A Child Needs Sedation: When Is It OK?

Krista Preisberga, MD


January 25, 2013

Update on Fasting Guidelines for Procedural Sedation

Nil per os (NPO), or nothing by mouth, guidelines have been established to avoid the serious, albeit rare, complication of pulmonary aspiration during sedation. Aspiration pneumonitis occurs when lung tissue is damaged due to inhalation of oropharyngeal or gastric contents into the larynx and lower respiratory tract. The clinical spectrum ranges from asymptomatic to bronchospasm, hypoxia, cough, dyspnea, and respiratory insufficiency that can progress to failure. The situation can be further complicated by aspiration pneumonia in which there is inhaled infected material or secondary bacterial infection following chemical pneumonitis.

The current recommendations, as outlined in the American Society of Anesthesiologists (ASA) guideline, for patients undergoing procedural sedation are the same as for general anesthesia.[1] Patients should be NPO according to the following schedule:

  • 2 hours for clear fluids;

  • 4 hours for breast milk;

  • 6 hours for a light meal, sweets, milk (including formula), and fluids with pulp; and

  • 8 hours for fried or fatty foods.

What Does the Evidence Say?

But where do these recommendations originate? It was originally observed in animals that instillation of gastric aspirate into the trachea led to the pathologic changes of aspiration pneumonitis. Subsequent studies have attempted to determine the pH and volume of gastric aspirate needed to cause pathologic changes. The commonly quoted figures of a critical volume of 25 mL, or 0.4-0.8 mL/kg of aspirate, with a pH < 2.5 being sufficient to cause aspiration pneumonitis, are derived from animal research and extrapolated to humans. It appeared logical that fasting would lead to smaller gastric volume and, hence, a decreased chance of aspiration in the event of regurgitation. In fact, the relationship between NPO times and gastric volume and gastric pH is not straightforward at all. More important, a relationship between gastric volume and pH and clinically evident aspiration has never been established.

Subsequent scientific research in humans has shown that silent aspiration occurs during sleep without evidence of symptoms. Several studies have noted that the gastric pH and volume are actually higher than the above stated thresholds even despite appropriate fasting times. Furthermore, several studies have now shown no benefit to routine use of acid-reducing medication prior to procedures requiring anesthesia.[2]

The summary of the literature reviewed in the 2011 ASA guideline included the following[1]:

  • Meta-analysis of randomized controlled trials examining fasting times for clear liquids actually showed higher gastric pH values and smaller gastric volumes in adults fasting 2-4 hours vs more than 4 hours.

  • Similarly, gastric pH was higher in children fasting 2-4 hours when compared with those fasting more than 4 hours. Studies examining volume were equivocal, however. The guideline authors concluded that data supported allowing intake of clear liquids up to 2 hours prior to a procedure instead of more prolonged fasting times.

  • The observational literature is equivocal regarding the risk of ingestion of breast milk 4 hours before a procedure on volumes or lower pH of gastric contents.

  • Studies examining nonhuman milk and solids have had equivocal findings in regard to pH and gastric volume.

Despite the lack of scientific clinical evidence, the consensus among the guideline authors was mostly unchanged in the 2011 update, and the fasting times noted above remained the same.

Studies documented the actual incidence of aspiration during general anesthesia have produced varying results. A retrospective study by Warner and colleagues[3] reported an overall incidence in all adult patients of 3.1 per 10,000 (2.6/10,000 for elective cases and 11.0/10,000 for emergency cases). The incidence was increased in patients in higher ASA physical status classes, a system that classifies patients by their baseline health status, with higher class indicating a greater degree of systemic disease (Table). Data on NPO times of patients in the study were not provided.

Table. ASA Physical Status Classification System

ASA Physical Status 1 A normal healthy patient
ASA Physical Status 2 A patient with mild systemic disease
ASA Physical Status 3 A patient with severe systemic disease
ASA Physical Status 4 A patient with severe systemic disease that is a constant threat to life
ASA Physical Status 5 A moribund patient who is not expected to survive without the operation
ASA Physical Status 6 A declared brain-dead patient whose organs are being removed for donor purposes

Adapted from the American Society of Anesthesiologists. https://www.asahq.org/Home/For-Members/Clinical-Information/ASA-Physical-Status-Classification-System

A separate study, also by Warner and colleagues,[4] found an incidence of pulmonary aspiration during general anesthesia of 3.8 per 10,000 in children (2.2/10,000 for elective cases and 27.0/10,000 for emergency cases). It is interesting to note that aspiration was diagnosed after emesis and visualization of bilious secretions or particulate matter in the tracheobronchial tree. Despite this, 63% of these patients had no symptoms identified in the postoperative period. Aspirations occurred primarily during induction, and bowel obstruction or ileus was present in a large portion of those patients. NPO times were not provided.

A study by Borland and colleagues[5] examined the clinical relationship between NPO times and actual aspiration events in children undergoing general anesthesia. The incidence of aspiration events was 9.3 per 10,000 in nonemergent cases and 19 per 10,000 in emergent cases but included aspiration of blood as well as gastric contents in this study. Of note, the researchers found no association between incidence of aspiration and fasting times.