Feed the
Babies
Susan C. Nicholson, MD and
Mark S. Schreiner, MD, Associate Professors of Anesthesiology University of Pennsylvania School of Medicine,
Senior Anesthesiologists The Children's Hospital of Philadelphia
Breastfeeding Abstracts,
August 1995, Volume 15, Number 1, pp. 3-4.
Pulmonary aspiration of gastric
contents is a potentially life-threatening complication of general anesthesia.
In an attempt to minimize the volume of the gastric residual, a preoperative
fast for eight or more hours prior to induction of anesthesia was adopted.
Infants are a subgroup of children for whom objective hemodynamic or
metabolic benefit is likely to be demonstrated by shortening the duration
of the preoperative fast. For aspiration to occur, gastric contents
capable of producing parenchymal lung damage must be regurgitated and
then aspirated. Vomiting is a complex physiologic process that is often
preceded by reflux of small intestinal contents back into the stomach
by a process known as retrograde giant contraction. Patients with little
or no gastric fluid in their stomach at the time of induction of anesthesia
may vomit a considerable volume, and patients with an initial acidic
gastric pH may vomit fluid which has been neutralized by the addition
of small bowel contents. Conditions which increase the likelihood of
regurgitation include pregnancy, obesity, gastrointestinal motility
problems, emergency surgery, and full stomach.
Patients have been defined
as at risk if they have a residual gastric fluid volume which exceeds
0.4 mL/kg with a pH below 2.5 units at the time of the aspiration. These
risk factors were extrapolated from unpublished data obtained in a study
of rhesus monkeys where an aliquot of acidic fluid was instilled directly
into the right bronchus of the subject.1 A subsequent study
in the same model showed that a minimum of 0.8 mL/kg of acidified gastric
fluid was required to produce pneumonia resulting in mortality.2
Both volumes represent the amount of fluid instilled into the lung,
and not the fluid contained in the stomach.
Although the association
of low pH gastric fluid with development of acid pneumonitis syndrome
can be documented in humans, there are no data to validate the residual
gastric fluid volume cited. It is not possible to define the minimum
volume that a patient must aspirate before manifesting sequelae of aspiration.
This, coupled with the fact that residual gastric fluid is but one component
of the potential volume available for regurgitation/aspiration, makes
suspect the custom of declaring patients at risk of developing aspiration
pneumonia based, all or in part, on their residual gastric fluid volume.
In pediatric patients, the
low incidence of acid aspiration syndrome,3 despite the fact
that most children, even after a prolonged fast, exhibit a large acidic
residual gastric fluid volume4 casts further doubt on the
utility of these criteria. The understanding that, unlike solids which
are emptied slowly from the stomach in a linear fashion, clear liquids
are emptied exponentially with a half-time of 10-20 minutes,5
prompted anesthesiologists to reappraise the preoperative feeding practices
in children. Between the late 1980s and early 1990s, a series of studies
compared the acidity and volume of the residual gastric fluid in children
who were either fasted in a conventional fashion or mandated to ingest
clear liquids as close as 2 hours prior to induction of anesthesia.
A limited number of children with a wide range in age, physical status,
and in-patient status were studied. No attempt was made to correlate
residual volume or pH with the incidence of aspiration. The data showed
no evidence that clear liquids consumed up to 2 hours before induction
of anesthesia adversely affect either the volume or acidity of residual
gastric fluid compared with the gastric content of those fasted for
longer intervals. Despite the study limitations, these findings resulted
in many anesthesiologists liberalizing the preoperative feeding guidelines
to allow children to drink clear liquids up to 2 hours prior to induction.6
In general, this change appears
to be safe, with no increase in the incidence of aspiration and a more
pleasant preoperative experience for both patients and their families.
However, many infants refuse clear liquids when offered for the first
time, especially those who are exclusively breastfed. In addition, little
data exists on the rate of gastric emptying of breast milk in infants.
Assessing gastric emptying
by repeated measure of intracastric volume reported that gastric emptying
was more rapid when infants were fed with human milk than when they
were fed infant formula.7 Other data showed that three hours
after the test meal, 75 percent of infants fed breast milk had entered
the fasting state compared with only 17 percent of those ingesting formula.8
Litman, et al. compared the volume and acidity of residual gastric fluid
volume in patients under 1 year of age who were either fed clear liquids
or nursed in close proximity to induction of anesthesia.9
No differences between the clear-liquid and breast-fed groups were demonstrated
for either residual volume or pH.
The authors tracked the number
of infants with a residual gastric fluid volume of >1 mL/kg. Significantly
more of the breastfed infants met this arbitrary criterion, prompting
the investigators to terminate the study. Litman recommended that breastfeeding
should be terminated 3 hours prior to induction, compared to 2 hours
prior for clear liquids. This study, like those preceding it, suffers
from conclusions which are not drawn from the incidence of aspiration
pneumonitis, but from the measurable variables of volume and acidity.
The study poses two additional questions. First, are we prepared to
adopt a new arbitrary gastric volume which places a child at risk without
coexisting conditions that predispose the child to pulmonary aspiration?
Second, are there sufficient data to define the safe fasting interval
for breast milk? The incidence of both risk factors were the same for
both groups of infants in Litman's study. If one agrees with previous
studies, it is possible to conclude that infants should be allowed to
ingest either clear liquids or breast milk up to 2 hours prior to induction
of anesthesia.
Considering the small sample
size, a more conservative approach might be to recommend cessation of
breastfeeding sooner until more data are available. Once sufficient
clinical experience has been accumulated for each fasting interval,
then it will be possible to determine whether this practice is safe.
However, the failure to show a change in the incidence of aspiration
pneumonitis in children allowed clear liquids ad libitum as close
as 2 hours prior to induction of anesthesia suggests that even less
restriction in feeding guidelines may be possible. To precisely define
the safe duration of fast for children, it is important not only to
focus on gastric volume, but also to pay close attention to the factors
known to be related to pneumonitis.
References
1. Roberts, R. B. and Shirley,
M. A. Reducing the risk of acid aspiration during Cesarean section.
Anesth Analg 1974; 53:859-68.
2. Raidoo, D. M., Rocke,
D. A., Brock-Utne, J. G. et al. Critical volume for pulmonary acid
aspiration: reappraisal in a primate model. Br J Anaesth 1990,65:248-50.
3. Tiret, L., Nivoche, Y.,
Halton, F. et al. Complications related to anaesthesia in infants
and children. Br J Anaesth 1988; 61:263-69.
4. Cote, C. J., Goudsouzian,
N. G., Liu, L. M. P. et al. Assessment of risk factors related to
the aspiration syndrome in pediatric patients' gastric pH and residual
volume. Anesthesiology 1982; 56:70-2.
5. McClelland, G. R., Sutton.
J. A. Epigastric impedance: a non-invasive method for the assessment
of gastric emptying and motility. Gut 1985; 26:607-14.
6. Martin. T. M. and Zagnoev,
M. B. NPO guidelines at twenty-four North American pediatric hospitals
[abstract]. Anesth Analg 1993; 76:S244.
7. Cavell, B. Gastric emptying
in infants fed human milk or infant formula. Acta Paediatr Scand
1981; 70:639-41.
8. Tomomasa, T., Hyman, P.
E., Itoh, K. et al. Gastrointestinal motility in neonates: response
to human milk compared with cows milk formula. Pediatrics 1987;
80:434-38.
9. Litman, R. S., Wu, C.
L., Quinlivan, J. K. Gastric volume and pH in infants fed clear liquids
and breast milk prior to surgery. Anesth Analg 1994; 79:482-85.
Page last edited Sun Oct 14 09:32:41 UTC 2007.
