PONV

Dr Owen McIntyre

Define PONV

•NAUSEA
•Sensation that precedes vomiting
•VOMITING
•Rapid expulsion of stomach contents through the mouth
•PONV
•Multifactorial
•Incidence in GA with volatile between 20-40%
(Anywhere between 10-90%)
•Early: within first 6 hours
•Late: within first 24 hours



Neural pathways mediating N+V?
•CTZ: medulla, floor of 4th ventricle, outside BBB
•Primary NT is Dopamine, D2 (+5HT3)
•Vestibular afferents
•Raised ICP via direct action
•Metabolic abnormalities; uraemia, hypernatraemia
• Drugs: opiates, volatiles, etomidate, neostigmine
sympathomimetics; ketamine, ephedrine
cytotoxics, cardiac glycosides, apomorphine
•Efferents to VC

Neural pathways mediating N+V?

•Vomiting Centre: medulla, same level as CTZ
inside BBB
•Primary NT is Acetylchloine, M3 (+H1, ?mu opioid)
•Cortical affferents, limbic, olfactory,visual
•Visceral afferents, gut and heart (X and symp)
•Occulovestibular afferents
•Efferent compose Vomiting reflex pathway



Neural pathways mediating N+V?
•Substance P
•Slow excitatory neurotransmitter
•Acting at Neurokinin-1 receptors
•Loads of NK-1 receptors at key sites in medulla
•Could be final common pathway
•Vofopitant

Describe the vomiting reflex
•Complex: central, peripheral and enteric NS
•Reflex is preceded by retrograde peristalsis
•Increased salivation
•Forceful inspiration, breath held mid-insp
•Raise hyoid and larynx; closes glottis and opens crico-oesophageal sphincter
•Elevation of soft palate closes nasopharynx
•Contraction of diaphragm, abdo muscles
•Opening of LOS and relaxation of oesophagus

What are the risk factors for PONV?
•Patient factors
•Female(2-4x)
•Past history of PONV(3x)
•History of motion sickness
•Non smoker
•Obesity
•Children
•Early ambulation

What are the risk factors for PONV?
•Anaesthetic factors
•Volatiles
•Opiates
•N2O
•Etomidate, Thiopentone
•Neostigmine
•Sympathomimetics
•Hypotension
•Hypoxia
•Bag-mask ventilation

How would you manage PONV?
•Assessment of risk
•Prevention
•Pre
•Peri
•Post-op
•Pharmacotherapy
•Multimodal, ‘Balanced anti-emetic therapy’
•Prophylaxis vs. treatment
•Others
•Acupuncture


Prevention
•Pre-operative
•Optimize fasting; clear fluid 2hours pre-op
•Pre-med; benzos, ?metoclopramide
•Peri-operative
•Regional anaesthesia
•Avoid volatiles and N2O in favour of Propofol TCI
•Avoid thio, etomidate, ketamine
•Avoid NMBAs and therefore neostigmine
•Avoid opioids if possible, alternate analgesia
•Generous fluid therapy
•Post-operative
•Adequate analgesia

Can you classify antiemetics?
•Mode of action or site of action
•Anti-dopaminergic(D2)
•Anti-histamines(H1)
•Anti-cholinergic(M3)
•Anti-serotinergic(5HT3)
•Others
•Corticosteroids
•Cannabinoids
•Propofol


What are the side effects of the anti-emetics you commonly use?
•Cyclizine
•Ondansetron
•Dexamethasone
•?Prochlorperazine
•?Others

Strategy for the management of PONV
•A Simplified Risk Score for Predicting Postoperative Nausea and Vomiting
–Apfel et al, Anesthesiology 1999 91:693-700
•4 patient risk factors were as accurate at predicting PONV as more complicated equations
Female
Past history of PONV or Motion Sickness
Non smoker
Post-op opiates
•No association with type or duration of surgery

Strategy for the management of PONV
•Number of Risk Factors Incidence of PONV
0 10%
1 21%
2 39%
3 61%
4 79%

•If 2+ present risk is high
•Modify anaesthetic technique
•?Prophylaxis
•Multimodal approach

Evidence for the management of PONV
•Too much information!!
•Cost effectiveness: Individual drugs
Prophylaxis vs Treatment
•Patient satisfaction
•NNT much better for high risk patients
•Single antiemetic: Ondansetron NNT 5-6
•Combination therapy significantly better than monotherapy with no increased SE (Ondan + dex /drop)


Evidence for the management of PONV
•Multimodal Approach
•Scuderi et al, Anaest Analg 2000; 91
•TIVA: Propofol and remifentanil
•No nitrous
•No NMBA
•Aggressive IV fluids(25ml/kg)
•3x prophylactic anti-emetics
•98% response rate