Dysphagia Knowledge Hub — 吞嚥困難知識庫
Penetration-Aspiration Scale (PAS)
Overview
The Penetration-Aspiration Scale (PAS) is the most widely used standardised scale for describing the depth of airway invasion and the patient’s response to that invasion during instrumental swallowing assessment (VFSS or FEES). Developed by Rosenbek et al. (1996), the 8-level ordinal scale has become the de facto standard for reporting swallowing safety in both clinical practice and research.
The PAS distinguishes between two clinically important phenomena:
- Penetration: Material enters the laryngeal vestibule but does not pass below the true vocal folds
- Aspiration: Material passes below the true vocal folds into the trachea
And further characterises patient response:
- Ejected: The patient coughs or swallows to clear the material
- Not ejected: Material remains in the airway
The 8 Levels
| Level | Description | Clinical Significance |
|---|---|---|
| 1 | Material does not enter the airway | Normal |
| 2 | Material enters the airway, remains above the vocal folds, and is ejected | Trace penetration; clinically normal or mild |
| 3 | Material enters the airway, remains above the vocal folds, and is not ejected | Retained penetration; mild clinical concern |
| 4 | Material contacts the vocal folds and is ejected | Penetration to fold level; moderate concern |
| 5 | Material contacts the vocal folds and is not ejected | Retained vocal fold penetration; high concern |
| 6 | Material passes below the vocal folds and is ejected into the larynx or pharynx | Sub-glottic aspiration with ejection; moderate-severe |
| 7 | Material passes below the vocal folds and is not ejected despite patient effort | Aspiration without clearance; severe |
| 8 | Material passes below the vocal folds; no effort to eject | Silent aspiration; most severe |
Reliability
Rosenbek et al. (1996) reported:
- Inter-rater reliability: Weighted κ = 0.79–0.80 for trained raters
- Intra-rater reliability: Weighted κ = 0.82–0.92
Reliability is highest when raters receive training with anchor examples. Novice raters frequently confuse Levels 3 and 4 (retained vestibular penetration vs. penetration at the fold level) and Levels 6 and 7 (ejected vs. not ejected sub-glottic aspiration).
PMID: 8695059
Clinical Significance of Each Level
Levels 1–2: Within normal limits. Many healthy adults show transient Level 2 penetration with thin liquids. No dietary modification indicated on PAS alone.
Level 3: Retained vestibular penetration without patient response — this suggests reduced laryngeal sensation. Monitor closely; consider thickening thin liquids.
Level 4–5: Penetration at or contacting vocal folds. Level 5 (not ejected) suggests significantly reduced protection. Texture modification and SLT intervention indicated.
Level 6: Aspiration with ejection — the patient’s cough reflex is functional. Protective cough is a positive prognostic sign. Texture modification and compensatory strategies; rehabilitation possible.
Level 7: Aspiration without successful ejection — poor prognosis for safe oral intake without intensive rehabilitation. High aspiration pneumonia risk.
Level 8 — Silent Aspiration: The most clinically dangerous. No cough, no awareness, no airway protection. Strongly associated with aspiration pneumonia. May require nil-by-mouth or enteral nutrition. Prevalence is 40–70% in stroke patients who aspirate (Ramsey et al., 2003; DOI: 10.1016/S0140-6736(03)14653-0).
PAS and Clinical Decision-Making
PAS scores alone should not dictate feeding decisions. They must be interpreted in context:
- Material type: PAS scores differ for thin liquids vs. solids. A patient may aspirate thin liquids (high PAS) but handle purée safely (low PAS). Report PAS per material tested.
- Volume: Small bolus volumes often show lower PAS than larger volumes.
- Patient context: A patient with PAS 8 who is medically frail, immunocompromised, or has chronic lung disease has higher aspiration pneumonia risk than a PAS 8 patient who is otherwise robust.
- Frequency: A single aspirated bolus out of 20 tested is clinically different from aspiration on every trial.
PAS in Research
The PAS is the primary safety outcome measure in most swallowing rehabilitation trials. A reduction of ≥2 PAS levels is commonly used as the threshold for clinically significant improvement in randomised controlled trials.
References
- Rosenbek JC, et al. (1996). A penetration-aspiration scale. Dysphagia, 11(2):93–8. PMID: 8721066
- Ramsey DJ, et al. (2003). Swallowing dysfunction after stroke. Lancet, 362(9398):1778–9. DOI: 10.1016/S0140-6736(03)14653-0
- Steele CM, Grace-Martin K (2012). Reflections on clinical and statistical use of the penetration-aspiration scale. Dysphagia, 27(4):496–500. DOI: 10.1007/s00455-012-9418-7
- Daggett A, et al. (2006). Laryngeal penetration during deglutition in normal subjects of various ages. Dysphagia, 21(4):270–4. DOI: 10.1007/s00455-006-9051-6