Prepared byDr. Mahmoud Abdel-Khalek

Post-operative Nausea& Vomiting(PONV)

Importance of PONV

Patient distress

Morbidity (aspiration, suture tension, oesophageal

rupture, electrolyte disturbances, dehydration)

Prolonged PACU stay

Unexpected hospital admission/re-admission

Physiology Vomiting Centre: no anatomical site, collection of

effector neurones in medulla, travels down vagus, phrenic nerves, spinal motor, to abdominal muscles/diaphragm/stomach/gut

VC input from: – Chemoreceptor Trigger Zone: floor of 4th ventricle

(functionally outside BBB)– Vestibular apparatus– Higher centres– Limbic cortex– Peripheral pain pathways– Vagal afferents

CTZ rich in dopamine and serotonin receptors vestibular apparatus uses ACh to transmit treatment aimed at afferent supply to VC

Apfel ScoreGeneral anaesthesia (volatiles) with no antiemetic therapy (age ≥ 18)Risk Factors1. Female Gender2. Non-smoker3. Post-operative use of opioids4. Previous PONV or motion sicknessApfel score1 10%2 21%3 39%4 79%

Children Studies limited to vomiting

Twice as frequent as adults

Risk increases as child ages! (decrease after

puberty)

No difference in sex before puberty

Stronger correlation with type of surgery

Reducing risk factors Avoiding GA (use regional)

Avoiding volatiles (use propofol)

Intra-operative O2 (FiO2 80%)

Adequate hydration

Avoiding nitrous oxide

Minimising length of operation

Minimising neostigmine

TYPES OF AGENTS USED IN PONV

1. Dopamine antagonists

Phenothiazine

Chlorpromazine

Thioridazine

Prochlorperazine

– less sedation/anticholinergic effects than other D2

antagonists

– more extrapyramidal effects: dystonias and akathisia

– erratic oral bioavailability, marked hepatic first-pass

metabolism

1. Dopamine antagonistsButyrophenones Droperidol

– FDA black box warning: QT prolongation/torsades

– sedation more pronounced, can occur 12hrs after administration

– Side effects: hyperprolactinemia, hypotension from alpha-adrenoceptor blockade

– extensively metabolised by liver Domperidone

– no IV formulation secondary to arrhythmias– less likely to have extrapyramidal SE as does

not cross BBB

1. Dopamine antagonists

Benzamides

Metoclopramide

– D2 antagonist, 5-HT antagonist (some) and

prokinetic for stomach

– conflicting studies, some demonstrated equal

efficacy to placebo in PONV

– more effective given at end vs induction

– variable oral bioavailability (30-90%),

conjugated in liver

2. Anticholinergics

Hyoscine

– previously used as pre-med for PONV, sedation and

amnesia

– less cardiac effects compared with

atropine/glycopyrrolate

– short duration of action, extensively metabolised by

liver, variable oral bioavailability

Atropine: cardiac effects too prominent

Glycopyrrolate: does not cross BBB

3. Antihistamines

Cyclizine

– IV/IM painful to inject (pH 3.2)

– H1 antagonist, but also anticholinergic properties

Promethazine

– traditional pre-med too

– significant anticholinergic/sedative effects

– urinary excreted

4. 5-HT3 Antagonists Ondansetron (Zofran)

– very good for chemo/radio or post anesthetic nausea

(peripheral and central)

– Most effective for PONV when given at end of

operation

– ineffective for motion sickness/dopamine induced

nausea

– Side effects: headache, flushing, constipation,

deranged LFTs, bradycardia (if rapid IV)

– conjugated in liver

5. Miscellaneous

Steroids– Dexamethasone

Uncertain mechanism - ?prostaglandin antagonism ?release of endorphins

More effective at start of anaesthesia SE of wound infection and adrenal

suppression, but not demonstrated in single bolus dose

Acupuncture Benzodiazepines