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Risk factors
Decreased consciousness
Impaired cough and gag reflex
- recent extubation
- neurological disease
- neck or pharyngeal trauma or surgery
- elderly patients
Passive regurgitation
- pregnancy
- emergency surgery with full stomach
- NG tubes
- reflux
- oesophagectomy
- oesophageal obstruction
- achalasia, scleroderma
- raised intra-abdominal pressure
Vomiting
Aspiration of solids
aspiration of large particles causes upper airway obstruction
smaller particles aspirated into lung where they may cause atelectasis
distal to the obstruction
some irritative particles (eg meat, vegetable products) may cause a
localized pneumonitis which may progress to necrotizing pneumonia, abscess
formation, and empyema. Bronchiectasis may follow.
presentation of small particle partially obstructive aspiration is with
dyspnoea, persistent coughing, wheeze, stridor and hypoxaemia
non-obstructive particulate aspiration causes a clinical and radiological
picture similar to that of acid aspiration
Acid aspiration
causes extensive lung damage that starts within minutes of aspiration.
Alveolar epithelial and endothelial damage with atelectasis from surfactant
dysfunction. Fluid and protein leak into alveoli and bronchi immediately,
becoming severe within an hour: permeability pulmonary oedema.
Polymorphonuclear infiltration leads to alveolar consolidation. Most severe
injury occurs with an aspirate pH<2.5
gastric contents in previously healthy patients are acidic and free from
bacterial colonization and therefore infection is not important in the early
stages of acid aspiration lung injury
causes vagally mediated bronchospasm
Non-acid liquid aspiration
blood, isotonic solutions, salt or fresh water produce limited pulmonary
injury. Usually resolves over days
large volume aspiration (eg near drowning) may be associated with severe
lung dysfunction
Aspiration of infected fluids
initial damage similar to acid aspiration but respiratory tract infection
and pneumonia supervene
in non-hospitalized patients anaerobic oral flora sensitive to penicillin
dominate
in critically ill enteric gram negatives dominate
microscopic aspiration thought to be a major factor in the development of
nosocomial pneumonia
Aspiration of hydrocarbons
20% of aspiration accidents in children < 5 yrs
pulmonary damage results from dissolution of membrane lipids and surfactant
inactivation
large aspirates associated wit pulmonary oedema and haemoptysis
Investigations
? evidence of risk factors
ETT suctioning to detect gastric contents or acidic pH on specific testing.
Aspirates should all be gram stained and cultured
fibreoptic bronchoscopy to identify particulate matter
clinical examination to detect laryngeal incompetence
Ba swallow in difficult cases
Management
correct hypoxaemia
inhaled/nebulized bronchodilators for aspiration induced bronchospasm
despite relatively poor efficacy. Aminophylline adds little and has
significant risks
outpouring of protein rich fluid into lung in severe acid aspiration may
lead to relative intravascular hypovolaemia. Whether the optimal fluid
management is fluid administration or restriction is unclear. Inotropes may be
required
therapeutic bronchoscopy if there is particulate aspiration, focal pulmonary
collapse or CXR evidence of foreign body. Rigid procedure of choice to remove
semisolid material and most inhaled objects. Flexible for small solid
particles
antibiotics for secondary bacterial infection and infected fluid aspiration.
Antibiotics depend on setting (ie community/hospital) and whether aspiration
was of liquid or solid. For pneumonia secondary to aspiration of solid
particles cover anaerobes with penicillin or clindamycin
steroids are not of proven benefit and may slow pulmonary healing
Further reading
Cooper DJ. Aspiration syndromes. In Oh TE (ed), Intensive Care Manual, 4th
Ed., Butterworth Heinemann, Oxford, 1997, pp 319-26
© Charles Gomersall December 1999 |
