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What is the most common side effect of general anesthesia?

General anesthesia is used during surgical procedures to induce a state of unconsciousness and prevent pain perception. It involves administering a combination of medications to achieve a controlled, reversible loss of consciousness, along with muscle relaxation, amnesia and loss of protective airway reflexes. While general anesthesia is very safe, it does carry some risks and potential side effects. One of the most common side effects of general anesthesia is postoperative nausea and vomiting (PONV).

What is postoperative nausea and vomiting (PONV)?

Postoperative nausea and vomiting refers to nausea, retching or vomiting that occurs after surgery. It is a common complication and is estimated to occur in around 30% of all surgical patients (1). However, some surgical procedures carry a higher risk than others. Surgeries with a high risk of PONV include:

– Laparoscopic surgery – Up to 70% risk
– Middle ear surgery – Up to 70% risk
– Strabismus (eye muscle) surgery – Up to 80% risk
– Gynecological surgery – Up to 70% risk (2)

The nausea and vomiting associated with PONV tends to occur within 24 hours after surgery. The exact cause is not always clear but is likely related to a number of factors including the medications used, surgical stimulation, inflammation and the patient’s individual characteristics.

Why is PONV a common side effect of anesthesia?

There are several reasons why postoperative nausea and vomiting occurs frequently after general anesthesia:

Medications used

Many medications used during general anesthesia can trigger nausea and vomiting by directly stimulating the chemoreceptor trigger zone in the brain. These include:

– Inhalational anesthetic agents like sevoflurane, desflurane and isoflurane. These stimulant the CTZ more than intravenous anesthetics (3).
– Narcotic pain medications like morphine, hydromorphone and fentanyl. These are commonly used for pain relief after surgery.
– Muscle relaxants such as rocuronium and vecuronium.
– Reversal agents that reverse muscle relaxation like neostigmine.

Surgical stimulation

The actual surgical procedure itself can increase the risk of PONV, especially operations involving the abdomen or inner ear. This is because the inner ear and gut are connected to the vomiting center in the brain. Manipulation of these areas during surgery triggers signals to the brain that induce nausea and vomiting reflexes after the procedure (4).


Surgery and anesthesia cause inflammation in the body from tissue damage and the release of mediators. This inflammatory response may contribute to postoperative nausea.

Individual patient factors

Certain individuals are more prone to nausea and vomiting after surgery including:

– Females – Especially during menstruation or pregnancy
– Non-smokers
– Those with a history of motion sickness or PONV
– Younger patients

What are the symptoms of PONV?

The hallmark symptoms of postoperative nausea and vomiting are:

– Nausea – This is a subjective sensation of wanting to vomit. The patient may be very uncomfortable but not actually vomit.
– Retching – Involuntary attempts to vomit without bringing up contents.
– Vomiting – Forceful expulsion of stomach contents through the mouth. Vomit may be clear, yellow or green fluid or contain recently eaten food.

Other associated symptoms can include:

– Excessive salivation
– Sweating
– Tachycardia (fast heart rate)
– Pallor
– Lightheadedness

Symptoms tend to be transient and occur in the early postoperative period. However, some patients experience delayed nausea and vomiting occurring 24-48 hours after surgery.

How is PONV assessed?

The severity of postoperative nausea and vomiting can be graded using a systematic scale such as the one below:

Grade Definition
0 No nausea or vomiting
1 Mild nausea, no vomiting
2 Moderate nausea, no vomiting
3 Severe nausea, incapacitating but no vomiting
4 Retching or mild vomiting
5 Severe vomiting

This helps quantify the severity of symptoms and monitor response to treatment. Asking patients to report a nausea score from 0 to 10 can also be helpful.

What are the consequences of PONV?

While not life-threatening, postoperative nausea and vomiting can have several detrimental effects including:

– Dehydration – From fluid loss during vomiting episodes. This can cause electrolyte imbalances.
– Aspiration – Inhaling vomit into the lungs can cause aspiration pneumonia.
– Wound dehiscence – Forceful vomiting can disrupt surgical wounds and stitches.
– Hematoma – Can occur if vomiting reopens surgical sites and causes bleeding.
– Esophageal tears – Prolonged retching and vomiting carries a small risk of esophageal rupture.
– Delayed recovery – Nausea and vomiting generally delays post-op recovery and return to normal function. Patients have impaired nutritional intake and mobility.

Severe or prolonged PONV is also very distressing for patients and can increase anxiety after surgery. Prevention is therefore important.

How can PONV be prevented?

Several strategies can help reduce the risk of postoperative nausea and vomiting:

Reduced anesthetic exposure

Limiting the dose and duration of inhaled anesthetic agents and opioid medications can help prevent PONV. Use of propofol infusion as the main anesthetic also lowers PONV risk.

Avoidance of volatile gases

Volatile inhaled gases like nitrous oxide increase nausea more than intravenous agents. Using total intravenous anesthesia (TIVA) avoids volatile gas exposure.


Good pre-operative and post-operative hydration status lowers the incidence of nausea and vomiting.

Minimally invasive surgery

Laparoscopic and endoscopic techniques are less stimulating and reduce PONV compared to open surgery.

Anti-nausea medications

Administering anti-emetic drugs around the time of surgery prevents nausea. Commonly used agents include:

– Ondansetron – A selective 5-HT3 antagonist
– Dexamethasone – A steroid with anti-inflammatory effects
– Droperidol – A dopamine antagonist
– Metoclopramide – Acts on dopamine and 5-HT3 receptors

These can be given intravenously or orally. Using a combination of anti-emetics from different drug classes provides better protection than single drugs alone.

How is PONV treated?

If postoperative nausea and vomiting does occur, treatment aims to:

– Provide symptomatic relief
– Correct any fluid/electrolyte abnormalities
– Address any underlying causes
– Prevent further episodes

Supportive care

For mild cases, supportive care may be sufficient:

– Intravenous fluids – To correct dehydration and electrolyte disturbance
– Antiemetics – Help control symptoms of nausea and vomiting
– Rest – Lying still in a quiet, darkened room can help relieve nausea
– Reassurance and relaxation techniques

Antiemetic medications

If nausea and vomiting persists, administering anti-nausea medications is the mainstay of treatment. This can include:

– 5-HT3 receptor antagonists – Ondansetron, granisetron, or tropisetron given IV or orally. These block serotonin mediated nausea signals.
– Dopamine antagonists – Droperidol, metoclopramide, promethazine. These block dopamine vomiting signals.
– Antihistamines – Dimenhydrinate, cyclizine, meclizine. These have anticholinergic and antihistamine effects to reduce nausea.
– Corticosteroids – Dexamethasone helps prevent recurrence of vomiting.
– Benzodiazepines – Lorazepam relieves anxiety associated with nausea.
– Cannabinoids – Nabilone, dronabinol have anti-nausea effects by interacting with cannabinoid receptors.

Using combination therapy with different drug classes provides more complete anti-vomiting effects.

Treatment of underlying causes

Ruling out and addressing any surgical or medical factors contributing to ongoing nausea and vomiting is also important. This may involve:

– Imaging studies to check for issues like intestinal obstruction
– Antibiotics if infection is suspected
– Treatment of electrolyte abnormalities
– Addressing any medication adverse effects
– Management of pain if inadequately controlled

Are there any long term consequences of PONV?

In most cases, postoperative nausea and vomiting resolves within 24-48 hours without any long lasting effects. However, severe intractable cases have been associated with:

– Postdischarge nausea and vomiting (PDNV) – Nausea persisting after discharge home from hospital. Reported to occur in around 10% of surgical patients (5).
– Postoperative ileus – Prolonged impairment of intestinal motility after surgery, increasing time to tolerate oral diet. Thought to be related to inflammation from PONV.
– Anxiety and distress – Those who experience severe PONV may experience anticipatory anxiety about future surgery. There is also an association between PONV and post-traumatic stress disorder symptoms after surgery (6).

Therefore, while PONV itself is transient, inadequate control of symptoms can potentially have longer lasting impacts on psychological wellbeing and recovery in some patients.


Postoperative nausea and vomiting is one of the most frequent side effects of general anesthesia and surgery. It occurs because of multiple factors including the medications used, surgical stimulation, inflammation and patient characteristics. While generally transient and self-limiting, uncontrolled PONV can lead to dehydration, electrolyte imbalance and delays in post-operative recovery. Preventative strategies include avoiding problematic medications, laparoscopic techniques, hydration and prophylactic anti-emetics. If PONV does occur, treatment is targeted at providing symptom relief, fluid replacement and administration of anti-nausea medications. While PONV normally resolves within 48 hours, inadequate control of symptoms may also contribute to prolonged nausea, post-discharge vomiting, ileus, anxiety and distress in some cases. Overall however, PONV is a common but manageable complication following general anesthesia.