Summary of Findings
Needle-related procedures (NRPs) are common medical procedures associated with pain and are used in testing, treatment and prevention. There are many occasions in which an NRP is necessary for both patients and healthy persons. Children in particular have a lower pain threshold than adults,1 and they experience unpredictable and severe pain in response to NRPs2,3 because their cognitive function is underdeveloped. Children's pain from NRPs can produce an emotional and cognitive negative impression toward NRP.4 Children's fear in response to painful NRPs activates the sympathetic nervous system and causes vasoconstriction, which reduces intravenous (IV) line success rates.5 When parents observe their children suffering from pain from NRPs, they and their children can become reluctant to undergo future NRPs.6,7 Parents and children may also delay treatment or avoid health care,8-12 exhibit poor compliance13 or develop needle phobia.9 Therefore, healthcare professionals are challenged to minimize children's pain during any type of NRP for any health condition.
The gate control theory is commonly used to explain pain perception and pain control.14 The theory proposes that when the pain stimulus occurs, an impulse is sent through A-delta nerve fibers via the spinal cord to open the “pain gate” and transmit the pain signal to the central nervous system, at which time the person perceives the stimulus as pain.15 In contrast, a distractive stimulus, such as rubbing the site of the NRP, activates A-beta fibers, which help close the pain gate, effectively reducing the transmission of the pain stimulus. One of the most effective ways to excite the A-beta fibers is vibratory stimulation.16
Vibratory stimulation is defined as the performance of continuous, quick, slight shaking movements on the skin using devices or fingers. Vibratory stimulation is noninvasive, simple, safe and highly effective, and has the added advantage of being inexpensive to implement and maintain.17 Based on the gate control theory, several clinical studies have been conducted to reduce pain during NRPs through the use of various vibration devices with pediatric patients18 or healthy children.19 Vibraject, a tubular vibration device (14 × 43 mm, ITL Dental LLC, San Francisco, USA), was developed to reduce pain during local anesthesia in dental practice and was released in 2000.20 The device attaches directly to the syringe used to administer local anesthesia in the periodontal area, and causes the syringe to vibrate. In 2009, BUZZY (MMJ Labs LLC, Atlanta, USA), a reusable 80 × 50 × 25 mm plastic bee containing a battery and a vibrating motor, was developed to alleviate pain from NRPs specifically in children.21 With its attached ice pack, the device can deliver vibration and cooling stimulation simultaneously. Several other vibration devices were developed to reduce needle-related procedural pain, including DentalVibe (BING Innovations, Boca Raton, USA),22 Vibration Anesthesia Device (Blaine Labs, Santa Fe Springs, USA)23 and Norco Mini Vibrator (North Coast Medical Inc., Gilroy, USA),24 to name a few.25,26 We conducted a preliminary search of the Cochrane Database of Systematic Reviews, MEDLINE and CINAHL; however, no systematic reviews or protocols that evaluated the effect of vibratory stimulation on pain from NRPs were found.
The purpose of this systematic review was to examine the effectiveness of vibratory stimulation for reducing pain in children during NRPs. This review was guided by an a priori published protocol.27
Is vibratory stimulation effective in reducing needle-related procedural pain in children aged 18 years and younger in comparison with no stimulation?
This review considered studies that included child participants with any condition who were undergoing an NRP. Needle-related procedures included puncture (finger, vein, artery, lumbar or bone marrow examination), injection (vascular, muscular, subcutaneous and intradermal) and IV catheter insertion.28 There were no exclusion criteria. The search was limited to pain from NRPs, which were among the most commonly occurring and feared procedures for both healthy and chronically ill children.3 We included studies with participants ranging from 0 to 18 years of age. This age limit was set to ensure that our search includes only children, as defined by the United Nations.29
This review considered studies of interventions that used a vibratory stimulation during NRPs. We included any vibration devices that were used to reduce pain from NRPs. Vibration devices that use an additional component to reduce pain, such as the cooling stimulation used in BUZZY, were also included.
This review considered studies that compared the intervention to a control group without vibratory stimulation during NRPs.
This review considered studies in which the outcome was pain measured using any pain scale. Although self-reporting was the gold standard for assessment of pain,12,30-32 limited verbal development or any health condition could render small children unable to make an accurate verbal report of their pain.32 A review commissioned by the Pediatric Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (Ped-IMMPACT) examined measures to assess pediatric pain and found that both self-rated and observer-rated pain scales were validated, and were used widely to assess pediatric pain.33 We included observer-rated pain scales such as the Face, Legs, Activity, Cry and Consolability (FLACC) Scale34 or the Children's Hospital Eastern Ontario Pain (CHEOP) Scale,35 which are commonly used assessments of children's pain based on behavioral changes.36 Self-rated pain scales included the visual analog scale and the Wong-Baker FACES pain rating scale,37 which were used when the participants were able to report by themselves.32 We included studies that used observer-rated pain scales, even if the children were old enough and had the capacity to self-report pain.
Secondary outcomes were the children's anxiety and heart rates. We assessed anxiety using validated scales such as the Children's Fear Scale (CFS)38 and the Children's Anxiety and Pain Scale (CAPS).39 Heart rate was included as an objective assessment of anxiety. In cases where the study targeted venipuncture as the NRP, data on the duration of the procedure and success rate of the first procedure were also collected as secondary outcomes. The duration of the procedure was defined as the time from placement of tourniquet to success of venipuncture. Success was defined as achievement of blood return. For consideration of confounders, we collected data on the type of medical service (e.g. pediatric emergency, dental procedure or immunization) and location of NRP (e.g. dorsum of the hand, intraoral, deltoid muscle). If a vibratory stimulation was used for reducing pain for venipuncture, data on time of NRP (first or multiple) were also collected.
Types of studies
This review considered all randomized controlled trials (RCTs) and quasi-randomized trials for inclusion. A quasi-randomized trial is defined as a study in which the method of allocation is known but is not considered strictly random.40
This systematic review was conducted in accordance with the Joanna Briggs Institute (JBI) methodology for systematic reviews of effectiveness.41 This review was conducted in accordance with an a priori protocol.27
The three-step search strategy for this review aimed to identify published and unpublished studies in English or Japanese. An initial limited search of MEDLINE and CINAHL was undertaken to establish appropriate search terms. Analysis of the words in the titles and abstracts of the initial papers, and of the index terms used to describe the studies, was performed. A second search using all identified keywords and index terms was then undertaken across all included databases. Finally, the reference lists of all identified reports and studies were searched for additional studies. Our search was not limited by release dates of devices, or by publication dates of studies, because the dates when some vibration devices became available were unknown. The initial search was conducted by two reviewers independently.
The databases searched included MEDLINE, CINAHL, Embase, Cochrane Central Register of Controlled Trials and Igaku Chuo Zasshi. The search for unpublished studies included ClinicalTrials.gov, EU Clinical Trials Register, UMIN Clinical Trials Registry and OpenGrey. The following initial keywords were used: pain, vibration, children and NRP.
Following the search, all identified citations were loaded into Microsoft Excel 2016 (Redmond, Washington, USA) and duplicates removed. Titles and abstracts were screened by two independent reviewers for assessment against the inclusion criteria for the review. The full text of potentially eligible studies was retrieved and assessed in detail against the inclusion criteria by two independent reviewers. The details of studies that met the inclusion criteria were imported into JBI's System for the Unified Management, Assessment and Review of Information (JBI SUMARI, Joanna Briggs Institute, Adelaide, Australia). Full-text studies that did not meet the inclusion criteria were excluded. Any disagreements that arose between the reviewers were resolved through discussion or with a third reviewer.
Assessment of methodological quality
Titles, abstracts and full texts (if necessary) were reviewed independently by the primary and secondary reviewers to determine whether the studies met inclusion criteria. Thereafter, papers selected for retrieval were assessed by two independent reviewers for methodological validity prior to inclusion in the review, using JBI's standardized critical appraisal instruments for RCTs (Table 1).41 Any disagreements that arose between the reviewers were resolved through discussion or with the help of a third reviewer. The results of the critical appraisal of studies are presented in a tabular format. To be included, studies must have met one of two criteria: question 1 (true randomization was used for assigning participants to treatment groups) or question 3 (treatment groups were comparable at baseline). Authors of papers were contacted to request missing or additional data where required. The two exclusion criteria were as follows: both Q1 and Q3 of methodological quality were unclear or inadequate, and ≥ 7 of 13 items were unclear or inadequate.
Data were extracted from papers that were included in the review using a standardized data extraction tool from RevMan V5 (Copenhagen: The Nordic Cochrane Centre, Cochrane). The extracted data included specific details regarding the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. To minimize data extraction errors, a pre-determined and standardized data extraction form was used. We piloted the data extraction form with all review team members prior to use, and two independent reviewers extracted the data. Authors of primary studies were contacted for missing information or for clarification of information.
Quantitative data were pooled in statistical meta-analysis using RevMan V5. All of the results were subject to double data entry. Effect sizes were expressed as odds ratios for categorical data and as standardized mean differences (SMDs) for continuous data when different instruments were used to measure the outcomes, and their 95% confidence intervals (95% CI) were calculated for analysis. Heterogeneity was assessed statistically using the standard chi-square test and I2 value, which indicate the percentage of variation across studies caused by heterogeneity. Because both clinical and methodological heterogeneity were observed in the retrieved studies, we applied a random-effects model.42 Where statistical pooling was not possible, the findings were presented in narrative form, including tables and figures to aid in data presentation where appropriate.
Sensitivity analyses were performed to confirm the robustness of the meta-analysis results. We excluded studies that did not achieve randomization or that exhibited inadequate randomization (“N” or “U” at Q1 in Table 1). Furthermore, we considered the exclusion of studies that received industry funding. We inspected the funnel plot to examine the possibility of publication bias. Visual inspection of a funnel plot provided an indication of publication bias when larger and smaller studies were asymmetrical.43 The presence of publication bias was further tested using Egger's test for asymmetry.44 R statistics, version 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria) was used to draw the funnel plot and perform Egger's test.
We considered a stratified analysis of potential confounders, such as age group, type of service, times of NRP (first or multiple) and location of NRP. There were some devices that provided vibration and an additional intervention, such as the BUZZY device (vibration and cooling stimulation). Therefore, we conducted a stratified analysis by type of vibration device. As previously described in the outcomes section, we also considered a stratified analysis of observer-rated vs. self-rated pain scales.
A subgroup analysis was also conducted to assess the differences in treatment of the control group. First, we selected the studies in which the difference in the treatment interventions in both groups was only vibratory stimulation (Q7). For example, studies using only topical anesthesia for the control group were excluded. A subgroup analysis was then conducted to assess the differences in the outcomes between studies that did not use a vibratory device in the control group (no-device group) and studies in which the vibratory device was placed without being turned on in the comparison group (switched-off group).
Assessing certainty in the findings
We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach45 to assess the confidence in the quality of evidence, which was evaluated across the domains of risk of bias, inconsistency, indirectness and imprecision. The results of this assessment are shown in a Summary of Findings created using GRADEpro (McMaster University, ON, Canada).
The literature search was carried out in recognized and relevant databases using specified search terms and with the supervision of a research librarian. The results of the search process are provided in Figure 1.46 The details of the search strategy among nine databases are presented in Appendix I. In total, 1436 records were identified by the search strategy. After reading the titles or abstracts, 802 records were excluded because they were unrelated to the review question. In 130 papers retrieved to assess eligibility, we found 56 duplications that were indexed in multiple databases. The reasons for excluding 50 records after reading of their full texts are listed in Appendix II. Twenty-four studies fulfilled our inclusion criteria. We performed a MEDLINE search to determine the presence of selection bias induced by limiting the language to only English and Japanese, and this search produced 302 publications. These titles and abstracts were screened, and the papers written in non-English languages did not pertain to the effect of vibratory stimulation. The language classification was as follows: English, n = 269; Japanese, n = 19; Chinese, n = 5; German, n = 4; French, n = 3; Polish, n = 1; and Italian, n = 1. Sufficient RCTs were identified; therefore, we did not consider other study designs such as experimental pre–post interventional studies and observational studies.
In total, 24 relevant articles were identified for inclusion in this review. Of these, three publications47-49 were conference proceedings. We contacted the corresponding authors of the proceedings to obtain the detailed methodologies and results, but we did not receive a response. After the methodological quality assessment, 21 studies qualified for inclusion in this review. The characteristics of these studies, which were published from 2008 to 2017, are shown in Appendix III. These studies were conducted in the USA, Turkey, India, Italy, Iran and Syria, and a total of 1727 participants were involved. All studies were RCTs, crossover RCTs or quasi-randomized trials. In the crossover RCTs, the participants underwent NRPs twice (with vibration and without vibration), and pain outcomes were measured each time.
Three studies described the results using the median and interquartile range, and one study reported the results using only the mean. For two of these studies, we obtained the mean and standard deviation (SD) of the outcomes after contacting the authors. However, we received no response from the authors of the two remaining studies. Therefore, we have narratively described these two studies.18,25
The first and second authors independently assessed the methodological quality of all 24 studies. The results of the critical appraisal are shown in Table 1. The first and second authors determined that 21 of all studies met the criteria of methodological quality and were appropriate for analysis. Regarding randomization, all 24 studies used randomization. However, the randomization strategy was unclear in eight studies. We determined that the randomization in one study23 was inadequate because it was based on the parents’ selection of either a yellow or red paper despite blinding the parents to the color assigned to the intervention group. For the remaining 15 studies, the methodologies for randomization were computer-based randomization,18,19,22,50-54 a random number table,21,24,25,55,56 and flipping a coin.26,57 Concealment was achieved by sequentially numbered opaque envelopes.18,21,58-60
We discussed the methodological quality of blinding the participants (Q4), treatment deliverers (Q5) and assessors (Q6). Blinding of the participants was mentioned in two studies,26,61 and blinding of the deliverers of NRPs was mentioned in only one study.61 However, these two studies reported the use of blinding without mentioning the methodology of blinding. In contrast, observer-rated outcome assessor blinding was performed in four studies: three by video recording55,56,61 and one by an assessor who was unaware of the treatment assignment.26 In one study, assessor blinding was achieved by the assessor turning away at the moment that the vibrator was turned on.58 We concluded that assessor blinding was not achieved because the assessor might have recognized the intervention by the sound of the vibration. All articles measured the outcomes in a reliable way and used appropriate trial design. We excluded three studies47-49 because the total number of “yes” answers was less than seven. Finally, we reviewed 21 studies.
Characteristics of included studies
The participants’ ages ranged from 15 days to 18 years. The mean age and age range for each study are shown in Figure 2. All studies were clinical trials at clinics or hospitals. All but three studies18,57,58 excluded participants with critical or chronic illness. Schreiber et al.18 recruited participants with cognitive impairment and no verbal communication as the inclusion criteria. In the study by Baba et al.,58 65% of newborn participants had respiratory distress. In the study by Moadad et al.,57 75% of participants had a cardiac diagnosis or cancer.
The procedure types were intraoral local anesthetic injection, venipuncture, intramuscular injection and heel lancing. Local anesthetic injections were conducted intraorally for dental treatment in nine studies.22,25,26,52,54-56,61,62 Venipuncture for blood specimen collection or IV cannulation was conducted on the dorsum of the hand in eight studies.18,21,23,50,51,57,59,60 Of those, three studies18,21,23 did not specify the location of venipuncture. Intramuscular vaccine injections were conducted in two studies.19,53 The locations of the intramuscular injections were the deltoid muscle in one study19 and not specified in the other.53 Heel lancing for blood sampling was conducted in two studies24,58 that recruited newborn infants aged < 1 year.
The devices used for vibratory stimulation were the BUZZY,18,19,21,50,51,53,57,59,60 DentalVibe,22,52,54,56,61,62 Norco Mini Vibrator,24 Vibration Anesthesia Device,23 Hitachi Magic Wand with Wonder Wand (Vibratex Inc., Vallejo, CA),58 and Vibraject.55 In the studies by Aminabadi et al.25 and Bagherian and Sheikhfathollahi,26 vibratory stimulation was provided by vibration of the investigator's finger (finger vibration). For usual care, six studies22,25,26,52,55,59 used topical anesthesia in both groups. Although the instruction manual for each of the above-mentioned devices did not specify the site of attachment, the BUZZY was used mainly for venipuncture and intramuscular injection, and the DentalVibe was used for intraoral local analgesia injection.
The comparators used in the studies were the nonuse of vibratory devices,18,19,23,24,25,50,51,53,57-59 placement of the devices without turning them on,22,26,52,54-56 topical anesthesia,60-62 and vapocoolant.21
The pain outcome measurements used were self-rated and/or observer-rated pain scales. Self-rated pain scales were evaluated by the participants. Observer-rated pain scales were evaluated by nurses, the participants’ parents or researchers. Thirteen studies measured self-rated pain outcomes using the Wong-Baker FACES Pain Rating Scale,19,22,51,52,54,56,57,59,60,62 a visual analog scale,51,55 or the Faces Pain Scale-Revised Scale.21,50 Eighteen studies measured observer-rated outcomes using the Wong-Baker FACES Pain Rating Scale19,57; the FLACC Pain Score23,52,53,54,56,60,61; the Noncommunicating Children's Pain Checklist Postoperative Version Scale18; the Faces Pain Scale-Revised Scale21,50; the Sound, Eye and Motor Scale25; the Neonatal Pain, Agitation, and Sedation Scale24; the Face, Head, Foot, Hand, Trunk, and Cry Scale26; the Neonatal Infant Pain Scale58; the CHEOP Scale59; or Child Pain Behavior.55
For secondary outcomes, four studies measured child anxiety using the Children Fear Scale,19,51 the Child Rating of Anxiety Scale,60 or the Children's Anxiety and Pain Scale.50 Only one study measured the child's heart rate as an objective measurement of anxiety.24
Among the studies that conducted venipuncture as the NRP, data on the duration of the procedure were collected in two studies,21,60 and the success rate of the first procedure was collected in four studies.18,21,50,60
Conflict of interest and source of funding
Conflicts of interest were disclosed in the study by Baxter et al.21 The first author developed and manufactured the BUZZY device. This author was not present for data collection. The second author, who had no financial conflict of interest, performed the data analysis for the study. The following four studies were funded by industry: Baxter et al.,21 McGinnis et al.,24 Bagherian and Sheikhfathollahi26 and Roeber et al.55 Sensitivity analysis excluding these studies shows that funding status had little impact on the study outcome.
The data were pooled in a meta-analysis to obtain an exact estimate of the effect of vibratory stimulation in reducing pain from NRPs in children. To control for potential confounders, we stratified the pain measurements by self-rated and observer-rated measurements.
Figure 3A shows a forest plot of 13 self-rated pain outcomes. The vibratory stimulation was significantly effective in reducing self-rated pain (SMD: –0.55, 95% CI: –0.92 to –0.18). Canbulat et al.51 used two pain measurement scales (Wong-Baker FACES Pain Rating Scale and visual analog scale). We chose the Wong-Baker FACES Pain Rating Scale because it was the most commonly used scale for child pain evaluation. The I2 value of heterogeneity was 92%.
Sixteen studies used observer-rated pain measurement scales (Figure 3B). The results of the meta-analysis regarding observer-rated pain measurement also showed a significant effect for reducing pain (SMD: –0.47, 95% CI: –0.76 to –0.18). Moadad et al.,57 Canbulat et al.19 and Inal and Kelleci50 used two types of pain observers. We chose one of the two based on the priority list of parents, nurses and researchers. Those who were more familiar with the child's usual pain status were given the priority. The I2 value was 88%.
Two studies lacking mean and standard deviation
Two studies18,25 did not report the mean and standard deviation of the pain score, although these studies conducted an appropriate statistical analysis. Therefore, we described the results of these two studies narratively.
Our finding supported the previous studies showing the effectiveness of vibratory stimulation.18,25 Schreiber et al.18 reported that the median of the observer-rated pain scores was significantly lower in the experimental group than in the control group (3.0 and 8.0, respectively; P = 0.03). Aminabadi et al.25 reported only the mean score of observer-rated pain, and the difference was significant (5.07 and 8.25, respectively; P < 0.05). The results of the following analysis excluded of these two studies.
We performed sensitivity analyses to confirm whether the main results would change if we excluded the six studies23,58-62 that did not achieve randomization or that had inadequate randomization (Q1 in Table 1 was “N” or “U”). We analyzed the self-rated outcome in 10 studies, and the result was similar to the main result (SMD: –0.55; 95% CI: –0.99 to –0.12; P = 0.01; I2 = 93%). In an analysis of 11 studies, the observer-rated outcome was also similar (SMD: –0.57; 95% CI: –0.96 to –0.18; P < 0.01; I2 = 91%). Next, we excluded an additional four studies21,24,26,55 that had received industry funding and then re-analyzed the data. The results were similar to the main results. The self-rated outcome was measured in eight studies (SMD: –0.66; 95% CI: –1.17 to –0.16; P = 0.01; I2 = 93%), and the observer-rated outcome was measured in seven studies (SMD: –0.58; 95% CI: –1.15 to –0.02; P = 0.04; I2 = 94%).
Assessment of publication bias
Figure 4 shows two funnel plots used to assess publication bias. Using Egger's test, we found that the risk of publication bias was significant in the studies that measured the outcome of self-rated pain (z = –2.183, P = 0.029) and was not significant in the studies that measured the outcome of observer-rated pain (z = –1.332, P = 0.183).
We conducted the following five-factor stratified analysis to identify potential confounders: i) age, ii) type of NRP, iii) type of vibration device, iv) topical anesthesia group and v) observer-rated outcome assessor blinding group. We did not conduct a stratified analysis of the number of times an NRP was performed because all studies obtained the children's pain outcomes at the first NRP. The location of the NRP was not specified in four studies18,21,23,53 previously described in participants’ characteristics. Therefore, we analyzed the type of NRP (venipuncture, intramuscular injection, heel lancing or intraoral local anesthesia injection). The type of service was consistent with the type of NRP. We did not plan to stratify whether topical anesthesia was used. However, some studies used topical anesthesia as usual care, and we decided to conduct the stratified analysis with or without the use of topical anesthesia. Blinding would bias pain assessment. Therefore, assessor blinding in the observer-rated outcomes was also added to the stratified analysis. The results of the stratified analyses are shown in Table 2. Most of the SMDs measured by the observer-rated outcomes were lower than those measured by the self-rated outcomes. Moreover, most of the I2 values in the meta-analysis measured by the observer-rated outcomes were lower than those measured by the self-rated outcomes.
The stratified analysis is shown in Table 2. We stratified age into the following four age groups: i) infant (< 1 year),23,24,53,58 ii) preschooler (1–5 years),26,53 iii) grade schooler (6–12 years),19,26,50-57,61,62 and iv) adolescent (13–18 years). Vibratory stimulation was significantly effective for preschoolers as indicated by measurement of the observer-rated pain outcome (SMD: –0.52; 95% CI: –0.93 to –0.11; I2: 0%) and for grade schoolers as indicated by measurement of both the self- and observer-rated pain outcomes (SMD: –0.74; 95% CI: –1.29 to –0.19; I2: 94% and SMD: –0.69; 95% CI: –1.26 to –0.12; I2: 93%, respectively). The effect of vibratory stimulation in infants as measured by the observer-rated pain outcome was not significant (SMD: –0.40; 95% CI: –0.91 to 0.11; I2: 62%). Participants in the infant and preschooler groups were assessed only by observer-rated pain scales. A self-rated and/or observer-rated pain scale was used in the grade schooler group. No study reported the results of the adolescent group.
Type of NRP
We stratified the studies by the four types of NRP (venipuncture, intramuscular injection, heel lancing and intraoral local anesthesia injection). For the self-rated pain outcome, a significant effect of vibratory stimulation was observed in venipuncture. For the observer-rated pain outcome, a significant effect of vibratory stimulation was found in heel lancing and intraoral local anesthetic injection.
Of the four types of NRP, venipuncture was conducted in seven studies. Of these seven studies, five measured both self-rated pain and observer-rated pain.21,50,57,59,60 One study measured only self-rated pain,51 and one study measured only observer-rated pain.23 Vibratory stimulation for venipuncture was significantly effective for reducing the self-rated pain outcome (SMD: –0.73; 95% CI: –1.35 to –0.11; I2: 93%), although the observer-rated pain outcome was not significant (SMD: –0.52; 95% CI: –1.12 to 0.08; I2: 92%). The BUZZY21,50,51,57,59,60 and Vibration Anesthesia Device23 were employed in these seven studies. Two studies19,53 focused on intramuscular injection and measured pain using an observer-rated pain scale. Vibratory stimulation was not significantly effective in reducing pain (SMD: –0.78; 95% CI: –2.45 to 0.89). A self-rated pain scale was used only in the study by Canbulat et al.,19 which reported that the vibratory stimulation was significantly effective (mean difference: –2.04; 95% CI: –3.03 to –1.05). Both studies used the BUZZY.
Two studies examined the effect of NRP by heel lancing24,58 in infants aged < 1 year. These studies measured pain only by observer-rated measurements, and the effect of the intervention was significant (SMD: –0.89; 95% CI: –1.37 to –0.42; I2: 0%). The vibration devices used were the Norco Mini Vibrator24 and the Hitachi Magic Wand with Wonder Wand.58
Local anesthetic injection was examined in eight studies.22,26,52,54-56,61,62 Self-rated pain measurements were used in six studies,22,52,54-56,62 and observer-rated pain measurements were used in six studies. 26,52,54-56,61 Observer-rated pain measurements were significantly effective (SMD: –0.21; 95% CI: –0.43 to –0.02; I2: 57%), but self-rated pain measurements were not (SMD: –0.33; 95% CI: –0.82 to 0.15; I2: 90%). The devices used for vibratory stimulation were the DentalVibe,22,52,54,56,61,62 finger vibration,26 and the Vibraject.55
Type of vibration device
The BUZZY and DentalVibe were used in multiple studies. The BUZZY was used in seven studies that utilized self-rated outcomes19,21,50,51,57,59,60 and in six studies that utilized observer-rated outcomes,19,21,50,57,59,60 and it significantly reduced the pain outcomes according to both measurements (SMD: –0.74; 95% CI: –1.26 to –0.21; I2: 92% for the self-rated pain outcome; SMD: –0.78; 95% CI: –1.47 to –0.10; I2: 94% for the observer-rated pain outcome). We excluded one study by Benjamin et al.53 because the authors did not use ice packs, while all other studies used ice packs.
The DentalVibe is used for local anesthetic injection in dentistry and was used in six studies of the present meta-analysis.22,52,54,56,61,62 Self-rated pain measurements were employed in five studies,22,52,54,56,62 and observer-rated pain measurements were used in four studies.52,54,56,61 The DentalVibe was not significantly effective for either measurement (SMD: –0.47, 95% CI: –1.02 to 0.09, I2: 91% for the self-rated pain outcome, SMD: –0.14, 95% CI: –0.36 to 0.09, I2: 45% for the observer-rated pain outcome).
Topical anesthesia only as a comparator
Topical anesthesia was used before NRP in both the intervention and control groups in five studies.22,26,52,54,59 Self-rated pain measurements were obtained in four studies,22,52,54,59 and observer-rated pain measurements were obtained in four studies.26,52,54,59 When using topical anesthesia in both the intervention and control groups, vibratory stimulation was not significantly effective for either measurement (SMD: –0.22; 95% CI: –0.68 to 0.25; I2: 83% for the self-rated pain outcome; SMD: –0.17; 95% CI: –0.47 to 0.14; I2: 69% for the observer-rated pain outcome).
Observer-rated outcome assessor blinding group
Assessor blinding for measurement of observer-rated outcomes was employed in four studies.26,55,56,61 The results of the observer-rated outcomes was significant (SMD: –0.34; 95% CI: –0.61 to –0.06). The I2 value was relatively low (47%).
We chose 15 studies in which the treatment groups were treated identically other than the intervention of vibratory stimulation (Q7 in Table 1). Of the 15 studies, we conducted a subgroup analysis to test the differences in the outcomes between studies that did not use a vibratory device in the control group (no-device group) and studies in which the vibratory device was placed without being turned on in the comparison group (switched-off group).
A no-device group was allocated in nine studies,19,23,24,50,51,53,57-59 and a switched-off group was allocated in six studies.22,26,52,54-56 The results of the subgroup analysis are shown in Figure 5. In the no-device group, vibratory stimulation was significantly effective for both the self- and observer-rated outcomes (SMD: –0.94; 95% CI: –1.54 to –0.35 for the self-rated outcome, and SMD: –0.72; 95% CI: –1.31 to –0.14 for the observer-rated outcome). However, the results from the switched-off group were not significant for either outcome (SMD: –0.07; 95% CI: –0.43 to 0.28 for self-rated outcome; SMD: –0.16; 95% CI: –0.40 to 0.07 for observer-rated outcome). The procedure in the studies using a switched-off device was local anesthesia injection. The test for subgroup differences showed significance for the self-rated outcome (P = 0.01) but not the observer-rated outcome (P = 0.08).
Because of the high heterogeneity in the subgroup analysis, we conducted a stratified analysis in each subgroup. Table 3 shows the results in the no-device group and switched-off group. In the nine studies without a vibratory device comparison group, the following five subgroups showed a significant difference: “grade schooler” for both the self- and observer-rated pain outcomes (P < 0.01 for both groups), “venipuncture” for the self-rated pain outcome (P = 0.01), “intramuscular injection” for the self-rated pain outcome (P < 0.01), “BUZZY” for both the self- and observer-rated pain outcomes (P < 0.01 and P = 0.03, respectively), and “no use of topical anesthesia” for both the self- and observer-rated pain outcomes (P < 0.01 and P = 0.01, respectively). Each absolute value of SMD was relatively high (range of SMD: –1.77 to –0.033). However, most I2 values were very high. In contrast, in six studies that used a vibratory device comparison group, no subgroup showed a significant difference, and the absolute value of SMD was relatively low (range of SMD: –0.30 to 0.14). Further, I2 tended to be lower than that of the subgroup analysis in which a vibratory device comparison group was not used.
We collected data regarding the child's anxiety, the duration of the procedure and the success rate as secondary outcomes. The results of these meta-analyses of secondary outcomes are described below.
Four studies19,50,51,60 collected data on the child's anxiety. Anxiety was measured using three observational assessment scales: the Children Fear Scale, Children's Anxiety and Pain Scale, and Child Rating of Anxiety Scale. The results of the meta-analysis are shown in Figure 6. The SMD of anxiety was significantly lower in the group with vibratory stimulation than without vibratory stimulation (SMD: –1.03, 95% CI: –1.85 to –0.20), and I2 was very high (96%). Only one study24 collected data on heart rate to assess anxiety. This study involved heel lancing in newborn infants. The mean heart rate in the experimental group increased slightly from baseline (mean = 8.67; SD = 11.40), and the mean heart rate in the control group increased considerably from baseline (mean = 21.11; SD = 11.37). The difference was significant (SMD: –1.08; 95% CI: –1.64 to –0.51).
Duration of the procedure
Venipuncture was conducted as the NRP in eight studies.18,21,23,50,51,57,59,60 Of these, two studies21,60 collected data regarding the duration of the procedure. However, these two studies differed in terms of how they measured the duration. Baxter et al.21 compared vibratory stimulation with no stimulation and measured the time required for the first venous access attempt. The difference in time between groups was not significant (SMD: –0.20; 95% CI: –0.64 to 0.24). Potts et al.60 compared vibratory stimulation with topical anesthesia using lidocaine cream and measured the duration of time from coating the lidocaine cream to successful venous access. In the control group using lidocaine cream, this duration was ≥ 30 minutes. This time duration included the duration of the procedure. In contrast, this duration was relatively short in the experimental group using vibratory stimulation (15–45 seconds). As a result, the duration of the procedure between groups differed significantly (SMD: –2.76; 95% CI: –3.13 to –2.39). Therefore, we decided that these two studies differed from each other in the measurement method and that meta-analysis was inappropriate.
Success rate of first venipuncture
Four studies18,21,50,60 collected data on the success rate of the first venipuncture. In total, 233 of 263 children in the vibratory stimulation group underwent successful first venipuncture. In contrast, 224 of 260 children who underwent NRPs without stimulation achieved successful first venipuncture. The difference in the success rates between the two groups was not significant (odds ratio: 1.23; 95% CI: 0.62 to 2.45; I2: 35%). This result is shown in Figure 7. All four studies used the BUZZY as the intervention.
Refusal rate and participants’ response to vibration devices
Dropouts after allocation were reported in two studies. Schreiber et al.18 reported that one participant did not receive the intervention (BUZZY) but did not report the child's background or the reason for dropout. Raslan and Masri61 reported that 17.5% of participants (ages 6–12 years) refused placement of the DentalVibe. The participants’ response to vibratory stimulation was reported in three studies.52,54,56 All of the studies used the DentalVibe. The mean age of the participants in these studies was within the same generation (8.32,52 7.31,54 and 8.20 years,56 respectively). Negative responses to the vibratory stimulation were reported in two studies; 63.3% of participants answered that use of the DentalVibe was more painful than without its use,52 and 67.0% of participants preferred not to use the DentalBibe.58 In contrast, Ching et al.22 conducted a crossover RCT and reported that the pain score for not using the DentalVibe was highly correlated with the pain score for using the DentalVibe (correlation coefficient = 0.79; P < 0.01). This means that the higher the self-rated pain score without use of the DentalVibe, the higher the self-rated pain score with use of the DentalVibe.
Adverse outcomes of using vibration devices
One study reported adverse outcomes of failed venipuncture while using the BUZZY, possibly due to vibration in two cases and arm stiffness due to icing in one case.18 However, the difference in the number of adverse events did not reach statistical significance.
The meta-analysis of this systematic review showed that vibratory stimulation was significantly effective according to both self-rated and observer-rated pain measurements regardless of age group, type of NPR or type of vibration device. Nevertheless, the presence of clinical, methodological and statistical heterogeneity makes it difficult to evaluate the effectiveness of vibration devices on pain during NPRs.
Quality of the included studies
A placebo effect was observed when the control group was treated equally other than the type of vibratory stimulation by using DentalVibe or Vibraject. Because of the nature of this intervention, blinding of the participants and treatment deliverers was impossible to achieve. Assessor blinding was therefore the most important factor for the quality of each study. In the stratified analysis, the I2 value tended to be lower for the observer-rated outcome group with than without assessor blinding. Four studies in a dentistry setting achieved assessor blinding.26,55,56,61 In particular, the assessment method that utilizes a silent videotape, which was performed in three studies, minimizes the risk of information bias.
Various scales are available to assess children's pain. The Wong-Baker FACES Pain Rating Scale was used to assess only the expression of the face, which is widely used for expression at all ages from childhood to adulthood. In the present systematic review, this scale was used in most of the self-rated pain outcome measurements. In contrast, the FLACC scale was used in most of the observer-rated pain outcome measurements. The FLACC scale utilizes not only the child's expression but also his or her crying voice, and it is not suited for evaluating pain through silent videotape. Assessor blinding can be achieved when using functional magnetic resonance imaging, which can display the network of neural activation in specific brain regions and detect the recognition of pain.1 However, use of this equipment is not simple or easy, and it is not practical for a clinical trial. The development of a pain measurement tool that can measure pain in children with assessor blinding is needed. The type of comparator is also important to improve study quality. A previous study on NPRs showed that applying pressure by the thumb at the injection site before the injection is performed can effectively reduce injection pain.63 This indicates that the reduced pain in our meta-analysis might have included the effect of pressure by applying the device. In our subgroup analysis, the comparator was placement of the vibratory device without turning it on. Therefore, future studies need to use comparators that exert pressure on NRP sites.
Effectiveness of each device
The most well-tested vibratory stimulation devices in this meta-analysis were the BUZZY18,19,21,50,51,53,57,59,60 and the DentalVibe.22,52,54,56,61,62 In the stratified analysis of device type, the effect size for the BUZZY tended to be higher than that for the other devices. The BUZZY was used by attaching an ice pad. Cooling stimulation might have contributed to the reduction in pain.64,65,66 Therefore, the effect of the BUZZY on the reduction in NRP pain might include the effect of the ice pad. For the DentalVibe,22,52,54,56,61,62 the effect size was relatively small. The participants’ responses to the vibration devices tended to be negative, and personal preference may have affected the outcomes. However, only three studies reported the participants’ responses. When recruiting grade schoolers for participation, their responses to vibratory stimulation should be collected. Further detailed analysis is needed.
The differences in the effectiveness among devices may reflect the study quality. All studies using the BUZZY used the lack of the device as the comparator. In contrast, all studies using the DentalVibe used placement of the device without turning it on as the comparator. In future studies of the efficacy of vibration devices, the control group should be treated by placement of the same device without turning it on to rule out the effect of pressure being applied.
The other vibratory stimulation devices used in the present review were the Norco Mini Vibrator,24 Vibration Anesthesia Device,23 Hitachi Magic Wand with Wonder Wand,58 Vibraject55 and finger vibration.25,26 Of these, the Norco Mini Vibrator and finger vibration were significantly effective in reducing pain; the other devices were not effective. Thus, the difference in the effects of various devices might be due to the strength of vibration or area of vibration. The area of vibratory stimulation by the BUZZY was wide; in contrast, the areas covered by the DentalVibe, Vibration Anesthesia Device, and Vibraject were relatively small. Moreover, the Hitachi Magic Wand with Wonder Wand was usually used to relieve tension and relax sore muscles. Therefore, this stimulation might be too strong for NRPs in children. It is necessary to determine the optimal stimulation strength and stimulation area for children. Various vibratory stimulation devices for adults are available. Randomized controlled trials have been conducted to examine the effect of the Vibration Anesthesia Device on facial injection pain67 and the effect of the Vibraject on local anesthesia injection pain68 in adult participants. These two studies reported that the device was significantly effective in reducing NRP pain. However, the sample sizes of these studies were small, and further studies are needed. The following vibratory stimulation devices for adult participants have been tested: battery-powered shaver (Windmere Corp., Miami, USA),69 HoMedics Atom massager (HoMedics Australia Pty Ltd., Clayton, Australia),70 Pin Point Personal Massager (Brookstone, Inc., Merrimack, USA),71,72 and AcuVibe SoftTouch (Human Touch, Long Beach, USA).73 Feasibility studies are needed to test the efficacy of these devices in children.
Effectiveness for secondary outcomes
Vibratory stimulation was significantly effective in reducing children's anxiety. In children, anxiety is closely linked with pain. One review74 on managing pain in pediatric patients showed that the higher the child's pain-related psychological responses such as fear and anxiety, the higher the pain level. Especially for children with chronic disease who require routine injections, anxiety associated with NRPs may reduce treatment adherence.75 Therefore, reducing anxiety associated with NRPs in children by vibratory stimulation can contribute to improving their perception of further pain from NRPs. The heart rate as an objective measurement of anxiety was reported in one study that examined the effectiveness of vibratory stimulation in infants undergoing heel lancing.24 The performance of treatments or tests that increase the heart rate, such as heel lancing, would increase the burden on the cardiovascular system in infants with heart disease. Prevention of increased heart rates could lead to safer and easier performance of treatments and tests.
The duration of venipuncture was examined in two studies for which a meta-analysis was not possible.21,60 The duration of venipuncture using vibratory stimulation was not significantly different when compared with non-vibratory stimulation.21 However, it was impossible to blind the provider of the NRP to the vibratory stimulation, resulting in a high probability of performance bias. Therefore, we could not determine in this review whether the vibratory stimulation effectively shortened the duration of venipuncture. The success rate was not significant in our review. Moreover, the device used to determine the success rate in all studies was the BUZZY.
We checked for potential bias associated with the language limitation. We used major worldwide databases and confirmed that all relevant papers were written in English and met the inclusion criteria. Therefore, we determined that limitation of publications to the English and Japanese languages did not result in severe bias in our findings. However, we did not use local databases except for one Japanese database (Igaku Chuo Zassi). We were unable to find any papers written in a language other than English that were only available in local databases. The main concern regarding restriction of research findings to the English language was that papers with positive results tend to be published in English-language journals and that papers with negative results tend to be published in non-English-language journals.76 The language limitation might have affected the result of publication bias, which was significant for studies measuring self-rated outcomes.
Participation bias was a limitation in this meta-analysis. All except three studies18,57,58 excluded participants with critical or chronic illness. In the clinical setting, children with chronic diseases such as diabetes, hemophilia, or cancer undergo repeated NRPs for treatment or testing and might have different thresholds of fear or pain from NRPs than healthy children. Different populations of patients who undergo NRPs should be considered for participation in further studies.
Statistical heterogeneity was high in most of the stratified meta-analyses. There may be some other factors that affect children's pain during NRPs, such as fear of treatment, which was not measured in the reviewed studies. The subgroup analysis of self-rated pain showed a significant group difference, and the outcome in the control group with the device switched off was comparable with that in the treatment group. This suggests a placebo effect. In future studies, the control group should be treated equally as opposed to receiving the usual treatment.
The difference in the type of usual care may have contributed to the high heterogeneity. Usual care administered by medical staff when conducting NRPs is also important. Four essential components for reducing and eliminating NRP pain have been reported: numbing with topical anesthesia, administering sucrose for children 0 to 12 months of age, positioning for comfort, and distraction.77 We conducted a stratified analysis of topical anesthesia as a confounder. However, the other components were not able to be controlled because the data were not available. In particular, distraction showed strong evidence of effective pain relief in a systematic review.28 Some distraction methods have recently been standardized for clinical use. Therefore, the studies included in the present review might have performed distractions as a part of usual care. In such cases, the child's pain might have been adequately reduced, leading to a non-significant difference in pain between the intervention and control groups.
The evidence from this systematic review demonstrates a benefit in the use of vibratory stimulation for reducing NRP pain. In particular, vibratory stimulations are more effective for venipuncture and intramuscular injection than for other NRPs, such as local anesthesia injection. With respect to the type of device, the BUZZY shows higher efficacy than the DentalVibe and topical anesthesia. In addition, vibratory stimulation reduces anxiety. Vibratory stimulations do not impact on the success rate of venipuncture. The results regarding the duration of the procedure and success rate have a probability of severe performance bias. None of the retrieved studies used blinding because of the nature of the intervention. Moreover, statistical heterogeneity was high. Therefore, the confidence of evidence is low. To improve the quality of future studies, assessor blinding is necessary, and the control group must be treated equally by placement of the vibratory device without turning it on.
Recommendations for practice
Vibratory stimulation devices may be useful for reducing NRP pain in children. Vibratory stimulation may also be useful to reduce anxiety and shorten the duration of venipuncture. However, high heterogeneity was observed in this meta-analysis, and few studies achieved assessment blinding. Therefore, the validity of the findings is low. In one study, a relatively large number of participants who were assigned to the intervention group refused the vibratory stimulation, although the reasons for refusal were not reported. Therefore, acceptance of the device by children remains an area of further study. The Grade of Recommendation for review findings was Grade B. We suggest that healthcare providers ask children about their feelings regarding vibratory stimulation and determine the reason why they refuse vibratory stimulation.
Recommendations for research
The low confidence of evidence was due to the nature of the intervention rather than low quality of the study design. Assessor blinding could be achieved by using a silent videotape. However, this assessment method excludes the use of pain scales that assess the child's cry. Development of a pain scale with which to objectively assess the symptoms of pain in children is needed. Such a development would contribute to higher confidence of evidence in future.
We would like to extend our appreciation to Mr. Toshiyuki Swa for his expert advice on the database search.
This work was supported by 2018–2020 Grant-in-Aid for Early-Career Scientists from the Japan Society for the Promotion of Science (Assignment no. 18K17594), Tokyo, Japan.
Appendix I: Search strategy
Search date: October 10, 2017
Search date: October 10, 2017
Search date: October 10, 2017
Search date: October 10, 2017
Igaku Chuo Zassi
Search date: October 22, 2017
Search date: October 22, 2017
EU Clinical Trials Register
Search date: October 22, 2017
UMIN Clinical Trials Registry
Search date: October 22, 2017
Search date: 22 October, 2017
Appendix II: Studies excluded on full text
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