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Dysphagia · Instrumental

Penetration-Aspiration Scale (PAS) calculator

Ordinal 1-8 grading of airway invasion observed on videofluoroscopy or FEES. Levels 2-5 are penetration (above the folds); 6-8 are aspiration (below the folds); 8 is silent aspiration.

PAS level observed during instrumental exam

PAS level

Select a level

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Pick the PAS level that matches the airway event observed on videofluoroscopy or FEES.

About the PAS

The Penetration-Aspiration Scale was developed by Rosenbek, Robbins, Roecker, Coyle, and Wood, and published in Dysphagia in 1996. It was designed to standardize how clinicians describe what happens to material that enters the airway during a swallow, based on videofluoroscopic or fiberoptic endoscopic observation. Rather than leaving the description as unstructured prose, the PAS bundles the depth of airway invasion and the patient response to that invasion into a single ordinal score from 1 to 8. It is now among the most widely used instrumental swallow scoring scales in research and clinical practice.

Structure

Level 1 is normal — material does not enter the airway at all. Levels 2 and 3 describe material that enters the airway but stays above the vocal folds: level 2 is ejected, level 3 is retained. Levels 4 and 5 are similar but with material reaching the vocal folds themselves: level 4 is ejected, level 5 is retained. Levels 6 through 8 describe aspiration, in which material passes below the vocal folds: level 6 is ejected back up into the larynx or airway, level 7 is retained despite effort, and level 8 is silent aspiration — no response at all from the patient.

How to use it

PAS is scored per swallow observed on videofluoroscopy or FEES. Most clinicians rate each trial (by consistency and by volume) and report either the worst PAS observed across the study, the PAS per consistency, or the distribution of PAS scores. Because PAS is ordinal, averaging across swallows is not meaningful — two PAS 4s are not equivalent to one PAS 8. When using PAS for outcome tracking, use the same consistencies and volumes across time points and report the PAS per consistency.

Clinical context

PAS is a descriptive scale, not a recommendation. A high PAS on one swallow does not automatically dictate NPO status or a specific diet level; clinical reasoning has to account for consistency, volume, frequency of events, response to compensatory strategies, and the patient’s broader medical situation. In research, PAS is often the primary outcome for swallow safety in intervention trials and is widely reported alongside DIGEST, MBSImP components, and residue scales.

Limitations

PAS captures airway invasion depth and response but not residue, timing impairments, or physiological mechanism. It is designed for instrumental observation — do not assign it from clinical swallow evaluation alone. Silent aspiration (level 8) is by definition missed at bedside, which is why PAS has its strongest role in instrumental contexts.

Primary source: Rosenbek JC, Robbins JA, Roecker EB, Coyle JL, Wood JL. A penetration-aspiration scale. Dysphagia. 1996;11(2):93-98.

Frequently asked questions

What does the PAS measure?
The Penetration-Aspiration Scale grades what happens to material that approaches or enters the airway during a swallow, as observed on videofluoroscopy or flexible endoscopic evaluation of swallowing. It combines the depth of airway invasion with the patient response into a single ordinal rating from 1 to 8.
Does PAS require an instrumental study?
Yes. PAS is scored on observed videofluoroscopic or FEES images. It is not a bedside rating and should not be assigned from a clinical swallow evaluation alone.
What is the difference between penetration and aspiration on PAS?
Penetration refers to material entering the laryngeal vestibule but remaining at or above the level of the true vocal folds (PAS 2-5). Aspiration refers to material passing below the vocal folds (PAS 6-8). Level 8 is silent aspiration — no patient response.
Can PAS be averaged across swallows?
It is an ordinal scale, and strict averaging is not meaningful. Many clinicians and researchers report the worst PAS observed across trials, the PAS per consistency, or the distribution of PAS scores — not a mean.
How does PAS interact with diet recommendations?
PAS describes a finding, not a recommendation. Diet decisions depend on the frequency and consistency of penetration or aspiration, whether it was effortfully cleared, response to compensations, and overall clinical picture. PAS is one input, not the answer.

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