eLFH - Antiemetic drugs

Question 1

How to assess risk for PONV after anaesthesia

Answer 1

Patient factors

Anaesthetic factors

Surgical factors

Question 2

Patient risk factors for PONV

Answer 2

Apfel score - in adults

POVOC score - in chlidren (Post Operative Vomiting of Children)

Question 3

Apfel score components

Answer 3

Each score 1 point

Female
Non smoker
History of motion sickness or prev PONV
Use of post operative opioids

Question 4

Apfel score interpretation

Answer 4

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

Question 5

POVOC score components

Answer 5

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

Question 6

POVOC score interpretation

Answer 6

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

Question 7

Anaesthetics risk factors for PONV

Answer 7

Volatile use

Nitrous oxide use

Opioid use

Duration of anaesthesia

Question 8

Surgical risk factors for PONV

Answer 8

Ophthalmological surgery (inc squint surgery)

Gynaecological surgery

ENT / middle ear surgery

Neurosurgery

Question 9

Number needed to treat for dexamethasone to reduced PONV

Answer 9

4

Question 10

Number needed to treat for TIVA to reduce PONV

Answer 10

5

Question 11

Pathways involved in emesis

Answer 11

Question 12

Location of chemoreceptor trigger zone

Answer 12

Area postrema at base of fourth ventricle
Within medulla oblongata

Outside of blood brain barrier - able to detect toxins

Question 13

Location of nucleus tractus solitarius

Answer 13

Area postrema and lower pons

Question 14

Location of vomiting centre

Answer 14

Medulla oblongata

Controls vomiting through stimulation by other pathways

Question 15

Strategies for managing PONV

Answer 15

Non pharmacological management

Pharmacological management

Anaesthetic alterations

Prophylaxis

Question 16

Non pharmacological methods to reduced PONV

Answer 16

Avoid gastric distention with bag mask ventilation

Minimise patient movement

Ensure adequate hydration

Question 17

Anaesthetic alterations to reduce PONV

Answer 17

TIVA

Regional anaesthesia

Question 18

Main types of pharmacological antiemetics used for PONV

Answer 18

Steroids
5-HT3 receptor antagonists (Serotonin)
H1 receptor antagonists (Histamine)
D2 receptor antagonists (Dopamine 2)
Neurokini-1 receptor antagonists

(TIVA)

Question 19

Steroid antiemetic examples

Answer 19

Dexamethasone

Technically 5-HT3 receptor antagonists are also steroids

Question 20

Dexamethasone mechanism of action

Answer 20

Unclear mechanism of antiemesis

Question 21

Caution with dexamethasone use

Answer 21

Diabetics

Question 22

Use of dexamethasone

Answer 22

Prophylaxis of PONV

Little use in acute management of PONV

Also associated with reduced post operative pain

Question 23

5-HT3 receptor antagonist examples (first generation)

Answer 23

Ondansetron

Question 24

5-HT3 receptor antagonist examples (second generation)

Answer 24

Palonosetron

Mainly used for N/V associated with chemotherapy

Question 25

Uses of Ondansetron

Answer 25

Antiemetic Reduces post operative shivering and itch of opioids If given prior to propofol may reduced injection pain

Question 26

Side effects of Ondansetron

Answer 26

Constipation Prolonged QT Serotonin syndrome risk with other serotonergic drugs Headache

Question 27

Ondansetron pharmacokinetics

Answer 27

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

Question 28

H1 receptor antagonist examples

Answer 28

Cyclizine Promethazine

Question 29

Cyclizine elimination half life

Answer 29

~ 20 hours

Question 29

Side effects of Cyclizine

Answer 29

Tachycardia Dry mouth Result from anticholinergic activity

Question 30

Administration of cyclizine

Answer 30

IV, IM or PO IV cyclizine is diluted to 5 mg/ml

Question 31

D2 receptor antagonist examples

Answer 31

Metoclopramide Prochlorperazine (mainly D2, but also H1 and muscarinic receptor action)

Question 32

Prochlorperazine pharmacokinetics

Answer 32

Large volume of distribution Lipophilic Highly membrane and protein bound Terminal half life ~ 7 hours

Question 33

Side effects of prochlorperazine

Answer 33

Sedation Dry mouth Hypotension Exacerbates Parkinson's sx Extrapyramidal SEs Neuroleptic malignant syndrome

Question 34

Metoclopramide effects

Answer 34

Antiemetic Prokinetic - therefore may be contraindicated in certain surgeries

Question 35

Side effects of Metoclopramide

Answer 35

Exacerbates Parkinson's sx Young females can cause oculogyric crisis - extrapyramidal SEs

Question 36

Neurokinin 1 receptor antagonist examples

Answer 36

Aprepitant New class of antiemetic - not widely used

Question 37

NK1 receptor antagonist side effects

Answer 37

Headache Constipation Raised ALT

Question 38

Antiemetics commonly used in pregnancy Note many have lack of evidence so are not licensed

Answer 38

Ondansetron Dexamethasone Cyclizine Metoclopramide Propofol

Question 39

Antiemetics NOT recommended for use in children

Answer 39

Metoclopramide Prochlorperazine Cyclizine

Question 40

Antiemetics used in children and doses

Answer 40

Ondansetron - 0.1 mg/kg (max 4 mg) Dexamethasone - 0.15 mg/kg