The document discusses preoperative fasting guidelines and the risks of pulmonary aspiration during surgery. It summarizes a study that compared gastric fluid volume and pH in patients who either fasted overnight or drank 150mL of water 2 hours before surgery. The study found that patients who drank the water had significantly lower gastric fluid volumes (5.5mL vs 17.1mL) after surgery, but similar pH levels. This suggests that allowing clear fluids like water 2 hours before surgery may be safe and help reduce patient discomfort from long fasting times.

1. Nil per os
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Nil per os (alternatively nihil/non/nulla per os) (NPO) is a medical instruction meaning to
withhold oral food and fluids from a patient for various reasons. It is a Latin phrase which
translates as "nothing through the mouth". In the United Kingdom, it is translated as nil by
mouth (NBM).
Typical reasons for NPO instructions are the prevention of aspiration pneumonia, e.g. in those
who will undergo general anesthetic, or those with weak swallowing musculature, or in case of
gastrointestinal bleeding, gastrointestinal blockage, or acute pancreatitis. Alcohol overdoses that
result in vomiting or severe external bleeding also warrants NPO instructions for a period.
When patients are placed on NPO orders prior to surgical general anesthesia, physicians would
usually add the exception that patients are allowed a very small drink of water to take with their
usual medication. This is the only exception to a patient's pre-surgery NPO status. Otherwise, if a
patient accidentally ingested some food or water, the surgery would usually be canceled or
postponed for at least 8 hours.
Preoperative fasting
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Preoperative fasting is the practice of a patient abstaining from oral food and fluid intake for a
time before an operation is performed. This is intended to prevent pulmonary aspiration of
stomach contents during general anesthesia.[1]
Pulmonary aspiration
The main reason for preoperative fasting is to prevent pulmonary aspiration of stomach contents
while under the effects of general anesthesia. Aspiration of as little as 30-40ml can be a
significant cause of suffering and death during an operation and therefore fasting is performed to
reduce the volume of stomach contents as much as possible. Several factors can predispose to
aspiration of stomach contents including inadequate anesthesia, pregnancy, obesity, difficult
airways, emergency surgery (since fasting time is reduced), full stomach and altered
gastrointestinal mobility. Increased fasting times leads to decreased injury if aspiration occurs.[1]
Gastric conditions
In addition to fasting, antacids are administered the night before (or in the morning of an
afternoon operation) and then once again two hours prior to surgery. This is to increase the pH
(make more neutral) of the acid present in the stomach, helping to reduce the damage caused by

2. pulmonary aspiration, should it occur. H2 receptor blockers should be used in high-risk
situations and should be administered in the same timing intervals as antacids.[1]
Gastroparesis (delayed gastric emptying) may occur and is due to metabolic causes (e.g. poorly
controlled diabetes mellitus), decreased gastric motility (e.g. due to head injury) or pyloric
obstruction (e.g. pyloric stenosis). Delayed gastric emptying usually only affects the emptying of
the stomach of high-cellulose foods such as vegetables. Gastric emptying of clear fluids such as
water or black coffee is only affected in highly progressed delayed gastric emptying.[1]
Occasionally, gastroesophageal reflux may be associated with delayed gastric emptying of
solids, but clear liquids are not affected. Raised intra-abdominal pressure (e.g. in pregnancy or
obesity) predisposes to regurgitation. Certain drugs such as opiates can cause marked delays in
gastric emptying, as can trauma which can be determined by certain indicators such as normal
bowel sounds and patient hunger.[1]
Minimum fasting times
The minimum fasting times prior to surgery have long been debated. The first proposition came
from British anesthetists stating that patients should be nil by mouth from midnight.[2] However,
since then, the American Society of Anesthesiologists (ASA), followed by the Association of
Anaesthestists of Great Britain and Ireland (AAGBI), recommended new fasting guidelines for
the minimum fast prior to surgery.[1] This was based upon evidence by Canadian
anesthesiologists who found that drinking clear fluids two hours prior to surgery decreased
pulmonary aspiration compared to those nil by mouth since midnight.[2] The following are the
recommended guidelines for nil by mouth prior to surgery:[3]
Age Solids Clear liquids
<6 months 4 hours 2 hours
6–36 months 6 hours 3 hours
>36 months (including adults) 6 hours 2 hours
When anaesthesia is required in an emergency situation, nasogastric aspiration is usually
performed to reduce gastric contents and the risk of its pulmonary aspiration.[4]

3. See also
Fasting
Surgery
General anesthesia
References
1. ^ Jump up to: a b c d e f Allman, Keith G.; Iain H. Wilson (2006). Oxford Handbook of
Anaesthesia, 2nd edition. Oxford University Press. ISBN 0-19-856609-0 Check |isbn=
value (help).
2. ^ Jump up to: a b Maltby JR (April 2006). "Preoperative fasting guidelines". Can J Surg
49 (2): 138–9; author reply 139. PMID 16630428. Retrieved 2008-08-20.
3. Jump up ^ Coté CJ (July 1999). "Preoperative preparation and premedication". Br J
Anaesth 83 (1): 16–28. PMID 10616330. Retrieved 2008-08-20.
4. Jump up ^ Legal review of need to place NG tube
2. Indian J Anaesth. 2010 Sep-Oct; 54(5): 445–447.
3. doi: 10.4103/0019-5049.71044
4. PMCID: PMC2991655
“Nil per oral after midnight”: Is it necessary for clear fluids?
Kajal S Dalal, Dhanwanti Rajwade, and Ragini Suchak
Author information ► Copyright and License information ►
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Abstract
Fasting before general anaesthesia aims to reduce the volume and acidity of stomach contents,
thus reducing the risk of regurgitation and aspiration. Recent guidelines have recommended a
shift in fasting policies from the standard ‘nil per oral from midnight’ to a more relaxed policy of
clear fluid intake a few hours before surgery. The effect of preoperative oral administration of
150 ml of water 2 h prior to surgery was studied prospectively in 100 ASA I and II patients, for
elective surgery. Patients were randomly assigned to two groups. Group I (n = 50) was fasting
overnight while Group II (n = 50) was given 150 ml of water 2 h prior to surgery. A nasogastric
tube was inserted after intubation and gastric aspirate was collected for volume and pH. The
gastric fluid volume was found to be lesser in Group II (5.5 ± 3.70 ml) than Group I (17.1 ± 8.2
ml) which was statistically significant. The mean pH values for both groups were similar. Hence,
we conclude that patients not at risk for aspiration can be allowed to ingest 150 ml water 2 h
prior to surgery.

4. Keywords: Clear fluids, preoperative fasting, pulmonary aspiration, stomach contents - pH,
volume
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INTRODUCTION
Long fasting hours prior to surgery is a great discomfort to the patient. Despite recent
guidelines stating that it is appropriate to reduce the interval of clear fluid ingestion to 2 h
prior to surgery,[1] it is common practice to follow “nothing by mouth” or Nulla per os
(NPO) after midnight for both solids as well as clear fluids. Decreasing the fasting period
enhances the quality and efficiency of anaesthesia care by decreasing the cost, increasing the
patient satisfaction and avoiding delays and cancellations. Also there is a decrease in the risk
of dehydration and hypoglycaemia and thereby decrease in the perioperative morbidity.
Previous studies have shown that pH< 2 and volume of gastric aspirate > 25 ml (0.4 ml/kg)
predispose a patient to pulmonary aspiration,[2] hence a strict overnight fasting regimen was
instituted. However, the cochrane database has reviewed several studies showing that
prolonged withholding of oral fluids does not improve gastric pH or volume, and permitting
a patient to drink fluids preoperatively may even result in significantly lower gastric fluid
volumes.[3] In an attempt to reduce the fasting hours of a patient preoperatively without
increasing the risk of pulmonary aspiration, we decided to assess the safety of ingestion of
150 ml of water 2 h prior to surgery in patients undergoing general anaesthesia with
endotracheal intubation.
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METHODS
After Ethics Committee approval with written informed consent, 100 ASA I and II patients
between 12 and 60 years of age, posted for elective orthopaedic, gynaecological,
otolaryngological and general surgery were divided into two groups. Emergency surgeries,
patients with history of acid peptic disease, anticipated difficult intubation, diabetes mellitus,
obesity, pregnancy, hiatus hernia[4] as well as those routinely taking any medications that
affected gastric motility or secretion were excluded from the study.
Group I was kept fasting overnight whereas Group II was given 150 ml water 2 h prior to
surgery. Patients were premedicated with midazolam and pentazocine, and general
anaesthesia was induced using intravenous thiopentone sodium followed by vecuronium. An
18 G and 16 G Ryle’s tube was inserted in male and female patients, respectively after
intubation and its position was confirmed by auscultation over the epigastrium for insufflated
air. Gastric aspirate was obtained through a 20 ml syringe with the patient supine with an
assistant massaging the upper abdomen, as well as with various other positions like
Trendelenburg, left lateral and right lateral positions to facilitate maximal aspiration.

5. Volume of aspirate was noted and pH measured using a standardized pH strip. Sex, age,
weight, type of surgery, duration of fasting and interval between ingestion of water and
surgery was documented. Results were given as mean ± SD. Data collected were analysed
using Student’s t-test. Differences were considered statistically significant if P values were
<0.05.
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RESULTS
There was no significant difference between the groups with regard to weight, age and sex.
Patients who were kept fasting overnight (Group I) had an average fasting time of 12 h. The
ingestion - surgery interval for Group II was on an average 2 h [Table 1].
Table 1
Patient demographics
Patients who had 150 ml of water (Group II) had lesser volume of gastric aspirate (5.5 ± 3.70
ml) than that of Group I (17.1 ± 8.21 ml) which was statistically significant [Table 2]. The
pH was found to be in the same range for both the groups (Group I: 1.7 ± 0.28, Group II: 1.6
± 0.26) [Table 2]. Patients at high risk i.e. gastric fluid volume > 25 ml and pH <2.5 are
shown in Table 3. Group I had four patients with a combination of both risk factors, while
none were present in Group II.
Table 2
Comparison of volume and pH of gastric fluid in both groups

6. Table 3
Incidence of risk factors
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DISCUSSION
Pulmonary aspiration of gastric contents during anaesthesia though a rare event,[5] with an
incidence of 1 in 7,000 to 8,000 in ASA I and II patients, and 1 in 400 ASA III to V
patients,[6] is still considered a significant cause of anaesthesia-related deaths. The severity
of pulmonary damage is related to both the volume and pH of the gastric fluid. A
combination of volume > 25 ml and pH < 2.5 is considered lethal.[2] Hence any safety
measure that reduces this hazard is preferred, so the routine preoperative practice of “nothing
by mouth after midnight” is followed. But unfortunately, the ‘nil per oral’ order is blindly
applied to both liquids and solids and has become engrained in our anaesthetic practice.[7]
The time required for solid food to liquefy and enter the small intestine depends on the type
of food ingested (being shorter for carbohydrates and proteins than for fats and cellulose) and
the food particle size.[8] Complete emptying of solids from the stomach takes 3 to 6 h, but
may be prolonged by fear, pain or opioids.[9] So it is appropriate that no solid food be eaten
on the day of surgery. However, the gastro-oesophageal emptying of liquids is rapid wherein
studies have shown that gastric emptying after intake of a carbohydrate drink is complete
within 2 h of ingestion.[10]
At the time of induction of anaesthesia, gastric fluid volume is quite variable in normal
people. Even if the patient is fasting, the stomach is not totally empty. On an average, 25 ml
to 35 ml of gastric fluid remains in the stomach.[6] Comparing this to the traditional cut-off
of gastric fluid volume >25 ml and pH < 2.5, 30-60% patients would be at a risk of
pulmonary aspiration, but on an average, the incidence is as low as 1 in 3000.[11] Passive
regurgitation of gastric contents can occur only if intragastric pressure exceeds the protective
tone of the lower oesophageal sphincter, and for pulmonary aspiration to occur, the
protective airway reflexes must also be abolished.[6]
Our study was undertaken to determine whether a 2 h fast with clear fluids was safe for
patients. Clear fluids would include black tea, coffee, water, carbonated drinks and fruit
juices without any particulate matter.[12] We chose 150 ml of water to be given 2 h prior to
surgery. We used a Ryle’s tube for aspiration of gastric contents which is a well accepted
method for assessment.[5,6,13,14] Our study confirmed the results of previous studies[3,5,6]
that even after 11-13 h of fasting, a large number of patients had gastric pH < 2.5 and gastric
fluid volume >25 ml.

7. Patients who received 150 ml water actually had decreased gastric fluid volume which was
statistically significant as seen in another study.[3] The pH remained unaffected, thereby not
increasing the risk of pulmonary complications due to aspiration. Studies have also shown
that giving clear fluids increased patient comfort, decreased anxiety and thirst.[10,15]
We conclude that it is safe to conduct general anaesthesia in patients who have ingested 150
ml of water 2 h prior to surgery. Prolonged withholding of oral fluid does not decrease
gastric fluid volume and pH. Clinicians should appraise this evidence and adopt the recent
ASA guidelines which recommend an evolution from the indiscriminate ‘NPO after
midnight’ blanket fasting policy. However, the customary 8 h fasting should be followed for
patients at a higher risk of aspiration like in diabetes mellitus, pregnancy, obesity, etc. as
more research is necessary to determine the safety in these patients. The risk of unexpected
regurgitation cannot be avoided even by overnight fasting, and anaesthesiologists must
always be prepared to deal with these complications.
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Footnotes
Source of Support: Nil
Conflict of Interest: None declared.
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REFERENCES
1. Practice guidelines for preoperative fasting and the use of pharmacological agents to
reduce the risk of pulmonary aspiration: Application to healthy patients undergoing elective
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anaesthesia. Am J Obstet Gynecol. 1946;52:191–205. [PubMed]
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complications. Cochrane Database Syst Rev. 2003;4:CD004423. [PubMed]
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2004;93:497–500. [PubMed]
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overweight/obesity and gastric fluid characteristics in pediatric day surgery: implications for
fasting guidelines and pulmonary aspiration risk. Anesth Analg. 2009;109:727–36. [PubMed]
6. Maltby JR, Pytka S, Watson NC, Cowan RA, Fick GH. Drinking 300ml of clear fluid 2
hours before surgery has no effect on gastric fluid volume and pH in fasting and non-fasting
obese patients. Can J Anaesth. 2004;51:111–5. [PubMed]

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after oral fluid ingestion for elective ambulatory surgery. CMAJ. 1989;141:1151–4. [PMC
free article] [PubMed]
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time: A trend based on evidence. World J Gastrointest Surg. 2010;2:57–60. [PMC free
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Gastroenterology. 1965;49:375–80. [PubMed]
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perioperative period. Can J Anesth. 1988;35:162–73. [PubMed]
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water in obese pregnant women at term. Anesth Analg. 2007;105:751–5. [PubMed]