This document summarizes the key points about pulmonary aspiration. It defines pulmonary aspiration as material entering the airways below the vocal cords. Aspiration remains a serious complication of anesthesia. The risk of aspiration is highest during laryngoscopy and extubation. Aspiration can cause pneumonitis, pneumonia or airway obstruction. Factors that increase aspiration risk include an incompetent lower esophageal sphincter, decreased consciousness, or a full stomach. The consequences of aspiration depend on the volume and pH of aspirated material and the patient's response.

1. Rawlinson, E. Pulmonary aspiration. Anesthesia and Intensive Care Medicine. 2007:8(9);365-367.
Pulmonary Aspiration

2. Introduction
• Defined as the inhalation of material into the airway below the
level of the true vocal cords (subglottic space)
• Occurs as a consequence of the passive regurgitation or active
vomiting of gastric contents in patients lacking sufficient
protective laryngeal reflexes
• Pulmonary aspiration remains one of the most feared
complications of anesthesia to this day, and its prevention is a
critical part of anesthetic practice

3. • Overall aspiration incidence in adults
is approximately 1 in 3000 patients:
– In those undergoing emergency
surgery this risesto 1 in 600-800
patients
– Caesarean section under general
anesthesia1 in 400-900 patients
• Of those patients who aspirate and
develop symptoms, mortality is
8% to 10%
• Aspiration occurs most frequently
during laryngoscopy and at extubation,
but can occur at any point in the
perioperative period
Incidence and Risk Factors

4. • There are many factors that may
predispose patients to a greater
risk of aspiration
– However, 50% of patients
will have no preoperatively
identifiable risk factor
• Although used and taught as a
means of preventing pulmonary
aspiration, cricoid pressure at
induction of anesthesia before
intubation does not guarantee that
aspiration will not occur
Incidence and Risk Factors

5. • Consequences of aspiration are
influenced by:
– The nature of the aspiration (fluid
or particulate)
– pH of aspirate
– Volume of aspirate
– The host response
• There is no critical amount of
substance that is completely safe to
aspirate
– Buffering gastric contents in an
attempt to reduce the severity of
pulmonary disease may not be
productive
Headline Initial Caps

6. • Aspiration may lead to a variety of
symptoms and diseases
• Three of the most clinically
important complications are:
– Aspiration pneumonitis
– Aspiration of particulate matter
– Aspiration pneumonia
Clinical Presentation

7. • A non-infective physiochemical
process caused by the
inhalation of sterile acid
• Consists of two phases:
– Initial phase
– Second phase
Aspiration Pneumonitis (Mendelson’s Syndrome)

8. • Involves a chemical burn to the airways,
occurs within 5 seconds of exposure
• Six hours later there is loss of ciliated
and non-ciliated cells, particularly
alveolar type II cells
• This leads to an increase in alveolar
permeability
Alveolar Capillary Junction
Aspiration Pneumontis – Initial Phase

9. Increase in alveolar permeability
Increased interstitial edema
Reduces lung compliance
Increases alveolar-arterial
oxygen tension difference
VQ mismatching
Aspiration Pneumontis – Initial Phase15

10. Acute lung injury ARDS Multi-organ failure
Release of
pro-inflammatory cells
What may ensue following the
release of pro-inflammatory cells is:
Aspiration Pneumontis – Second Phase5

11. • May cause airway obstruction of either
large or small airways
• Complete obstruction causes
immediate arterial hypoxemia and may
be rapidly fatal
• Partial obstruction leads to atelectasis
distal to the obstruction
Aspiration of Particulate Matter

12. • Infective process caused by the
inhalation of gastric contents or
bacterial super infection of the
lung damaged by acid aspiration
– A patient who has aspirated
gastric content is at a greater
risk of developing pneumonia
Aspiration Pneumonia

13. • Aspiration may be diagnosed
from direct visualization of gastric
contents on the vocal cords and in
the trachea during laryngoscopy
• Or, it may not be directly observed
and can occur silently at any point
in the perioperative period
• Aspiration should be considered as
part of the differential diagnosis of
a number of clinical emergencies
presenting under anesthesia
Clinical Features of Aspiration

14. • Airway obstruction
• Bronchospasm
• Cyanosis
• Laryngospasm
• Pulmonary edema
• Reduced compliance and
increased ventilator pressures
• Tachypnoea
Differential Diagnosis of Pulmonary Aspiration

15. • Inherent (GERD, hiatal hernia)
• Pregnancy
• Raised abdominal pressure (obesity)
• Endocrine disease
Incompetent lower
esophageal sphincter
• Decreased consciousness
• Topically anesthetized airway
• Prolonged intubation
• General anesthesia
Decreased laryngeal
reflexes
• Full stomach
• Decreased gastric emptying
• Intestinal obstruction
• Pyloric stenosis
Increased gastric
volumes
Aspiration Risk Factors; Patients

16. Aspiration Risk Factors, Patients
• Surgical procedure
• Laparoscopic techniques
• Position
Operation factors
• Insufficient depth of anesthesia
• Gas Insuffiation from mask
ventilation of LMA ventilation
• Early removal of ETT
Anesthetic factors

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