eLFH - Antiemetic drugs Flashcards
How to assess risk for PONV after anaesthesia
Patient factors
Anaesthetic factors
Surgical factors
Patient risk factors for PONV
Apfel score - in adults
POVOC score - in chlidren (Post Operative Vomiting of Children)
Apfel score components
Each score 1 point
Female
Non smoker
History of motion sickness or prev PONV
Use of post operative opioids
Apfel score interpretation
0 risk factors: 10% incidence of PONV
1 risk factor: 20% incidence of PONV
2 risk factors: 40% incidence of PONV
3 risk factors: 60% incidence of PONV
4 risk factors: 80% incidence of PONV
POVOC score components
Each score 1 point
Surgery duration 30 mins or more
Age 3 years or older
Strabismus surgery
History of PONV in the child or relatives
POVOC score interpretation
0 risk factors: 9% incidence of POV
1 risk factor: 10% incidence of POV
2 risk factors: 30% incidence of POV
3 risk factors: 55% incidence of POV
4 risk factors: 70% incidence of POV
Anaesthetics risk factors for PONV
Volatile use
Nitrous oxide use
Opioid use
Duration of anaesthesia
Surgical risk factors for PONV
Ophthalmological surgery (inc squint surgery)
Gynaecological surgery
ENT / middle ear surgery
Neurosurgery
Number needed to treat for dexamethasone to reduced PONV
4
Number needed to treat for TIVA to reduce PONV
5
Pathways involved in emesis
Location of chemoreceptor trigger zone
Area postrema at base of fourth ventricle
Within medulla oblongata
Outside of blood brain barrier - able to detect toxins
Location of nucleus tractus solitarius
Area postrema and lower pons
Location of vomiting centre
Medulla oblongata
Controls vomiting through stimulation by other pathways
Strategies for managing PONV
Non pharmacological management
Pharmacological management
Anaesthetic alterations
Prophylaxis
Non pharmacological methods to reduced PONV
Avoid gastric distention with bag mask ventilation
Minimise patient movement
Ensure adequate hydration
Anaesthetic alterations to reduce PONV
TIVA
Regional anaesthesia
Main types of pharmacological antiemetics used for PONV
Steroids
5-HT3 receptor antagonists (Serotonin)
H1 receptor antagonists (Histamine)
D2 receptor antagonists (Dopamine 2)
Neurokini-1 receptor antagonists
(TIVA)
Steroid antiemetic examples
Dexamethasone
Technically 5-HT3 receptor antagonists are also steroids
Dexamethasone mechanism of action
Unclear mechanism of antiemesis
Caution with dexamethasone use
Diabetics
Use of dexamethasone
Prophylaxis of PONV
Little use in acute management of PONV
Also associated with reduced post operative pain
5-HT3 receptor antagonist examples (first generation)
Ondansetron
5-HT3 receptor antagonist examples (second generation)
Palonosetron
Mainly used for N/V associated with chemotherapy
Uses of Ondansetron
Antiemetic
Reduces post operative shivering and itch of opioids
If given prior to propofol may reduced injection pain
Side effects of Ondansetron
Constipation
Prolonged QT
Serotonin syndrome risk with other serotonergic drugs
Headache
Ondansetron pharmacokinetics
Large volume of distribution (140 L)
Moderately plasma protein bound (70 - 76%)
95% Hepatic metabolism and clearance
5% Renal clearance unchanged
Elimination half life ~ 3 hours
H1 receptor antagonist examples
Cyclizine
Promethazine
Cyclizine elimination half life
~ 20 hours
Side effects of Cyclizine
Tachycardia
Dry mouth
Result from anticholinergic activity
Administration of cyclizine
IV, IM or PO
IV cyclizine is diluted to 5 mg/ml
D2 receptor antagonist examples
Metoclopramide
Prochlorperazine (mainly D2, but also H1 and muscarinic receptor action)
Prochlorperazine pharmacokinetics
Large volume of distribution
Lipophilic
Highly membrane and protein bound
Terminal half life ~ 7 hours
Side effects of prochlorperazine
Sedation
Dry mouth
Hypotension
Exacerbates Parkinson’s sx
Extrapyramidal SEs
Neuroleptic malignant syndrome
Metoclopramide effects
Antiemetic
Prokinetic - therefore may be contraindicated in certain surgeries
Side effects of Metoclopramide
Exacerbates Parkinson’s sx
Young females can cause oculogyric crisis - extrapyramidal SEs
Neurokinin 1 receptor antagonist examples
Aprepitant
New class of antiemetic - not widely used
NK1 receptor antagonist side effects
Headache
Constipation
Raised ALT
Antiemetics commonly used in pregnancy
Note many have lack of evidence so are not licensed
Ondansetron
Dexamethasone
Cyclizine
Metoclopramide
Propofol
Antiemetics NOT recommended for use in children
Metoclopramide
Prochlorperazine
Cyclizine
Antiemetics used in children and doses
Ondansetron - 0.1 mg/kg (max 4 mg)
Dexamethasone - 0.15 mg/kg
