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.
There are a number of risk factors for PONV. They can be divided into patient factors, surgical factors, and anaesthetic factors.
- Previous PONV or motion sickness
- Use of opioid analgesics
- 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
- 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)
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.
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.
The management of post-operative nausea and vomiting can be divided into three areas; prophylactic, conservative and pharmaceutical.
- Anaesthetic measures – reduce opiates, reduce volatile gases, avoiding spinal anaesthetics
- Prophylactic antiemetic therapy
- Dexamethasone* at induction of anaesthesia
*A recent study showed 8mg dexamethasone significantly reduces the incidence of PONV at 24 hours and the need for rescue antiemetics for up to 72 hours in patients following large and small bowel surgery
- Adequate fluid hydration
- Adequate analgesia
- Ensure no obstructive cause
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 trialled on a prokinetic agent, such as metoclopramide 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 metoclopramide
- 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.
- 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.