Postoperative Nausea

Etiology

The highest risk patients for PONV appear to be young to middle-aged, non-smoking females with a history of PONV or motion sickness (all are independent risk factors). The use of volatile anesthetics (inhalational anesthesia agents), prolonged surgery, use of nitrous oxide, and the postoperative need for opioids all increase the risk of PONV. The source of PONV is multifactorial and believed to be from the chemoreceptor trigger zone in the brainstem, from opiate-induced, direct effects on the gastrointestinal (GI) tract and other anesthetics as well as in the vestibular system through movement and from the sensitization of this system by agents commonly used in anesthesiology. Type and location of surgery play a role as well, and ocular and tympanic surgery, intracranial, abdominal, and gynecological surgeries pose an increased risk for PONV. Dehydration, aspiration, electrolyte changes, and other perioperative complications or comorbidities can worsen PONV. A vicious cycle can occur where vomiting worsens the comorbidity that may be causing the PONV in the first place.[4][5]

Epidemiology

Extremes of age seem to be protective for postoperative nausea and vomiting. Meanwhile, there is an increased risk of PONV in female patients, in certain types of surgery. One of the few benefits of tobacco use, particularly smoking, may decrease the risk of developing postoperative nausea and vomiting.[6][7]

Pathophysiology

The chemoreceptor trigger zone in the medulla oblongata plays an important role in the initiation of vomiting. Several neurotransmitters play a role in this response to noxious stimuli including acetylcholine, dopamine, and substance P, explaining the different potential prevention and treatment modalities available for PONV. While incompletely elucidated, stimulation in other neurons and from other areas of the body (GI tract, inner ear) may lead the chemoreceptor trigger zone to trigger vomiting. Additionally, opiates may act directly on this part of the brain to stimulate PONV.

History and Physical

Patients may appear pale and diaphoretic in response to the subjective sensation of nausea. Anxiety may lead to tachycardia and tachypnea. Active vomiting can stimulate a sympathetic response leading to hypertension and tachycardia. The Valsalva associated with active vomiting can lead to bradycardia and leads to increased intrathoracic pressure and intracranial pressure which can be detrimental to patients after certain procedures or with certain illnesses. History and physical should focus on eliminating other causes of nausea and vomiting including but not limited to ischemia and potential bowl issues.

Evaluation

Concomitant sources of nausea including cardiac ischemia, ileus, hypotension, hypoxia, metabolic abnormalities, and other postoperative surgical complications should be considered. Patients in the postoperative period are monitored closely which allows healthcare providers to evaluate more severe nausea causes more easily. Extensive vomiting can cause electrolyte imbalances and acid-base disturbances and may need to be evaluated with laboratory testing. As with any perioperative complication, a focused history and physical exam and further evaluation of the patient should be performed in the setting of unexpected or severe PONV.[8][9]

Treatment / Management

 The treatment of PONV is most effective with a combination of agents and prevention is more effective than initiating therapy after the onset of symptoms. Many facilities have developed standardized algorithms based on risk scores from the factors listed above. For instance, having 4 risk factors may correlate to approximately 80% chance of PONV. In these instances, some algorithms would recommend 4 antiemetic agents be used prophylactically for prevention. Agents used as antiemetics include serotonin antagonists (5-HT3 antagonists) such as ondansetron, antidopaminergic agents such as droperidol, antihistamines such as dimenhydrinate, and the anticholinergic transdermal medication scopolamine (best applied preoperatively). Additionally, low doses of the steroid dexamethasone are commonly given as a first or second-line treatment, and new medication aprepitant (NK1 antagonist) has proven particularly useful for prevention of PONV when given in the preoperative period. Metoclopramide, in addition to decreasing aspiration risk through increasing lower esophageal sphincter tone and enhancing gastric emptying, also has antiemetic effects.[3][10][11][10](A1)

Propofol, an IV-induction agent, has short antiemetic properties in low doses and is useful in high-risk patients as part of a total intravenous anesthetic (avoidance of inhalational agents). All opioids utilized in the perioperative period have been associated with PONV, so mitigating the exposure to these agents using multimodal pain therapy including regional and epidural anesthesia where appropriate can decrease the rate of PONV. Some newer sedative agents such as dexmedetomidine and alternative pain medications (NSAIDs, acetaminophen) can be utilized to decrease the exposure to inhalational agents and traditional opiate pain medications. While avoiding opiates provides benefits in decreasing the risk of PONV, one should be careful to recognize the additional side effects caused by adjuvant therapy, for instance, nonsteroidal, anti-inflammatory agents may cause dyspepsia and may mirror some of the symptoms and complaints of PONV. Promethazine is commonly utilized in the PACU as a rescue antiemetic. Restriction of movement, removal of noxious stimuli, and application of oxygen may prove useful to the patient experiencing PONV.

The commonly utilized antiemetic agents are not without potential side effects, some which could be serious and warrant additional evaluation and monitoring. Promethazine has some sedative properties so it must be used with caution in this population and in itself can prolong PACU recovery times. 5-HT3 antagonists can cause a headache and can slightly prolong the QT interval. The antidopaminergic agents, particular droperidol, can also significantly prolong the QT interval and can exacerbate Parkinson disease. Meanwhile, the antihistamine and anticholinergic agents can cause sedation as well as visual changes and confusion and should be used with caution in elderly patients. Aprepitant can make oral contraceptives ineffective through alteration of hepatic metabolism. Dexamethasone, in addition to the other side effects of glucocorticoids, can lead to hyperglycemia. Theoretically, osteoclast activity can be decreased and wound healing may be inhibited so some surgeons may request the avoidance of glucocorticoid agents.

Some nontraditional methods for prevention of postoperative nausea and vomiting have shown promise in studies. Stimulation of the olfactory center with various agents including isopropyl alcohol swabs has shown promise or been associated with decreased nausea in the perioperative setting in some studies and had little effect on others. Additionally, numerous studies have looked at stimulation of the P6 acupoint (on the palmar surface of the wrist, near or between the palpable flexor tendons) utilizing acupuncture, electro-acupuncture, transcutaneous nerve stimulation, laser stimulation, capsicum plaster, and acupressure during the operative procedure as a means to control PONV with documented success. Finally, supplemental oxygen and hydration (intravenous) can reduce the incidence or severity of PONV. Calculation of fluid deficits from fasting and replacement in a directed manner can be helpful. Oral intake may worsen or even initiate the symptoms of postoperative nausea and vomiting in the recovery units while certain beverages have been historically related to decreasing nausea.

Postoperative nausea and vomiting is a poor outcome in the perioperative period. It is multifactorial, has known risk factors, is more easily prevented than treated, and is of significant detriment to patient satisfaction, healthcare costs, and lengths of stay.  Health care providers should pay close attention to prevention, rule out more serious causes or comorbidities, and work within their systems to decrease its prevalence in this patient population.[12]

Differential Diagnosis

• Antiarrhythmics

• Anticonvulsants

• Chronic intestinal pseudo-obstruction

• Digoxin

• Gastroparesis

• Hormonal preparations

• Hydrocephalus

• Irritable bowel syndrome

• Labyrinthitis

• Mass lesion

• Motion sickness

• Non-ulcer dyspepsia

• Opiates

• Spontaneous bacterial peritonitis

• Urinary tract infection/pyelonephritis

Prognosis

Postoperative nausea and vomiting are generally self-limited and as mentioned, easier to prevent than to treat. As the effects of inhalational agents dissipate and the exposure to opiate pain medications decreases, the severity of PONV tends to decrease. PONV has been shown to extend the time in the hospital and lengthen stays for outpatient procedures including increase admission rates; however, PONV that does not decrease with time after surgery should be evaluated for other potential causes listed above.