Case 32 - Full stomach

Question 1

What are mechanisms a conscious person has to prevent regurgiation and pulm aspiration?

Answer 1

1. Lower esophageal sphincter

• swallowing - peristaltic contractions to allow passage of food, LES relaxes.
• Barrier pressure = LES pressure - gastric pressure. Usually maintained in normal patients
• normal pts - increase in abdominal pressure triggers an increase in lower esophageal pressure = maintain barrier pressure
• GERD - LES pressure decrease or gastric pressure increase (barrier pressure decreases)

2. Gastroesophageal angle

• angle where esophagus meets stomach
• oblique angle - high gastric pressures needed for reflux
• small angle (as occurs with morbit obesity or gravid uterues) - lower gastric pressures needed for reflux

3. Diaghramagmatic crura
   * tighetens the lower esophagus to prevent reflux
4. upper esophageal sphincter
   * all general anesthetics including muscle relaxants casue relaxation of this sphincter
5. airway reflexes

• cough
• laryngospasm and apnea
• spasmodic panting (rapid shallow breathing)

Question 2

What are the risk factors for regurgitation and pulmonary aspiration during general anesthesia?

Answer 2

Key concepts:

• any condition associated with increase in intragastric volume, increase in intragastric pressure, or a decrease in LES tone places pt at risk for regurg and pulm aspiration
• general anesthesia is associated with loss upper airway reflexes

Conditions assoc with regurg and pulm asp

• obesity
• abdominal surgery
• decreased level of consciousness
• gastritis/ulcer
• bowel obstruction
• pain/stress
• emergent surgery
• ASA IV-V
• esophageal disorder/previous surgery
• recent meal
• DM with assoc gastroparesis
• ileus
• trauma
• symptomatic hiatal hernia

Question 3

When does aspiration mostly occur?

Answer 3

aspiration can occur at any during the perioperative period (before induction, during induction before DL, mask ventilation, DL, extubate, pacu, etc…)

most of the time, aspiration occurs at induction during laryngoscopy.

Question 4

Explain problems assoc with pulm aspiration

Answer 4

1. aspiration of large gastric particles can obstruct airway anywhere along tracheobronchial tree –> ventilation and oxygenation become difficult
2. acidic pH (pH < 2.5) and a volume grater than 0.4 ml/kg causes chemical pneumonitis (mendelson syndrome), which can result in ARDS.

Question 5

What is the initial treatment of aspiration?

Answer 5

1. oral pharynx should be suctioned
2. if patient supine, turn head to side to faciliate suctioning
3. palce in T-berg position to allow pooling of regurgitatn in oropharhynx, thereby lessing volume of pulm aspiration
4. supplemental oxygen should be given, if patient quickly desats, secure airway and use mech ventilation
5. consider bronchoscopy to remove large particulate matter.

Things to consider

• do not irrigate airway as this can send gastric contents into distal airways
• steroids is not beneficial
• ABX should not routinely be given. Start only after positive culture.
• bronchospasm/weezing due to irritable gastric contents is common, consider B2 andrenergic agonsit inhaler.

Question 6

Usual course and prognosis of aspiration

Answer 6

Course

• clinically significant aspiration occurs within 2 hours of event
• S/sx: bronchospasm, decrease SaO2, A-a gradient > 300 on 100% O2, CXR showing infiltrate (MC on RLL)
• significant aspiration can lead to pulmonary damage –> interstital and alveolar edema, ARDS

Prognosis:

• aspiration in patients with good health has favorable prognosis
• aspiration in patients with multible comorbid condtions results in a poor outcome

Question 7

How should nasogastric tube be managed?

Answer 7

Controversial, three schools of thought.

1) Leave NGT in place, decompress stomach to reduce gastric pressure.
* gastric pressure is increased during induction due to abdominal contents pushing up against the laxed diaphragm.
2) remove NGT
* presence of NGT decreases both LES and upper esophageal sphincter tone (due to mechanical interference).
3) pull back NGT to mid-esophagus (30cm from nares)
* allows for an increase in LES tone (since mechanical obstruction of NGT is gone), which may decrease risk of regurgitation.

Question 8

How does Metoclopramide decrase risk of aspiration?

Answer 8

MOA - dopamine and serotonin receptor antagonist

Function - facilitates gastric emptying by causing gastric peristalsis and relaxation of pylorus

Onset - 20 to 30 min

SE: avoid in bowel obstruction patients, dopamine antagonism can casue extrapyramidal side effects

Question 9

What are other pharacologic intervetions that can decrease risk of aspiration

Answer 9

1) Metoclopramide
2) H2 blockers - cimetidine and ranitidine

• decrease basal acid secretion.
• onset is 20 to 30 min

3) sodium bicitrate

• nonparticulate antacid that immediately increases gastric pH.
• nonparticulate formula is important because aspiration of particulate alkalis can cause chemical pneumonitis

4) PPI (-prazole)

• block H+/K+ ATP enzyme system on secretory surface of parietal cells in stomach.
• decrease volume, increase pH

5) anticholinergics (glyco/atropine)

• increase gastric pH by inhibiting vagal mediated gastric acid production
• glyco decreases LES tone, atropine does not

Question 10

How does cricoid pressure work?

Answer 10

• cricoid cartilage is the only complete cartilaginous circular ring in the trachea
• posterior pressure applied to cricoid cartilage occludes upper esophagus against cervical vertabrae and prevent regurgiation of gastric contents into oropharynx.
• 30N of force should be applied to cricoid catialge until trachea is successfully intubated.

Question 11

pitfalls of cricoid pressure in RSI

Answer 11

• cricoid pressure is poorly tolerated in awake patients, retching can cause increase in intraesophageal pressure and predispose to esophageal rupture
• can incrase difficulty of mask ventilation
• obscure laryngeal view during laryngoscopy
• **may even decrease LES tone and may promote gastric reflux. **
• **at this moment, cricoid pressure is standard of care for induction of anesthesia in patients at increased risk for aspiration**

Question 12

Describe drugs that increase LES prssure and increase barier pressure

Answer 12

Drugs that increase LES pressure and **increase **barrier pressure (LES pressure - gastric pressure):

• alpha adrenergic agnoists
• antacids
• antiemetics
• cholindergics
• endrophonim
• histamines
• meoclopramide
• metoprolol
• neostigmine
• panc
• sux

Question 13

describe drugs that decrease LES tone and decrease barrier pressure

Answer 13

drugs that **decrease **LES tone and **decrease **barrier pressure (LES pressure - gastric pressure):

• beta-adrenergic agonists
• dopamine
• glyco
• inhalation agents
• nitroglycerin
• opioids
• thiopental

Question 14

drugs with no effects on LES Tone

Answer 14

h2 receptor blockers

propanolol

vecuronium

propofol

Question 15

RSI Sequence

Answer 15

Look at Flow Chart