Aspiration

Question 1

Prevention of aspiration:

Answer 1

The lower oesophageal sphincter has a pressure of 20 cm H2O
With a lot of stomach content intragastric pressure becomes higher than the lower oesophageal sphincter pressure
- reduce stomach vol keep pt NPO before surgery. Do rapid sequence induction avoid blowing stomach up
- promote stomach emptying
- stomach pH incr to >2.5 reduces the severity of the CONSEQUENCE of aspiration, rather than actually PREVENITNG aspiration.

Question 2

NPO rules (ASA) – minimum fasting periods:

Answer 2

Clear liquids → black tea/coffee, fruit juice without pulp, carbonated drinks (no alcohol!) > 2 hours

Breastmilk > 4 hours

Infant formula > 6 hours

Non-human milk > 6 hours

Light meal → liquid and toast > 6 hours

Fat/big meal → fatty meal may take longer > 8 hours

Question 3

The barrier pressure of the stomach

Answer 3

the difference between the LESP (area of high tone that usually prevents the gastric contents from being regurgitated into the pharynx) and the IGP
* barrier pressure = LESP – IGP

Question 4

How can you Increase lower oesophageal sphincter pressure

Answer 4

o Metoclopramide ** They ask this
Avoid anticholinergics increases risk of gastro-oesophageal reflux
Manage factors that increase intragastric pressure
o Decompress stomach with NGT
o Avoid stomach inflation when ventilating

Question 5

Identify at risk patients for aspiration

Answer 5

• Stomach contents volume (> 0.4) & pH (< 2.5)
• Barrier pressure inadequate
• Protective laryngeal reflexes depressed / absent

Question 6

Factors delaying stomach emptying:

Answer 6

• Gastric stasis  pyloric stenosis, intestinal obstruction, ileus
• Post-vagotomy
• Diabetes  diabetics often have gastroparesis!
• Renal failure
• Pain
• Anxiety
• Opioids
• Fatty meals
• Pregnancy

Question 7

Factors increasing intrabdominal pressure:

Answer 7

• Intraabdominal masses tumours, pregnancy, organomegaly, ascites
• Coughing or bucking
• Gas

Question 8

Factors decreasing LESP:

Answer 8

• Pregnancy
• High sympathetic nervous system activity
• Drugs  anticholinergics, opioids, alcohol, nicotine

Question 9

Factors decreasing laryngeal reflexes:

Answer 9

• Unconsciousness / reduced GCS
  o Induction of general anaesthesia
  o CNS  brain injury, intoxication, seizures
• Muscle relaxants (not protected with ETT)
• Local anaesthesia of the airway

Question 10

Reasons why pregnant patients are at risk:

Answer 10

• Difficult airway
• Delayed gastric emptying in labour
• Opioids
• Increased intraabdominal pressure
• Decreased LESP
• Obesity
• Less experience with general anaesthesia (spinal anaesthesia)

Question 11

Pathophysiology of aspiration:

Answer 11

• Aspirated acid or liquid spreads to lung periphery within seconds (i.e. lavage of little value)
  o Surfactant loss
  o Inflammation  endothelial damage & alveolar permeability
  o Fluid filled alveoli  hypoxia, pulmonary oedema, stiff lungs
• Results in exudate patchy process with fluid filled alveoli