Post-Operative Nausea and Vomiting

Post-operative nausea and vomiting (PONV) can be one of the most distressing parts of the surgical journey. It affects approximately 20-30% of patients within the first 24 hours post-surgery.

The consequences of PONV can include increased anxiety for future surgical procedures, increased recovery time and hospital stay, and, in severe cases, aspiration pneumonia, incisional hernia, bleeding, and metabolic alkalosis.


Risk Factors

There are a number of risk factors for PONV. They can be divided into patient factors, surgical factors, and anaesthetic factors.

Fig 1 - Opoid analgesics, such as diamorphine hydrochloride, can induce nausea and vomiting.

Fig 1 – Opoid analgesics, such as diamorphine hydrochloride, can induce nausea and vomiting.

Patient factors

  • Female
  • Previous PONV or motion sickness
  • Use of opioid analgesics
  • Non-smoker

Surgical factors

  • Intra-abdominal laparoscopic surgery
  • Intracranial or middle ear surgery
  • Squint surgery (highest incidence of PONV in children)
  • Gynaecological surgery, especially ovarian
  • Prolonged operative times
  • Poor pain control post-operatively

Anaesthetic Factors

  • Opiate analgesia
  • Inhalational agents (e.g. Isoflurane)
  • Prolonged anaesthetic time
  • Spinal anaesthesia
  • Intraoperative dehydration or bleeding
  • Overuse of bag and mask ventilation (due to gastric dilatation)

Pathophysiology

There are two areas in the brainstem that play a key role in the control of vomiting and nausea

  • Vomiting centre – located within the lateral reticular formation of the medulla oblongata. It controls and coordinates the movements involved in vomiting.
  • Chemoreceptor trigger zone – located in the area postrema (situated at the inferoposterior aspect of the 4th ventricle). It is located outside the blood brain barrier, and can therefore respond to stimuli in the circulation.

The vomiting centre receives input from the chemoreceptor trigger zone, gastro-intestinal tract, vestibular system and higher cortical structures (such as sight, smell and pain). If the stimuli is sufficient, it acts on the diaphragm, stomach and abdominal musculature to initiate vomiting.

A number of neurotransmitters are involved in the control of vomiting. This is important clinically, as they can be targeted by anti-emetic medications. A summary of the neurotransmitters in the vomiting process:

  • Chemoreceptor trigger zone: Dopamine and 5HT3 receptors.
  • Vestibular apparatus: Acetylcholine and Histamine receptors.
  • GI tract: Dopamine receptors.
  • Vomiting centre: Histamine and 5HT3 receptors.
Fig 2 - The pathways and neurotransmitters involved in the control of vomiting.

Fig 2 – The pathways and neurotransmitters involved in the control of vomiting.


Clinical Assessment

When assessing a patient suffering with PONV, the first priority is to ensure that they are safe and stable. If in any doubt, an ABCDE approach should be taken. If the patient is drowsy and/or vomiting there is a risk of aspiration, so careful airway assessment and protection with the use of an NG tube may be required.

Consider the following questions during your assessment of the patient:

  • What was the operation? Is it likely to cause PONV?
  • Which anaesthetic agents/post operative drugs have been used?
  • Are there other factors contributing to nausea?
  • Which antiemetic therapy would suit this patient best?

In addition, it is important to be aware of alternative causes of nausea and vomiting in the post-operative patient, such as infection, gastrointestinal causes (post-operative ileus, bowel obstruction), metabolic causes (hypercalcaemia, uraemia, DKA), medication (antibiotics, opioids), CNS causes (raised ICP), or psychiatric causes (anxiety). These should all be managed as necessary.


Management

The management of post-operative nausea and vomiting can be divided into three areas; prophylactic, conservative and pharmaceutical.

Fig ? - IV fluid infusion is a conservative treatment for PONV

Fig 3 – IV fluid infusion is a conservative treatment for PONV

Prophylactic Measures

  • Anaesthetic measures – reduce opiates, reduce volatile gases, avoiding spinal anaesthetics
  • Prophylactic antiemetic therapy
  • Dexamethasone at induction of anaesthesia

Conservative Measures

  • Adequate fluid hydration
  • Adequate analgesia
  • Ensure no obstructive cause

Pharmaceutical Measures

A wide variety of pharmacological options are available for anti-emetic action and it is important that the choice of antiemetic is considered by the likely cause of the nausea. Multimodal therapy is often more effective, therefore add in a different antiemetic to that given in theatre.

Patients with impaired gastric emptying or gastric stasis should be trialed on a prokinetic agent (such as metochlopramide or domperidone), unless bowel obstruction is suspected. Hyoscine can help to reduce secretions and subsequent N&V in patients with bowel obstruction.

A suspected metabolic or biochemical imbalance, such as uraemia, electrolyte imbalance, or cytotoxic agents, causing N&V should be trialled on metochlorpamide, yet any specific opioid-induced N&V typically responds well to ondasteron.

Any higher cortical input, as previously discussed, should be treated appropriately, so ensure patient is well-hydrated, any pain is well controlled, and anxiety is treated appropriately.

Key Points

  • Identifying patients who are at risk of PONV will aid in their management.
  • Prophylactic measure includes anaesthetic approaches, conservative measure and prophylaxis.
  • A range of antiemetic medications are available and are often used in combination.
  • Nausea and vomiting may be a sign of post-operative complication like bleeding or ileus. Consider these carefully in the assessment of these patients.

Quiz

Question 1 / 4
Which two areas of the brainstem have a role in the control of vomiting?

Quiz

Question 2 / 4
Which ventricle of the brain does the chemoreceptor trigger zone lie in?

Quiz

Question 3 / 4
What is the most appropriate management of a patient with PONV?

Quiz

Question 4 / 4
Which of the following is NOT a patient factor that pre-disposes to PONV?

Results

Further Reading

A factorial trial of six interventions for the prevention of postoperative nausea and vomiting
IMPACT Investigators, New England Journal of Medicine

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