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
What are ‘current’ recommendations concerning fasting in human patients?
- Unrestricted clear liquids 2-3hr prior to GA
- No solid food the day of surgery
Fasting guidelines for large ruminants
- Off feed 18-24hrs
- Water 12-18hrs
Fasting guidelines for small ruminants
- Off feed 12-18hrs
- Water 8-12hrs
How do you recognize reflux or regurgitation and aspiration in an anesthetized dog or cat?
- 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
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?
- 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
T/F: Small amounts of aspiration may not produce clinical signs
True
What are clinical signs of aspiration?
- Bronchospasm
- Abnormal breath sounds
- Increased respiratory rate/effort
- Hypoxia
- Cyanosis
If it appears that a dog has aspirated, what should be done?
- 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
Should gastrokinetic medications (metoclopramide, H2 blockers like cimetidine) be used routinely to prevent regurgitation and minimize consequences of aspiration?
- 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
