Predictors of Topical Anesthetic Effectiveness in Children

The Journal of Pain, Vol 8, No 2 (February), 2007: pp 168-174 Available online at www.sciencedirect.com

Predictors of Topical Anesthetic Effectiveness in Children Charmaine Kleiber,* Debra L. Schutte,* Ann Marie McCarthy,* Milena Floria-Santos,* Jeffrey C. Murray,† and Kirsten Hanrahan* *College of Nursing and †College of Medicine, University of Iowa, Iowa City, Iowa.

Abstract: Some children report significant pain with peripheral intravenous catheter (IV) insertion, despite the appropriate use of topical lidocaine anesthetics. This analysis of data from an existing study identified factors related to variation in topical anesthetic effectiveness used for IV insertion. The children (n ⴝ 218) in this investigation were 4 to 10 years old and undergoing a scheduled IV insertion. Inclusion criteria were (1) topical anesthetic was used according to manufacturer’s recommendations, (2) DNA material was available, and (3) child completed a self-report measure of pain intensity (Oucher scale). Low pain phenotype was defined as a pain intensity score of 0 to 3, and high pain phenotype was an intensity score of 4 to 10. Potential predictor variables included child age, gender, number of previous painful procedures, state and trait anxiety, temperament characteristics, and alleles in 3 candidate genes in a pain pathway influenced by topical anesthetics (endothelin-1 [EDN1], endothelin receptor A [EDNRA], endothelin receptor B [EDNRB]). All subjects were genotyped for a single-nucleotide polymorphism in each gene. Children in the high pain group (n ⴝ 89) were significantly younger (P < .0001), more active (P ⴝ .0029), scored higher for trait (P ⴝ .0009) and state anxiety (P ⴝ .0312), and had the EDNRA TT genotype (high pain group, TT 67.35%; low pain group, TT 39.47%; P ⴝ .026). Perspective: The identification of factors that influence peripheral pain sensation aids in selecting the most appropriate pharmacologic and nonpharmacologic interventions. Until genotyping is available at a clinically prescriptive level, other predictors (eg, age and activity level) can be used to tailor pain-relieving strategies for children undergoing needle sticks. © 2007 by the American Pain Society Key words: Child, anesthetic, lidocaine, anxiety, genetics, pain.

C

hildren consistently report that needle stick procedures are frightening and painful. The application of lidocaine topical anesthetics, such as EMLA (AstraZeneca, Wilmington, DE) and LMX4 (previously labeled ELA-Max; Ferndale Laboratories, Inc, Ferndale, MI), has been shown to significantly reduce the pain of needle sticks.11,29 However, topical lidocaine anesthetics are more successful for some children than for others. Several groups9,20,24,31 have reported variability in children’s pain sensation after the application of topical lidocaine anesthetics. Ranges of pain scores after treatment with EMLA or LMX4 have been reported as 0 to 70 Received February 1, 2006; Revised July 30, 2006; Accepted August 2, 2006. Supported by the National Institute of Nursing Research (NR05269-01A2). LMX4 was donated by Ferndale Laboratories. Address reprint requests to Charmaine Kleiber, RN, PhD, FAAN, Associate Professor, College of Nursing, NB 364, University of Iowa, Iowa City, IA 52242. E-mail: [email protected] 1526-5900/$32.00 © 2007 by the American Pain Society doi:10.1016/j.jpain.2006.08.002

168

on a 0 to 100 point scale20 and 0 to 9.4 on a 0 to 10 point scale.9 These ranges for pain scores reveal that some children experienced significant pain despite pretreatment with topical anesthetics. Little is known about the factors contributing to variability in the effectiveness of topical anesthetics. Lander et al22 and Kleiber et al20 reported an association between children’s state anxiety and pain with peripheral intravenous catheter (IV) insertion after pretreatment with EMLA. Other researchers have described variables associated with children’s pain and distress with needle sticks but not specifically when the needle stick site was pretreated with topical lidocaine. Children who are younger8,16,21 and who have more difficult temperaments5,7,23 are likely to report more pain and display more distress behavior during needle sticks. Genetic variations also might influence pain sensation.17,26 Genes involved in peripheral nociception at the site of topical anesthetic action are particularly good candidates for influencing the effectiveness of topical anesthetics. For example, endothelin 1 (ET-1)

ORIGINAL REPORT/Kleiber et al codes for a potent vasoconstrictive peptide that induces pain through a direct effect on sodium channel polarization in sensory neurons.15,36 The pain signaling action of endothelin is mediated through 2 receptors, endothelin receptor A (EDNRA) and endothelin receptor B (EDNRB).18,27,36 The relationship of common variations within these and other candidate genes has not been explored in the context of pain sensation in children after venipuncture. The purpose of this study was to describe the variability of topical anesthetic effectiveness and identify predictors of children’s self-reported pain during an IV insertion after pretreatment with topical lidocaine anesthetic (EMLA or LMX4). The potential predictors were child age, gender, history of previous painful procedures, anxiety, temperament, and variations within candidate genes for pain sensation.

Materials and Methods Participants Data for this analysis were drawn from a larger study,25 approved by the Institutional Review Board, that investigated parent distraction coaching during IV insertion. Participants in the larger study were children from 4 to 10 years old who were scheduled to have an IV inserted for diagnostic or treatment purposes. Their biologic parents gave informed consent, provided cheek swabs for DNA genetic analysis, and answered questionnaires. Inclusion criteria were that participants spoke English, and the children did not have significant developmental delays. Parents were contacted by mail before the scheduled appointment to inform them about the study and ask them to bring their children to the clinic 1 hour early so that a local anesthetic could be applied to the IV site. The application of a topical anesthetic was encouraged for all children involved in the larger study, but it was not a requirement for participation. Sometimes children did not arrive at the clinic early enough to benefit from the optimal anesthetic dwell time. The subgroup of participants selected from the larger study for this analysis met these additional inclusion criteria: (1) either EMLA was in place for at least 60 minutes or LMX4 was in place for at least 30 minutes before insertion of the IV; (2) children completed the Oucher pain scale after the IV insertion; and (3) sufficient genetic material was obtained from the children and biologic parents for genotyping. Of the 303 children enrolled in the larger study, 218 met the inclusion criteria for this analysis.

Topical Anesthetics Two forms of topical lidocaine anesthetic creams were used in this study, EMLA and LMX4. Eutectic Mixture of Local Anesthetics (EMLA) is an emulsion of 2 well-known amino-amide class anesthetics, lidocaine 2.5 mg/g and prilocaine 2.5 mg/g. Information from the manufacturer indicates that the efficacy of the medication depends on proper application.3 The dose must be correct, the med-

169 ication should be covered with an occlusive dressing, and the medication must be left in place at least 60 minutes before venipuncture. The active ingredient in LMX4 is lidocaine 4%. According to the manufacturer, it must be left in place for at least 30 minutes before venipuncture.10 The equivalence of EMLA and LMX4 for needle stick pain relief in children has been reported.9,20

Measures Pain The Oucher pain scale was used to measure the child’s perception of pain at the IV site. The Oucher scale is a self-report scale for pain intensity in children ages 3 to 12 years.2 Children point to a face in a series of 6 photographs showing a child in varying degrees of discomfort, or they can point to a vertical numeric scale positioned next to the faces. Before administering this tool, children are screened for understanding of quantity by asking them to arrange 3 measuring cups in order from smallest to largest. Construct validity of the Oucher pain-rating scale has been reported.2 The correlation between the Oucher scale and the visual analogue scale for pain was 0.89 (P ⬍ .01). Discriminate validity was established by investigating the relationships between the Oucher scale and 2 scales that measured children’s fear. The associations between the numeric Oucher scale and the Hospital Fears Rating Scale and Scare Scale were very low, with gamma coefficients of –.003 and .075, respectively.4

Child Temperament The Dimensions of Temperament Survey–Revised (DOTS-R) by Windle and Lerner34 is a 54-item questionnaire completed by parents to assess 9 dimensions of temperament from early childhood to young adulthood. Four choices are given for each item: usually false, more false than true, more true than false, or usually true. Windle and Lerner reported reliability and validity data for 115 preschool children. Cronbach alpha coefficients for each dimension ranged from .70 to .91. The specific dimensions chosen for inclusion in this study were general activity level, approach/withdrawal, and task orientation. Coefficient alphas ranged from .78 to .92 for these subscales when used with children between the ages of 4 and 10 years who were hospitalized or attending a clinic for treatment of a chronic condition.19

Child Anxiety A visual semantic differential scale, in the form of a thermometer marked with 10 evenly spaced lines, was used to measure children’s anxiety. The instructions to the children were “pretend that all of your worried or nervous feelings are in the bulb or bottom part of the thermometer. If you are a little bit worried or nervous, the feelings might come up in the thermometer just a little bit. If you are very very worried or nervous, the feelings might go all the way to the top. Put a line on the thermometer showing how much worry or nervousness you feel.” To measure state and trait anxiety, children

170

Predictors of Topical Anesthetic Effectiveness

Table 1.

Characteristics of the Candidate Genes and SNPs

GENE

Locus

Endothelin (EDN1) Endothelin A (EDNRA) Endothelin B (EDNRB)

6p24 4q31.22 13q22

NUCLEOTIDE CHANGE G¡T C¡T A¡G

AMINO ACID CHANGE

SNP rs*

ABI ASSAY†

Lys198Asn None None

5370 5333 7319342

C_598677-1 C_1736670-1 C_1923554-10

*NCBI reference SNP cluster ID.

were asked to rate their worry or nervousness twice by using thermometers on 2 different pieces of paper. “How you feel right now” was the question for state anxiety, and “How you feel usually at home” was the question for trait anxiety. This scale has been used successfully in other studies.14,20 For example, in our study of children’s distress and anxiety in a children’s hospital,19 88% of the children rated their state anxiety higher than trait anxiety, as would be expected. As evidence of the scale’s validity, the 8 children who rated higher trait anxiety were able to explain why they felt more anxious at home. For example, one youngster explained that he felt safe in the hospital, but at home his brother was aggressive. When parents of children with high trait anxiety scores were asked about the child’s usual state, parents concurred that the children were normally anxious at home.

Genotyping Methods DNA for genotyping was obtained from the children by drawing blood from the IV or by collecting buccal cells with cheek swabs swirled on the inner surface of each cheek. DNA material was obtained from the biologic parents with cheek swabs. DNA was extracted and purified from both whole blood and cheek swabs by using PUREGENE DNA isolation kits.13 Genotyping for all single-nucleotide polymorphisms (SNPs) was performed by using TaqMan SNP Genotyping Assays.1 An automated sequence-detection system (ABI Prism 7900HT; Applied Biosystems, Foster City, CA) was used to discriminate alleles for each SNP. SNP probes and assays were obtained from Applied Biosystems through the Assay on Demand service. Reactions were performed by using conditions specified by the manufacturer. To assess the reliability of genotypes, approximately 5% of samples were genotyped in duplicate. In addition, observed allele and genotype frequencies were compared with those predicted by Hardy-Weinberg equilibrium.30 Table 1 provides additional information about the candidate genes and SNPs.

Procedure Data for this analysis were gathered from a larger study. For the larger study, parents were asked to bring their children to the clinic at least 1 hour before the scheduled IV insertion so that a topical anesthetic could be applied. If an hour was available, EMLA was usually applied, and LMX-4 was used if less than an hour was available. Approximately 2.5 g of topical anesthetic was applied to each of 2 possible IV sites, usually on the dorsal aspects of the hands or antecubital areas. The sites

were covered with transparent dressings, and the time of application was marked to assure that they would not be removed until adequate time had passed for anesthetic effectiveness. While the family waited for the topical anesthetic to take effect, one of the parents completed the demographic and DOTS-R questionnaires. Parents were asked to estimate the number of painful procedures the child had experienced, not including routine immunizations. A research assistant (RA) assessed the child’s ability to use the Oucher pain scale and administered the anxiety measures to the child. When possible, both biologic parents provided cheek swabs for genotyping, either in the clinic or by returning cheek swabs from home via standard mail.28 IVs were inserted by registered nurses in the pediatric specialty clinic who routinely perform venipuncture with children. Blood was taken from the IV site for genetic analysis. Immediately after the IV insertion, the RA administered the Oucher scale to the child by using the culturally appropriate version of the tool.

Analyses Data Management and Statistical Analysis Data were double entered by 2 individuals into a relational database program. Discrepancies were resolved by the data manager, who referred back to the original written data sheets. Analysis of data was done with SAS programs (SAS Institute, Inc, Cary, NC). Ordinal level variables were assessed for normality to determine the appropriate statistical analysis. Relationships between the ordinal and categorical variables were examined with correlation and ␹2, respectively. Low and high pain phenotype definitions were based on previous studies and our data. The literature suggests that a pain score of 4 or more is unacceptable to children.6,12,22 The mean score in this study was 3.34, with 59% of the scores between 0 and 3. Therefore, we defined low pain phenotype as an Oucher score from 0 to 3 and high pain phenotype as an Oucher score from 4 to 10. Phenotypes were defined before the genetic analysis was undertaken. The Wilcoxon rank sum test was used to compare low and high pain score groups on ordinal level data, and the Pearson ␹2 test was used to compare the genotype frequencies between low and high pain phenotype groups. Significant variables were entered into a logistic regression model to determine odds ratios for each variable. With level of significance set at .05 and a sample of 129 in

ORIGINAL REPORT/Kleiber et al

171 nal membranes required to initiate and conduct nerve impulses. The 3 candidate genes in this analysis included the EDN1, EDNRA, and EDNRB genes. Table 2 provides a summary of genotype and allele frequencies for each SNP. All genotypes were in Hardy-Weinberg equilibrium; 100% concordance in genotypes was observed between duplicate samples.

30 25 P 20 e r c 15 e n t 10

Potential Predictors and Pain Phenotypes

5 0

0

1

2

3

4

5

6

7

8

9

10

Oucher Scores

Figure 1. Oucher scores (x axis) by % of participants (y axis).

the low Oucher group and 89 in the high Oucher group, the power was .80 to detect a difference of at least .39 standard deviation for the continuous variables (eg, age and activity) and an odds ratio of at least 2.3 for the genetic analysis.

Results Subjects Two hundred eighteen children met the inclusion criteria for this analysis. The mean age for children in this sample was 7 years (⫾1.9), and they had experienced an average of 4 previous painful medical procedures. Fiftyone percent were male, and 84% were white.

Neither gender nor ethnicity was associated with pain group. For the high pain group, 48% were male (␹2 ⫽ .26, P ⫽ .40), and 81% were white (␹2 ⫽ .37, P ⫽ .54). The majority of children received EMLA as the topical anesthetic, but the proportion was not significantly different for children in the low and high pain groups receiving EMLA versus LMX4. EMLA was used for 79% of the subjects categorized as low pain and for 73% categorized as high pain (␹2 ⫽ 1.07, P ⫽ .30). Interquartile comparisons between low and high pain groups are provided in Table 3. Children in the high pain group were significantly younger (Z ⫽ 5.62, P ⬍ .001) and scored higher for general activity (Z ⫽ 2.98, P ⫽ .003). Children in the high pain group scored higher for both state (Z ⫽ 2.16, P ⫽ .031) and trait anxiety (Z ⫽ 3.31, P ⫽ .001). However, anxiety measures were available for only 167 children in this sample, with a disproportionate number missing in the high pain group. Genotype frequencies for each SNP were compared between the high and low pain phenotype groups by using ␹2 analysis (Table 4). The presence of the EDNRA gene–TT genotype was significantly higher (␹2 ⫽ 7.68, P ⫽ .022) in the high pain group. Genotype frequencies did not differ according to ethnicity (␹2 ⫽ 1.94, P ⫽ .38).

Pain Scores Pain scores ranged from 0 to 10, with a mean of 3.34 ⫾ 3.38, median of 2, and mode of 0. Figure 1 shows the percentage of participants at each Oucher score. The pain score data did not meet the criteria for normality (Kolmogorov-Smirnov statistic, .245; P ⬍ .010), and logarithmic manipulation did not normalize the data. Therefore, pain scores were categorized into low and high levels for further analysis.

Genotype and Allele Frequencies All subjects were genotyped for SNPs in 3 genes hypothesized to influence topical anesthesia effectiveness as a result of their role in the stabilization of the neuro-

Table 2.

Regression Analyses As explained above, the pain score data did not meet the assumption of normality. Therefore, logistic regression techniques were used to identify predictors of low and high pain groups. Child age and general activity scores were entered as continuous variables, and the EDNRA TT genotype was entered as a dichotomous variable. Because state and trait anxiety scores were missing for 51 children, with a disproportional number from the high pain group, those variables were not used in the regression. The adjusted odds ratios shown in Table 5 indicate that for every year younger, children were 1.527 times more likely to be in the high pain group, and chil-

Genotype and Allele Frequencies

GENE (SNP rs*) EDN1 (rs5370) EDNRA (rs5333) EDNRB (rs7319342) *NCBI reference SNP cluster ID.

GENOTYPE FREQUENCY N (%) GG 132 (.601) TT 116 (.540) AA 106 (.486)

GT 78 (.358) TC 89 (.414) AG 92 (.422)

ALLELE FREQUENCY (%) TT 8 (.037) CC 10 (.047) GG 20 (.092)

G .784 T .747 A .697

T .216 C .253 G .303

172

Predictors of Topical Anesthetic Effectiveness

Table 3.

Interquartile Ranges and Differences Between Low and High Pain Groups LOW OUCHER (n ⫽ 129)

Age (y) Previous procedures Child Temperament General activity Approach/Withdrawal Task orientation Child Trait Anxiety Child State Anxiety

MEDIAN

25th %

8 4

6 2

16.0 20.0 21.0 .5 2.5

HIGH OUCHER (n ⫽ 89)

75th %

25th %

6 4

5 2

9 10

13.0 21.0 18.0 23.0 18.0 23.0 LOW OUCHER (n ⫽ 114) .0 1.0

MEDIAN

19.0 20.0 20.0

1.0 4.5

75th %

Z SCORE* (P VALUE)

7 12

5.62 (⬍.001) .45 (.656)

15.5 24.0 17.8 23.0 17.0 23.0 HIGH OUCHER (n ⫽ 53)

1.0 3.0

.0 1.5

2.98 (.003) .93 (.351) 1.62 (.105)

4.8 6.0

3.31 (.001) 2.16 (.031)

*Wilcoxon rank sum test.

dren with the EDNRA TT genotype were 2.612 times more likely to be in the high pain group. For every 5-point increase in the general activity scale score, children are 1.386 times more likely to report higher pain scores.

Discussion This is the first study to report an association between the EDNRA rs5333 SNP and increased self-reported pain in children after pretreatment with lidocaine anesthetics. Research to explicate the role of EDN1 and its 2 primary receptors, EDNRA and EDNRB, in peripheral nociception is an active area of inquiry, particularly in animal and in vitro models.15,33 Although a polymorphism in the regulatory region of the EDNRA gene has been previously associated with increased risk for migraine headaches,33 limited research on the effect of genetic variation within genes in the endothelin pathway on topical anesthetic effectiveness has been reported. These findings are an important first step in understanding variation in anesthesia effectiveness, despite the application of best clinical practices.

Table 4.

Comparison of Genotype Between Low and High Pain Groups TOTAL (N ⫽ 218)

GENE EDN1 rs5370

EDNRA rs5333

EDNRB rs7319342

*Pearson ␹2.

EMLA and LMX4 act through the accumulation of the cationic forms of lidocaine near nociceptors and nerve endings, blocking transmission of nerve impulses by influencing ion movement across the cell membrane.3 There is evidence that the peptide endothelin-1 (ET-1), encoded by the EDN1 gene, also influences ion movement to trigger pain. Further evidence suggests this action is mediated through the endothelin type A (ETA) receptors,36 peptides that are coded by the EDNRA gene. The biologic mechanism underlying the association between EDNRA rs5333 and pain response in children, however, is unknown. The EDNRA rs5333 SNP does not result in an amino acid change and would not be expected to alter gene function. Additional research is needed to determine whether and how this SNP, or a tightly linked sequence variant, influences gene expression and the resultant phenotype. Identifying the etiologic variant will provide potential targets for new pharmacologic intervention. However, even without a clear understanding of the mechanism behind this association, this EDNRA rs5333 SNP could play a clinically useful role in identifying children who might not respond well

LOW OUCHER (N ⫽ 129)

HIGH OUCHER (N ⫽ 89)

GENOTYPE

N

%

N

%

N

%

␹2* (P VALUE)

GG GT TT

132 78 8

60.55 35.78 3.67

83 40 6

64.34 31.01 4.65

49 38 2

55.06 42.70 2.25

3.59 (.174)

CC TC TT

10 89 116

4.65 41.40 53.95

8 61 60

6.20 47.29 46.51

2 28 56

2.33 32.56 65.12

7.68 (.022)

AA AG GG

106 92 20

48.62 42.20 9.17

59 58 12

45.74 44.96 9.3

47 34 8

52.81 38.20 8.99

1.12 (.572)

ORIGINAL REPORT/Kleiber et al Table 5.

173

Logistic Regression for Likelihood of High Pain

Child age: unit ⫽ 1 year younger General activity: unit ⫽ 5.0 EDNRA TT vs TC/CC: unit ⫽ 1

ADJUSTED ODDS RATIO

95% CONFIDENCE INTERVAL

WALD ␹2 (P VALUE)

1.527 1.386 2.612

1.288-1.811 1.045-1.838 1.391-4.906

23.678 (⬍.001) 5.129 (.024) 8.916 (.003)

to topical anesthetics. These children might require modifications in the recommended application procedures for existing topical anesthetics or different pharmacologic interventions. In addition, more intensive biobehavioral interventions might be required during painful medical procedures to decrease child pain and distress. This study corroborates previous research showing that younger children report more pain with needle stick procedures. Despite the correct application of topical anesthetic before IV insertion, 41% of subjects in this study reported pain between 4 and 10 on the Oucher scale. The Oucher scores in this study had a bias toward even numbers. This is a reflection the Oucher tool, which allows children to point to 1 of 6 faces (translating into pain scores of 0, 2, 4, 6, 8, or 10) or to point to a vertical numeric scale (ranging from 0 to 10) that is printed next to the faces. Many of the children in this study chose to point to a face rather than the vertical numeric scale. Measuring pain in young children is always problematic. Children’s comprehension of the concept “quantity” and their understanding of the word pain develop rapidly during the grade-school years. Including preschool children in pain studies can increase the risk of incomplete or inaccurate data. However, pediatric pain specialists maintain that self-report of pain is the most valid indicator of pain, and that a child’s perception of pain should be the gold standard for that individual.35 A limitation of this study is that the design is descriptive with no placebo control group. Preexisting data from another study, in which all children were offered a

topical anesthetic, were used in this analysis. Another limitation is that scores for state and trait anxiety were missing for 51 participants, with a disproportionate number missing from children in the high pain group. The high pain group was also significantly younger. It is not surprising that the younger children would have more difficulty with the anxiety scale. According to several expert consensus guidelines,32,35 children who need nonemergent invasive procedures on intact skin should be pretreated with topical anesthetics. However, because currently available topical lidocaine anesthetics do not eliminate pain for some children, it is important for the practitioner to acknowledge this possibility with the child and family. When a child complains of pain despite pretreatment with topical anesthetics, the practitioner should not disregard the child’s comments. Rather than telling children that the lidocaine cream will take all of the pain away, a better approach would be to say “Lots of children don’t feel much pain at all after having the cream on before the needle stick.” In summary, young children who were more active and had the EDNRA TT genotype were more likely to report higher pain with IV insertion despite pretreatment with topical lidocaine anesthetics. Gender, ethnicity, number of previous painful procedures, and type of topical anesthetic were not associated with pain scores. For these children at risk for higher pain, clinicians should teach parents to distract them during needle stick procedures or involve Child Life Specialists to provide distraction.

References

ley GA: A randomized double-blind, placebo-controlled trial of the EMLA patch for the reduction of pain associated with intramuscular injection in four to six-year-old children. Acta Paediatr 90:1329-1336, 2001

1. Applied Biosystems: http://www.appliedbiosystems.com/ 404.cfm?requested_url⫽pc/ 2005. Accessed October 27, 2005 2. Aradine CR, Beyer JE, Tompkins JM: Children’s pain perception before and after analgesia: A study of instrument construct validity and related issues. J Pediatr Nurs 3:11-23, 1988 3. AstraZeneca Pharmacueticals: http://www.astrazenecaus.com/content/products/product. Accessed October 27, 2005 4. Beyer JE, Aradine CR: Content validity of an instrument to measure young children’s perceptions of the intensity of their pain. J Pediatr Nurs 1:386-395, 1986 5. Broome ME, Savedra MC: Pain in children: Progress and challenges. J Pediatr Nurs 13:1-2, 1998 6. Cassidy KL, Reid GJ, McGrath PJ, Smith DJ, Brown TL, Fin-

7. Chen E, Craske MG, Katz ER, Schwartz E, Zeltzer LK: Painsensitive temperament: Does it predict procedural distress and response to psychological treatment among children with cancer? J Pediatr Psychol 25:269-278, 2000 8. Dahlquist LM, Power TG, Cox CN, Fernbach DJ: Parenting and child distress during cancer procedures: A multidimensional assessment. Children’s Health Care 23:149-166, 1994 9. Eichenfield LF, Funk A, Fallon-Friedlander S, Cunningham BB: A clinical study to evaluate the efficacy of ELA-Max (4% liposomal lidocaine) as compared with eutectic mixture of local anesthetics cream for pain reduction of venipuncture in children. Pediatrics 109:1093-1099, 2002 10. Ferndale Laboratories: http://www.ferndalelabs.com/ inc/frameset.asp?page⫽professionals/LMX4_pediatrics.asp. Accessed October 27, 2005

174 11. Fetzer SJ: Reducing venipuncture and intravenous insertion pain with eutectic mixture of local anesthetic: A metaanalysis. Nurs Res 51:119-124, 2002 12. Gauthier JC, Finley GA, McGrath PJ: Children’s self-report of postoperative pain intensity and treatment threshold: Determining the adequacy of medication. Clin J Pain 14:116-120, 1998 13. Gentra Systems: Serious nucleic acid purification. Available at: http://www.gentra.com/ Accessed October 27, 2005 14. Gerard L, Cooper C, Duethman K, Gordley B, Kleiber C: Effectiveness of lidocaine lubricant for discomfort during pediatric urethral catheterization. J Urol 170:564-567, 2003 15. Gokin AP, Fareed MU, Pan HL, Hans G, Strichartz GR, Davar G: Local injection of endothelin-1 produces pain-like behavior and excitation of nociceptors in rats. J Neurosci 21:5358-5366, 2001 16. Humphrey GB, Boon CM, van Linden van den Heuvell GF, van de Wiel HB: The occurrence of high levels of acute behavioral distress in children and adolescents undergoing routine venipunctures. Pediatrics 90:87-91, 1992 17. Julius D, Basbaum AI: Molecular mechanisms of nociception. Nature 413:203-210, 2001 18. Khodorova A, Navarro B, Jouaville LS, Murphy JE, Rice FL, Mazurkiewicz JE, Long-Woodward D, Stoffel M, Strichartz GR, Yukhananov R, Davar G: Endothelin-B receptor activation triggers an endogenous analgesic cascade at sites of peripheral injury. Nat Med 9:1055-1061, 2003 19. Kleiber C, McCarthy AM: Evaluating instruments for a study on children’s responses to a painful procedure when parents are distraction coaches. J Pediatr Nurs 21:99-107, 2006 20. Kleiber C, Sorenson M, Whiteside K, Gronstal BA, Tannous R: Topical anesthetics for intravenous insertion in children: A randomized equivalency study. Pediatrics 110:758761, 2002 21. Lander J, Fowler-Kerry S: Age differences in children’s pain. Percept Mot Skills 73:415-418, 1991 22. Lander J, Hodgins M, Nazarali S, McTavish J, Ouellette J, Friesen E: Determinants of success and failure of EMLA. Pain 64:89-97, 1996 23. Lee LW, White-Traut RC: The role of temperament in pediatric pain response. Issues Compr Pediatr Nurs 19:49-63, 1996 24. Luhmann J, Hurt S, Shootman M, Kennedy R: A comparison of buffered lidocaine versus ELA-Max before peripheral intravenous catheter insertions in children. Pediatrics 113: e217-220, 2004 (Pt 1)

Predictors of Topical Anesthetic Effectiveness 25. McCarthy AM, Kleiber C: A conceptual model of factors influencing children’s responses to a painful procedure when parents are distraction coaches. J Pediatr Nurs 21: 8898, 2006 26. Mogil JS, Max MB: The genetics of pain, in Koltzenburg M, McMahon SB (eds): Melzack’s Textbook of Pain. London, UK, Elsevier Churchill Livingstone, 2005 27. Pomonis JD, Rogers SD, Peters CM, Ghilardi JR, Mantyh PW: Expression and localization of endothelin receptors: Implications for the involvement of peripheral glia in nociception. J Neurosci 21:999-1006, 2001 28. Richards B, Skoletsky J, Shuber AP, Balfour R, Stern RC, Dorkin HL, Parad RB, Witt D, Klinger KW: Multiplex PCR amplification from the CFTR gene using DNA prepared from buccal brushes/swabs. Hum Mol Genet 2:159-163, 1993 29. Rogers TL, Ostrow CL: The use of EMLA cream to decrease venipuncture pain in children. J Pediatr Nurs 19:3339, 2004 30. Schaid DJ, Jacobsen SJ: Biased tests of association: Comparisons of allele frequencies when departing from HardyWeinberg proportions. Am J Epidemiol 149:706-711, 1999 31. Taddio A, Soin HK, Schuh S, Koren G, Scolnik D: Liposomal lidocaine to improve procedural success rates and reduce procedural pain among children: A randomized controlled trial. Can Med Assoc J 172:1691-1695, 2005 32. Paediatrics and Child Health Division of the Royal Australasian College of Physicians: Guideline Statement: Management of Procedure-related Pain in Children and Adolescents. Royal Australasian College of Physicans, 2005 33. Tzourio C, El Amrani M, Poirier O, Nicaud V, Bousser MG, Alperovitch A: Association between migraine and endothelin type A receptor (ETA ⫺231 A/G) gene polymorphism. Neurology 56:1273-1277, 2001 34. Windle M, Lerner RM: Reassessing the dimensions of temperamental individuality across the life span: The Revised Dimensions of Temperament Survey (DOTS-R). J Adolesc Res 1:213-229, 1986 35. Zempsky WT, Cravero JP, Committee on Pediatric Emergency Medicine and Section on Anesthesiology and Pain Medicine: Relief of pain and anxiety in pediatric patients in emergency medical systems. Pediatrics 114:1348-1356, 2004 36. Zhou Z, Davar G, Strichartz G: Endothelin-1 (ET-1) selectively enhances the activation gating of slowly inactivating tetrodotoxin-resistant sodium currents in rat sensory neurons: A mechanism for the pain-inducing actions of ET-1. J Neurosci 22:6325-6330, 2002