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PONV – Risk Stratification and Treatment Jimmy Fu.

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Presentation on theme: "PONV – Risk Stratification and Treatment Jimmy Fu."— Presentation transcript:

1 PONV – Risk Stratification and Treatment Jimmy Fu

2 Importance of PONV  Patient distress  Morbidity (aspiration, suture tension, oesophageal rupture, electrolyte disturbances, dehydration)  Prolonged PACU stay  Unexpected hospital admission/re- admission

3 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


5 Types of agents used in PONV

6 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

7 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

8 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

9 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

10 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

11 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

12 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 P6  Cannabinoids  Use in chemotherapy, not established for PONV  Benzodiazepines

13 Risk Stratification  Patient factors  Gender  Non-smoker  History of PONV/motion sickness  Anaesthetic factors  Use of volatile agents  Nitrous Oxide  Use of intra/post operative opioids  Surgical factors  Duration of surgery  Type of surgery (laparoscopy/ENT/neuro/breast/strabismus/laparotomy/plastics)

14 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 score 110% 221% 339% 479%

15 Type of Surgery?  Distribution of risk factors?  Different anaesthetic technique?  Different length of operation?  Operation itself?  Inconclusive, conflicting results, evidence rating B

16 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

17 Reducing risk factors  Avoiding GA (regional)  Avoiding volatiles (propofol)  Intra-operative O2 (FiO2 80%)  Adequate hydration  Avoiding nitrous  Minimising length of operation  Minimising neostigmine

18 “Consensus Guidelines”  Identify and stratify risk  Reduce risk factors (previous slide)  Multimodal approach for high risk  Children do better with 5-HT3 antagonists  Rescue therapy should not be same agent as prophylactic unless > 6hrs since dose  Dexamethasone works well for prophylaxis but not rescue


20 References  Apfel et al: A Simplified Risk Score for Predicting Postoperative Nausea and Vomiting: Conclusions from Cross-validations between Two Centers. ANESTHESIOLOGY 1999; 91:693  Gan et al: Consensus Guidelines for Managing Postoperative Nausea and Vomiting. ANESTHESIA & ANALGESIA 2003; 97:62-71  Apfel et al: A Factorial Trial of Six Interventions for the Prevention of Postoperative Nausea and Vomiting. The New England Journal of Medicine 2004; 350:2441-2451  Henzi et al: Dexamethasone for the Prevention of Postoperative Nausea and Vomiting: A Quantitative Systematic Review. ANESTHESIA & ANALGESIA 1999; 90(1):186

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