Comparison of Breastmilk Odor and Vanilla Odor on Mitigating Premature Infants' Response to Pain During and After Venipuncture

Abstract

Objective:

The main purpose of this study was to investigate the calming effects of breastmilk odor and vanilla odor on preterm infants during and after venipuncture.

Subjects and Methods:

One hundred thirty-five preterm infants were randomly selected and divided into three groups: control, vanilla odor, and breastmilk odor. Infants in the breastmilk group were exposed to breastmilk odor, and infants in the vanilla group were exposed to vanilla odor from 5 minutes before the start of sampling until 30 seconds after sampling. The Premature Infant Pain Profile was used for calculating quality of pain in infants during and after sampling.

Results:

Statistical analyses showed that both vanilla and breastmilk odors had calming effects on premature infants during sampling, but just breastmilk odor had calming effects on infants after the end of sampling. Compared with vanilla odor, breastmilk odor has more calming effects on premature infants.

Conclusions:

Breastmilk odor can be used for calming premature infants during and after venipuncture.

Introduction

Previously, the general belief was that premature infants could not understand pain, but nowadays it is proven that premature infants can feel pain during painful procedures. Recent studies have shown that infants can feel pain after 26 weeks of gestational age.¹ Premature infants are exposed frequently to painful procedures during the first few days of their life in neonatal care intensive units (NICUs), so proposing methods that calm newborn infants is necessary.

There are some studies that have focused on methods of calming newborn infants during painful procedures. Infant calming methods can be divided into two main groups: pharmaceutical and nonpharmaceutical methods. Because of the lack of biological harm, nonpharmacological methods are discussed by researchers frequently. Nonpharmacological methods generally use the ability of human senses for pain reduction. Different methods based on infants' sense of taste,² smell,³ hearing,⁴ touch,⁵ and sight were used in the literature frequently. Previously published studies showed that the sense of smell is more mature at birth than the other senses. Newborn infants can detect their mother's nipple odor and get breastmilk within the first days of their life.⁶ Effects of breastmilk odor^3,6 and vanilla odor^1,7,8 on calming the infants were discussed previously. The cited studies are different in infants' gestational age, sampling methods, and pain measurement scales. There are numerous studies that have discussed effects of the odor used on term infants, but the number of studies about preterm infants is negligible. Some researchers believe that premature infants cannot recognize maternal breastmilk odor because they are not fed by mother's milk, but nowadays mother's milk is used for feeding premature infants in NICUs in many countries.

One of the main studies about the calming effects of different odors on preterm infants was done by Goubet et al.,¹ who studied the effect of familiar and nonfamiliar vanilla odor on response to pain in preterm infants during venipuncture and heel stick. Sample size was small, and each group had eight or nine infants. Crying time and grimacing quality were used for investigation of odor calming effects. Results showed infants who were exposed to a familiar vanilla odor had no significant increase in crying and grimacing during venipuncture. Infants in the nonfamiliar odor group and the control group showed a significant increase in crying time during venipuncture. Another important study is that of Badiee et al.^3,9 They focused on the effect of breastmilk odor and formula milk odor on preterm infants' responses to pain during and after heel lancing. They used the Premature Infant Pain Profile (PIPP) scale for pain score measurement. Results showed that after the heel lancing, the PIPP score was significantly lower in the breastmilk group than in the formula milk group.

Previous studies show that breastmilk odor and familiar vanilla odor affect responses to pain in premature infants, but there are some differences among studies. Infants' gestational age and other characteristics and the pain measurement tool are the main differences. Moreover, in all of the published studies just one of breastmilk odor or vanilla odor has been discussed, and there is no comparison between them. Another deficiency of published research is the lack of a standard pain measurement scale.

The main purpose of this study is to investigate the effectiveness of both breastmilk odor and familiar vanilla odor on premature infants' responses to pain during and after venipuncture using a standard pain measurement tool.

Materials and Methods

The current study was done at the NICU of Al-Zahra Hospital, affiliated with Tabriz University of Medical Sciences, Tabriz, Iran. The study was confirmed by the Ethics Committee of Tabriz University of Medical Sciences, and consent of the parents was obtained. Sample size was determined using the Pocock sample size formula. Level of statistical significance is considered as 0.05 and represents when the desired power is considered as 0.2. Blood oxygen saturation is considered as the main outcome of the study, and the difference between the estimated proportion of study outcome in the exposed group and the unexposed group is considered as 1. As a result of calculations, a sample size of 135 infants was required. The sample population was divided into three groups with 45 infants each. Infants who participated in the current study were premature infants with gestational ages of 28–34 weeks and postnatal ages of 3–28 days. They were breastfed and had no congenital or systemic abnormalities. They had experienced venipuncture before and had physiological stability. Their Apgar scores were higher than 7 at 5 minutes after birth. Lack of intraventricular hemorrhage, lack of periventricular leukomalacia, no need for surgery, and receiving no analgesic were other requirements. Lack of any above-mentioned terms excluded the infant from the sample.

Infants who were eligible for inclusion in the study were assigned randomly into three groups using Rand List software. Each group had 45 members, and the infants were not fed 30 minutes before venipuncture, and their weights were measured before sampling.

Infants in the breastmilk group and the vanilla group were exposed to breastmilk odor (their own mother's milk) and the familiar vanilla odor, respectively, 5 minutes before the start of sampling to 30 seconds after the end of sampling. Infants of the vanilla group were familiarized with vanilla odor by a 10-g clean cotton ball dipped in 10 drops of vanilla solution. The vanilla solution had 0.64% vanilla (by mass), and for its preparation, vanilla was mixed with glycerin using a hot plate stirrer (model MR 3001 K; Heidolph Group, Schwabach, Germany) at 300 rpm. The vanilla and glycerin was obtained from Merck KGaA (Darmstadt, Germany). Cotton balls were placed in the incubators 10 cm from the infant's nose 12 hours before sampling. Sampling was conducted from 7:30 a.m. to 8:30 a.m. Previous research showed that the time of painful procedures may affect the intensity of pain,¹⁰ so the sampling time was similar for all infants. During the procedure all infants were kept at 37°C.

Heart rate, blood oxygen saturation, and infants' facial actions were recorded 30 seconds before the start of sampling until 30 seconds after its end. Two cameras (Olympus, Center Valley, PA) were used for recording sampling procedure. Two observers watched the recorded videos, measured the infants' grimacing time during sampling period, and expressed the results as percentages of measured times to sampling duration time. After the end of venipuncture, grimacing durations were measured for 30 seconds, and results were reported as percentage of measured times to 30 seconds. Observers did not know to what odor the infants were exposed.

The PIPP score was used as the pain measurement tool before, during, and after venipuncture. PIPP is a scale for pain score measurement including seven indicators. Three of the indicators are facial actions (duration of eye squeeze, brow bulge, and deepening of the nasolabial furrow), two of them are for changes in heart rate and blood oxygen saturation, one of them is for gestational age, and one is for behavioral state before painful stimulus. There are different pain assessment tools for premature infants^11–13 that use different indicators for pain measurement. PIPP score is one of the complete pain measurement scores and uses different behavioral, physiologic, and contextual factors for premature infants' pain measurement. Every variable is scored on a scale from 0 to 3, and the total pain score is the sum of the variables score and can be a number between 0 and 21. A score between 0 and 6 indicates lack of pain, between 7 and 12 shows mild moderate pain, and between 13 and 21 indicates severe pain. This scale has been described and used in several studies previously.^9,14,15

Sampling was continued until the number of infants for every group reached 45, and as was mentioned above, for each infant group, identifying is done applying Rand List software. Statistical analyses were performed on the data obtained using SPSS (Chicago, IL) software, and p<0.05 was considered statistically significant.

Results

Table 1 shows the demographic characteristics of infants in the three groups. It can be seen that there are no significant differences among the three groups in demographic characteristics. Analysis of variance is used to determine whether there are any significant differences between the demographic characteristics or not.

Table 1.

Demographic Characteristics of Infants in the Breastmilk Odor, Vanilla Odor, and Control Groups

	Gender
Group	Girl	Boy	Gestational age (weeks)	Age (days)	Birth weight (g)	Weight (g) on sampling day
Breast milk odor	18 (40%)	27 (60%)	31.64±2.1	10.03±7.08	1,566.9±414.89	1,575.6±322.93
Vanilla odor	30 (66.7%)	15 (33.3%)	30.93±2	11.38±7.06	1,505.3±409.12	1,587.8±365.84
Control	25 (55.4%)	20 (44.6%)	31.46±1.96	10.60±7.89	1,569.8±405.93	1,578.4±354.63
p	0.16		0.22	0.89	0.17	0.175

Another important factor that might affect the results of study is the infants' behavioral state before sampling. Each state is organized into a pattern that differs from the other states. Table 2 shows the distribution of behavioral states for infants of different groups. The chi-squared test shows that there is no significant difference between behavioral states of infants in the different groups (p=0.36).

Table 2.

Behavioral States of Infants in the Breastmilk Odor, Vanilla Odor, and Control Groups

Group	Awake–active	Awake–quiet	Sleep–active	Sleep–quiet
Breastmilk odor	12 (26.7%)	3 (6.7%)	16 (35.6%)	14 (31.1%)
Vanilla odor	13 (28.9%)	6 (13.3%)	11 (24.4%)	15 (33.3%)
Control	13 (28.9%)	10 (22.2%)	13 (28.9%)	9 (20%)
p	0.36

Sampling duration is another parameter that can affect the study results. Analyses of variance showed that there was no significant difference between sampling duration among the three groups (p=0.847).

PIPP score is indicated in Table 3. There was no significant difference among infants' PIPP score in all groups before the start of sampling (p=0.44). Infants' PIPP scores in the different groups were significantly different from each other during sampling (p=0.01). During sampling, PIPP score for infants of the breastmilk odor group was lower than PIPP scores of the other groups of infants. Statistical analyses between results of the breastmilk odor group and the control group showed that there was a significant difference between PIPP scores of these two groups during sampling (p=0.01). Comparison between PIPP scores of the vanilla group and the control group during sampling showed that vanilla odor has reduced the response to pain significantly (p=0.031). More statistical analyses show that there was a significant difference between infants' PIPP score in the breastmilk group and the vanilla group (p=0.037). This means that breastmilk odor has more calming effects than vanilla odor on premature infants during venipuncture. The p values that are reported in Table 3 are the minimums of p values obtained from comparison between the PIPP score of each group with PIPP scores of the other groups.

Table 3.

Infants' Premature Infant Pain Profile Score Before, During, and After Sampling

Group	Before sampling	During sampling	After sampling
Breastmilk odor	4.71±1.17	7.31±2.52	6.08±2.87
Vanilla odor	4.56±1.19	9.21±2.78	8.13±2.93
Control	4.28±1.61	10.61±2.60	8.84±2.81
p	0.44	0.01	0.021

Table 3 shows that infants' PIPP scores after sampling were significantly different among the three groups. These data show that after the end of sampling, breastmilk odor has made infants calmer. Statistical analyses show that there were significant differences between infants' PIPP scores of the breastmilk odor group and the vanilla odor group (p=0.043) and the breastmilk odor group and the control group (p=0.021). This result indicates that breastmilk odor has calming effects on premature infants after the end of the sampling more than vanilla odor. Statistical analyses show that by comparison with the control group, vanilla odor has no significant effect on premature infants' responses to pain after the end of sampling (p=0.28).

Repeated-measures analyses of variance found that the PIPP score during sampling was significantly more than that before the start of sampling (p<0.01) for all groups. Therefore, using familiar odors has not caused distress elimination in premature infants during sampling.

Discussion

The results of the current study show that smelling breastmilk odor and vanilla odor could not eliminate the effects of a painful procedure on premature infants completely but could decrease them. Similar results were reported previously.^6,9

The most important finding of this article is that breastmilk odor can decrease infants' responses to pain during venipuncture. This result is in good agreement with published results. Nishitani et al.⁶ showed that smelling the breastmilk odor reduces the pain felt during heel prick. They studied term infants and had used salivary cortisol as an index of biochemical responses to pain. Similar results were reported by Rattaz et al.⁸ Results of their research showed that duration of crying, head movements, and facial changes in infants who were exposed to smell breastmilk odor were significantly lower than those of other infants. Badiee et al.⁹ studied the effect of breastmilk odor on response to pain in premature infants. As mentioned above, they used PIPP to score pain measurement. PIPP reduction due to breastmilk odor smelling was the main result of their study.

Another finding of the current study is that vanilla odor has a significant effect on premature infants' responses to pain during venipuncture. Goubet et al.¹ reported similar results. Although in their study the method of vanilla familiarization was different from that in the current study, the results were similar to each other.

The results of the current study show that breastmilk odor had a significant calming effect on premature infants and resulted in a lower PIPP score after the end of sampling. Badiee et al.³ showed that smelling the breastmilk odor decreased the PIPP score after heel lancing. Similar results were reported by Nishitani et al.⁶ Unlike breastmilk odor, vanilla odor has not significantly affected infants' PIPP score after the end of sampling. Goubet et al.¹ showed that vanilla odor decreased durations of both crying and facial actions after the end of sampling. Premature infants' mean gestational age in the study of Goubet et al.¹ was 32.3 weeks, but in current study it was between 28 and 32 weeks. When the infants have a greater gestational age, their responses to pain are more evolved, and they show more responses to pain. In addition to gestational age, using different scales for pain measurement can cause different results.

The results show that both vanilla and breastmilk odors affect the premature infants' responses to pain during and after venipuncture and can be used as a nonpharmaceutical sedative in NICUs. Breastmilk odor has more calming effects than vanilla odor on premature infants and leads to a lower PIPP score during and after venipuncture.

Conclusions

The purpose of this study was to investigate the effectiveness of breastmilk odor and familiar vanilla odor on premature infants' responses to pain during and after venipuncture. One hundred thirty-five infants participated in this study, and their pain scores were calculated 30 seconds before the start of sampling, during sampling, and 30 seconds after the end of sampling. The findings showed that breastmilk odor affects the premature infants' responses to pain during and after venipuncture and has calming effects on premature infants during a painful procedure. Vanilla odor has calming effects just during sampling, and it is less effective after the end of sampling. Compared with vanilla odor, breastmilk odor has more calming effects on premature infants during and after a painful procedure. The current study indicates that having infants exposed to breastmilk odor can decrease the effects of a painful procedure and that breastmilk odor can be a good alternative in the management of premature infants' responses to pain, and it can be easily used by nurses in NICUs during and after venipuncture.

Footnotes

Acknowledgments

The authors thank all staff and nurses of Al-Zahra Hospital, affiliated with Tabriz University of Medical Sciences, for their assistance for this project.

Disclosure Statement

No competing financial interests exist.

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