Post on 01-Jan-2016
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