Pro/Con

An Argument Against Fasting…

By Libby EM Elliott, MD; Rebecca S. Isserman, MD; and John E. Fiadjoe, MD
Children’s Hospital of Philadelphia
University of Pennsylvania
Philadelphia, Pennsylvania

Pulmonary aspiration has been a dreaded complication of anesthesia since the first reported death under anesthesia in 1848.1 Various recommendations to prevent aspiration of gastric contents have been implemented over the years. Dr. Mendelson’s landmark paper published in 1946 described pulmonary aspiration in obstetric patients, and resulted in the recommendation that patients should fast for both solids and liquids for at least eight hours prior to anesthesia and surgery.2 This recommendation persisted for half a century, when anesthesiologists began to question the universal application of an eight hour fast, especially in children. Soon after, evidence supporting shorter fasting times began to appear in the anesthesia literature.

In 1999, the American Society of Anesthesiologists published the first preoperative fasting practice guidelines to reduce the risk of pulmonary aspiration in healthy patients of all ages undergoing elective procedures.3 These guidelines were updated in 2011 and 2017, however the relevant population has remained healthy patients presenting for elective surgery. Specifically, these guidelines do not address the question of how long an intubated child should fast prior to a procedure when they are being fed through a post-pyloric tube. I will present the evidence for the safety and superiority of continuing trans-pyloric feeds in intubated patients until the time of the procedure, with a few minor caveats.

A six hour fast is recommended for a small meal, formula, or milk in healthy children prior to receiving anesthesia. In considering this guideline, we must assume a common-sense approach. The ASA guideline was envisioned for a bolus meal: a glass of milk, a bottle of formula, a slice of toast taken over a discrete, and presumably small period of time. When considering post-pyloric feeds, we must consider that they are given as a rate over time. The volume administered in any discrete amount of time will be significantly less than the bolus meal presumed by the guidelines. Furthermore, since the nutrition is given distal to the pylorus, there is scarcely any concern for gastric residual volume unless the patient is actively vomiting or otherwise not tolerating feeds.

Clinically significant aspiration is rare under anesthesia4-6, but silent micro-aspiration is common in children who are intubated and mechanically ventilated in the PICU.7 Gopalreddy, et al. found that micro-aspiration, as determined by the presence of pepsin in tracheal aspirate, was ubiquitous in the 10 children who were mechanically ventilated via uncuffed tracheostomy, or uncuffed endotracheal tube in their PICU. A cuffed endotracheal tube provided some protection against aspiration, but, 53% of these patients had at least one tracheal aspirate positive for pepsin. The researchers stated that despite the fact that there was evidence of micro-aspiration in 70% of all the patients studied, there was no radiologic evidence to indicate frank aspiration or pneumonia. Furthermore, they reported that a slight increase in aspiration among patients who were fed while mechanically ventilated was not statistically significant. While micro-aspiration is common, clinically significant aspiration was not seen.

In light of the lack of evidence for the harm of continuing post-pyloric feeds in intubated patients, the focus must shift to the benefit of such practice. The importance of feeding the critically ill patient has been established, and enteral feeding has proven to be superior in patients that are able to tolerate feeds.8,9 Loss of lean muscle mass and protein malnutrition in critically ill patients can lead to infections, increased length of stay, more ventilator days, and possible increases in mortality. Enteral feeds maintain mucosal integrity of the bowel. Furthermore, feeds may oppose gut translocation of microbes. For patients with gastric intolerance of feeding, transpyloric feeds may be safely initiated, and goal feeds quickly attained.8,9

Much of the data on continuous transpyloric feeds comes from studies in burn patients. Children suffering from burn injury are particularly vulnerable and may have metabolic demands up to 200% of normal controls.10 In pediatric patients, with higher baseline metabolic needs, burn injury can make it especially challenging to meet protein calorie demands when feeds are held for any reason. Jenkins et al. looked at patients at Shriners Burns Institute in Cincinnati from 1986-1990. Eighty patients, all of whom had nasoduodenal or jejunal feeding tubes, were matched for age, inhalational injury, and total body surface burn, and placed into two equal groups: fed versus fasted through surgery. The fed group totaled 161 surgical procedures, while the fasted group totaled 129 procedures. The authors found that the fasted patients suffered a significant caloric deficit, experienced more wound infections, and required more IV albumin to normalize serum levels. No aspiration was noted in either group, and even though pneumonia was higher in the fed group, this was not statistically significant.11

Various studies have shown that the common practice of withholding feeds for six hours before a case and waiting two hours before resuming feeds leads to fasting times that far exceed eight hours. Despite active management of fasting recommendations in clinical practice, patients are usually fasted significantly longer than guidelines, and this needless interruption in feeds leads to caloric deficits.12,13 In one study of 41 adult burn patients who underwent 109 surgeries, fasting times were nine hours to surgery start and 14 hours to resumption of feeds. They calculated a 50% calorie deprivation for the day. In their protocol, they had a “catch-up” plan, spreading the calorie deficiency over five days, but this may not be possible in children, due to very high metabolic demand.10,12

Surgical procedures and anesthesia are cited as the primary reason for interrupted feeding in children. For procedures that do not involve airway manipulation or abdominal surgery, it is safe to continue post-pyloric feeds, especially in intubated patients. Many burn centers now continue feeding their patients throughout the course of the surgery, IR procedure or diagnostic imaging.10,11,14,15 Most of these patients have post-pyloric tubes placed quickly after presentation, and as long as the tube is confirmed distal to the pylorus preoperatively, there is no need to withhold feeds. Indeed, some institutions will continue feeds regardless of intubation or not.10,15 While the patient populations are small, it should comfort the anesthesiologist to know that aspiration in these patients is rare. In the absence of known feeding intolerance, and in the presence of data confirming the trans-pyloric feeding tube, one can be assured that gastric residual volumes will be minimal and aspiration unlikely.

In the critical care setting, it is common to initiate enteral feeds within 24-48 hours in intubated patients.16 These patients often require sedation in order to tolerate endotracheal intubation, manage pain, and induce coma for brain injury. It is common for these children to undergo imaging procedures, such as CT scans and magnetic resonance imaging while intubated and sedated, under the care of the critical care clinicians. Few Intensivists would argue that withholding the patient’s feeds makes the procedures safer. Indeed, in many critical care units, enteral feeds are not held for imaging studies.17 Critically ill patients are already sedated and intubated, and increasing the level of sedation to general anesthesia is unlikely to increase the risk of aspiration provided endotracheal intubation, mechanical ventilation, and sedation are maintained.

Some anesthesia clinicians have been concerned that prone or lateral positioning of patients may lead to aspiration, however, various studies have shown that the prone, Trendelenburg or lateral decubitus positions are safe in patients that fed intraoperatively and ventilated in the ICU.17,18 Though these studies were small, the cumulative evidence suggests the safety of these positions in intubated and fed patients.

Clinical judgement remains critical for the safe practice of anesthesia. There are always exceptions to any guideline, and there will be patients that should fast even when fed post-pylorically with an endotracheal tube in place. Any procedure or surgery that requires the removal of the endotracheal tube, for example, tracheostomy or suspension laryngoscopy would require a longer fasting time. A six-hour fasting time would be prudent for abdominal surgery or bowel resection. Finally, patients on high dose pressors who are at risk for gut ischemia should have their feeds held.

All versions of the ASA preoperative fasting guidelines contain the caveat: “Practice guidelines are subject to revision as warranted by the evolution of medical knowledge, technology, and practice.” We have accumulated enough evidence on the safety (indeed, the necessity in some) of continuing post-pyloric feeds in intubated patients that we must consider revising our guidelines to accommodate the evolution of medical knowledge and changing practice. In fact, as I have outlined above, we are more likely to cause harm by withholding post-pyloric feeds in these vulnerable patients.

In summary, mounting evidence for the safety of decreased fasting time for intubated patients receiving post-pyloric feeds demands that we re-evaluate our practices. The ASA guidelines recommend that a healthy patient fasts for at least six hours prior to anesthesia when fed either a small meal or formula. These guidelines take into account the need for induction of anesthesia and management of the airway. But what if the airway is already managed; the airway is secured with a cuffed endotracheal tube? At this point, the guidelines are not clear and we must use our clinical judgement. In light of evidence for the safety of continuing post-pyloric feeds in intubated children, we should take advantage of the caveat in the ASA guidelines on fasting and modify our practice based on the evolution of medical knowledge.

References

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2. Mendelson CL. “The aspiration of stomach contents into the lungs during obstetric anesthesia.” American Journal of Obstetrics and Gynecology. 1946; 52(2): 191-205
3. American Society of Anesthesiologists: Practice guidelines for pre-operative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: Application to healthy patients undergoing elective procedures–a report by the American Society of Anesthesiologists Task Force on Preoperative Fasting. Anesthesiology. 1999; 90:896 –905
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