How long do you have to be NBM before surgery?

December 22, 2025 •

3 min read

Modern guidelines have liberalized preoperative fasting times to improve patient comfort and outcomes. A 2014 study noted many patients fast longer than necessary.

Quick Summary

Surgical fasting requires six hours without solid food and two hours without clear liquids for healthy adults. Adherence is vital to prevent aspiration under anesthesia, though timelines differ for foods and patient groups.

Key Points

Standard Fasting: Healthy adults fast from solid food for at least six hours and from clear liquids for at least two hours before surgery.
Clear Liquids vs. Solids: Understand the difference; clear liquids are treated differently than solids and milk.
Aspiration Risk: NBM prevents pulmonary aspiration, a dangerous complication during anesthesia where stomach contents enter the lungs.
Special Populations: Fasting guidelines vary for children (based on age and feeding type), pregnant women, and high-risk patients like those with diabetes.
Consult Your Team: Always defer to the specific instructions given by your surgical and anesthesia teams, as they provide personalized guidance.
Updated Protocols: Modern guidelines have moved away from the universal 'NPO after midnight' rule to more flexible, patient-centric protocols.
Consequences: Failure to follow fasting instructions can result in the delay or cancellation of your surgery.

Understanding the 'Nil by Mouth' Principle

'Nil by Mouth' (NBM), also nil per os (NPO), is a key medical instruction before procedures needing anesthesia. The main goal is an empty stomach to minimize aspiration risk. Aspiration, where stomach contents enter the lungs, can cause life-threatening complications like aspiration pneumonia. Under anesthesia, protective reflexes are suppressed, preventing aspiration. Following preoperative fasting rules is fundamental for safe surgery preparation.

The Standard Adult Fasting Guidelines

The American Society of Anesthesiologists (ASA) offers fasting recommendations for healthy adults undergoing elective procedures. These guidelines replace the older 'nothing by mouth after midnight' rule with instructions based on the ingested material.

Typical rules for adults:

Solid Foods: No solid food for at least six hours before the procedure. This includes light meals, toast, biscuits, and milk, considered a solid. Fatty foods may require longer fasting, eight hours or more.
Clear Liquids: Clear liquids can be consumed up to two hours before surgery. Examples include water, pulp-free juices, clear tea, and black coffee. Chewing gum and sweets are generally not permitted during this time.
Necessary Medications: Routine medications approved by a doctor can be taken with a small sip of water up to two hours before, unless other instructions are given.

Pediatric and Specific Patient Guidelines

Fasting rules differ for children and certain high-risk patients. Following specific instructions from the medical team is crucial for balancing safety with comfort.

Infants and Children: Pediatric guidelines vary by age. Breast milk needs a shorter fasting time than formula or cow's milk. For healthy children, breast milk is withheld four hours before surgery, while infant formula and non-human milk are withheld for six hours. Clear fluids are generally permitted up to one or two hours before the procedure, depending on hospital protocol.
Pregnant Patients: Women who are not in labor but require elective surgery often follow the standard adult fasting guidelines. Pregnancy can increase aspiration risk, so instructions from the anesthesiologist should be followed carefully.
High-Risk Patients: Patients with conditions affecting gastric emptying, like obesity, diabetes, and gastroesophageal reflux disease (GERD), may need modified instructions or precautions. The anesthesiologist may recommend a longer fasting period or a different plan based on individual risk factors.

The Shift from 'NPO After Midnight'

The 'NPO after midnight' policy was simple but often restrictive. Modern medicine uses a more nuanced approach, influenced by protocols like Enhanced Recovery After Surgery (ERAS). ERAS programs often use carbohydrate-rich drinks before surgery, which improves well-being, reduces hunger, and can shorten hospital stays. Prolonged fasting can negatively impact a patient's metabolic state and comfort.

Fasting Guidelines Comparison


Food/Liquid Type	Standard Adults	Children (>6 months)	Pregnant Adults (Elective)	High-Risk Adults
Solids	Minimum 6 hours	Minimum 6 hours (formula/milk)	Minimum 6 hours	Often >6 hours (consult doctor)
Breast Milk	Not applicable	Minimum 4 hours	Not applicable	Not applicable
Clear Liquids	Up to 2 hours	Up to 1-2 hours	Up to 2 hours	Up to 2 hours (consult doctor)
Fatty/Heavy Meal	8+ hours	8+ hours	8+ hours	Consult doctor for specific advice

Conclusion

The duration of NBM before surgery depends on food type, age, and health. For most healthy adults, it's six hours for solids and two for clear liquids, an improvement over past practices. Always follow surgical or anesthesiology team instructions, as they tailor guidelines to the medical profile. Failure to adhere can delay or cancel the procedure, stressing its importance for a safe surgical experience. Review the American Society of Anesthesiologists' recommendations for further guidance.

Frequently Asked Questions

Clear liquids are transparent, including water, clear juices without pulp, black coffee, clear tea, and carbohydrate-loading drinks used in some programs.

Milk is not a clear liquid and is treated like solid food for fasting, requiring a six-hour fasting period.

Inform your medical team immediately if you eat or drink after the fasting time. Your surgery will likely be delayed or rescheduled.

Yes, breast milk is typically allowed closer to surgery than formula. Pediatric guidelines recommend a four-hour fast for breast milk versus six hours for formula.

Fasting is crucial because anesthesia can cause a loss of protective airway reflexes, which can allow stomach contents to enter the lungs if the stomach is not empty. This can lead to pulmonary aspiration, a serious complication.

Avoid chewing gum or sucking on hard candies before surgery. Chewing stimulates stomach acid production. While some guidelines permit it if not swallowed, it's safest to avoid it.

In most cases, essential medications can be taken with a small sip of water up to two hours before the procedure. Confirm which medications to take with your doctor.