Why is it Important?
A very common problem in the ambulatory surgery patient population,
occurring in an estimated 35% of all patients. If high-risk patients are
considered as a separate group, then as much as 70% of these patients will
Before the 1960s, when older inhalational anesthetic agents such as ether and
cyclopropane were widely used, the incidence of vomiting in general
population was as high as 60%.
Patients rank PONV as one of the most unpleasant memories associated with
their hospital stay.
Patient satisfaction with their anaesthetic is highly linked to their experience
(or lack of ) of PONV. In surveys, many state they prefer to experience pain
When severe it can lead to increased length of hospital stay, increased
bleeding, incisional hernias and even life threatening aspiration pneumonia.
Despite decades of progress in surgical and anaesthetic techniques, effective
prevention and Tx of PONV has been elusive.
Physiology of PONV
N + V can be induced by many factors (physiological, pathological and even
psychological), as well as drugs or toxins.
The part of the brain related to emesis is an ill-defined area located in the
lateral reticular formation of the medulla.
Afferent stimuli arrive from chemoreceptors and pressure receptors in the gut
and CNS, as well as peripheral pain receptors. Other sites of input in the CNS
include the cerebral cortex (pain, fear and anxiety), vestibular and cerebellar
nuclei and the Chemoreceptor Trigger Zone (CTZ).
The CTZ is outside the blood-brain barrier and is extremely sensitive to emetic stimuli.
The neurotransmitters implicated in the control of nausea and vomiting
include acetylcholine, dopamine and 5-HT. Hence anti-emetics have been
targeted to antagonise one or more of these neurotransmitters.
Physiology of PONV
Multidisciplinary panel of experts convened to
review med literature on PONV (published till
Developed guidelines in risk stratification and
Postoperative nausea and vomiting is a multifactorial
entity, comprising patient, surgical, and anesthetic
Due to the cost of pharmacological Tx of
emesis, risk stratification is important.
By focusing attention (and resources) on those groups
of patients most likely to develop PONV, the overall
cost of dealing with PONV is reduced.
A number of studies have looked into PONV risk
factors and risk stratification.
Incidence increases during menstruation and decreases after the menopause. After 70
years of age, both sexes are equally affected.
(suggested but no strong evidence).
POV in under 2yr olds is rare. From >3yrs to puberty, risk is higher than adults.
Previous history of PONV/motion sickness
Early ambulation, early postoperative eating and drinking.
Type of Surgery
Intracranial, middle ear
The highest PONV risk surgery in children
Especially T & As (? due to blood in upper GIT)
Significant surgical pain
Well known for emetogenic potential but remember untreated pain can also be
Isoflurane++, Etomidate, ketamine, methohexitone. Propofol considered one of the
Spinal anaesthesia (blocks above T5), hypotension.
Intraoperative & Preoperative dehydration
Eg aggressive mask ventilation
Quick Risk Factor Chart
Four primary Risk Factors
History of PONV
No of Risk Factors vs Risk %
None= 10% 2RF=40% 4RF=80%
1 RF= 20% 3RF=60%
Low Risk of PONV pts
No prophylaxis or minimal prophylaxis is likely
the best choice
Moderate Risk of PONV pts
Prophylaxis followed by aggressive treatment if
nausea and vomiting develop.
High Risk of PONV pts
Aggressive prophylaxis + treatment. Expensive but becomes cost-effective when
the issues of patients satisfaction and avoidance of unplanned admission are
considered. Multi-modal therapy widely accepted as providing the best results
Some of the treatments used around the world include:
5HT3-receptor ondansetron , tropiseron,
Anti-cholinergic scopolamine (L-hyoscine)
Dopamine antagonists metoclopramide
Four types of serotonergic (5-HT) receptors (5-HT1-4). 5-HT1 receptors
are subdivided further (5-HT1A etc). Ondansetron is a highly selective
antagonist at 5-HT3 receptors; it has an affinity 250-1000 times greater for
the 5-HT3 receptor than for any other receptor. The drug antagonises 5-
HT3 receptors both centrally and peripherally. Emetogenic stimuli result in
the release of 5-HT in the small intestine and initiate a vomiting reflex (via
vagal afferents, via 5-HT3 receptors). Thus, Ondansetron blocks the
initiation of this reflex.
Drug of choice in children. Dose =350mcg/kg
Recent evidence has shown that dexamethasone is effective prophylaxis for
PONV, at least as effective as droperidol and the serotonin antagonists
when used as a single agent. It is orders of magnitude cheaper than the
5HT3 anatagonists. Dose required for this effect is very low (eg 2.5-5 mg
IV and as such it causes no significant side effects) given early during the
However has no role in the treament of established PONV, thus serotonin
antagonists remain the mainstay in such circumstances.
For many years, droperidol (in very small
doses) was very popular in any strategy against
PONV. Droperidol is very effective in small
doses (0.625-1.25mg) for the prevention and
treatment of PONV and was once considered
almost as a gold standard when it came to
comparing the efficacy of other medications.
Being very inexpensive also further added to
Unfortunatey its use has declined after its
association with rare fatal arrythmias (although
at higher doses)
Used in the prophylaxis of motion sickness and as
Competitive antagonism of acetylcholine at
muscarinic receptors. Hyoscine has been shown to
reduce postoperative nausea and vomiting related to
opiods. It also decreases muscle tone and secretions
in the gut, which may contribute to its antiemetic
Antagonism of peripheral dopaminergic D2
receptors. Results in increased gastrointestinal
motility and tone. Although metoclopramide
has prokinetic effects that enhance gastric and
upper intestinal motility, it is no more
effective as an antiemetic than a placebo
according to some trials.
If a dose of a single agent is ineffective,
additional dose of same agent is unlikely to
increase efficacy. In fact it is likely to
increase the risk of side effects
Non Pharmacological Therapy
Acupuncture, TENS, accupressure,
Have shown quite significant efficacy when
used before surgery.
Obviously cost and effort of administering is
a big drawback
Identify Pts at risk
Attempt to stratify in low, moderate and high risk
Reduce Baseline Risk Factors
Use Regional anaesthesia when possible
Use propofol for induction and maintenance
Use intra-operative supplemental oxygen
Avoid Nitrous oxide, volatiles
Minimise opiod use
Minimise neostigmine use
Prophylaxis for moderate & high risk
Multimodal drug prophylaxis
Aggressively Tx PONV
For pts where prophylaxis failed or was not used
Ondansetron as first line Tx
Add additional agents if PONV continues
PONV is one of the most distressing aspects of an
anaesthetic for a patient.
Be aware of Risk Factors and give pre-emptive
prophylaxis if suitable. It’s best (and easier) to
prevent than to treat.
Combination therapy is much more effective and
associated with less risk than repeat doses of same