Chp. 28 Aspiration

Question 1

Def: vomiting

Answer 1

• Forceful expulsion of gastric contents into the pharynx
• Involves diaphragmatic and abdominal muscle contractions

Question 2

Def: regurgitation/reflux

Answer 2

• Passive action that results in gastric contents entering the esophagus and oropharynx

Question 3

How does GER occur?

Answer 3

• Lower esophageal sphincter (LES) acts as a barrier in preventing regurgitation of stomach contents into esophagus
• Barrier pressure may be reduced the gastric pressure increases or LES pressure decreases

Question 4

GER and Ruminants

Answer 4

• Ruminants = predisposed to regurg owing to large volumes of GIT contents and excessive gas production
• Fasting in sheep and cattle does not eliminate incidence of regurgitation

Question 5

T/F: endotracheal intubation attempts during light planes of anesthesia may initiate regurgitation, esp in ruminants

Answer 5

True

Question 6

What are the consequences of GER?

Answer 6

• Pulmonary aspiration of gastric contents –> significant morbidity, possible mortality
• Esophageal mucosal damage
• Esophagitis and in severe cases, stricture
• More often there are no serious consequences

Question 7

Def: barrier pressure

Answer 7

Difference between the esophageal sphincter pressure and gastric pressure

Question 8

Causes of increased gastric pressure

Answer 8

• Increased abdominal pressure
• Straining against the endotracheal tube
• Coughing

Question 9

Causes of decreased LES pressure

Answer 9

Drug-induced

Question 10

What positioning or features predispose animals to regurgitation?

Answer 10

• Positions of recumbency, esp dorsal or head down positions
  -Restrictive tight belly bands

Question 11

How can anesthesia affect LES and barrier pressure

Answer 11

• Many drugs - likely all drugs - administered during the ax period lower LES pressure -> reflux more likely

Question 12

How common is GER in the ax period?

Answer 12

• Few clinical veterinary studies -> two similar studies in dogs reported an incidence of reflex during ax as 16.3 and 17.4%
• Reflux defined by documenting esophageal pH <4.0, >7.5
• Study of 40 dogs: no GER reported
• Study of 100 humans for elective surgery: incidence of GER was 0

Question 13

How common is GER in the ax period for ruminants?

Answer 13

• Quite common to observe rumen and gastric contents passively draining from pharynx during GA
• Incidence in ax’d, non-fasted sheep = 60-80%
• At greater risk of aspiration in the ax period

Question 14

How common is pulmonary aspiration of gastric contents?

Answer 14

• Several human population studies found incidence to be minimal - 0.01% with low mortality
• Small veterinary patients: specific incidence unknown, but appears to be low
• High incidence of reflux in anesthetized ruminants, pulmonary aspiration likely to be higher

Question 15

What are the pulmonary consequences of aspiration?

Answer 15

• Will depend on the amounts, contents aspirated which can be liquid acid, liquid non-acid, particle related or combinations

Question 16

Pulmonary complications from aspiration of small amounts of food, liquid?

Answer 16

• Often well-tolerated
• May not cause significant complications

Question 17

What are the pulmonary consequences of acid fluid aspirates?

Answer 17

• Acid fluid aspirates generally have pH <2.5
• In high enough volumes, can immediately result in chemical pneumonitis –> hypoxia, interstitial edema, intra-alveolar hemorrhage and atelectasis
• IFM phase occurs few hours later that could lead to respiratory failure

Question 18

What are the pulmonary consequences of non-acidic fluid aspirates?

Answer 18

• May produce hypoxia, alveolar collapse, atelectasis
• Late inflammatory response not as severe as with acidic aspirates

Question 19

What are the pulmonary consequences of aspiration of particulate matter?

Answer 19

• Hypoxemia, atelectasis, acute airway obstruction, immediate death
• Signs may appear several hours after the event –> coughing, tachypnea, dyspnea
• Later, inflammatory response occurs similar to FB reaction

Question 20

What is important to remember about the regurgitant material in ruminants compared to cats and dogs?

Answer 20

• Regurgitant material more particulate but pH is less acidic than small animals

Question 21

Name some risk factors for aspiration

Answer 21

• Not protecting airway with endotracheal intubation
• Uncuffed, inadequately inflated ETT will not protect from aspiration if regurgitation occurs
• Inadequate fasting of solid food increase risk of aspiration if regurgitation occurs, as will premature extubation, before protective laryngeal reflexes have returned

Question 22

List some diseases or physiologic conditions that place a patient at risk for aspiration

Answer 22

• Hx/CC vomiting
• Undergoing esophageal, gastric, intestinal sx
• Recumbent or mentally depressed
• Heavily pregnant, severely obese
• Laryngeal paralysis
• Esophageal motility dz
• Are ruminants

Question 23

Will increasing the duration of fasting minimize incidence of regurgitation in SA?

Answer 23

• NO!
• Study in dogs: increasing during of fasting Assoc with increased incidence of reflux, lower gastric pH

Question 24

What are ‘current’ recommendations concerning fasting in adult SA patients?

Answer 24

• Withhold solid food for cats and dogs for 6-12hrs
• Water allowed up to 3hr prior to ax, some advocate no water withhold

Question 25

What are ‘current’ recommendations concerning fasting in human patients?

Answer 25

• Unrestricted clear liquids 2-3hr prior to GA
• No solid food the day of surgery

Question 26

Fasting guidelines for large ruminants

Answer 26

• Off feed 18-24hrs
• Water 12-18hrs

Question 27

Fasting guidelines for small ruminants

Answer 27

• Off feed 12-18hrs
• Water 8-12hrs

Question 28

How do you recognize reflux or regurgitation and aspiration in an anesthetized dog or cat?

Answer 28

• If material does not reach the oropharynx, reflux may go unrecognized
• When material enters the pharynx, often noticed as fluid (brown or yellow) in the mouth or on the table
• Clinical signs from aspiration depend on volume, composition of material aspirated

Question 29

Some brown fluid is noticed under a dog’s mouth on the surgery table. More fluid along with pieces of partially digested food can be seen in the mouth. It is obvious the dog has refluxed. What should be done?

Answer 29

• Verify cuff adequately inflated
• Position head so nose is pointing downward
• Lavage mouth and esophagus until clear –> leaving material in the esophagus can lead to esophagitis and stricture
• If aspiration is suspected, suction down the ETT into the trachea
• If appears dry and clean, significant aspiration unlikely
• Extubate with cuff slightly inflated to remove any material that may be left around the laryngeal opening

Question 30

T/F: Small amounts of aspiration may not produce clinical signs

Answer 30

True

Question 31

What are clinical signs of aspiration?

Answer 31

• Bronchospasm
• Abnormal breath sounds
• Increased respiratory rate/effort
• Hypoxia
• Cyanosis

Question 32

If it appears that a dog has aspirated, what should be done?

Answer 32

• Prophylactic ABX = controversial –> ideally abs started after positive culture from trach wash
• Advocate good supportive care: immediate suctioning, careful physical evaluation lung sounds, respiratory rate/character
• Patient should be monitored over the next several hours
• TXR may not always reflect CS
• ABG/SpO2 measurement will identify patients that are hypoxemic and require oxygen support
• Severe cases: vent support

Question 33

Should gastrokinetic medications (metoclopramide, H2 blockers like cimetidine) be used routinely to prevent regurgitation and minimize consequences of aspiration?

Answer 33

• Metoclopramide increases LES tone, promotes gastric emptying
• H2 blockers: decrease production of gastric acid
• Current recommendations in human literature do not support routine administration of these drugs to patients not at risk for aspiration –> rational use for them in patients who are at risk