PONV/GI Flashcards
How is “early” PONV defined?
occurs within the first 6 hours of surgery
How is “late” PONV defined?
occurs 6-24 hours after surgery
What is the incidence of PONV?
40% in general anesthesia
80% in high risk population
What patient factors put someone at risk for PONV?
female
non-smoker
hx of motion sickness
previous incidence of PONV
What surgical factors put a patient at risk for PONV?
long procedure
laparotomies, gyn sx, laparoscopic, ENT, breast, ortho
What anesthesia factors put a patient at risk for PONV?
inhalational agents
N2O
neostigmine
narcotics
etomidate
Where is the vomiting center located?
medulla oblongata
What are the 4 areas that trigger N/V?
chemoreceptor trigger zone
vestibular apparatus
thalamus & cerebral cortex
neurons in the GI tract
Describe the pathway of N/V
efferent signal travels via cranial nerves through vagal sympathetic fibers and parasympathetic chains that trigger a motor process to occur (emesis)
List the NT associated with PONV
dopamine
serotonin
acetylcholine
histamine
substance P
What receptors/NT play a role in PONV in the vestibular system?
H1 receptor (histamine)
M1 receptor (ACh)
What receptors/NT play a role in PONV in the CTZ?
chemoreceptors
D2 receptors (dopamine)
NK receptors (Substance P)
5-HT3 receptors (serotonin)
What receptors/NT play a role in PONV in the vomiting center?
H1 (histamine)
M1 (ACh)
NK (Substance P)
5-HT3 (serotonin)
What receptors/NT play a role in PONV in the GI tract?
mechanoreceptors (stretch)
chemoreceptors
5-HT3 (serotonin)
H1 (histamine)
NK (substance P)
M1 (ACh)
List the anticholinergics used to treat PONV
atropine
hyoscine
scopolamine
List the benzamides used to treat PONV
metoclopramide (Reglan)
List the benzos used to treat PONV
midazolam
List the butrophenones used to PONV
droperidol
haloperidol
List the cannabinoids used to treat PONV
dronabinol
nabilone
List the glucocorticoids used to treat PONV
dexamethasone
List the 5-HT3 antagonists used to treat PONV
dolasetron
granisetron
ondansetron
palonosetron
ramosetron
tropisetron
List the neurokinin-1 antagonists used to treat PONV
aprepitant
fosprepitant
List the phenothiazines used to treat PONV
prochoperazine
promethazine
chlorpromazine
How does scopolamine work to combat PONV?
-blocks transmission of impulses from vestibular apparatus to medulla
What is the dose of scopolamine for PONV and how is it delivered?
5mcg/hr x 72 hours
best if given at least 4 hours before stimulus
transdermal delivery allows for slow and sustained dosing and prevents anticholinergic side effects
List the common uses for scopolamine
motion sickness
middle ear surgery
N/V with PCA or epidural morphine
Describe the MOA of metoclopramide for PONV
stimulates the GI tract via cholinergic and anti-dopaminergic effects
-contracts lower esophageal sphincter & gastric fundus
-increases gastric and small intestine motility
-decreased muscle activity in pylorus & duodenum w/ stomach contraction
What populations should metoclopramide be cautiously used in and why?
Parkinson’s
RLS
d/t anti-dopaminergic effects
What is the MOA of midazolam for PONV?
decrease synthesis & release of dopamine within the CTZ
When should midazolam be given for PONV?
at the end of the case
What is the MOA of droperidol for PONV?
competitive dopamine antagonist @ D2 receptor (blocks dopamine and GABA)
What is the dose of droperidol given for PONV?
0.625mg-1.25mg prophylactically
In which populations should droperidol be cautiously used?
Parkinson’s
RLS
potential for prolonged QTc (high doses)
What is the MOA of dexamethasone for PONV?
inhibits prostaglandin synthesis and controls endorphin release
What is the typical dose of dexamethasone given for PONV?
4mg
In what patient populations should dexamthasone be cautiously used?
obese
DM (increased r/f hyperglycemia)
What type of receptor is the 5-HT3 receptor? What NT acts on it?
ligand-gated (Na+ and K+) cation channel
depolarizes the plasma membrane
excitatory
acted on by serotonin
Besides nausea, what other effects does serotonin have on the body?
addiction
aggression
vasoconstriction
increased intestinal motility
learning and memory consolidation
Why are 5HT-3 antagonists not useful for motion sickness or vestibular stimulation?
no 5HT-3 receptors located in those areas
What is the typical dose of ondansetron?
4mg, onset 30-60min
What are some side effects of ondansetron?
headache (major)
diarrhea
QTc prolongation
Which 5HT-3 antagonist has an active metabolite?
dolasetron
What is the typical dose of granisetron? How often is it dosed?
0.1mg
lasts 24 hours
Which 5HT-3 antagonist is used to treat symptoms with carcinoid syndrome?
tropisetron
Describe Substance P
primary NT produced by pain & temp afferent peripheral neurons
What receptors does substance P act on and where are they located?
neurokinin (NK1, NK2, NK3)
located in gut and nausea pathways
What is the MOA of aprepitant? What is the most common type of NV that it is used for?
competitive antagonist at NK1 receptors, inhibits substance P from binding
used in chemotherapy-induced NV
What is a noteworthy side effect of aprepitant?
inhibition of steroidal contraceptives x 7-10 days
What is the MOA of phenothiazines? Give some examples
antagonize H1 and M1 receptors, preventing histamine and ACh from binding
E.g. promethazine, procholoperazine, chlorpromazine
Histamine is synthesized from what substance?
histadine
in the CNS, immune cells, and GI tract
Where are histamine receptors located?
H1: vascular smooth muscle, bronchial smooth muscle, CNS
H2: stomach
H3: presynaptic cleft
List examples of H1 receptor antagonists
diphenhydramine (Benadryl)
hydroxyzine (Atarax, Vistaril)
phenergan
meclizine
What is the typical dosage/onset/duration of diphenhydramine?
dose: 25-50mg IV
onset: 3 min (or less)
duration: 1-7hrs
Describe dimenhydrinate
aka dramamine
antagonizes H1 and M1 receptors
used for motion sickness & sleep aid
What are some side effects of H1 receptor antagonists that are unrelated to the H1 blockade?
sedation
anti-nausea/anti-emetic
adrenoceptor blocking (esp Phenergan which may cause orthostatic hypotension)
What two methods are used to prevent aspiration?
antacids (increase gastric pH)
prokinetics (decrease gastric fluid volume)
Is aspiration more or less common in pediatric patients?
more common (r/t use of inhaled anesthetics for induction??)
Which patient populations present with a higher r/f aspiration?
pregnant
diabetic
mask induction
emergent case
What is the most common oral antacid given in anesthesia?
Bicitra
15-30mL given right before induction
used in C-sections
tastes awful
List the four H2 drugs currently available
cimetidine
ranitidine
famotidine
nizatidine
What is the MOA of H2 blockers?
selective, reversible competition with histamine at H2 sites
What are the clinical uses for H2 receptor antagonists?
peptic duodenal ulcer
gastric ulcer
erosive esophagitis
hypersecretory conditions
What are the s/s of H2 receptor antagonist toxicity?
CNS dysfunction (slurred speech, delirium, confusion)
liver toxicity
(mostly with cimetidine)
H2 receptor antagonists interact with which drugs?
inhibits the cytochrome P450 system
(esp warfarin, dilantin, propranolol, metoprolol, labetalol, diazepam, CCBs)
List some commonly used PPIs
omeprazole
pantoprazole
esomerprazole
lansoprazole
What effect do PPIs have on the body?
increase gastric fluid pH
decrease gastric fluid volume
*must be metabolized
*can take days for effect
*crosses BBB (HA, agitation, confusion)
Which drug is used to treat Zollinger-Ellison syndrome?
omeprazole
What do GI prokinetics do? List 2 examples
increase LES sphincter tone, enhance peristaltic contractions, accelerate the rate of gastric emptying
E.g. metoclopramide, domperidone
What is the MOA of metoclopramide in the GI system?
involves cholinergic stimulation and dopamine antagonism
-contract LES and gastric fundus (prevents reflux)
-increase gastric emptying
-decrease pylorus and duodenum muscle activity
-crosses BBB and affects CTZ
What is the typical dose of metoclopramide?
10-30mg over 3-5 mins
What effect does metoclopramide have on gastric pH?
no effect
What are some side effects of metoclopramide?
crosses the placenta
abdominal cramping if given fast
extrapyramidal reactions (d/t dopaminergic effects)
prolongs succs metabolism
