abdominal hypertension is responsible for false negatives to the passive leg raising test. Crit Care Med. 2019;47:e639-e647.