88. Vomiting and day surgery Flashcards
A 32-year-old female patient presents for a day case laparoscopy as part
of investigation of infertility. She has a previous history of vomiting
after anaesthetics.
Is providing anti-emesis important?
Post-operative nausea and vomiting (PONV) may be the most
unpleasant memory that a patient remembers about their operation.
The incidence of PONV in adults is approximately 25%, ranging from
5%–75% in the literature.
Severe cases can lead to
Increased length of hospital stay
Aspiration pneumonia
Retching resulting in increased bleeding and incisional hernias
Prolonged vomiting results in loss of hydrogen ions, chloride,
potassium, sodium and water.
Dehydration, metabolic alkalosis and total body potassium depletion
may occur.
What factors pre-dispose to Post-Operative Nausea and Vomiting?
patient, surgical and anaesthetic-related factors
The commonest factors are:
Children
Female sex
Previous history of PONV
History of motion sickness
Opioids
Sympathomimetics
Gynae/ear/squint/laparoscopic surgery.
In principle, how would you reduce the risk of emesis?
Pre + Induction
Pre-operatively
Ensure adequate hydration
Keep fasting times to the minimum
Normalise electrolytes and glucose if necessary
Induction
Avoid etomidate and keep opioid use as low as possible.
Avoid hypotension, coughing and straining.
Avoid inflating the stomach with gas.
Avoid tracheal intubation if possible (physical stimulation and drugs
required).
Avoid volatile anaesthetics (if particularly high risk) and nitrous oxide, i.e.
use TCI propofol.
Give anti-emetics in combination, based on risk factors.
Intra-operatively
Ensure adequate hydration.
Minimise visceral traction/distension.
Encourage the surgeon to use minimal access surgery and ensure the
abdomen is deflated as much as possible to reduce pain post-op.
Give paracetamol and NSAIDs as opioid sparing agents if appropriate.
Use local infiltration.
Emergence
Post-operatively
Avoid neostigmine if possible.
Consider emptying the stomach if it is likely to be full of gas.
Avoid rapid movements and turns on the way to recovery.
_____________________________
Regular anti-emetics.
Avoid opioids if possible, with regular adjuvant analgesia.
Avoid rapid oral intake
Discuss your anaesthetic technique
Use a TCI Propofol technique.
Following a standard general and anaesthetic assessment and assuming
routine preparation of the patient, theatre and equipment, give fentanyl
1 mcg/kg and commence TCI Propofol after pre-oxygenation.
Paralyse the patient with Atracurium 0.5 mg kg and ventilate in oxygen
(taking care not to over-inflate with the bag-valve-mask) until intubating
conditions are achieved. Intubate carefully.
Give paracetamol 1g, Diclofenac 75 mg with ondansetron 4 mg and
dexamethasone 8 mg as anti-emetics.
Intravenous Hartmann’s solution throughout.
Reserve morphine for pain in recovery.
Neuromuscular monitoring will guide the need for reversal.
It should ideally be avoided.
Some anaesthetists use LMAs or Proseal LMAs for laparoscopies,
usually in thin patients.
In the exam it is best to stick to the safe bet of intubating a head
down patient with a pneumoperitoneum (in order to guard against
aspiration) and accept that this may not be the ideal anaesthetic for
preventing emesis.
Which volatile anaesthetic is most likely to cause emesis?
Volatiles and emesis
A randomised controlled trial of 1180 patients at high risk for PONV
found that, in the early post-operative period (two hours or less), the
leading risk factor for vomiting was dose-dependent use of volatile
anaesthetics.
Similar odds ratios found for isoflurane (odds ratio 19.8).
Enflurane (16.1)
Sevoflurane (14.5)
Desflurane has been shown to have similar rates in other studies.
Nitrous oxide probably causes PONV.
Name some anti-emetic agents. Where do they act?
- Anticholinergics
which cross the blood-brain barrier can
reduce the vestibular component of PONV.
An example would be hyoscine.
Cyclizine has anticholinergic and central antihistamine activity. - Dopamine antagonists
D2 antagonists act on central (and some peripheral)
dopamine receptors.
Examples are prochlorperazine, metoclopramide and droperidol. - 5HT3 antagonists
Act on receptors found in the chemoreceptor trigger
zone (CTZ) and peripherally in gut. Ondansetron is an example - Dexamethasone
is a corticosteroid and may reduce 5HT3 secretion in
the gut, but its mechanism of anti-emesis is unknown. - Benzodiazepines and cannabinoids also have actions on the CTZ.
When would you admit someone overnight with vomiting post-op?
- Persistent nausea/vomiting despite multi-modal treatment.
- Unable to tolerate oral intake.
- Still requiring intravenous anti-emetics.
- If it is felt that intravenous fluids may be necessary to correct electrolyte
imbalance and provide hydration.
Factors pre-disposing a patient to PONV
Patient factors
Patient factors
Children – risk of PONV is almost twice that for adults with an equal
distribution between boys and girls until puberty.
Adults – female sex (3× more likely).
Incidence increases during menstruation and decreases after the menopause.
After 70 years of age, both sexes are equally affected.
Previous history of PONV or motion sickness.
Smokers have 0.6× risk of non-smokers.
Early ambulation.
Early post-operative eating and drinking.
Intestinal obstruction.
Metabolic, e.g. hypoglycaemia, uraemia.
Hypoxia.
Factors pre-disposing a patient to PONV
Surgical factors
Surgical factors
Intra-abdominal-laparoscopic.
Intracranial (especially posterior fossa).
Middle ear.
Squint surgery (highest incidence of PONV in children).
Gynaecological, especially ovarian.
Tonsillectomy and adenoidectomy.
Prolonged surgery.
Factors pre-disposing a patient to PONV
Anaesthetic factors
Opioids (untreated pain is also emetogenic).
Sympathomimetics.
Inhalational agents.
Etomidate and ketamine (compared with propofol and thiopentone).
Neostigmine.
Nitrous oxide (GIT distension/expansion of middle ear cavities).
Prolonged anaesthesia.
Hypotension.
Intra-operative dehydration.
Inexperienced bag and mask ventilation (gastric dilatation).
GA has 11× risk of regional technique
