Nausea and Vomiting After Surgery
Highlights
- Postoperative nausea and vomiting (PONV) is defined as any nausea, retching, or vomiting occurring during the first 24–48 h after surgery in inpatients. (View Highlight)
- the brain structures involved in the pathophysiology of vomiting are distributed throughout the medulla oblongata of the brainstem, not centralized in an anatomically defined ‘vomiting centre’.1 Such structures include the chemoreceptor trigger zone (CRTZ), located at the caudal end of the fourth ventricle in the area postrema, and the nucleus tractus solitarius (NTS), located in the area postrema and lower pons (View Highlight)
- The CRTZ receives input from vagal afferents in the gastrointestinal tract, and it can also detect emetogenic toxins, metabolites, and drugs circulating in the blood and cerebrospinal fluid due to its lack of the blood–brain barrier (View Highlight)
- The CRTZ projects neurones to the NTS, which receives input from vagal afferents and from the vestibular and limbic systems. The NTS triggers vomiting by stimulating the rostral nucleus, the nucleus ambiguous, the ventral respiratory group, and the dorsal motor nucleus of the vagus. (View Highlight)
- Enterochromaffin cells in the gastrointestinal tract release serotonin, and the vagus nerve communicates with the CRTZ via 5-HT3 receptors (View Highlight)
- CRTZ communicates with the NTS primarily via dopamine-2 (D2) receptors. (View Highlight)
- The vestibular system, which detects changes in equilibrium, communicates with the NTS via histamine-1 (H1) and acetylcholine (mACh) (View Highlight)
- Anticipatory or anxiety-induced nausea and vomiting appears to originate in the cerebral cortex, which communicates directly with the NTS via several types of neuroreceptors (View Highlight)
- Female gender is consistently the strongest risk factor for PONV with an odds ratio (OR) of ∼3 (View Highlight)
- The specific mechanism underlying smoking's protective effect is unknown. One of the most commonly believed theories is that polycyclic aromatic hydrocarbons in cigarette smoke induce cytochrome P450 enzymes, thereby increasing the metabolism of emetogenic volatile anaesthetics (View Highlight)
- For adult patients, age is a statistically, though not clinically, relevant risk factor, with the incidence of PONV decreasing as patients age. For paediatric patients, however, age increases the risk of postoperative vomiting (POV), such that children older than 3 yr have been shown to have an increased risk of POV compared with children younger than 3 (View Highlight)
- the use of volatile anaesthetics is the single most important factor for predicting emesis in the first 2 postoperative hours (View Highlight)
- Volatile anaesthesia may increase PONV by decreasing serum levels of anandamide, an endogenous cannabinoid neurotransmitter that acts on cannabinoid-1 and transient receptor potential vanilloid-1 receptors to suppress nausea and vomiting (View Highlight)
- Nitrous oxide increases the relative risk of PONV by 1.4—less of an effect than previously believed. (View Highlight)
- Intraoperative and postoperative opioid use increases the risk of PONV in a dose-dependent manner. Opioids reduce muscle tone and peristaltic activity, thereby delaying gastric emptying, inducing distension, and triggering the vomiting reflex. (View Highlight)
- The duration of anaesthesia, which is closely linked to the duration of surgery, can help predict the patient's risk of PONV, since the duration of anaesthesia describes the patient's exposure to emetogenic stimuli like volatile anaesthetics and intraoperative opioids. (View Highlight)
- In general, the type of surgery cannot provide reliable, reproducible, and clinically relevant information for assessing the patient's risk of PONV in adult patients. Conversely, in children, strabismus surgery was identified as an independent risk factor for POV. (View Highlight)
- Three classes of antiemetic drugs,56 serotonin antagonists (e.g. ondansetron), corticosteroids (e.g. dexamethasone), and dopamine antagonists (e.g. droperidol) have similar efficacy against PONV, with a relative risk reduction of ∼25%. Moreover, they act independently and, when used in combination, have additive effects (View Highlight)
- At low doses, dexamethasone is not only effective against PONV but also against post-surgical pain and fatigue. (View Highlight)
- Metoclopramide is a widely used D2 antagonist. Contrary to popular belief, the 10 mg dose has no effect on PONV, but 25–50 mg has similar efficacy compared with other antiemetics. Metoclopramide use has been associated with extrapyramidal and sedative side-effects. (View Highlight)
- patients at low-to-moderate risk can be given one or two interventions (e.g. TIVA, antiemetic drugs), whereas patients at high risk can receive three or four interventions (View Highlight)
- ondansetron is no more effective than placebo for rescue treatment if the patient received a 5-HT3 receptor antagonist intraoperatively as prophylaxis. Therefore, antiemetics administered as rescue treatment for PONV should be of a different class than the drug administered as prophylaxis (View Highlight)