We reviewed the evidence available from clinical studies to find out about exposing infants born early (preterm) to the smell and taste of milk with feedings given by a tube which goes through the nose or mouth into the stomach. We compared this with not exposing preterm infants to the smell and taste of milk during tube feeds, to see which approach would decrease the time required to achieve full sucking feeds, without causing side effects.
Preterm infants often need to be fed via a thin tube inserted through the mouth or nose into the stomach (orogastric or nasogastric) until they are able to suck all of their feeds. Initially, only small volumes of milk are given, and this is gradually increased depending on how well feeds are tolerated. Infants who are fed by tube may not experience the smell and taste of milk because the milk is placed directly into the stomach. Smell and taste have a significant role in assisting with digestion and absorption of food. Therefore, providing some milk for the infant to smell and to taste when milk is given via an orogastric or nasogastric tube could potentially help them tolerate greater volumes of milk more quickly.
In a search up to 1 June 2018, we identified three completed studies involving 161 preterm infants admitted to a neonatal intensive care unit (NICU) at a tertiary hospital. One study involved 51 preterm infants, and each infant had an equal chance of being chosen to receive either treatment (a randomised controlled trial). One study involved 80 preterm infants who were sequentially assigned to control and treatment groups (a quasi-randomised trial). One study was a prospective randomised trial involving 30 infants, but the way it was reported meant there was not enough information for us to include in our analyses.
We found that exposure to the smell and taste of milk with orogastric or nasogastric tube feedings had no clear effect on the time to reach full sucking feeds. One study reported no adverse effects. Exposure to the smell and taste of milk also had no clear effect on time to reach full tube feeding, feed tolerance, incidence of late infection and severe intestinal infection, duration of intravenous nutrition, and growth. Very low-quality evidence from two studies suggested that exposure to the smell and taste of milk decreased the length of hospital stay by almost four days compared to no exposure to the smell and taste of milk. However, the included studies were small and had several limitations in terms of how they were done.
Exposure to the smell and taste of milk with orogastric or nasogastric tube feedings may decrease length of hospitalisation for preterm infants. However, the effect of this treatment to accelerate feeding in preterm infants is uncertain due to limited and very low-quality evidence. Future research needs to explore the effect of exposure to the smell and taste of milk with tube feedings on important clinical outcomes, such as time to full sucking feeds, adverse effects, time to reach full tube feedings, feed tolerance, incidence of infection, and growth.
Evidence from two trials suggests that exposure to the smell and taste of milk with tube feedings has no clear effect on time taken to reach full sucking feeds, but it may decrease length of hospitalisation. However, these results are uncertain due to the very low quality of the evidence. There is also limited evidence about the impact on other important clinical outcomes and on safety. Future research should examine the effect of exposure to the smell and taste of milk with tube feedings on clinical outcomes during hospitalisation, such as attainment of full enteral and sucking feeds, safety, feed tolerance, incidence of infection, and infant growth. Additionally, future research should be sufficiently powered to evaluate the effect of the intervention in infants of different gestational ages, on each sex separately, and on the optimal frequency and duration of exposure.
Preterm infants are often unable to co-ordinate sucking, swallowing and breathing for oral feeding because of their immaturity; in such cases, initial nutrition is provided by orogastric or nasogastric tube feeding. Feed intolerance is common and can delay attainment of full enteral feeds and sucking feeds, which prolongs the need for intravenous nutrition and hospital stay. Smell and taste play an important role in the activation of physiological pre-absorptive processes that contribute to food digestion and absorption. However, during tube feedings, milk bypasses the nasal and oral cavities, which limits exposure to the smell and taste of milk. Provision of the smell and taste of milk with tube feedings is non-invasive and inexpensive; and if it does accelerate the transition to enteral feeds, and then to sucking feeds, it would be of considerable potential benefit to infants, their families, and the healthcare system.
To assess whether exposure to the smell or taste (or both) of milk administered with tube feedings can accelerate progress to full sucking feeds without adverse effects in preterm infants.
We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL 2018, Issue 5), MEDLINE via PubMed (1966 to 1 June 2018), Embase (1980 to 1 June 2018), and CINAHL (1982 to 1 June 2018). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised and quasi-randomised trials.
We included randomised and quasi-randomised studies that compared the provision of the smell or taste of milk (or both) immediately before or at the time of tube feedings, with no provision of smell or taste.
Two review authors independently abstracted data according to Cochrane Neonatal methodology; they also assessed risk of bias, and the quality of evidence at the outcome level using the GRADE approach. We performed meta-analyses using risk ratio (RR) for dichotomous data and mean difference (MD) for continuous data, with their respective 95% confidence intervals (CIs).
Three trials involving a total of 161 preterm infants were included in this review, but only two trials (131 infants) contributed data for meta-analysis. There was no evidence of a clear effect of exposure to the smell and taste of milk with tube feedings on time taken to reach full sucking feeds (MD -2.57 days, 95% CI -5.15 to 0.02; I2 = 17%; 2 trials, 131 infants; very low-quality evidence). One trial reported no adverse effects. There was no evidence of a clear effect of exposure to the smell and taste of milk on the following outcomes: time taken to reach full enteral feeds (MD -1.57 days, 95% CI -6.25 to 3.11; 1 trial, 51 infants; very low-quality evidence), duration of parenteral nutrition (MD -2.20 days, 95% CI -9.49 to 5.09; 1 trial, 51 infants; very low-quality evidence), incidence of necrotising enterocolitis (RR 0.62, 95% CI 0.15 to 2.48; 1 trial, 51 infants; low-quality evidence), and late infection (RR 2.46, 95% CI 0.27 to 22.13; 1 trial, 51 infants; low-quality evidence). There was very low-quality evidence demonstrating that exposure to the smell and taste of milk decreased duration of hospitalisation by almost four days (MD -3.89 days, 95% CI -7.03 to -0.75; I2 = 51%; 2 trials, 131 infants). In two trials, an increased growth velocity was noted in infants exposed to the intervention, but we were unable to combine data to perform meta-analysis. No data were available to assess feed intolerance and rates of exclusive breastfeeding at discharge. Included trials were small and had methodological limitations including lack of randomisation (one trial), lack of blinding, and different inclusion criteria and administration of the interventions.