Peri-operative regurgitation, nausea, and vomiting

What is vomiting?

Forceful active process w/ involuntary muscle contractions

Associated with nausea

Can happen at any time

What does vomiting happen in response to?

Illness, drugs, motion sickness

What is regurgitation?

Passive process not associated with nausea

What causes regurgitation?

Frequently after eating especially if eaten too fast

When is the vomiting reflex blunted?

3rd plane of anesthesia

What typically occurs during anesthesia, vomiting or regurgitation?

Regurgitation

What contributes to regurg and post-op vomiting?

Species, drug choice, level of nociception/pain, aerophagia, hematophagy

When does peri-operative nausea and vomiting occur?

First 24 hours

What is the biggest concern of peri-operative nausea and vomiting?

Discomfort causing prolonged recovery and discharge

What species are more prone to PONV (peri-operative nausea and vomiting)?

Cats and dogs more than horses and rodents

What breeds are more susceptible to PONV (peri-operative nausea and vomiting)?

Brachiocephalic

What age of patients are more susceptible to PONV (peri-operative nausea and vomiting)?

Younger

What gender is more susceptible to PONV?

Intact females

What BCS correlates with PONV?

Higher BCS

How do inhalants cause PONV?

Acts on the CTZ and cumulative

How do opioids cause PONV?

Directly stimulate VC

How does anesthesia effect GIT causes of PONV?

Increased GIT pressure due to aerophagia causing PONV

T/F inadequate analgesia can cause PONV?

True

What procedures are more likely to cause PONV?

Endoscopies

Ear canal surgeries

GIT surgeries

What do lower doses of opioids do?

Increase emetic/nausea effects

What are all the ways opioids cause emesis?

Directly affect CTZ

Increased vestibulocochlear sensitivity

Decrease of GIT motility

Alpha-2s cause emesis in what species more?

Cats

How do alpha 2 agonists cause emesis?

Stimulation of CTZ

Why do alpha-2s rarely cause emesis in dogs?

They have more dopamine receptors in CTZ instead of alpha-2 receptors

How does lidocaine cause emesis?

Does not directly cause emesis, but nausea by stimulating VC

When are lidocaine doses able to cause emesis?

Systemically with a CRI of 200mcg

How does metoclopramide prevent emesis?

Action of D2 (dopamine) receptors in the CTZ

What species is more responsive to metoclopramide?

Dogs (more dopamine receptors)

When is metoclopramide more effective in cats?

High doses can have S5H receptor effects in the CTZ

What does metoclopramide do in the GIT?

Prokinetic effect via release of ACh which

• Promotes better smooth muscle contraction, increases peristalsis, increases lower esophageal tone, reducing reflux, relaxes pylorix sphincter

How can you give metoclopramide?

PO, SC, IM, IV

What is the MOA of ondansetron?

Serotonin 5HT3 receptor antagonist  which are found in the CTZ and vagal afferent pathway

What nausea is ondansetron not useful against?

Vestibulocochlear system

When is ondansetron a good choice?

Surgical, radiation, and chemotherapy nausea

How can you give ondansetron?

PO, SC, IV

What species has a higher bioavailability of ondansetron?

Cats compared to dogs

What is the MOA of maropitant?

Potent and selective neurokinin-1 receptor antagonist located in the CTZ, VC<, and GUT

Why does maropitant also cause analgesia?

Inhibits release of substance P which p=binds to NK1 receptors causing pain

How can maropitant be given?

PO, SC, IV

What is the onset time of maropitant?

IV says 3-5 minutes but it is generally thought that maropitant takes a while, so it must be given before other premeds if that is the goal

Why is PO maropitant not ideal?

Suffers first-passage metabolism PO

What animal has a higher bioavailability of maropitant?

Cats

What anti-nausea med is a concern in MDR1 dogs?

Maropitant and acepromazine

How does acepromazine cause antiemesis?

D2 receptor antagonism

Alpha 1 blockade also helps

Antihistamine through H1 receptors

What breed does not metabolize acepromazine well?

Boxers

What is the biggest side effect of acepromazine?

Hypotension due to muscle relaxation

What is the MOA of butorphanol?

Partial Mu and full Kappa agonist

How does butorphanol cause antiemesis?

Kappa can suppress emetic effect

Mu effects are not strong enough to trigger emesis

What are the two butyrophenones?

Droperidol and holoperidol

What are the effects of butyrophenones?

Antipsychotic with moderate sedative effects affecting D2 in the CTZ

Also weak H1 and anticholinergic effects and reduces amount of serotonin being re-uptake

How does benzodiazepines cause antiemesis?

Not directly, but anxiolytic effects helps by depressing CNS through GABA receptors

Dexamethasone can be used as antiemesis in what animal?

Cats

How does dexamethasone provide antiemesis in cats?

Modulates neuronal activity through glucocorticoid receptors reducing excitability of the VC and vomit reflex

Reducing PGA reduces pain and long-term nausea

What are the natural barriers that prevent GER (gastroesophageal reflux)?

Lower esophageal sphincter

Crus of the diaphragm

Crural junction of the diaphragm curve

Cardia sphincter

What is the main concern of a lost GER (gastroesophageal reflux)

Regurgitation leading to aspiration pneumonia

What changes in pressure cause GER (gastroesophageal reflux)?

Intragastric pressure is equal to or higher than esophageal pressure

What surgeries can increase GER risk?

GIT surgeries, laparoscopic, endoscopies

How does anesthesia increase GER risk?

Sphincter relaxation

Reduction of esophageal peristalsis

Increased gastric pressures

Pre-op fasting

How common in GER?

25-88% of the time in cats and dogs but only about 2% of the time is it clinical relevant

How do you treat GER?

Suction of remaining material while under prior to extubating

Lavage of esophagus

What is nausea?

Conscious recognition of the vomiting center (VC)

What is vomiting?

VC sends impulses through sympathetic and parasympathetic systems to GIT, diaphragm, and abdominal muscles to contract and generate the action of vomiting

What is regurgitation?

Normally refers to passive backflow of gastric contents

T/F nausea is a very common adverse effect of anesthesia?

True

What are some common causes of nausea?

Fasting, transportation, drugs (opioids, antibiotics, NSAIDs, chemo drugs)

What are the C/S of nausea?

Drooling, lip-licking, excessive swallowing, loss of appetite, lethargy, and restlessness

Where is the chemoreceptor trigger zone?

Located in CNS, not protected by BBB

Area postrema

How does the CTZ work (chemoreceptor trigger zone)?

Does not need VC to be activated but CTZ can stimulate the VC

What stimulates the CTZ (chemoreceptor trigger zone)?

Dopamine, serotonin, histamine, opioids, alpha-2 adrenergic agonists

What stimulates the vomiting center?

Histamine, Ach, dopamine, serotonin, NK1, substance P

What gives feedback to the vomiting center?

Vestibular apparatus

GIT

Cerebral cortex

CTZ

What forms teh vestibular apparatus?

Bone structure called labyrinth

What does the vestibular apparatus do?

Spatial orientation via CN VIII (vestibulocochlear)

How does the vestibulocochlear nerve work/

Muscarinic and histaminic receptors that are activated by movement

This sends feedbacks to the CTZ activating the VC

How can the GIT stimulate the VC?

Enteric cell damage form cytotoxins

Distension of GI wall causing release of serotonin and stimulation of the VC

How can the cerebral cortex cause vomiting?

An extreme sadness or anxiety. Unsure if this is present in animals

What are the steps of the vomiting reflex?

Relaxation of the LES
Contraction of diaphragm and abd muscles

Increase of intra-abdominal pressure

Tachycardia

Increased peristalsis and salivation

Close of the epiglottis

What CNs are required for vomiting?

V, VII, IX, X, XII