# Aspiration Pneumonia and Pneumonitis

> Aspiration pneumonia and pneumonitis for NEET-PG Medicine covering Mendelson syndrome, dependent lung segments, antibiotic choice and abscess risk.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/aspiration-pneumonia-and-pneumonitis
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Murray and Nadel's Textbook of Respiratory Medicine; Davidson's Principles and Practice of Medicine
- How to cite: "Aspiration Pneumonia and Pneumonitis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/aspiration-pneumonia-and-pneumonitis

## Direct answer

Aspiration pneumonia is bacterial infection of the lung after oral or gastric contents are inhaled, while aspiration pneumonitis is a sterile chemical injury, most often from acidic gastric contents. Both favour dependent segments, most often the right lower lobe. Chemical pneumonitis appears within hours, as in Mendelson syndrome, and antibiotics are withheld unless infection develops. Anaerobic cover is reserved for abscess or empyema under current guidance.

## What you must remember

- **Aspiration pneumonia:** infection after inhaling oropharyngeal flora, with oral streptococci and anaerobes in community cases and Gram-negative bacilli more typical in hospital cases.
- **Chemical pneumonitis:** Mendelson syndrome follows aspiration of stomach acid, usually below pH 2.5, during anaesthesia or vomiting, and it is sterile at onset.
- **Dependent segments:** the right lower lobe is most often involved, and in supine patients the posterior upper lobe and superior lower lobe segments are also at risk.
- **Risk factors:** stroke, dysphagia, reduced consciousness, seizures, sedation, alcohol and gastro-oesophageal reflux.
- **Antibiotics:** for community-acquired aspiration pneumonia, amoxicillin with clavulanate is a common first choice, following local and current guidance.
- **Complications:** lung abscess and empyema, most often when infection is anaerobic or aspiration recurs.

## An elderly stroke patient with a fever after feeding

A 78-year-old woman with a recent left hemisphere stroke has coughed while eating. Two days later she has fever, a productive cough and a right lower zone shadow on the chest film.

Aspiration should be suspected in a patient who chokes while eating, has a stroke or is sedated, and then develops a dependent infiltrate. The steps below separate infection from chemical injury and direct treatment.

1. **Identify the event:** A witnessed choking episode, vomiting, a swallowing problem or sedation is the strongest clue.
2. **Localise the infiltrate:** Dependent segments on the chest film support aspiration, though imaging alone cannot separate infection from chemical injury.
3. **Decide infection or pneumonitis:** Fever, purulent sputum and a rising inflammatory marker favour infection, while sudden hypoxia after vomiting with clear sputum favours pneumonitis.
4. **Treat the infection:** Empirical antibiotics suited to the setting are started for suspected infection, with cultures sent where possible.
5. **Support and assess swallowing:** Oxygen, upright positioning and early speech and swallow assessment reduce the risk of recurrence.
6. **Watch for complications:** Persisting fever, cavitation or a loculated effusion suggest abscess or empyema, and imaging is repeated.

## Where the exam tests aspiration

The exam tests whether you distinguish the two conditions and avoid routine antibiotics or steroids.

- **Trap:** giving antibiotics routinely for every aspiration — **Correct:** chemical pneumonitis does not need antibiotics unless infection develops.
- **Trap:** choosing anaerobic cover for every case — **Correct:** routine anaerobic cover is not favoured for uncomplicated aspiration pneumonia, and it is kept for abscess or empyema.
- **Trap:** giving steroids for Mendelson syndrome — **Correct:** steroids are not established for aspiration pneumonitis, and supportive care is the mainstay.
- **Trap:** discharging a stroke patient without a swallow assessment — **Correct:** recurrent aspiration is common without evaluation, so swallowing is assessed before feeding.

## Frequently asked questions

### What is Mendelson syndrome?

Mendelson syndrome is chemical pneumonitis caused by aspiration of acidic gastric contents, typically during anaesthesia or vomiting. It presents within hours with hypoxia and infiltrates, and it is managed with supportive care, with antibiotics added only if infection develops.

### Why is the right lower lobe most often involved in aspiration?

The right lower lobe is most often involved in aspiration because the right main bronchus is more vertical and wider than the left. In a supine or recumbent patient, the dependent segments of the lower lobes and the posterior upper lobe are also at risk.

### Is anaerobic antibiotic cover always needed in aspiration pneumonia?

Anaerobic antibiotic cover is not routinely needed in uncomplicated aspiration pneumonia under current guidance. It is reserved for lung abscess or empyema, where anaerobic infection is more likely and drainage may also be required.

### What are the complications of aspiration pneumonia?

Lung abscess and empyema are the main complications of aspiration pneumonia, especially when the infection is anaerobic or aspiration recurs. Persistent fever, cavitation or a loculated effusion on follow-up imaging suggests these complications and needs review.