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 These risk factors were extrapolated from unpublished data obtained in a study of rhesus monkeys where an aliquot of acidic fluid was instilled directly into the right bronchus of the subject.1 A subsequent study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.
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