Antiemetics Flashcards
Percent in children that PONV occurs
25-39% in children over the age of 3
Increased anesthetic duration ____ risk
increases
At risk patients benefit from _____
one or more prophylactic measures
Risk factors for PONV
females, history of PONV or motion sickness, nonsmoker, younger, apprehension, gastroparesis, recent food ingestion
Surgical risk factors for PONV
increased duration of anesthesia, type of surgery: laparoscopy, eye, T&A, breast, GU/GYN, preop administered opioid, inhalational induction, volatile anesthetics, NO
each 30 minute increase in duration increases PONV risk by ____
60%
Postanesthetic related factors for PONV
ambulation, postural hypotension, uncontrolled pain, postop opioid administration, early oral intake, lower FiO2 concentration, reversal agents (neostigmine >2.5mg)
SAMBA guidelines
- identify pts at risk
- employ management strategies
- employ one or more prophylactic measures for moderate risk
- use multiple interventions for high risk
- administer antiemetic to kids at high risk
- provide antiemetic with PONV who did not receive prophylactic therapy or prophylaxis failed
Apfel score
risk score 0-4
3 or 4 high risk- use multi-modal strategy
female (1)
nonsmoker (1)
hx of PONV (1)
postop opioids (1)
What is the benefit of combination therapy?
Targets multiple receptors
What kind of agents should be used in combination therapy?
a rapid onset agent + longer duration of action agent
How can vomiting be triggered?
directly or indirectly
Direct pathways that trigger vomiting
noxious stimuli, toxins, drugs, irritants
Indirect pathways that trigger vomiting
stimulation of vomiting center in medulla oblongata
- cerebral cortex/thalamus
- vestibular apparatus
- vagal afferent GI tracts
- chemoreceptor trigger zone (CTZ)
What is significant about the chemoreceptor trigger zone?
it is close to the medulla in the floor of the 4th ventricle, not protected by BBB
Once activated, efferent motor nerves travel thru ___
CN V, VII, IX, X, XII, sympathetic, and spinal nerves to stimulate various parts of the body to trigger vomiting
What receptors are thought to be activated?
- histamine
- muscarinic
- opioid
- dopamine (D2)
- 5-hydroxytryptamine (serotonin)
What is the most common class of antiemetics?
serotonin receptor antagonist
Which subtype of 5-HT receptor mediates vomiting and where is it found?
subtype 3; 5-HT3 receptor in the GI tract and brain (CTZ and NTS)
Trigger zone of serotonin activated by ___
anesthetics and opioids
Serotonin CV effects
vasoconstrictor, vasodilator effect in heart is endothelium dependent
Serotonin respiratory and GI effects
resp: increased airway resistance
gi: release of ACh in myenteric plexus increases peristalsis
What kind of receptors are 5- HT3?
gated Na+/K+ channels
When are the serotonin receptor antagonists best administered?
end of surgery
Example of a serotonin receptor antagonist
Ondansetron, Palonosetron, Dolasetron
Dose of Ondansetron
PO 4 or 8mg
IV 4mg
0.1 mg/kg if <40 kg (kids)
Half life and onset time of Zofran
Half life: 4 hours
Onset: 30 minutes
Metabolism of Zofran
liver by hydroxylation and conjugation
no need to adjust for renal
Dose of Palonosetron
- 75 mg for PONV
0. 25 chemo-induced
Half life of Palonosetron
40 hours
Dose of Dolasetron
12.5 mg IV
MOA of Dolasetron
reduce activity of vagus nerve to limit activation of the vomiting center in medulla oblongata
When should you administer dolasetron?
within 15 minutes before the end of anesthesia
Active metabolite of dolasetron
hydrodolasetron
Droperiol is part of what class and MOA
butyrophenone/dopamine receptor antagonist
MOA: blocks dopamine receptors that contribute to development of PONV
Dose of droperidol
0.625-1.25 mg IV or IM
What does droperidol cause?
QT interval prolongation
What class and MOA of prochlorperazine (compazine)
antipsychotic/antiemetic
MOA: affects multiple receptors - histaminergic, dopaminergic (D2 blockade), muscarinic
Dose of compazine
5-10 mg IM/IV before induction
What kind of side effects could prochlorperazine cause?
extrapyramidal and anticholinergic side effects (muscarinc side effects)
sedation, blurry vision, hypotension, dizziness, neuroleptic malignant syndrome, restlessness, dystonia
What class is metoclopramide in and MOA?
dopamine receptor antagonist
MOA: centrally acting as dopamine receptor antagonist in CTZ, peripherally acting as cholinomimetic in GI tract
Which antiemetic is a good choice for patients at risk of aspiration?
metoclopramide (reglan)
Dose for metoclopramide
10 mg IV or 0.1 - 0.25 mg/kg q 6-8h
When should reglan be avoided?
pheochromocytoma (can cause HTN crisis), parkinson’s, seizure, GI obstruction (can cause extrapyramidal effects)
What class and MOA of Aprepitant (Emend)
neurokinin-1 receptor antagonist
MOA: NK-1 antagonist inhibit substance P at central and peripheral receptors
Dosing considerations with Emend
want to decrease dose of zofran if given together because Emend increases activity of serotonin receptor antagonists
if administered with dexamethasone, reduce dose by half to keep dexamethasone concentrations
Effects of Emend on oral contraceptives
makes ineffective for 28 days!
MOA of dexamethasone (decadron)
long acting corticosteroid with anti-inflammatory and immunosuppressant properties
Dose of Dexamethasone
4-10mg IV
peds: 0.2 - 0.5 mg/kg IV
Contraindications with Dexamethasone
uncontrolled infections, known hypersensitivity, cerebral malaria, systemic fungal infection, concurrent treatment with live virus vaccine
Class and MOA of Dimenhydrinate
histamine1 receptor antagonist
MOA: competes with histamine at H1 receptor sites in GI tract, blood vessels, and respiratory tract, blocks CTZ, depresses labyrinthine function and vestibular stimulation
Dose of dimenhydrinate
50-100mg IV/IM q4h (max dose 100mg q4h)
Promethazine MOA
antihistamine (H1 antagonist) and anticholinergic/muscarinic blocking effects
Dose of promethazine
12.5-25 mg q4-6h
IM route preferred
low dose (5-10) for prophylaxis/rescue
Class and MOA of Scopolamine
muscarinic antagonist/anticholinergic
inhibits action of Ach at parasympathetic sites in smooth muscle, CNS, and secretory glands, competitively blocks binding of ACh
What allows anticholinergics to bind to Ach receptors?
ester linkage
What can you give to reverse scopolamine?
physostigmine
0.01-0.03 mg/kg
Dose of scopolamine
1.5 mg transdermal patch behind the ear the evening before surgery
Adverse effects of scopolamine
dry mouth, increased thirst, dry skin, constipation, drowsy, dizzy, blurry, dilated pupils, light sensitive
ephedrine dose
10-25mg IV for NV associated with postural hypotension
0.5 mg/kg IM at end of surgery = droperidol
40mcg/kg IM minimizes NV with less sedation
Midazolam dose
peds: 50-75mcg/kg IV
adult: 2mg IV
What is a good combination for midazolam in kids
midazolam + dexamethasone = zero incidence of PONV in kids undergoing strabismus surgery
what nonpharmacological intervention can we use for NV?
P6 acupuncture point stimulation
isopropyl alcohol inhalation
