Episode Transcript
Hello everybody. My name is Dr. Robb Wasserman. I am an assistant clinical professor at the University of North Carolina who specializes in general anesthesiology. Today, I would like to talk to you about preoperative fasting requirements (also known as NPO guidelines). Over the next 10 to 15 minutes, we will go over how the preoperative NPO guidelines were formulated and how they are to be used. We will follow a single fictional patient as they go through various life stages and surgical procedures while attempting to correctly adhere to the NPO guidelines. By the end of this podcast, you should be able to identify if a patient has correctly followed the preoperative NPO guidelines as well as understand both why these guidelines exist and their limitations. Let’s get started.
First, I would like to talk with you about what exactly is a practice guideline. A practice guideline is a recommendation that has been developed in order to help the anesthesiologist make decisions regarding patient care. This is in contract to a practice standard of care which is a process or treatment that the anesthesiologist should follow for a specific type of patient or disease state. Of note, guidelines can be modified due to specific patient conditions or needs. Guidelines should not replace the policies of your local institution and are subject to revisions as new medical knowledge and/or technology emerges. For NPO guidelines, the purpose is specifically to reduce the risk of perioperative pulmonary aspiration.
According to “An updated report by the American Society of Anesthesiologists Task Force on preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration” in the journal Anesthesiology, perioperative pulmonary aspiration is defined as “aspiration of gastric contents occurring after induction of anesthesia, during a procedure, or in the immediate postoperative period.” Preoperative fasting is defined as “the period of time before a procedure when patients are not allowed the oral intake of liquids or solids”.
The NPO guidelines were formulated by an ASA-appointed task force of ten members. The ten members consisted of both academic and private practice anesthesiologists from various locations around the United States and were formulated using a seven-step process. Step one was “reaching a consensus on the criteria for evidence”. Step two reviewed published research relevant to fasting and aspiration. Step three provided opinion surveys to expert consultants regarding preoperative fasting strategies. Step four involved collecting opinions regarding guideline recommendations from a random sample of ASA members. Step five held an open forum to solicit input. Step six surveyed the consultants regarding the feasibility of implementing the guidelines. And finally, step seven used all the collected information to formulate a consensus within the task force to create the guidelines. These guidelines were then approved by the ASA House of Delegates - the legislative body of anesthesiology prior to being enacted.
Now that we have an idea of how the NPO guidelines were formulated, let’s move on to their implementation and the specifics of these guidelines. These guidelines were formulated specifically for healthy patients undergoing elective procedures under general anesthesia, regional anesthesia, or procedural sedation and analgesia. The guidelines may need to be modified for patients with conditions that affect gastric emptying or volume, including gastroesophageal reflux, gastroparesis, hiatal hernias, diabetes, pregnancy and bowel obstructions. Prior to a procedure, it is of the utmost importance that patients are informed of their fasting requirements and that their compliance is verified. Compliance with the NPO guidelines minimizes the risk of perioperative pulmonary aspiration by ensuring a gastric volume of less than 25mL and a pH of greater than 2.5 while also keeping patient thirst, hunger and blood glucose within optimal ranges.
Let’s now move on to our fictional patient. Our patient is an otherwise healthy 3-month-old male named Simon who presents for the placement of ear tubes which will require general anesthesia. Simon’s parents provide him multiple meals throughout the day consisting of both breast milk and infant formula. The day prior to the procedure, Simon’s mother states he gets very fussy if he goes without a meal for too long and she asks you how long he must go without any breast milk or infant formula prior to his procedure.
What should you tell her?
You should tell her that for healthy infants, breast milk must be held for a minimum of four hours prior to a procedure and that infant formula must be held for a minimum of six hours prior to a procedure. Let me repeat that again to drive this point home, for breast milk, the NPO time is four hours. For infant formula, the NPO time is six hours. This is a good time to bring up the NPO time required for non-human milk (such as cow’s milk). Is it recommended to withhold non-human milk for a minimum of six hours prior to a procedure requiring anesthesia. It is important to note here, however, that since nonhuman milk is similar to solids in gastric emptying time, the amount ingested must be considered and prolonging the fasting time may be required.
Simon’s ear tube placement proceeds without issue, and he requires no further procedures until the age of 18 when he presents for an inguinal hernia repair. He states that as of recently he is trying to increase his water intake during the day since he is exercising daily, and he inquires when the last time he is allowed to drink any water prior to his procedure.
What should you tell him?
For water or any clear liquid (examples of which include fruit juices without pulp, carbonated beverages, clear tea and black coffee) fasting must occur for at least two hours prior to a procedure. The NPO time for clear liquids is two hours. The ingested volume of clear liquids is unrestricted in both adults and children. There is an important caveat, however: patients with disease states that limit gastric emptying should restrict their consumption of clear liquids to a minimum and keep the volume to a minimum. As mentioned before, such conditions may include gastroesophageal reflux, gastroparesis, hiatal hernias, diabetes, pregnancy and bowel obstructions. Please note, clear liquids do not include alcohol.
The next time Simon presents to the hospital isn’t until the age of 71. All his daily exercise has taken a toll on his joints, and he presents for a total shoulder replacement which will require general anesthesia. He eats a breakfast of plain toast with black coffee every morning and wants to know when is the latest time he can eat his breakfast. What should you tell Simon? You should tell Simon that for a light meal (which, per official guideline recommendations, consists of toast and clear liquids) that he must remain NPO for a minimum of six hours prior to his procedure. It should be noted here for the “light meal” NPO guideline recommendations that one MUST take into account both the amount and type of foods ingested. If Simon was to get fancy and put avocado on his toast, this would change the official recommended fasting time to a minimum of eight hours. Also, something to consider here is the black coffee. Since black coffee is considered a clear liquid, Simon may drink his black coffee up to two hours prior to his procedure time. After you tell Simon he must refrain from eating his light meal for at least six hours prior to his procedure he tells you that he is confused since his procedure is scheduled for 2pm but always thought he wasn’t supposed to eat after midnight on his procedure day. He knows he will be very hungry (and cranky) if he goes without his morning toast and coffee asks if it is OK if he eats after midnight.
What should you tell him?
You should tell that he is allowed to eat his morning toast and black coffee after midnight. Since his procedure is scheduled for 2pm, the latest he can finish eating his toast is six hours prior to his procedure (which would be 8am) and the latest he can finish drinking his black coffee would be two hours prior to his procedure (which would be 12pm).
Let’s fast forward two years. Simon is presenting to the hospital to have his other knee replaced. The day prior to surgery, he inquires how many hours prior to surgery he can have a ham and cheese sandwich.
What should you tell him?
The fasting recommendations for “fried foods, fatty foods, or meat” is a minimum of eight hours. This is because fried foods, fatty foods or meat may prolong gastric emptying time and therefore increase the risk of perioperative aspiration if consumed within eight hours of a procedure requiring anesthesia.
Now that we have gone over the various pre-operative NPO guidelines, I want to summarize them all for you one more time. Again, I would like to emphasize that these recommendations apply to healthy patients of all ages who are undergoing elective procedures. Following these guidelines does not guarantee complete gastric emptying. For clear liquids (i.e. water, fruit juices without pulp, carbonated beverages, clear tea and black coffee) the minimum fasting period is two hours. For infants who consume breast milk, the minimum fasting period is four hours. For nonhuman milk, however, the minimum fasting period is six hours. For infant formula, the minimum fasting period is six hours. Finally let us summarize the recommendations for solid foods. For a light meal which consists of toast and clear liquids, the minimum fasting time is six hours. For a typical meal consisting of fried foods, fatty foods or meat a minimum fasting period of eight hours is required. Both the type of food consumed, and the amount must be considered when one is determining an appropriate NPO time.
Thank you so much for taking the time to listen to this Anesthesia Toolbox podcast on NPO guidelines. I hope it was informative.
