Chp. 28 Aspiration Flashcards
Def: vomiting
- Forceful expulsion of gastric contents into the pharynx
- Involves diaphragmatic and abdominal muscle contractions
Def: regurgitation/reflux
- Passive action that results in gastric contents entering the esophagus and oropharynx
How does GER occur?
- 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
GER and Ruminants
- 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
T/F: endotracheal intubation attempts during light planes of anesthesia may initiate regurgitation, esp in ruminants
True
What are the consequences of GER?
- 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
Def: barrier pressure
Difference between the esophageal sphincter pressure and gastric pressure
Causes of increased gastric pressure
- Increased abdominal pressure
- Straining against the endotracheal tube
- Coughing
Causes of decreased LES pressure
Drug-induced
What positioning or features predispose animals to regurgitation?
- Positions of recumbency, esp dorsal or head down positions
-Restrictive tight belly bands
How can anesthesia affect LES and barrier pressure
- Many drugs - likely all drugs - administered during the ax period lower LES pressure -> reflux more likely
How common is GER in the ax period?
- 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
How common is GER in the ax period for ruminants?
- 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
How common is pulmonary aspiration of gastric contents?
- 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
What are the pulmonary consequences of aspiration?
- Will depend on the amounts, contents aspirated which can be liquid acid, liquid non-acid, particle related or combinations
Pulmonary complications from aspiration of small amounts of food, liquid?
- Often well-tolerated
- May not cause significant complications
What are the pulmonary consequences of acid fluid aspirates?
- 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
What are the pulmonary consequences of non-acidic fluid aspirates?
- May produce hypoxia, alveolar collapse, atelectasis
- Late inflammatory response not as severe as with acidic aspirates
What are the pulmonary consequences of aspiration of particulate matter?
- 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
What is important to remember about the regurgitant material in ruminants compared to cats and dogs?
- Regurgitant material more particulate but pH is less acidic than small animals
Name some risk factors for aspiration
- 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
List some diseases or physiologic conditions that place a patient at risk for aspiration
- Hx/CC vomiting
- Undergoing esophageal, gastric, intestinal sx
- Recumbent or mentally depressed
- Heavily pregnant, severely obese
- Laryngeal paralysis
- Esophageal motility dz
- Are ruminants
Will increasing the duration of fasting minimize incidence of regurgitation in SA?
- NO!
- Study in dogs: increasing during of fasting Assoc with increased incidence of reflux, lower gastric pH
What are ‘current’ recommendations concerning fasting in adult SA patients?
- Withhold solid food for cats and dogs for 6-12hrs
- Water allowed up to 3hr prior to ax, some advocate no water withhold