Understanding Anesthesiology - The Global Regional Anesthesia ...

NPO Status
The induction of anesthesia abolishes the normal laryngeal
reflexes that prevent inhalation (“aspiration”) of
stomach contents. Due to gastric, biliary and pancreatic
secretions (which are present even during fasting), a
stomach is never “empty”. NPO (nil per os) indicates
the restriction of oral intake for a period of time prior
to surgery, minimizing the volume, acidity and solidity
of stomach contents. Such measures reduce both the
risk of aspiration occurring as well as the severity of
pneumonitis, should an aspiration event occur.
For elective surgery, patients should not have solid
food for 8 hours prior to anesthesia. Traditionally, patients
were ordered to refrain from all fluids for the 8
hour pre-operative period as well. However, more recent
studies have shown that the time of the last (clear)
fluid intake bears little relation to the volume of gastric
contents present at the induction of anesthesia. Thus,
most institutions are allowing unrestricted intake of
clear fluids until 2-4 hours prior to scheduled surgery.
Guidelines for pediatric patients vary from institution
to institution but generally are more liberal than in the
adult population. For example, infants may be allowed
breast milk up to 4 hours pre-operatively and formula
up to 6 hours pre-operatively.
It is important to recognize that some patients remain
at risk for aspiration despite strict application of NPO
guidelines. Known risk factors are outlined in Table 7.
When it is possible to identify these patients preoperatively,
measures can be taken to reduce their risk
of aspiration syndrome. Firstly, pre-medication can be
given to increase gastric motility (metoclopromide) or
to decrease gastric acidity (ranitidine or sodium citrate).
Risk can also be reduced through careful airway
management that may include the use of the Sellick
Maneuver on its own or as part of a rapid sequence induction.
Table 7 Risk factors for aspiration
RISK FACTORS FOR
ASPIRATION
• Gastroesophageal reflux
• Pregnancy
• Trauma
• Diabetes Mellitus
• Recent oral intake
• Bowel obstruction
• Intra-abdominal pathology
• Obesity
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