Dysphagia Knowledge Hub — 吞嚥困難知識庫

Volume-Viscosity Swallow Test (V-VST) — Complete Clinical Guide for Bedside Dysphagia Screening

The Volume-Viscosity Swallow Test (V-VST), developed by Pere Clavé and colleagues at Hospital de Mataró in Spain, is one of the most widely used and best-validated bedside screening tools for oropharyngeal dysphagia (OD). Unlike single-bolus water tests (such as the 3-oz Yale protocol) that answer only “pass/fail,” the V-VST is built around a deliberate progression of two variables — bolus volume (5 mL → 10 mL → 20 mL) and bolus viscosity (nectar → liquid → pudding) — so that a single 5- to 10-minute exam tells the clinician three things simultaneously:

  1. Is dysphagia present?
  2. Is the swallow unsafe (penetration or aspiration risk)?
  3. What bolus characteristics are safest for this patient right now — information that directly informs the choice of IDDSI level for thickened fluids and the initial diet recommendation while the patient awaits instrumental assessment.

This guide walks SLPs, dysphagia nurses, geriatricians, and stroke unit clinicians through the rationale, the exact protocol, scoring rules, diagnostic accuracy, common modifications, and how to translate V-VST findings into actionable diet and posture orders.

Why the V-VST exists: the problem with single-consistency screens

For decades, bedside screening for dysphagia has been dominated by simple water-swallow tests. The 3-oz water test (Suiter & Leder), the Burke Dysphagia Screening Test, and various single-cup protocols are quick — but they share a structural weakness. Water is the most demanding consistency for a neurologically impaired swallow because it travels fast, splashes pharyngeal walls, and gives a patient with delayed swallow initiation almost no time to protect the airway. A patient who fails a 3-oz water test has dysphagia; a patient who passes may still aspirate on something easier to mishandle.

More importantly, a binary pass/fail screen tells the team that something is wrong but offers no guidance on what to feed next. The patient ends up either NPO (with all the malnutrition and morale consequences that entails) or on an empirically chosen “dysphagia diet” that may be more — or less — restrictive than necessary.

Clavé’s V-VST was designed around a clinical insight backed by videofluoroscopy: most patients with neurogenic OD swallow safely if bolus volume is reduced and bolus viscosity is increased, with the optimal combination differing by individual. A screening test that systematically probes both dimensions can therefore not only detect dysphagia but also identify the safest starting consistency for oral feeding.

Equipment you need

The V-VST is intentionally low-tech. To run a complete test you need:

The protocol, step by step

The original Clavé protocol uses a 3 × 3 matrix — three viscosities crossed with three volumes — administered in a fixed safety-first order. The progression always starts with nectar viscosity at the smallest volume because this combination is the safest for a patient with unknown swallow status. Only after a viscosity is tolerated at all three volumes does the clinician step down to the more difficult liquid viscosity. Pudding is reserved for last.

Series 1 — Nectar (IDDSI Level 2, ~270 mPa·s)

  1. Position the patient upright (≥80°), with chin in neutral.
  2. Place the pulse oximeter and record baseline SpO₂ for 60 seconds.
  3. Deliver 5 mL nectar by spoon or syringe. Observe the swallow.
  4. If no safety signs (see below), deliver 10 mL nectar.
  5. If no safety signs, deliver 20 mL nectar.

Series 2 — Liquid (IDDSI Level 0, water)

If — and only if — Series 1 was completed without any safety signs, the test proceeds to liquid.

  1. Deliver 5 mL water, then 10 mL, then 20 mL, observing after each.

Series 3 — Pudding (IDDSI Level 4)

Regardless of what happened with the liquid series, all patients who did not aspirate on liquid (or who completed Series 1 safely if Series 2 was stopped early) move on to pudding.

  1. Deliver 5 mL pudding, then 10 mL, then 20 mL.

Stopping rules

The test is stopped immediately within a viscosity series if any major safety sign appears:

When a safety sign appears, the clinician records the volume and viscosity at which it occurred and skips the remaining boluses of that viscosity. They then move to the next safer viscosity (or, if pudding was the culprit, stop entirely).

What you are scoring: efficacy vs safety

The V-VST evaluates two clinically distinct dimensions, and it is critical that screening staff understand the difference.

Impaired safety signs

These signal that the bolus is — or may be — entering the airway:

Any safety sign means the patient cannot be safely managed on that volume/viscosity combination. In the V-VST framework, a positive safety sign is a flag for likely penetration or aspiration and triggers urgent referral for instrumental assessment (VFSS or FEES).

Impaired efficacy signs

These tell you the bolus is staying out of the airway but is not being cleared efficiently:

Efficacy problems do not, on their own, indicate aspiration risk. They predict malnutrition, dehydration, and prolonged mealtimes, and they should drive interventions such as smaller bites, frequent oral hygiene, alternating consistencies, and a slower feeding pace.

Diagnostic accuracy — what the evidence says

The V-VST has been the subject of multiple validation studies and at least one systematic review (Riera et al., 2021). The figures most often cited are:

The high sensitivity for aspiration is the V-VST’s headline strength: a patient who clears every viscosity-volume combination with no safety signs is unlikely to be a clinically meaningful aspirator. The trade-off is modest specificity — a positive V-VST does not confirm aspiration, only that the airway protection is suspect. This makes the V-VST an excellent screening tool and a poor stand-in for instrumental assessment. Patients who screen positive should be referred for VFSS or FEES whenever possible.

A 2022 study in Frontiers in Neurology validated a modified V-VST (mV-VST) in neurological patients, reporting sensitivity of 96.6% and specificity of 83.3% for OD — confirming that the test performs robustly even in heterogeneous stroke, dementia, and Parkinson’s populations.

Translating V-VST results into a diet recommendation

The V-VST’s most underused output is the safe-and-effective combination matrix — the cells of the 3 × 3 grid the patient cleared without any safety sign. The cell with the largest volume and lowest viscosity the patient handled safely defines the upper limit of what oral intake can begin with.

Common patterns and their IDDSI-aligned recommendations:

It is essential that the team document not just the screening outcome but the volume × viscosity combination at which problems emerged. This single piece of information — for example, “safety signs at 10 mL liquid; safe at all nectar and pudding volumes” — is far more useful to the ward than “failed swallow screen.”

Common modifications and pitfalls

The modified V-VST (mV-VST)

Several research groups have proposed modifications:

These adaptations preserve the test’s structure while making it more practical in settings without lab-grade viscosity measurement.

Pitfalls to avoid

Who should — and should not — be screened with V-VST

Strong candidates:

Contraindications / cautions:

Integrating the V-VST into a dysphagia care pathway

The V-VST works best as the second step in a tiered screening pathway, after a questionnaire-based screen such as the EAT-10. A typical workflow:

  1. EAT-10 ≥ 3 triggers clinical bedside screening.
  2. V-VST performed by a trained nurse or SLP within 24 hours.
  3. Diet and posture orders issued based on the safe-and-effective matrix, mapped to IDDSI levels.
  4. Referral for VFSS or FEES if any safety sign was positive, if the clinical picture is complex, or if the patient is not progressing as expected.
  5. Re-screening at intervals (e.g., weekly during stroke rehabilitation) to upgrade diet as recovery permits.

This staged approach — questionnaire → physiological bedside test → instrumental assessment — is endorsed in the European Society for Swallowing Disorders (ESSD) position statement and is consistent with the World Gastroenterology Organisation’s dysphagia guideline.

Practical bedside script for the V-VST

For staff training, this short script captures the essentials:

“Mrs Chan, I’m going to give you small amounts of liquid in three different thicknesses. After each one, I’ll ask you to say ‘ah’ so I can listen to your voice. If at any point you cough or feel something go down the wrong way, please tell me — we’ll stop immediately. Are you ready?”

[Baseline SpO₂ recorded.] [5 mL nectar by spoon. Wait. Observe lips, oral cavity, swallow. Ask: “Say ‘ah.’” Note voice quality. Watch SpO₂ for 1 minute.] [Proceed with 10 mL, 20 mL nectar; then 5/10/20 mL liquid; then 5/10/20 mL pudding — stopping the series if any safety sign appears.] [Document the safe-and-effective combinations on the V-VST grid.] [If any safety sign was positive, place patient NPO pending SLP review and request instrumental assessment.]

Where V-VST fits in the global dysphagia toolkit

Compared with other widely used bedside tools:

The V-VST occupies a unique position: it is short enough to be a screen, but its 3 × 3 matrix produces a prescription-quality output that directly maps to IDDSI diet levels, which is why it has become the default bedside tool in many European and Latin American dysphagia services.

Key takeaways

Used thoughtfully, the V-VST gives a multidisciplinary team a defensible, evidence-based starting point for oral intake — replacing arbitrary “thicken everything” defaults with a measurement-driven recommendation that respects the patient’s actual swallow physiology.

References