Prepared byDr. Mahmoud Abdel-Khalek

Risk Stratification and Treatment

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 Score

General anaesthesia (volatiles) with no antiemetic therapy (age ≥ 18)Risk Factors 1. Female Gender 2. Non-smoker 3. Post-operative use of opioids 4. Previous PONV or motion sickness

Apfel 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

PhenothiazineChlorpromazineThioridazineProchlorperazine

– less sedation/anticholinergic effects than other D2 antagonists

– more extrapyramidal effects: dystonias and akathisia

– erratic oral bioavailability, marked hepatic first-pass metabolism

1. Dopamine antagonists

Butyrophenones Droperidol

– FDA black box warning: QT prolongation/torsades, based on 10 reported cases. ?validity, nil case-reports in a peer-reviewed journal of these complications in doses used for PONV

– sedation more pronounced, can occur 12hrs after administration

– SE: hyperprolactinaemia, 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

BenzamidesMetoclopramide

– 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 prominentGlycopyrrolate: 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– very good for chemo/radio or post

anaesthetic nausea (peripheral and central)– Most effective for PONV when given at end

of case– ineffective for motion sickness/dopamine

induced nausea– SE: 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 – Point P6Cannabinoids

– Use in chemotherapy, not established for PONVBenzodiazepines