Aspiration Pneumonitis

Reviewed and revised 26 September 2015

OVERVIEW

  • Aspiration = inhalation of oropharyngeal or gastric contents into the larynx and lower respiratory tract
  • Aspiration pneumonitis, or Mendelson syndrome, is chemically induce inflammation of the lungs  as a result of aspiration of gastric contents
  • Aspiration pneumonia is infection of the lungs following aspiration by micro-organisms colonising the GI tract
  • Distinguishing from aspiration pneumonitis may be difficult, and the distinction is controversial

PATHOPHYSIOLOGY

Aspiration is more likely when there are factors contributing to:

  • increased intragastric pressure
  • decreased upper and lower oesophageal sphincter tone, and/or
  • obtunded upper airway reflexes

Factors that reduce lower esophageal pressure

  • Gastric fluid components
  • Increased acidity
  • Lipids
  • Hyperosmolar fluid
  • Progesterone
  • Pharmacologic agents
  • Dopaminergic agonists
  • β-Adrenergic agonists
  • Theophylline and caffeine
  • Anticholinergics
  • Opioids

Aspiration pneumonitis

  • chemical burn of the tracheobronchial tree and pulmonary parenchyma
  • this causes an intense inflammatory reaction

Aspiration pneumonia

  • the contents of the stomach are normally sterile; however, superinfection can take place subsequently
  • bacteria more likely if
    • patient on antacids, H2 antagonist or PPI
    • receiving enteral feed
    • gastroparesis
    • small bowel obstruction
    • elderly: increased colonization with S. aureus, aerobic gram-negative bacilli (Klebsiella and Escherichia coli)

Segments affected

  • those that aspirate in recumbent position -> posterior segments of upper lobes
  • those that aspirate upright -> basal segments of lower lobes

Complications

  • ARDS
  • pneumonia, abscess formation and cavitation

CLINICAL FEATURES

  • aspiration may range from asymptomatic to severe respiratory failure
  • respiratory symptoms and signs include cough, wheeze, crackles, dyspnoea, soiling of the airway, tachypnoea, tachycardia decreased lung compliance (increased airway pressures), hypoxia and cyanosis
  • even in the absence of infection a SIRS response may occur, including raised WBC, fever, tachycardia and hypotension

RISK FACTORS

Patient factors

  • full stomach (fasting guidelines: 2 hr – clear fluids, 4 hr – breast milk, 6 hr – food)
  • opioid use
  • pain
  • pregnancy
  • increased BMI
  • distended abdomen – mass, ascites, bowel obstruction
  • GORD
  • decreased level of consciousness
  • gastric mass (malignancy)
  • DM
  • oesophageal motility disorders
  • anxiety
  • chronic neurological conditions – bulbar palsy from CVA, MS, MG, myotonic dystrophy
  • scleroderma

Anaesthetic

  • anaesthesia with an unprotected airway (induced unconsciousness)
  • instrumentation of airway with inadequate depth of anaesthesia
  • paralysis
  • head down positioning
  • inadequate cricoid pressure
  • use of other airways other than cuffed endotracheal tube
  • opioids
  • use of inhalational agent (N2O)

Surgical

  • laparoscopic insufflation of abdomen
  • bowel or visceral manipulation
  • pain

PREVENTION OF ASPIRATION

This applies particularly to patients receiving sedation or induction of anaesthesia

  • Adequately starved patients
  • Prophylactic anti-emetic use
  • Adequate analgesia
  • RSI (pre-oxygenation, suction readily available, induction with cricoid pressure, suxamethonium, no bag-mask ventilation)
  • If bag-masking required – use small shallow breaths (LOS pressure 20 cmH2O)
  • Low threshold for use of a cuffed endotracheal tube
  • Prokinetics pre-induction and extubation (high risk times)
  • Extubating at risk patient once return of laryngeal reflexes apparent
  • Use of agent like remifentanil and propofol so patients can wake quickly and clear headed with intact laryngeal reflexes
  • Minimise opioid use
  • No N2O

MANAGEMENT

IMMEDIATE

  • minimised further aspiration
  • if awake -> suction and place in recovery position
  • if breathing spontaneously -> recovery position
  • if unconscious and apnoeic
  • secure airway (ETT)
  • suction until airway clear
  • 100% O2
  • CPAP

SUBSEQUENTLY

  • empty stomach with NG tube
  • CXR – diffuse infiltrate (often in RLL) – on table CXR
  • bronchoscopy +/- lavage
  • chest physiotherapy
  • ICU referral if appropriate
  • ?corticosteroids – may dampen down inflammation but don’t effect outcome
  • ?antibiotics not indicated unless aspiration of infected material is a particular concern or has other risk factors (see above)

Aspiration pneumonia

  • first line antibiotics:
    -> benzylpenicillin + metronidazole
    -> or clindamycin
  • if aerobic gram –ve bacilli suspected (alcoholic patients)
    -> metronidazole + ceftriaxone/cefotaxime/piperacillin-tazobactam/ticarcillin+clavulanate
  • once defervesce -> amoxicillin-clavulanate or clindamycin po
  • 7 days of total therapy usually adequate

References and Links

Journal articles

  • Marik PE. Aspiration pneumonitis and aspiration pneumonia. The New England journal of medicine. 344(9):665-71. 2001. [pubmed]

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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