Postoperative Nausea and Vomiting (PONV) is a frequent and often distressing complication experienced by patients recovering from surgery and general anesthesia. While not typically life-threatening, PONV significantly impacts a patient’s comfort and can delay discharge from the hospital. Uncontrolled episodes may lead to more serious issues like dehydration, bleeding, and wound dehiscence. Effective prevention and management are high priorities in modern surgical care.
The Medical Definition of PONV
PONV is medically defined as any episode of nausea, retching, or vomiting that occurs within the first 24 to 48 hours following a surgical procedure involving anesthesia. The symptoms are categorized by their timing: early PONV typically manifests within the first six hours, while late PONV occurs after this initial period. The overall incidence is around 30% in the general surgical population, but this figure can soar to 80% for those identified as high-risk patients.
The underlying mechanism involves the central nervous system, specifically the “vomiting center” located in the brainstem’s medulla. This center integrates signals from multiple pathways, including the Chemoreceptor Trigger Zone (CTZ), the vestibular system in the inner ear, the gastrointestinal tract, and the cerebral cortex. General anesthesia and opioids stimulate the CTZ, which is situated outside the blood-brain barrier, making it sensitive to circulating toxins or drugs.
Nausea is the subjective, unpleasant sensation of needing to vomit, which does not involve expulsive muscular action. Vomiting, or emesis, is the forceful, involuntary expulsion of stomach contents, a coordinated reflex orchestrated by the vomiting center. Anesthesia-related drugs, particularly volatile anesthetic gases and high-dose opioids, trigger this cascade by activating various receptors, including dopamine, serotonin, and neurokinin-1 receptors, within the CTZ.
Key Factors That Increase Risk
Identifying a patient’s vulnerability is the first step in preventing PONV, and risk is assessed using established criteria like the simplified Apfel score. This system identifies four primary patient-specific factors. The presence of these factors incrementally increases a patient’s risk profile, ranging from approximately 10% with zero factors to nearly 80% with all four.
- Being female.
- Having a history of PONV or motion sickness.
- Being a non-smoker.
- The requirement for postoperative opioid pain medication.
Anesthetic practices are also a major contributing factor, as many common agents are inherently emetogenic. The use of volatile inhalation anesthetics, such as sevoflurane or desflurane, significantly raises the risk compared to total intravenous anesthesia (TIVA) using propofol. Additionally, the intraoperative use of nitrous oxide and a prolonged duration of anesthesia, typically exceeding one hour, are independently associated with higher PONV rates.
Specific types of surgery also create a higher predisposition to the complication due to the nature of the surgical stimulation. Procedures involving the eye, such as strabismus surgery, or those affecting the middle ear, are known to have a high incidence due to stimulation of the vestibular pathway. Furthermore, abdominal and gynecological surgeries, particularly those performed laparoscopically, increase the risk through direct manipulation of the gastrointestinal tract and the subsequent inflammatory response.
Proactive Measures to Stop PONV
The gold standard for high-risk patients is multimodal prophylaxis, which involves combining two or more antiemetic medications with non-overlapping mechanisms of action. This strategy targets different receptor pathways feeding into the vomiting center, maximizing the chance of complete prevention. For a patient with two or more risk factors, two or three prophylactic agents are routinely administered before the end of the operation.
One primary class of medication used is the 5-HT3 receptor antagonists, such as ondansetron, which block serotonin receptors in both the CTZ and the gastrointestinal tract. Corticosteroids, typically dexamethasone, are also highly effective. These drugs are often given at the start of the anesthetic to ensure peak effect during the recovery period.
Newer agents, such as Neurokinin-1 (NK-1) receptor antagonists like aprepitant, work by blocking substance P receptors in the vomiting center and are increasingly used for high-risk cases. Non-pharmacological interventions are equally important in reducing the baseline risk for all patients. Utilizing a propofol-based TIVA technique instead of volatile agents, minimizing the use of postoperative opioids through multimodal pain management, and ensuring adequate intravenous hydration are all effective preventative measures.
Addressing Symptoms When They Occur
Despite best efforts, established PONV—when symptoms manifest—requires prompt management, known as rescue therapy. The first principle of rescue is that the antiemetic administered must belong to a different pharmacological class than the drug or drugs used for prophylaxis. This approach ensures a new receptor pathway is targeted to interrupt the emetic reflex successfully.
For a patient who received a 5-HT3 antagonist for prevention, a rescue dose of a dopamine antagonist like metoclopramide or droperidol would be an appropriate choice. Similarly, if a steroid was used for prophylaxis, a drug from the 5-HT3 class could be given as the rescue agent. Administration of a second dose of the same prophylactic drug is generally avoided unless at least six hours have passed since the initial dose.
Supportive care is a simple yet crucial component of rescue therapy, particularly the administration of intravenous fluids. Dehydration often accompanies vomiting and can independently worsen nausea, so restoring fluid balance helps to alleviate symptoms. In refractory cases that do not respond to initial antiemetics, a low, sub-hypnotic dose of propofol may even be administered in the recovery unit due to its inherent antiemetic properties.