Achievement of adequate nutrition, as soon as possible after birth, is the ultimate goal for all low birth weight infants (<1250 g); however, the best methods by which sufficient enteral nutrition can be provided remain controversial. Continuous nasogastric gavage (CNG) was introduced in 1972¹ and became widely accepted because of the ease of administration, the potential for sustaining growth,² and the decreased time for steady weight gain.³ Advantages and disadvantages of different feeding methods have been proposed.^4,5 In a survey of neonatologists in 1985, intermittent bolus gavage (IBG) was the preferred method of feeding low birth weight infants.⁶ Prospective controlled studies comparing these two methods are limited in number and either do not focus on very low birth weight infants (<1250 g) or do not include similar isoenergetic feeding protocols.

This study was designed to test the hypothesis that infants who weigh between 700 and 1250 g and are fed by CNG would have improved feeding tolerance and, therefore, would reach full enteral feedings at an earlier postnatal age than those fed by IBG.

METHODS

Eligibility

Protocol

Parenteral nutrition, including lipid emulsion, was started on days 2 to 3 and continued until each infant tolerated full enteral feedings. All infants were fed undiluted 20 cal/oz Similac Special Care formula (Ross Laboratories, Columbus, OH). Feeding protocols were designed for each 50 to 100 g weight category as shown in Table 1. Patients were started on 12 to 16 mL/kg/d and the feedings were advanced by a maximum of 25 mL/kg/d. Feedings were advanced at a similar increment of mL/kg/d for both groups. The caloric and protein intake was identical in the two groups. Successful achievement of enteral feedings was defined as the ability to tolerate enteral feedings of 100 kcal/kg/d for at least 48 hours. Nipple feedings were initiated when infants reached a weight of 1500 g; feedings were then advanced by the neonatologist as tolerated by the infant.

Table 1. Feeding Protocol [View Table]

Arbitrary guidelines for excessive residual were developed based on consensus among the study staff and the attending neonatologists. Thus, excessive residual was defined in the CNG group as a GR volume >2.5 times the hourly volume of formula when the rate of infusion was <2 mL/h; >1.5 times when the rate was 2 to 3 mL/h; more than the hourly rate when the rate was 3 to 5 mL/h, or more than half when the rate was >5 mL/h. In the IBG group, the residual was defined as excessive when the amount of formula was more than half of the preceding feeding. Except in rare instances, GR was refed in either group.⁸

Feedings were discontinued for 3 hours if residual was excessive and there were no other clinical findings. Guidelines for withholding feedings for longer periods included two or more of the following: excessive GR, increase in abdominal girth measured at the umbilicus by 2 cm or more⁹ in 6 hours, guaiac positive stools, dilated loops of bowel, abnormal abdominal roentgenograms, possible sepsis, apnea, and bradycardia occurring more than 3 times per 8 hour shift (cessation of breathing for more than 20 seconds and heart rate <80 beats/min). Any infant whose feedings were withheld for more than 12 hours was considered to have an episode of feeding intolerance (FI). NEC was defined by modified Bell's criteria.¹⁰

Daily weight, intake and output, number of stools, number of guaiac positive stools, number of hours that feedings were withheld, episodes of apnea, and bradycardia were recorded. All stools were tested for blood and abdominal circumference was measured every 8 hours routinely and more often depending on clinical status.

Statistical Analysis

RESULTS

Demographic data of the 80 patients (39 CNG, 41 IBG) who completed the study are provided in Table 2. There were 40 patients who weighed 1000 g at birth and 40 who weighed between 1001 and 1250 g at birth. No significant differences were seen between the CNG and IBG groups at the onset of the study. Feedings were initiated in the CNG group at 5.7 ± 2.1 days and in the IBG at 5.6 ± 2.2 days.

Table 2. Demographic Characteristics [View Table]

Infants regained their birth weight (CNG, 12.6 ± 5 days vs IBG, 12.5 ± 3.7 days), reached successful feeding criteria of 100 kcal/kg/d (CNG, 17 ± 8.9 days vs IBG, 15.5 ± 5.5 days), and reached discharge weight of 2040 g (CNG, 60 ± 13.4 days vs IBG, 62 ± 13.6 days) at similar time periods regardless of the feeding methods. There were also no significant differences between CNG and IBG methods when the results were examined within each weight category (Table 3), although the smaller infants took longer than their larger counterparts to reach full enteral feeds (18.7 ± 5.9 vs 12.8 ± 4.6, P < .0001) and discharge weight (68 ± 9.8 vs 48.7 ± 6.6 P < .0001). In addition, there were no differences between the groups in the number of days spent on the ventilator (CNG, 8.9 ± 10.9 days vs IBG, 9.4 ± 9.8 days).

Table 3. Analysis of Outcome Based on Weight Groups [View Table]

FI was diagnosed in 28 patients, 14 in each group. In general, a larger proportion of infants whose feedings were discontinued because of excessive residual were in the CNG group, whereas apnea and bradycardia were more often seen in the IBG group. Of the 14 infants with FI in the CNG group, 4 had suspect NEC (Bell's stage 1) and 2 had Bell's stage 2 or greater; 1 of the 2 required surgery and the other was treated medically. In the IBG group, 1 patient had suspect NEC and 2 had Bell's Stage 2 or greater; 1 of the 2 required surgery and the other was treated medically.

Infants with FI were smaller at birth, and were on the ventilator longer when compared (Table 4) with those without FI. The presence of FI was not a factor in the time to regain birth weight as caloric intake was primarily supplied by parenteral nutrition. FI was associated with time to reach full enteral feedings as well as with time to reach discharge weight most likely because 20 of the 28 infants with FI weighed less than 1000 g at birth.

Table 4. Comparison of Infants With and Without Feeding Intolerance (FI) [View Table]

DISCUSSION

CNG methods have been recommended as a way of increasing energy efficiency because of improved absorptive capacity by the gut,^16,17 as a means of decreasing the amount of time required to reach full feedings^3,12 and as the best method for infants with intestinal disease.¹⁸ Others have suggested that IBG may be more beneficial because of lower risk of precipitation into the delivery system or because of ease of administration because it does not require as much equipment;^4,5 however, this may be compensated by the nursing time required to deliver a bolus feeding. IBG, on the other hand, has been associated with increasing gastroesophageal reflux, abdominal distention, apnea, and bradycardia attributable to increased vagal stimulation and aspiration because of poor gastric motility.^4,5,19 Increased cyclic surges of gut hormones are found in infants fed intermittently; however, higher peak levels of insulin, gastrin, and other gut hormones are maintained by continuous feedings.²⁰ The clinical significance of these findings in improving nutrition could not be established as weight gain was not different between intermittent and continuous groups.

In general, the literature suggests that birth weight is usually regained in an inverse relation to birth weight.²¹ In our study, birth weight was regained at similar times regardless of method of feeding or birth weight category, this was most likely attributable to the early and liberal use of parenteral nutrition (on day 2 or 3) when the infants were considered metabolically stable.^22,23

Our hypothesis that infants fed by CNG would achieve caloric feedings earlier than their IBG counterparts was based on our assumption that CNG infants would have less FI. Unlike the findings of Silvestre et al¹¹ the number of infants in our study who developed FI were the same regardless of method of feeding. Although the study sample was not based on the incidence of FI, the sample size was adequate to show some important differences between infants who developed FI and those who did not: infants with FI were more likely to weigh <1000 g and require ventilator support for longer periods of time than their non-FI counterparts. As a result, infants with FI reached full enteral feeds and discharge weights significantly later than those without FI.

Our study may have set higher arbitrary guidelines for excessive GR than used by others. Had these guidelines been lower, an even greater number of infants would have had feedings discontinued for more than 3 hours. On the other hand, none of the infants who had excessive residual without other signs or symptoms developed NEC or FI. Hence, excessive residual, per se, is not an indication for withholding feedings for prolonged periods.

In summary, the method of feeding is not associated with differences in outcome when similar energy intakes are provided and when guidelines for discontinuation of feedings are followed. The final choice of method of feeding remains that of clinical judgment based on the tolerance and the clinical condition of the infant.