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Nipple Feeding for Preterm Infants With Bronchopulmonary Dysplasia
JOGM CLINICAL STUDIES K A R E N F. P R I D H A M , R N , P h D , F A A N SHERIE SONDEL, RD, M E d AUDREY CHANG, PhD CHRISTOPHER GREEN, MD
Nipple Feeding for Preterm Infants with Broncbopulmonay Objective: To examine the influence of an infant’s physical condition on nipple-feeding practices and the contribution of the infant’s age at complete nipple feeding to dietary intake and somatic growth outcomes. Design: A retrospective, correlational study. Setting: Two Level 111 nurseries. Participants: Records of 55 preterm infants with bronchopulmonary dysplasia. Main outcome measures: The infant’s intake of kcalbg on Day 1 of complete nipple feeding and the weight gain per day between complete nipple feeding and discharge. Results: Gestational age and days on mechanical ventilation, continuous positive airway pressure, or supplementary oxygen influenced age at start and at completion of nipple feeding (p < .05). The infant’s weight when nipple feeding was introduced was the primary determinant of age at introduction of nipple feeding (B = S O , p < .001). The physical condition variables did not influence the transition timefrom introduction of nipple feeding to complete nipple feeding. Neither the physical condition variables nor the feeding practice variables contributed to caloric intake. Weightgain between the time of complete nipple feeding and hospital discharge was less for infants who were on supplementary oxygen longer and who were older when completely nipple fed ( p < .Ol). Accepted: August 1992
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he caloric intake and somatic growth of preterm infants with bronchopulmonary dysplasia (BPD) when fully nipple fed is an important clinical issue. Optimal nutrition is critical to tissue repair and organ growth in infants in the chronic stage of BPD. During this stage, when the infants become more stable physiologically, oral feedings are generally started (Oh, 1986). Because the completely nipplefed infant presumably has more opportunity for selfregulation of the diet than the gavage-fed infant, the former’s caloric intake may or may not meet recommended levels. Examination of the outcomes of feeding practices could help determine their soundness and aid nurses who must make decisions about the timing of introduction of nipple feeding and advancement to complete nipple feeding. In addition, knowledge of the contribution that infant-related factors make to nipple-feeding practices and to the infant’s caloric intake and somatic growth is needed in making decisions about feeding practices that are sensitive to variations among infants (Lund & Collier, 1990). The purpose of this study was to explore such factors affecting nipple-feeding practices for preterm infants with BPD and to examine clinically relevant outcomes of these practices. The timing of introduction of nipple feeding and the rapidity with which nipple feeding is advanced to full nipple feeding are clinical issues for which clear answers do not yet exist. The introduction of nipple feeding as early as neurologic development and physical condition perfnit may be advantageous for several reasons. First, gavage feeding not only deprives an infant of sucking pleasure, but may provide aversive stimulation to the mouth, pharynx, and esophagus (Geertsma, Hyams, Pelletier, & Reiter, 1985). Second, sucking may help pacify the infant and reduce restlessness and expenditure of energy (Weaver & Anderson, 1988). Third, although gavage feeding can be given on an infant’s cues of hunger and terminated at signs of satiation, such as release of or turning the head away from the nipple, it does not help an infant learn patterns of sucking, swallowing, and breathing in relation to internal signals (Erikson, 1963). Finally, patterns of sucking, swallowing, and breathing provide cues to caregivers and assist them in providing sensitive and responsive feeding (Saunders, Friedman, & Stramoski, 1991). Arguments in support of a cautious approach to introducing nipple feeding to preterm infants with BPD also exist. For example, too early introduction of nipple feeding or advancement to complete nipple feeding for these infants may increase energy expenditure and reduce calories available for growth (Scherf & Arndt, 1990). Accordingly, before a case can be
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Before a case can be made for Jtber a cautious or a liberal approach to introducing nipple feeding and advancing to complete nipple feeding, factors tbat influencefeeding practices and tbe eflect of tbese practices on infant dietary intake and weight gain must be examined.
made for either a cautious or a liberal approach to introducing nipple feeding and advancing to complete nipple feeding, factors that influence nipple feeding practices and the effect of these practices on the infant’s dietary intake and weight gain must be examined. Little is known about nipple-feeding practices chosen by nurses for preterm infants with BPD, infantrelated factors that influence these practices, and outcomes of these practices in regard to caloric intake and weight gain. The literature suggests that both the infant’s maturity and physical status are likely to affect nipple-feeding practices. Bu’Lock, Wooldridge, and Baum (1990) reported that a coordinated pattern of sucking, swallowing, and breathing in preterm infants depended more on physiologic maturity than on experience. Lund and Collier (1990) claimed that most premature infants exhibit signs of readiness for nipple feeding by 34 weeks. Authors of reference works for nurses on preterm infant feeding generally recommend that nipple feeding be approached cautiously before 33 to 35 weeks’ postconceptional age. This recommendation assumes that, by this age, the sucking reflex and pattern have matured and sucking, swallowing, and breathing are likely to be coordinated (Boynton & Jones, 1988; Lefrak-Okikawa, 1990; Shaker, 1990). The extent to which the recommendation is applicable to preterm infants with BPD is not documented in the literature. The influence of the infant’s physical condition on nurses’ decisions regarding the timing of initiation of and advancement to complete nipple feeding is thus far only speculative. Physical condition variables that are relevant to feeding practices and their outcomes include gestational age at birth, duration of assisted ventilation, duration of supplemental oxygen, and
Little i s known about tbe eflects of nipple-feeding on preterm infants witb BPD.
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weight. The younger the infant at birth, the more likely it is that assisted ventilation and supplemental oxygen will be needed and prolonged. As a consequence, initiation of nipple feeding is likely to be delayed, because infants requiring mechanical ventilation are generally gavage fed and infants requiring supplementary oxygen may tire during nipple feeding (Lund & Collier, 1990). Respiratory difficulties, displayed by such signs as duskiness, tachypnea, irregular breathing, apneic spells, and bradycardia, may accompany nipple feeding in preterm infants (Guilleminault & Coons, 1984; Mathew, 1988; Shivpuri, Martin, Carol, & Fanaroff, 1983) and influence how rapidly the infant is advanced to full nipple feedings (Lund & Collier, 1990). The infant’s weight may indicate the infant’s robustness and be used as a criterion of readiness to begin nipple feeding and to advance to complete nipple feeding.
Tbe eflect of tbe infant’s pbysical condition on tbe nurse’s decision regarding tbe timing of introduction of and advancement to complete nipple feeding is tbus far only speculative.
One purpose of this exploratory study concerning nipple-feeding practices used for preterm infants with BPD was to examine the influence of variables related to the infant’s physical condition on the timing of introducing the nipple and advancing to complete nipple feeding. A second purpose was to learn which physical condition variables and nipple-feeding practices contributed to the infant’s caloric intake. The third purpose was to examine the contribution of the physical condition variables, the infant’s postconceptional age when completely nipple fed, and caloric intake to the infant’s rate of weight gain between full nipple feeding and hospital discharge. The severity of the infant’s pulmonary disease, indicated by oxygen and diuretic therapy, may influence caloric intake and rate of weight gain once the infant is completely nipple fed (Oh, 1986). Similarly, infants who are older in postconceptional age when completely nipple fed may feed and grow less well than infants who are fully nipple fed earlier if self-regulatory mechanisms are more likely to be operative earlier with earlier nipple feeding. In general, an infant’s rate of weight gain is highly associated with caloric intake (Carlson & Barness, 1985); it has also been reported to be a function of gestational age (Babson & Benda, 1976).
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Methods Setting and Sample After approval from the hospital’s Institutional Review Board and the university’s Clinical Sciences Center Human Subjects Committee, the study commenced using retrospective data from the hospital inpatient records of infants of 32 weeks or less gestation at birth who were diagnosed with BPD and who had a requirement for supplementary oxygen beyond 3 weeks (Farrell & Palta, 1986). The records of these infants, all born between late 1982 and early 1988, an approximately 6-year period, were reviewed to identify infants who met the criteria for selection, namely, that their birth weights were appropriate for gestational age because somatic growth may be different for infants who are small for gestational age (Hack & Fanaroff, 1988; Vohr & Garcia-Coll, l988), that they either were born in the neonatal intensive-care nursery or were transferred there within 24 hours of birth, and that they were on full nipple feedings when discharged to their homes from the intensive-care nursery. Infants with medical or congenital conditions potentially interfering with feeding, including tracheal-esophageal fistula, cleft palate, gastroschisis, necrotizing enterocolitis, and gastrostomy, were excluded from the study. The sample included 55 preterm infants with BPD. The infants were patients in either of two Level I11 (regional) neonatal intensive-care nurseries. In each of the two nurseries, readiness for progression to nipple feeding was determined for each infant by nurses using their own criteria rather than a nurserywide protocol. Weighing by electronic scale was used in both nurseries by 1987. Before that time, mechanical scales were used. Measures Data were collected on demographic, medical, and feeding-related variables. The infant’s attributes at birth, including Apgar scores, gestational age, weight, medical conditions, and therapies, were obtained from the physicians’ notes. Gestational age was estimated by Ballard examination (Ballard, Novak, & Driver, 1979). Intraventricular hemorrhage was scored 0 if not present, 1 if graded 1 or 2, and 2 if graded 3 or 4. The number of days the infant was on mechanical ventilation or continuous positive airway pressure (CPAP) and the number of days the infant was given supplementary oxygen were computed. The infant who was on diuretic therapy once completely nipple fed was given a score of 1; if not on diuretic therapy at this time, the infant was given a
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score of 0. Respiratory difficulties during feeding were determined by a review of the nursing record, beginning with the first nipple feeding and continuing until the infant was completely nipple fed. Respiratory difficulty was scored 1 if tachypnea, irregular breathing, apneic spells, bradycardia, fatigue, duskiness, or pallor during feeding was reported. A score of 0 was given if none of these signs of respiratory difficulty were noted. Infant weights, including the weight on the day nipple feeding was started, were obtained from the nurses’ flow sheets. Information was obtained from the nurses’ flow sheets for three nipple-feeding practice variables as well: (1) postconceptional age upon introduction of nipple feeding, that is, the 1st day the nipple was offered to the infant for nutritive purposes; (2) postconceptional age on the day the infant was first completely nipple fed, that is, all subsequent feedings were by nipple and were not supplemented or alternated with gavage feeding; and (3) transition time, that is, the number of days between the introduction of nipple feeding and complete nipple feeding. The record of the 24-hour volume of dietary intake on the nurses’ flow sheet on the 1st day that the infant was completely nipple fed was used for the assessment of kcal/kg intake on that day. Any supplements to the formula or breast milk that the infant received were included in the calculation of caloric intake. For this calculation, the Ross Laboratories (1990) publication of the nutritional content of milks and formulas was used. Infant weight gain was recorded as the number of grams gained per day between the 1st day of complete nipple feeding and the day of discharge from the hospital. This value was divided by the infant’s weight on the 1st day of complete nipple feeding to get a measure of growth velocity per unit of body size (Brosius, Ritter, & Kenny, 1984; Gill, Yu, Bajuk, & Astbury, 1986; Shaffer, Quimiro, Anderson, & Hall, 1987).
Analysis of variance (ANOVA) revealed no significant differences in infant attributes, days on mechanical ventilation or CPAP, days on supplementary oxygen, or feeding practices among any of the years of the study (1982-88). A t-test showed that the two nurseries did not differ in these variables either. Therefore, the data for all 6 years of the study and for the two nurseries were combined. Thirty-one (56.4%) of the 55 infants were male. The demographic characteristics of the communities served by the nurseries were reflected in the ethnicity of the infants studied: 40 were white, 4 were black, 2 were Latino, and 1was Asian. The ethnicity of 8 infants
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was not reported. Thirteen infants had a 5-minute Apgar score of 5 or less ( M = 6.3, SD = 1.7, range = 1-9). None had seizures. Thirty-five were on a diuretic medication sometime during their hospitalization, and 13 were on a diuretic when they went home. Ten of the infants had a Grade 1 or 2 intraventricular hemorrhage (IVH), and 6 had a Grade 3 or 4 IVH. When t-tests were done to compare male with female infants, white with nonwhite infants, and infants whose 5-minute Apgar score was 5 or less with infants whose score was greater than 5 on feeding practice, caloric intake, and weight gain variables, no significant differences were found. With ANOVA as the test, IVH made no difference in feeding practice, caloric intake, or weight gain variables. The only significant difference, revealed by a t-test,was between infants on supplementary oxygen at the time they became completely nipple fed ( n = 23) and infants who were no longer on supplementary oxygen at that time ( n = 32). Infants on oxygen at complete nipple feeding had more days on oxygen, on the average ( M = 102.2 days, SD = 54.1), than infants who were not on supplementary oxygen by the time nipple feeding was complete ( M = 63.5 days, SD = 24.9). Descriptive statistics for variables pertaining to the infant’s physical condition and for variables pertaining to nipple-feeding practice are shown in Table 1. On the average, the gestational age of the infants at birth was almost 2 8 weeks. Birth weight averaged just over 1,000 g.
The number of days infants received mechanical ventilation or CPAP or were on supplementary oxygen varied widely from infant to infant. A majority ( n= 43) were receiving supplementary oxygen when nipple feeding was introduced, and 23 were on supplementary oxygen when they achieved full nipple feeding. Fourteen infants, about one fourth of the sample, were still on supplementary oxygen when they were discharged from the hospital. At the time they were completely nipple fed, 13 infants were receiving diuretic therapy. Seventeen had respiratory difficulty of some type during nipple feeding. Feeding history also varied widely. All the infants had received total parenteral nutrition and had been gavage fed. The nurses’ records indicated that all had had an opportunity for nonnutritive sucking on a pacifier before the introduction of nipple feeding. On the average, the infants were almost 2 months postnatal age before nipple feedings were started, and they weighed more than 1,800 g. However, the variability in the infant’s weight when first nipple fed was high, ranging from 1,315 g to 3,670 g. Considering that the mean length of hospitalization was 99 days ( S D = 37.4, range = 51 to 226 days), on the average, infants spent more than half the hospitalization time without nipple feeding. In general, when nipple feeding was introduced, infants were 36.2 weeks postconceptional age. Again, the variability in postconceptional age when nipple feeding was introduced was great, beginning as early as 30.4 weeks and as late as 47.7 weeks. None of
Table 1. Descriptive Statistics f o r Physical Condition and Feeding Practice Variables (N
=
55)
Type/uartable
M
SD
Infant’s physical condition Birth weight
1,002.5
274.2
581-1,616
1,821.4
411.6
1,315-3,670
27.7
2.1
35.0 79.7
23.3 43.8
Weight when first nipple fed Gestational age (weeks) Days on mechanical ventilation or CPAP Days on supplementary oxygen Nipple-feeding practice Postnatal age (days) Introduction of nipple feeding Completely nipple fed Postconceptional age (weeks) Introduction of nipple feeding Completely nipple fed Days between introduction and completion of nipple feeding (transition time)
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Range
23-32.5 0-103 1,315-3,670
59.8
19.8
17-117
76.0
20.2
31-125
36.2
2.4
30.4-47.7
38.5
2.5
33.3-48.8
16.2
8.7
4-40
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the infants were completely nipple fed before 33 weeks postconceptional age, and one infant was not on full nipple feedings until almost 49 weeks postconceptional age. The transition time between the introduction of nipple feeding and full nipple feeding also varied widely, ranging from 4 to 40 days. Once completely nipple fed, infants remained in the hospital for 3 weeks, on average. Ten infants received breast milk when nipple fed. Breast milk was fed by bottle, except when the mother was present to nurse her infant. For almost all breastfeeding mothers, this happened once a day at most. Student’s t-tests showed that infants fed breast milk and infants fed formula did not differ significantly on feeding practice variables. Descriptive statistics for caloric intake and for weight gain between complete nipple feeding and discharge from the hospital are shown in Table 2. The caloric density of the formula approximately 74% of the infants ( n = 41) had when they were first completely nipple fed was at least 24 cal/oz. Three of the formula-fed infants and three of the infants who were fed breast milk received fortifiers, such as mediumchain triglycerides oil. Caloric intake on the day the infant was first completely nipple fed varied widely (45.7 kcal/kg to 164.6 kcal/kg). The rate of weight gain, corrected for weight at the time the infant was first completely nipple fed, ranged between 3.4 and 28.5 g/kg per day. Infants who were on a diuretic medication after they were completely nipple fed did not differ significantly in rate of weight gain from those infants who were not on a diuretic. On the average, the 41 infants not on a diuretic gained 14.6 g/day, corrected for their weight when first completely nipple fed ( S D = 6.0), whereas the infants on a diuretic
Table 2. Descriptive Statistics for Caloric Intake and Weight Gain Variables (N = 55)
Type/vardable Kcalories/kg/day, 1st day of complete nipple feeding Weight gain (g/day) between complete nipple feeding and discharge Uncorrected for weight Corrected for weight”
M
SD
Range
110.2
20.0
45.7-164.6
23.8
7.7
14.0
5.9
7.2-44.4 3.4-28.5
a Weight gain (g/day) was divided by weight on the day the infant was first completely nipple fed and multiplied by 1,000 to obtain a value larger than 1.
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gained 12.8 g/day, thus corrected ( S D = 5.6) [ F = .93 (1, 52 d f ) , p = .34]. Because the rate of weight gain could be a function of the infant’s length of stay in the hospital after nipple feeding was complete, we examined the rate of weight gain by this length of stay. The median length of stay after nipple feeding was complete was 16 days. Infants whose rate of weight gain was less than the 25th percentile of the distribution for days stayed in the hospital after nipple feeding was complete (11 days) numbered 14; 28 infants were in the group between the 25th and 75th percentile, and 13 were in the group whose length of stay was greater than the 75th percentile (23.2 days). The second group had the greatest rate of weight gain ( M = 16.05 g, SD = 5.77, corrected for weight). The rate of weight gain for infants whose length of stay was less than the 25th percentile was 12.11 g/day, on the average ( S D = 5.33). The rate of weight gain was lowest ( M = 11.6, SD = 5.76) for the group of infants whose length of stay was greater than the 75th percentile. Results of oneway ANOVA showed a significant difference in rate of weight gain among these three groups of infants [ F = 3.81 (2, 52 d f ) , p = 0.031. Regression analysis was used to address the research objectives. First, the contribution of the physical condition variables to the feeding practice variables was explored. The physical condition variables included in this analysis were gestational age, days on mechanical ventilation or CPAP, days on supplementary oxygen, the presence or absence of respiratory difficulties during feeding, and infant weight on the day nipple feeding was started. Examination of the Pearson coefficients showed that the correlations among the physical condition variables were low enough ( r c .70) to include all of them in the regression analysis. Gestational age, days on mechanical ventilation or CPAP, and infant weight on the day nipple feeding was started made a significant positive contribution to the infant’s postconceptional age when nipple feeding was introduced (RZ= .73,p < .OOl). The specific contribution of each of these variables is shown in Figure 1. None of the physical condition variables contributed to transition time (R2 = .08). Gestational age, days on mechanical ventilation or CPAP, days on oxygen, and infant weight on the day nipple feeding was started contributed significantly and positively to the infant’s postconceptional age when nipple feeding was completed (R2 = .71, p < .OOl). The contribution of feeding practice variables to caloric intake and weight gain was examined with hierarchical set regression (Cohen & Cohen, 1983). This type of regression permitted examination of the con-
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.50'"
M.nt weld% day nipple leading was mart&
>
introduction ot nipple teeding R = .73-
Reaplratorv d~cultlasduring
fdho
Gmtatlaui age
\ .37.r
Days on medmnlcal Hntiwan u CPAP
DaY.~urpplemsnterv myosn
3 1 . '
>
Postconceptional age, complete nipple feeding
ff
=
.71'"
lnlant weipM, day nipple bedlngwrnaaned R a a p t W dHfmitlrn durhg
leadhll
Note: The numben shown above the arrows am beta weights, which indicate the rpeciRc wntfibutim to the rariance in the dependent variable.
'P < .05.
'b< .01.
-p < .Wi.
ggure 1. Contribution o f infant.physica1condition variables to nipplerfeeding practices.
cal condition variables affected weight gain significantly, accounting for 17% of the variance. However, the only such variable to affect weight gain significantly was the number of days the infant was on supplementary oxygen. The more days the infant was on oxygen, the poorer was the weight gain (see Figure 2 ) . Postconceptional age when nipple feeding was complete contributed 11%of the variance to weight gain, in the negative direction. That is, the older the infant was when completely nipple fed, the less was the infant's weight gain. When physical condition and feeding practice variables were controlled, caloric intake did not make a significant contribution to weight gain, accounting for only 1%of the variance. In total, only 29% of the variance in weight gain was accounted for by the physical condition, feeding practice, and caloric intake variables.
Discussion The preterm infants in the study were, for the most part, very young and low in weight at birth. On the whole, nipple feeding was introduced several weeks later than when preterm infants are reported in the nursing literature to be developmentally ready for the practice. Although the small, nonrandom sample limits generalization of the study's findings, the findings document the contribution of physical condition variables to nipple-feeding practices and the contribution of the infant's postconceptional age at full nipple feeding to the infant's rate of weight gain between full nipple feeding and discharge from the hospital. Much of the variance in the infant's postconceptional age when nipple feeding was introduced and when nipple feed-
tribution of the feeding practice variables independently of the contribution of the physical status variables. The infant's postconceptional age when nipple feeding was introduced was correlated highly ( r = .87) with the postconceptional age when completely nipple fed and was not included in further analysis. The first of the regression analyses controlled for the effects of infant gestational age, days on supplementary oxygen, and the presence or absence of respiratory difficulties during feeding, and it examined the direct contribution to caloric intake of postconceptional age when nipple feeding was complete and transition time from introduction to complete nipple feeding. Neither the infant's physical condition variables (gestational age, days on supplementary oxygen, and respiratory difficulties) nor feeding practice variables made a significant contribution to caloric intake. Three types of variables were included in the regression analysis of the rate of weight gain between the time the infant was completely nipple fed and the time the infant was discharged from the hospital. The first included gestational age, days on supplementary oxygen, and diuretic therapy; the second was postconceptional age when nipple feeding was complete; and the third was caloric intake. The contribution of each type of variable to weight gain was examined, controlling for the effect of the other types. The infant physi-
I"
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Figure 2. Contribution of infant physical condition variables, feeding practices. and caloric intake to infant weight gain. Gestationai a@
1 ,
Days cn supplenmnwy Owen
-.42t*
Diuretk therapy
-.15
Pan~ncepflonalage,
>
+
Weight gain (g/day. comcted lor weight) between complete nipple heding and discharge R = 30'
Noh: The numbers shown above the anows am beta weights, which indicate the specific wnbibution to the variance in the dependent variable. p < .01.
-p < .001.
Nipple Feeding
ing was complete is explained by the physical condition variables. The substantial contribution of the infant’s weight to the infant’s postconceptional age at initiation of nipple feeding suggests that weight may be an important guide to decision making about starting nipple feeding. Why the transition times between the introduction and completion of nipple feedings were so different among the infants requires an examination of variables that were not included in the study. Transition time may be influenced by environmental conditions. Little is known about the approaches nurses take to advance nipple feedings for infants with BPD and about the decision-making criteria they use. The work of Lund and Collier (1990) is an exception in its presentation of guidelines for this advancement. Perhaps nursing staff characteristics, including the nurse-infant ratio, the continuity of assignment of nurses to infants, and the beliefs that individual nurses have about advancing nipple feeding will help to explain the variation in transition time. Once an infant is physiologically stable, the consistency and continuity of the nursing staff may be particularly important in determining cues pertaining to the infant’s readiness to nipple feed and to the infant’s advancement to full nipple feeding. Prospective studies are needed to determine the extent to which nurses’ assessments relative to nipple-feeding practice concern such criteria as an infant’s robustness, experience with nonnutritive sucking, cues regarding readiness to nipple feed, vigor and interest in sucking, respiratory stability, and tolerance of the diet. Neither the physical condition variables nor postconceptional age when completely nipple fed contributed to the infant’s caloric intake. On the average, caloric intake was lower than the 120-130 kcal/kg per day recommended by Oh (1986) for the convalescent phase of BPD. Explanations for the wide range of kilocalories consumed per kilogram of body weight on the first day of complete nipple feeding must be sought. Perhaps caloric intake increases or stabilizes once infants have adapted to being completely nipple fed. Caloric intake after advancement to full nipple feeding should be examined over several days to determine the degree of fluctuation in intake. The caloric density of the feeding substance may also influence caloric intake (Fomon, 1974). Another factor that may explain variability in caloric intake is the caregiver’s behavior. Infants with BPD are generally fed prescribed amounts at scheduled times because of concern about their weight gain or management of fluid balance. Given these concerns, one might expect nurses to attempt to feed an infant the prescribed amount. Perhaps some infants were
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more difficult to feed than others. Or nurses may have varied skill in feeding infants. Some infants may have been given more opportunities for self-regulated feeding than others, depending on the infant and the feeding practices of specific nurses. Saunders et al. (1991) found that, on the average, schedule-fed preterm infants took a greater volume of formula than infants fed on demand. The behavior of both nurses and infants during feeding warrants assessment. Altered breathing patterns and interference with ventilation have been demonstrated during breastfeeding and bottle feeding of preterm infants (Guilleminault &Coons, 1984; Lund &Collier, 1990;Mathew, 1988; Meier, 1988). Bu’Lock et al. (1990) postulated that preterm infants may learn ineffective feeding patterns as a consequence of early breathing difficulties during feeding. The difference that the timing of introduction of the nipple and the timing of advancement to full nipple feeding makes to coordinated sucking, swallowing, and breathing; to the clarity of hunger and satiety cues; to uninterrupted sleep; and to caloric intake should be examined. The small amount of variance in the infant’s weight gain between complete nipple feeding and discharge from the hospital that was explained by the infant’s physical condition, feeding practice variables, and caloric intake indicates that variables other than those examined in this study account for weight gain. What cannot be concluded from the results is that delaying nipple feeding until an older postconceptional age is detrimental to infant weight gain. The high correlation of the infant’s postconceptional age when completely nipple fed with the postconceptional age upon introduction of nipple feeding suggests that a systematic factor is operating. Both the number of days the infant was on supplementary oxygen and the infant’s postconceptional age when completely nipple fed may be indices of the severity of the infant’s respiratory disease; hence the negative effect both variables had on weight gain. The negligible contribution of caloric intake to weight gain may be explained by the more potent effect of severity of respiratory illness. Other factors, as yet unexplained, may influence weight gain. Kurzner, Garg, and Bautista (1988) found
The negative effect on weight gain of both the days the infant was on supplementary oxygen and the postconceptional age when completely nipple fed may be the result of the severity of respiratory disease these two variables potentially represent.
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A more precise measure of respiratory dificulty during feeding is needed to determine its e#ects on nipple feeding practices.
that infants with BPD who were failing to thrive had a higher resting metabolic expenditure than infants who were gaining adequate weight. Another issue is the composition of the body mass deposited. Putet, Sinterri, Rego, and Salle (1987) report that, for neonates, the amount of fat deposited rises with the increasing amount of energy absorbed, without any evidence of more weight gain. Measures of energy expenditure, body composition, and the accretion of lean muscle mass with increasing caloric intake may help to explain the absence of any relationship between weight gain and caloric intake found in this study. The current study has several limitations, including the hospital record as the source of data. Whether or not infants were neurologically and physically ready to begin nipple feeding at or before the time they did in fact begin cannot be determined from the record. The specification of physical condition variables was hampered by the need to rely exclusively on the hospital record. The severity of the infants’ BPD was only roughly estimated by the number of days the infant was on supplementary oxygen. The fact that the severity of illness could not be classified precisely hampers the identification of the population of infants to which the study findings are applicable. A more precise measure of respiratory difficulty during feeding is needed to determine its effects on nipple-feeding practices and on patterns of sucking, swallowing, and breathing associated with initiation and completion of nipple feeding. The study also was limited by variability in hospitalization practices. For examining infants’ rate of weight gain, a defined period of at least 7 days after complete nipple feeding would be preferable to the period defined by the length of stay between complete nipple feeding and discharge from the hospital. In fact, because five of the infants remained hospitalized fewer than 7 days once they were completely nipple fed, it was impossible to use a standard, yet adequately lengthy period without losing subjects from the study. What is needed for the advancement of both research and nursing practice is a conceptual framework of variables involved in nipple-feeding practice and its outcomes. This framework or model should include more precise measures of the infant’s physical condi-
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tion, fuller descriptions of feeding practices (including infant cue-based approaches to feeding), and assessments of caretaker-infant interaction during feeding. In addition to caloric intake and weight gain, outcomes should include patterns of sucking, - swallowing, and breathing; clear hunger and satiety cues; patterns of sleep and awake states; the infant’s development of feeding skill; and effectiveness in the nurse-infant dyad. How nipple-feeding practice influences not only these outcomes, but also somatic growth and the development of the aforesaid feeding skills, requires refinement and better specification of feeding practice variables. Nurses can help to specify these variables by describing their practice when nipple feeding preterm infants with BPD. Study of the relationships among these variables could assist nurses in designing nipple-feeding plans with an increased likelihood of advancing the somatic growth and feeding skill of infants with BPD.
Acknowledgment This project was supported in part by Grant No. BRSG 2-SO7 PR05866-05, awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health; by the Wisconsin Perinatal Foundation; by University of Wisconsin-Madison Graduate School and School of Nursing research funds; and by NIH Grant No. M01 RR03186 from the National Center for Research Resources to the University of Wisconsin Medical School.
References Babson, S. G., & Benda, G. I. (1976). Growth graphs for the clinical assessment of infants of varying gestational age. Journal of Pediatrics, 89,814-820. Ballard, J. L., Novak, K., & Driver, M. (1979). A simplified score for assessment of fetal maturation of newly born infants. Journal of Pediatrics, 95(5,Pt. I ) , 769-774. Boynton, C. A., &Jones, B. (1988). Nursing care of the infant with bronchopulmonary dysplasia. In T. A. Merritt, W. H. Northway, Jr., & B. R. Boynton (Eds.), Contemporary issues in fetal and neonatal medicine (pp. 313-329). Boston: Blackwell Scientific Publications. Brosius, K. K., Ritter, D. A., & Kenny, J. D. (1984). Postnatal growth curve of the infant with extremely low birth weight who was fed enterally. Journal of Pediatrics, 74, 778-782.
Bu’Lock, F., Wooldridge, M. W., & Baum, J. D. (1990).Development of coordination of sucking, swallowing and breathing ultrasound study of term and preterm infants. Developmental Medicine and Child Neurology, 32,669678.
Carlson, S. E., & Barness, L. A. (1985). Macronutrient re-
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quirements for growth. In W. A. Walker & J. B. Watkins (Eds.), Nutrition in pediatrics: Basic science and clinical application (pp. 3-15). Boston: Little, Brown, & Co. Cohen, J., & Cohen, P. (1983). Applied multiple regression/ correlation analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum. Erikson, E. H. (1963). Childhood and society (pp. 72-80). New York: W. W. Norton. Farrell, P. M., & Palta, P. (1986). Bronchopulmonary dysplasia. In P. M. Farrell & L. M. Taussig (Eds.), Bronchopulm o n a y dysplasia a n d related chronic respiratory disorders (pp. 1-7). Columbus, OH: Ross Laboratories. Fomon, S. J. (1974). Infant nutrition (2nd ed.). Philadelphia: W.B. Saunders. Geertsma, M. A,, Hyams, J. S., Pelletier, J. M., & Reiter, S. (1985). Feeding resistance after parenteral hyperalimentation. American Journal of Diseases of Children, 139, 255-256. Gill, A., Yu, V. Y. H., Bajuk, B., &Astbury, J. (1986). Postnatal growth in infants born before 30 weeks’ gestation. Archives of Disease in Childhood, G1, 549-553. Guilleminault, C., & Coons, S. (1984). Apnea and bradycardia during feeding in infants weighing > 2,000 gm. Journal of Pediatrics, 104, 932-935. Hack, M., & Fanaroff, A. A. (1988). Growth patterns in the ICN graduate. In R. A. Ballard (Ed.), Pediatric care of the ICN graduate (pp. 33-39). Philadelphia: W. B. Saunders. Kurzner, S., Garg, M., & Bautista, D. B. (1988). Growth failure in infants with bronchopulmonary dysplasia: Nutrition and elevated resting metabolic expenditure. Pediatrics, 81, 379-384. Lefrak-Okikawa, L. (1990). Nutritional management of the very low birth weight infant. Journal of Perinatal and Neonatal Nursing, 2, 66-77. Lund, C. H., & Collier, S. B. (1990). Nutrition and bronchopulmonary dysplasia. In C. H. Houska Lund (Ed.), Bronchopulmona y dysplasia: Strategies for total patient care (pp. 98-101). Petaluma, CA: Neonatal Network. Mathew, 0. P. (1988). Respiratory control during nipple feeding in preterm infants. Pediatric Pulmonology, 5, 220-224. Meier, P. P. (1988). Bottle- and breast-feeding: Effects on transcutaneous oxygen pressure and temperature in preterm infants. Nursing Research, 37, 36-41. Oh, W . (1986). Nutritional management of infants with bronchopulmonary dysplasia. In P. M. Farrell & L. M. Taussig (Eds.), Bronchopulmonary dysplasia a n d related chronic respiratoy disorders (pp. 96-105). Columbus, OH: Ross Laboratories. Putet, G., Sinterri, J., Rego, J., & Salle, B. (1987). Energy
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balance and composition of body weight. Biology of the Neonate, 52 (Supplement l ) , 17-24. Ross Laboratories. (1990). Milk-based a n d soy-based infant formulas. Columbus, OH: Author. Saunders, R. B., Friedman, C. B., & Stramoski, P. R. (1991). Feeding preterm infants: Schedule or demand?Journal of Obstetric, Gynecologic, and Neonatal Nursing, 20, 212-218. Scherf, R. F., & Arndt, S. (1990). Complications in infants with bronchopulmonary dysplasia. In C. H. Houska Lund (Ed.), Bronchopulrnona y dysplasia: Strategies for total patient care (pp. 35-53). Petaluma, CA: Neonatal Network. Shaffer, S. G., Quimiro, C. L., Anderson, J. V., & Hall, R. T. (1987). Postnatal weight changes in low birth weight infants. Journal of Pediatrics, 79, 702-705. Shaker, C. S. (1990). Nipple feeding premature infants: A different perspective. Neonatal Network, 8(5), 9-17. Shivpuri, C. R., Martin, R. J., Carol, W. A., & Fanaroff, A. A. (1983). Decreased ventilation in preterm infants during oral feeding. Journal of Pediatrics, 103, 285-289. Vohr, B. R., & Garcia-Coll,C. T. (1988). Follow-up studies of high-risk, low-birth-weight infants. In H. E. Fitzgerald, B. M. Lester, & M. W. Yogman (Eds.), Theory and research in behavioralpediatrics (Vol. 4, pp. 1-65). New York: Plenum Press. Weaver, K. A., & Anderson, G. C. (1988). Relationship between integrated sucking pressures and first bottle-feeding scores in premature infants. Journal of Obstetric, Gynecologic, a n d Neonatal Nursing, 17, 113-120. Address for correspondence: Dr. Karen F. Pridham, RN, PhD, FAAN, University of Wisconsin-Madison, School of Nursing, Department of Family Medicine and Practice, 600 Highland Avenue, Madison, WI 53792.
Karen I? Pridham is a professor of nurstng and family medtctne and practice at the University of Wisconsin tn Madison. Sherie Sonde1 ts a nutrition education coordinator in the pediatric pulmonary center at the University of Wisconsin tn Madison. Audrey Chang is a statistictan at Walter Reed Army Medical Center in Washtngton, DC. Chrtstopher Green Is an associate professor of pediatrics at the University of Wtsconstn tn Madtson.
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Nipple Feeding for Preterm Infants with Broncbopulmonay Objective: To examine the influence of an infant’s physical condition on nipple-feeding practices and the contribution of the infant’s age at complete nipple feeding to dietary intake and somatic growth outcomes. Design: A retrospective, correlational study. Setting: Two Level 111 nurseries. Participants: Records of 55 preterm infants with bronchopulmonary dysplasia. Main outcome measures: The infant’s intake of kcalbg on Day 1 of complete nipple feeding and the weight gain per day between complete nipple feeding and discharge. Results: Gestational age and days on mechanical ventilation, continuous positive airway pressure, or supplementary oxygen influenced age at start and at completion of nipple feeding (p < .05). The infant’s weight when nipple feeding was introduced was the primary determinant of age at introduction of nipple feeding (B = S O , p < .001). The physical condition variables did not influence the transition timefrom introduction of nipple feeding to complete nipple feeding. Neither the physical condition variables nor the feeding practice variables contributed to caloric intake. Weightgain between the time of complete nipple feeding and hospital discharge was less for infants who were on supplementary oxygen longer and who were older when completely nipple fed ( p < .Ol). Accepted: August 1992
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he caloric intake and somatic growth of preterm infants with bronchopulmonary dysplasia (BPD) when fully nipple fed is an important clinical issue. Optimal nutrition is critical to tissue repair and organ growth in infants in the chronic stage of BPD. During this stage, when the infants become more stable physiologically, oral feedings are generally started (Oh, 1986). Because the completely nipplefed infant presumably has more opportunity for selfregulation of the diet than the gavage-fed infant, the former’s caloric intake may or may not meet recommended levels. Examination of the outcomes of feeding practices could help determine their soundness and aid nurses who must make decisions about the timing of introduction of nipple feeding and advancement to complete nipple feeding. In addition, knowledge of the contribution that infant-related factors make to nipple-feeding practices and to the infant’s caloric intake and somatic growth is needed in making decisions about feeding practices that are sensitive to variations among infants (Lund & Collier, 1990). The purpose of this study was to explore such factors affecting nipple-feeding practices for preterm infants with BPD and to examine clinically relevant outcomes of these practices. The timing of introduction of nipple feeding and the rapidity with which nipple feeding is advanced to full nipple feeding are clinical issues for which clear answers do not yet exist. The introduction of nipple feeding as early as neurologic development and physical condition perfnit may be advantageous for several reasons. First, gavage feeding not only deprives an infant of sucking pleasure, but may provide aversive stimulation to the mouth, pharynx, and esophagus (Geertsma, Hyams, Pelletier, & Reiter, 1985). Second, sucking may help pacify the infant and reduce restlessness and expenditure of energy (Weaver & Anderson, 1988). Third, although gavage feeding can be given on an infant’s cues of hunger and terminated at signs of satiation, such as release of or turning the head away from the nipple, it does not help an infant learn patterns of sucking, swallowing, and breathing in relation to internal signals (Erikson, 1963). Finally, patterns of sucking, swallowing, and breathing provide cues to caregivers and assist them in providing sensitive and responsive feeding (Saunders, Friedman, & Stramoski, 1991). Arguments in support of a cautious approach to introducing nipple feeding to preterm infants with BPD also exist. For example, too early introduction of nipple feeding or advancement to complete nipple feeding for these infants may increase energy expenditure and reduce calories available for growth (Scherf & Arndt, 1990). Accordingly, before a case can be
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S T U D I E S
Before a case can be made for Jtber a cautious or a liberal approach to introducing nipple feeding and advancing to complete nipple feeding, factors tbat influencefeeding practices and tbe eflect of tbese practices on infant dietary intake and weight gain must be examined.
made for either a cautious or a liberal approach to introducing nipple feeding and advancing to complete nipple feeding, factors that influence nipple feeding practices and the effect of these practices on the infant’s dietary intake and weight gain must be examined. Little is known about nipple-feeding practices chosen by nurses for preterm infants with BPD, infantrelated factors that influence these practices, and outcomes of these practices in regard to caloric intake and weight gain. The literature suggests that both the infant’s maturity and physical status are likely to affect nipple-feeding practices. Bu’Lock, Wooldridge, and Baum (1990) reported that a coordinated pattern of sucking, swallowing, and breathing in preterm infants depended more on physiologic maturity than on experience. Lund and Collier (1990) claimed that most premature infants exhibit signs of readiness for nipple feeding by 34 weeks. Authors of reference works for nurses on preterm infant feeding generally recommend that nipple feeding be approached cautiously before 33 to 35 weeks’ postconceptional age. This recommendation assumes that, by this age, the sucking reflex and pattern have matured and sucking, swallowing, and breathing are likely to be coordinated (Boynton & Jones, 1988; Lefrak-Okikawa, 1990; Shaker, 1990). The extent to which the recommendation is applicable to preterm infants with BPD is not documented in the literature. The influence of the infant’s physical condition on nurses’ decisions regarding the timing of initiation of and advancement to complete nipple feeding is thus far only speculative. Physical condition variables that are relevant to feeding practices and their outcomes include gestational age at birth, duration of assisted ventilation, duration of supplemental oxygen, and
Little i s known about tbe eflects of nipple-feeding on preterm infants witb BPD.
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weight. The younger the infant at birth, the more likely it is that assisted ventilation and supplemental oxygen will be needed and prolonged. As a consequence, initiation of nipple feeding is likely to be delayed, because infants requiring mechanical ventilation are generally gavage fed and infants requiring supplementary oxygen may tire during nipple feeding (Lund & Collier, 1990). Respiratory difficulties, displayed by such signs as duskiness, tachypnea, irregular breathing, apneic spells, and bradycardia, may accompany nipple feeding in preterm infants (Guilleminault & Coons, 1984; Mathew, 1988; Shivpuri, Martin, Carol, & Fanaroff, 1983) and influence how rapidly the infant is advanced to full nipple feedings (Lund & Collier, 1990). The infant’s weight may indicate the infant’s robustness and be used as a criterion of readiness to begin nipple feeding and to advance to complete nipple feeding.
Tbe eflect of tbe infant’s pbysical condition on tbe nurse’s decision regarding tbe timing of introduction of and advancement to complete nipple feeding is tbus far only speculative.
One purpose of this exploratory study concerning nipple-feeding practices used for preterm infants with BPD was to examine the influence of variables related to the infant’s physical condition on the timing of introducing the nipple and advancing to complete nipple feeding. A second purpose was to learn which physical condition variables and nipple-feeding practices contributed to the infant’s caloric intake. The third purpose was to examine the contribution of the physical condition variables, the infant’s postconceptional age when completely nipple fed, and caloric intake to the infant’s rate of weight gain between full nipple feeding and hospital discharge. The severity of the infant’s pulmonary disease, indicated by oxygen and diuretic therapy, may influence caloric intake and rate of weight gain once the infant is completely nipple fed (Oh, 1986). Similarly, infants who are older in postconceptional age when completely nipple fed may feed and grow less well than infants who are fully nipple fed earlier if self-regulatory mechanisms are more likely to be operative earlier with earlier nipple feeding. In general, an infant’s rate of weight gain is highly associated with caloric intake (Carlson & Barness, 1985); it has also been reported to be a function of gestational age (Babson & Benda, 1976).
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Methods Setting and Sample After approval from the hospital’s Institutional Review Board and the university’s Clinical Sciences Center Human Subjects Committee, the study commenced using retrospective data from the hospital inpatient records of infants of 32 weeks or less gestation at birth who were diagnosed with BPD and who had a requirement for supplementary oxygen beyond 3 weeks (Farrell & Palta, 1986). The records of these infants, all born between late 1982 and early 1988, an approximately 6-year period, were reviewed to identify infants who met the criteria for selection, namely, that their birth weights were appropriate for gestational age because somatic growth may be different for infants who are small for gestational age (Hack & Fanaroff, 1988; Vohr & Garcia-Coll, l988), that they either were born in the neonatal intensive-care nursery or were transferred there within 24 hours of birth, and that they were on full nipple feedings when discharged to their homes from the intensive-care nursery. Infants with medical or congenital conditions potentially interfering with feeding, including tracheal-esophageal fistula, cleft palate, gastroschisis, necrotizing enterocolitis, and gastrostomy, were excluded from the study. The sample included 55 preterm infants with BPD. The infants were patients in either of two Level I11 (regional) neonatal intensive-care nurseries. In each of the two nurseries, readiness for progression to nipple feeding was determined for each infant by nurses using their own criteria rather than a nurserywide protocol. Weighing by electronic scale was used in both nurseries by 1987. Before that time, mechanical scales were used. Measures Data were collected on demographic, medical, and feeding-related variables. The infant’s attributes at birth, including Apgar scores, gestational age, weight, medical conditions, and therapies, were obtained from the physicians’ notes. Gestational age was estimated by Ballard examination (Ballard, Novak, & Driver, 1979). Intraventricular hemorrhage was scored 0 if not present, 1 if graded 1 or 2, and 2 if graded 3 or 4. The number of days the infant was on mechanical ventilation or continuous positive airway pressure (CPAP) and the number of days the infant was given supplementary oxygen were computed. The infant who was on diuretic therapy once completely nipple fed was given a score of 1; if not on diuretic therapy at this time, the infant was given a
March/April 1993
score of 0. Respiratory difficulties during feeding were determined by a review of the nursing record, beginning with the first nipple feeding and continuing until the infant was completely nipple fed. Respiratory difficulty was scored 1 if tachypnea, irregular breathing, apneic spells, bradycardia, fatigue, duskiness, or pallor during feeding was reported. A score of 0 was given if none of these signs of respiratory difficulty were noted. Infant weights, including the weight on the day nipple feeding was started, were obtained from the nurses’ flow sheets. Information was obtained from the nurses’ flow sheets for three nipple-feeding practice variables as well: (1) postconceptional age upon introduction of nipple feeding, that is, the 1st day the nipple was offered to the infant for nutritive purposes; (2) postconceptional age on the day the infant was first completely nipple fed, that is, all subsequent feedings were by nipple and were not supplemented or alternated with gavage feeding; and (3) transition time, that is, the number of days between the introduction of nipple feeding and complete nipple feeding. The record of the 24-hour volume of dietary intake on the nurses’ flow sheet on the 1st day that the infant was completely nipple fed was used for the assessment of kcal/kg intake on that day. Any supplements to the formula or breast milk that the infant received were included in the calculation of caloric intake. For this calculation, the Ross Laboratories (1990) publication of the nutritional content of milks and formulas was used. Infant weight gain was recorded as the number of grams gained per day between the 1st day of complete nipple feeding and the day of discharge from the hospital. This value was divided by the infant’s weight on the 1st day of complete nipple feeding to get a measure of growth velocity per unit of body size (Brosius, Ritter, & Kenny, 1984; Gill, Yu, Bajuk, & Astbury, 1986; Shaffer, Quimiro, Anderson, & Hall, 1987).
Analysis of variance (ANOVA) revealed no significant differences in infant attributes, days on mechanical ventilation or CPAP, days on supplementary oxygen, or feeding practices among any of the years of the study (1982-88). A t-test showed that the two nurseries did not differ in these variables either. Therefore, the data for all 6 years of the study and for the two nurseries were combined. Thirty-one (56.4%) of the 55 infants were male. The demographic characteristics of the communities served by the nurseries were reflected in the ethnicity of the infants studied: 40 were white, 4 were black, 2 were Latino, and 1was Asian. The ethnicity of 8 infants
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S T U D I E S
was not reported. Thirteen infants had a 5-minute Apgar score of 5 or less ( M = 6.3, SD = 1.7, range = 1-9). None had seizures. Thirty-five were on a diuretic medication sometime during their hospitalization, and 13 were on a diuretic when they went home. Ten of the infants had a Grade 1 or 2 intraventricular hemorrhage (IVH), and 6 had a Grade 3 or 4 IVH. When t-tests were done to compare male with female infants, white with nonwhite infants, and infants whose 5-minute Apgar score was 5 or less with infants whose score was greater than 5 on feeding practice, caloric intake, and weight gain variables, no significant differences were found. With ANOVA as the test, IVH made no difference in feeding practice, caloric intake, or weight gain variables. The only significant difference, revealed by a t-test,was between infants on supplementary oxygen at the time they became completely nipple fed ( n = 23) and infants who were no longer on supplementary oxygen at that time ( n = 32). Infants on oxygen at complete nipple feeding had more days on oxygen, on the average ( M = 102.2 days, SD = 54.1), than infants who were not on supplementary oxygen by the time nipple feeding was complete ( M = 63.5 days, SD = 24.9). Descriptive statistics for variables pertaining to the infant’s physical condition and for variables pertaining to nipple-feeding practice are shown in Table 1. On the average, the gestational age of the infants at birth was almost 2 8 weeks. Birth weight averaged just over 1,000 g.
The number of days infants received mechanical ventilation or CPAP or were on supplementary oxygen varied widely from infant to infant. A majority ( n= 43) were receiving supplementary oxygen when nipple feeding was introduced, and 23 were on supplementary oxygen when they achieved full nipple feeding. Fourteen infants, about one fourth of the sample, were still on supplementary oxygen when they were discharged from the hospital. At the time they were completely nipple fed, 13 infants were receiving diuretic therapy. Seventeen had respiratory difficulty of some type during nipple feeding. Feeding history also varied widely. All the infants had received total parenteral nutrition and had been gavage fed. The nurses’ records indicated that all had had an opportunity for nonnutritive sucking on a pacifier before the introduction of nipple feeding. On the average, the infants were almost 2 months postnatal age before nipple feedings were started, and they weighed more than 1,800 g. However, the variability in the infant’s weight when first nipple fed was high, ranging from 1,315 g to 3,670 g. Considering that the mean length of hospitalization was 99 days ( S D = 37.4, range = 51 to 226 days), on the average, infants spent more than half the hospitalization time without nipple feeding. In general, when nipple feeding was introduced, infants were 36.2 weeks postconceptional age. Again, the variability in postconceptional age when nipple feeding was introduced was great, beginning as early as 30.4 weeks and as late as 47.7 weeks. None of
Table 1. Descriptive Statistics f o r Physical Condition and Feeding Practice Variables (N
=
55)
Type/uartable
M
SD
Infant’s physical condition Birth weight
1,002.5
274.2
581-1,616
1,821.4
411.6
1,315-3,670
27.7
2.1
35.0 79.7
23.3 43.8
Weight when first nipple fed Gestational age (weeks) Days on mechanical ventilation or CPAP Days on supplementary oxygen Nipple-feeding practice Postnatal age (days) Introduction of nipple feeding Completely nipple fed Postconceptional age (weeks) Introduction of nipple feeding Completely nipple fed Days between introduction and completion of nipple feeding (transition time)
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Range
23-32.5 0-103 1,315-3,670
59.8
19.8
17-117
76.0
20.2
31-125
36.2
2.4
30.4-47.7
38.5
2.5
33.3-48.8
16.2
8.7
4-40
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the infants were completely nipple fed before 33 weeks postconceptional age, and one infant was not on full nipple feedings until almost 49 weeks postconceptional age. The transition time between the introduction of nipple feeding and full nipple feeding also varied widely, ranging from 4 to 40 days. Once completely nipple fed, infants remained in the hospital for 3 weeks, on average. Ten infants received breast milk when nipple fed. Breast milk was fed by bottle, except when the mother was present to nurse her infant. For almost all breastfeeding mothers, this happened once a day at most. Student’s t-tests showed that infants fed breast milk and infants fed formula did not differ significantly on feeding practice variables. Descriptive statistics for caloric intake and for weight gain between complete nipple feeding and discharge from the hospital are shown in Table 2. The caloric density of the formula approximately 74% of the infants ( n = 41) had when they were first completely nipple fed was at least 24 cal/oz. Three of the formula-fed infants and three of the infants who were fed breast milk received fortifiers, such as mediumchain triglycerides oil. Caloric intake on the day the infant was first completely nipple fed varied widely (45.7 kcal/kg to 164.6 kcal/kg). The rate of weight gain, corrected for weight at the time the infant was first completely nipple fed, ranged between 3.4 and 28.5 g/kg per day. Infants who were on a diuretic medication after they were completely nipple fed did not differ significantly in rate of weight gain from those infants who were not on a diuretic. On the average, the 41 infants not on a diuretic gained 14.6 g/day, corrected for their weight when first completely nipple fed ( S D = 6.0), whereas the infants on a diuretic
Table 2. Descriptive Statistics for Caloric Intake and Weight Gain Variables (N = 55)
Type/vardable Kcalories/kg/day, 1st day of complete nipple feeding Weight gain (g/day) between complete nipple feeding and discharge Uncorrected for weight Corrected for weight”
M
SD
Range
110.2
20.0
45.7-164.6
23.8
7.7
14.0
5.9
7.2-44.4 3.4-28.5
a Weight gain (g/day) was divided by weight on the day the infant was first completely nipple fed and multiplied by 1,000 to obtain a value larger than 1.
March/April 1993
gained 12.8 g/day, thus corrected ( S D = 5.6) [ F = .93 (1, 52 d f ) , p = .34]. Because the rate of weight gain could be a function of the infant’s length of stay in the hospital after nipple feeding was complete, we examined the rate of weight gain by this length of stay. The median length of stay after nipple feeding was complete was 16 days. Infants whose rate of weight gain was less than the 25th percentile of the distribution for days stayed in the hospital after nipple feeding was complete (11 days) numbered 14; 28 infants were in the group between the 25th and 75th percentile, and 13 were in the group whose length of stay was greater than the 75th percentile (23.2 days). The second group had the greatest rate of weight gain ( M = 16.05 g, SD = 5.77, corrected for weight). The rate of weight gain for infants whose length of stay was less than the 25th percentile was 12.11 g/day, on the average ( S D = 5.33). The rate of weight gain was lowest ( M = 11.6, SD = 5.76) for the group of infants whose length of stay was greater than the 75th percentile. Results of oneway ANOVA showed a significant difference in rate of weight gain among these three groups of infants [ F = 3.81 (2, 52 d f ) , p = 0.031. Regression analysis was used to address the research objectives. First, the contribution of the physical condition variables to the feeding practice variables was explored. The physical condition variables included in this analysis were gestational age, days on mechanical ventilation or CPAP, days on supplementary oxygen, the presence or absence of respiratory difficulties during feeding, and infant weight on the day nipple feeding was started. Examination of the Pearson coefficients showed that the correlations among the physical condition variables were low enough ( r c .70) to include all of them in the regression analysis. Gestational age, days on mechanical ventilation or CPAP, and infant weight on the day nipple feeding was started made a significant positive contribution to the infant’s postconceptional age when nipple feeding was introduced (RZ= .73,p < .OOl). The specific contribution of each of these variables is shown in Figure 1. None of the physical condition variables contributed to transition time (R2 = .08). Gestational age, days on mechanical ventilation or CPAP, days on oxygen, and infant weight on the day nipple feeding was started contributed significantly and positively to the infant’s postconceptional age when nipple feeding was completed (R2 = .71, p < .OOl). The contribution of feeding practice variables to caloric intake and weight gain was examined with hierarchical set regression (Cohen & Cohen, 1983). This type of regression permitted examination of the con-
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S T U D I E S
C L I N I C A L
.50'"
M.nt weld% day nipple leading was mart&
>
introduction ot nipple teeding R = .73-
Reaplratorv d~cultlasduring
fdho
Gmtatlaui age
\ .37.r
Days on medmnlcal Hntiwan u CPAP
DaY.~urpplemsnterv myosn
3 1 . '
>
Postconceptional age, complete nipple feeding
ff
=
.71'"
lnlant weipM, day nipple bedlngwrnaaned R a a p t W dHfmitlrn durhg
leadhll
Note: The numben shown above the arrows am beta weights, which indicate the rpeciRc wntfibutim to the rariance in the dependent variable.
'P < .05.
'b< .01.
-p < .Wi.
ggure 1. Contribution o f infant.physica1condition variables to nipplerfeeding practices.
cal condition variables affected weight gain significantly, accounting for 17% of the variance. However, the only such variable to affect weight gain significantly was the number of days the infant was on supplementary oxygen. The more days the infant was on oxygen, the poorer was the weight gain (see Figure 2 ) . Postconceptional age when nipple feeding was complete contributed 11%of the variance to weight gain, in the negative direction. That is, the older the infant was when completely nipple fed, the less was the infant's weight gain. When physical condition and feeding practice variables were controlled, caloric intake did not make a significant contribution to weight gain, accounting for only 1%of the variance. In total, only 29% of the variance in weight gain was accounted for by the physical condition, feeding practice, and caloric intake variables.
Discussion The preterm infants in the study were, for the most part, very young and low in weight at birth. On the whole, nipple feeding was introduced several weeks later than when preterm infants are reported in the nursing literature to be developmentally ready for the practice. Although the small, nonrandom sample limits generalization of the study's findings, the findings document the contribution of physical condition variables to nipple-feeding practices and the contribution of the infant's postconceptional age at full nipple feeding to the infant's rate of weight gain between full nipple feeding and discharge from the hospital. Much of the variance in the infant's postconceptional age when nipple feeding was introduced and when nipple feed-
tribution of the feeding practice variables independently of the contribution of the physical status variables. The infant's postconceptional age when nipple feeding was introduced was correlated highly ( r = .87) with the postconceptional age when completely nipple fed and was not included in further analysis. The first of the regression analyses controlled for the effects of infant gestational age, days on supplementary oxygen, and the presence or absence of respiratory difficulties during feeding, and it examined the direct contribution to caloric intake of postconceptional age when nipple feeding was complete and transition time from introduction to complete nipple feeding. Neither the infant's physical condition variables (gestational age, days on supplementary oxygen, and respiratory difficulties) nor feeding practice variables made a significant contribution to caloric intake. Three types of variables were included in the regression analysis of the rate of weight gain between the time the infant was completely nipple fed and the time the infant was discharged from the hospital. The first included gestational age, days on supplementary oxygen, and diuretic therapy; the second was postconceptional age when nipple feeding was complete; and the third was caloric intake. The contribution of each type of variable to weight gain was examined, controlling for the effect of the other types. The infant physi-
I"
152 J O G N N
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Figure 2. Contribution of infant physical condition variables, feeding practices. and caloric intake to infant weight gain. Gestationai a@
1 ,
Days cn supplenmnwy Owen
-.42t*
Diuretk therapy
-.15
Pan~ncepflonalage,
>
+
Weight gain (g/day. comcted lor weight) between complete nipple heding and discharge R = 30'
Noh: The numbers shown above the anows am beta weights, which indicate the specific wnbibution to the variance in the dependent variable. p < .01.
-p < .001.
Nipple Feeding
ing was complete is explained by the physical condition variables. The substantial contribution of the infant’s weight to the infant’s postconceptional age at initiation of nipple feeding suggests that weight may be an important guide to decision making about starting nipple feeding. Why the transition times between the introduction and completion of nipple feedings were so different among the infants requires an examination of variables that were not included in the study. Transition time may be influenced by environmental conditions. Little is known about the approaches nurses take to advance nipple feedings for infants with BPD and about the decision-making criteria they use. The work of Lund and Collier (1990) is an exception in its presentation of guidelines for this advancement. Perhaps nursing staff characteristics, including the nurse-infant ratio, the continuity of assignment of nurses to infants, and the beliefs that individual nurses have about advancing nipple feeding will help to explain the variation in transition time. Once an infant is physiologically stable, the consistency and continuity of the nursing staff may be particularly important in determining cues pertaining to the infant’s readiness to nipple feed and to the infant’s advancement to full nipple feeding. Prospective studies are needed to determine the extent to which nurses’ assessments relative to nipple-feeding practice concern such criteria as an infant’s robustness, experience with nonnutritive sucking, cues regarding readiness to nipple feed, vigor and interest in sucking, respiratory stability, and tolerance of the diet. Neither the physical condition variables nor postconceptional age when completely nipple fed contributed to the infant’s caloric intake. On the average, caloric intake was lower than the 120-130 kcal/kg per day recommended by Oh (1986) for the convalescent phase of BPD. Explanations for the wide range of kilocalories consumed per kilogram of body weight on the first day of complete nipple feeding must be sought. Perhaps caloric intake increases or stabilizes once infants have adapted to being completely nipple fed. Caloric intake after advancement to full nipple feeding should be examined over several days to determine the degree of fluctuation in intake. The caloric density of the feeding substance may also influence caloric intake (Fomon, 1974). Another factor that may explain variability in caloric intake is the caregiver’s behavior. Infants with BPD are generally fed prescribed amounts at scheduled times because of concern about their weight gain or management of fluid balance. Given these concerns, one might expect nurses to attempt to feed an infant the prescribed amount. Perhaps some infants were
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more difficult to feed than others. Or nurses may have varied skill in feeding infants. Some infants may have been given more opportunities for self-regulated feeding than others, depending on the infant and the feeding practices of specific nurses. Saunders et al. (1991) found that, on the average, schedule-fed preterm infants took a greater volume of formula than infants fed on demand. The behavior of both nurses and infants during feeding warrants assessment. Altered breathing patterns and interference with ventilation have been demonstrated during breastfeeding and bottle feeding of preterm infants (Guilleminault &Coons, 1984; Lund &Collier, 1990;Mathew, 1988; Meier, 1988). Bu’Lock et al. (1990) postulated that preterm infants may learn ineffective feeding patterns as a consequence of early breathing difficulties during feeding. The difference that the timing of introduction of the nipple and the timing of advancement to full nipple feeding makes to coordinated sucking, swallowing, and breathing; to the clarity of hunger and satiety cues; to uninterrupted sleep; and to caloric intake should be examined. The small amount of variance in the infant’s weight gain between complete nipple feeding and discharge from the hospital that was explained by the infant’s physical condition, feeding practice variables, and caloric intake indicates that variables other than those examined in this study account for weight gain. What cannot be concluded from the results is that delaying nipple feeding until an older postconceptional age is detrimental to infant weight gain. The high correlation of the infant’s postconceptional age when completely nipple fed with the postconceptional age upon introduction of nipple feeding suggests that a systematic factor is operating. Both the number of days the infant was on supplementary oxygen and the infant’s postconceptional age when completely nipple fed may be indices of the severity of the infant’s respiratory disease; hence the negative effect both variables had on weight gain. The negligible contribution of caloric intake to weight gain may be explained by the more potent effect of severity of respiratory illness. Other factors, as yet unexplained, may influence weight gain. Kurzner, Garg, and Bautista (1988) found
The negative effect on weight gain of both the days the infant was on supplementary oxygen and the postconceptional age when completely nipple fed may be the result of the severity of respiratory disease these two variables potentially represent.
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A more precise measure of respiratory dificulty during feeding is needed to determine its e#ects on nipple feeding practices.
that infants with BPD who were failing to thrive had a higher resting metabolic expenditure than infants who were gaining adequate weight. Another issue is the composition of the body mass deposited. Putet, Sinterri, Rego, and Salle (1987) report that, for neonates, the amount of fat deposited rises with the increasing amount of energy absorbed, without any evidence of more weight gain. Measures of energy expenditure, body composition, and the accretion of lean muscle mass with increasing caloric intake may help to explain the absence of any relationship between weight gain and caloric intake found in this study. The current study has several limitations, including the hospital record as the source of data. Whether or not infants were neurologically and physically ready to begin nipple feeding at or before the time they did in fact begin cannot be determined from the record. The specification of physical condition variables was hampered by the need to rely exclusively on the hospital record. The severity of the infants’ BPD was only roughly estimated by the number of days the infant was on supplementary oxygen. The fact that the severity of illness could not be classified precisely hampers the identification of the population of infants to which the study findings are applicable. A more precise measure of respiratory difficulty during feeding is needed to determine its effects on nipple-feeding practices and on patterns of sucking, swallowing, and breathing associated with initiation and completion of nipple feeding. The study also was limited by variability in hospitalization practices. For examining infants’ rate of weight gain, a defined period of at least 7 days after complete nipple feeding would be preferable to the period defined by the length of stay between complete nipple feeding and discharge from the hospital. In fact, because five of the infants remained hospitalized fewer than 7 days once they were completely nipple fed, it was impossible to use a standard, yet adequately lengthy period without losing subjects from the study. What is needed for the advancement of both research and nursing practice is a conceptual framework of variables involved in nipple-feeding practice and its outcomes. This framework or model should include more precise measures of the infant’s physical condi-
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tion, fuller descriptions of feeding practices (including infant cue-based approaches to feeding), and assessments of caretaker-infant interaction during feeding. In addition to caloric intake and weight gain, outcomes should include patterns of sucking, - swallowing, and breathing; clear hunger and satiety cues; patterns of sleep and awake states; the infant’s development of feeding skill; and effectiveness in the nurse-infant dyad. How nipple-feeding practice influences not only these outcomes, but also somatic growth and the development of the aforesaid feeding skills, requires refinement and better specification of feeding practice variables. Nurses can help to specify these variables by describing their practice when nipple feeding preterm infants with BPD. Study of the relationships among these variables could assist nurses in designing nipple-feeding plans with an increased likelihood of advancing the somatic growth and feeding skill of infants with BPD.
Acknowledgment This project was supported in part by Grant No. BRSG 2-SO7 PR05866-05, awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health; by the Wisconsin Perinatal Foundation; by University of Wisconsin-Madison Graduate School and School of Nursing research funds; and by NIH Grant No. M01 RR03186 from the National Center for Research Resources to the University of Wisconsin Medical School.
References Babson, S. G., & Benda, G. I. (1976). Growth graphs for the clinical assessment of infants of varying gestational age. Journal of Pediatrics, 89,814-820. Ballard, J. L., Novak, K., & Driver, M. (1979). A simplified score for assessment of fetal maturation of newly born infants. Journal of Pediatrics, 95(5,Pt. I ) , 769-774. Boynton, C. A., &Jones, B. (1988). Nursing care of the infant with bronchopulmonary dysplasia. In T. A. Merritt, W. H. Northway, Jr., & B. R. Boynton (Eds.), Contemporary issues in fetal and neonatal medicine (pp. 313-329). Boston: Blackwell Scientific Publications. Brosius, K. K., Ritter, D. A., & Kenny, J. D. (1984). Postnatal growth curve of the infant with extremely low birth weight who was fed enterally. Journal of Pediatrics, 74, 778-782.
Bu’Lock, F., Wooldridge, M. W., & Baum, J. D. (1990).Development of coordination of sucking, swallowing and breathing ultrasound study of term and preterm infants. Developmental Medicine and Child Neurology, 32,669678.
Carlson, S. E., & Barness, L. A. (1985). Macronutrient re-
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quirements for growth. In W. A. Walker & J. B. Watkins (Eds.), Nutrition in pediatrics: Basic science and clinical application (pp. 3-15). Boston: Little, Brown, & Co. Cohen, J., & Cohen, P. (1983). Applied multiple regression/ correlation analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum. Erikson, E. H. (1963). Childhood and society (pp. 72-80). New York: W. W. Norton. Farrell, P. M., & Palta, P. (1986). Bronchopulmonary dysplasia. In P. M. Farrell & L. M. Taussig (Eds.), Bronchopulm o n a y dysplasia a n d related chronic respiratory disorders (pp. 1-7). Columbus, OH: Ross Laboratories. Fomon, S. J. (1974). Infant nutrition (2nd ed.). Philadelphia: W.B. Saunders. Geertsma, M. A,, Hyams, J. S., Pelletier, J. M., & Reiter, S. (1985). Feeding resistance after parenteral hyperalimentation. American Journal of Diseases of Children, 139, 255-256. Gill, A., Yu, V. Y. H., Bajuk, B., &Astbury, J. (1986). Postnatal growth in infants born before 30 weeks’ gestation. Archives of Disease in Childhood, G1, 549-553. Guilleminault, C., & Coons, S. (1984). Apnea and bradycardia during feeding in infants weighing > 2,000 gm. Journal of Pediatrics, 104, 932-935. Hack, M., & Fanaroff, A. A. (1988). Growth patterns in the ICN graduate. In R. A. Ballard (Ed.), Pediatric care of the ICN graduate (pp. 33-39). Philadelphia: W. B. Saunders. Kurzner, S., Garg, M., & Bautista, D. B. (1988). Growth failure in infants with bronchopulmonary dysplasia: Nutrition and elevated resting metabolic expenditure. Pediatrics, 81, 379-384. Lefrak-Okikawa, L. (1990). Nutritional management of the very low birth weight infant. Journal of Perinatal and Neonatal Nursing, 2, 66-77. Lund, C. H., & Collier, S. B. (1990). Nutrition and bronchopulmonary dysplasia. In C. H. Houska Lund (Ed.), Bronchopulmona y dysplasia: Strategies for total patient care (pp. 98-101). Petaluma, CA: Neonatal Network. Mathew, 0. P. (1988). Respiratory control during nipple feeding in preterm infants. Pediatric Pulmonology, 5, 220-224. Meier, P. P. (1988). Bottle- and breast-feeding: Effects on transcutaneous oxygen pressure and temperature in preterm infants. Nursing Research, 37, 36-41. Oh, W . (1986). Nutritional management of infants with bronchopulmonary dysplasia. In P. M. Farrell & L. M. Taussig (Eds.), Bronchopulmonary dysplasia a n d related chronic respiratoy disorders (pp. 96-105). Columbus, OH: Ross Laboratories. Putet, G., Sinterri, J., Rego, J., & Salle, B. (1987). Energy
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balance and composition of body weight. Biology of the Neonate, 52 (Supplement l ) , 17-24. Ross Laboratories. (1990). Milk-based a n d soy-based infant formulas. Columbus, OH: Author. Saunders, R. B., Friedman, C. B., & Stramoski, P. R. (1991). Feeding preterm infants: Schedule or demand?Journal of Obstetric, Gynecologic, and Neonatal Nursing, 20, 212-218. Scherf, R. F., & Arndt, S. (1990). Complications in infants with bronchopulmonary dysplasia. In C. H. Houska Lund (Ed.), Bronchopulrnona y dysplasia: Strategies for total patient care (pp. 35-53). Petaluma, CA: Neonatal Network. Shaffer, S. G., Quimiro, C. L., Anderson, J. V., & Hall, R. T. (1987). Postnatal weight changes in low birth weight infants. Journal of Pediatrics, 79, 702-705. Shaker, C. S. (1990). Nipple feeding premature infants: A different perspective. Neonatal Network, 8(5), 9-17. Shivpuri, C. R., Martin, R. J., Carol, W. A., & Fanaroff, A. A. (1983). Decreased ventilation in preterm infants during oral feeding. Journal of Pediatrics, 103, 285-289. Vohr, B. R., & Garcia-Coll,C. T. (1988). Follow-up studies of high-risk, low-birth-weight infants. In H. E. Fitzgerald, B. M. Lester, & M. W. Yogman (Eds.), Theory and research in behavioralpediatrics (Vol. 4, pp. 1-65). New York: Plenum Press. Weaver, K. A., & Anderson, G. C. (1988). Relationship between integrated sucking pressures and first bottle-feeding scores in premature infants. Journal of Obstetric, Gynecologic, a n d Neonatal Nursing, 17, 113-120. Address for correspondence: Dr. Karen F. Pridham, RN, PhD, FAAN, University of Wisconsin-Madison, School of Nursing, Department of Family Medicine and Practice, 600 Highland Avenue, Madison, WI 53792.
Karen I? Pridham is a professor of nurstng and family medtctne and practice at the University of Wisconsin tn Madison. Sherie Sonde1 ts a nutrition education coordinator in the pediatric pulmonary center at the University of Wisconsin tn Madison. Audrey Chang is a statistictan at Walter Reed Army Medical Center in Washtngton, DC. Chrtstopher Green Is an associate professor of pediatrics at the University of Wtsconstn tn Madtson.
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