Secondary Logo

Journal Logo

Sensory Stimuli and Anxiety in Children Undergoing Surgery: A Randomized, Controlled Trial

Kain, Zeev N. MD*†‡,; Wang, Shu-Ming MD*,; Mayes, Linda C. MD†‡,; Krivutza, Dawn M. MA*,; Teague, Barbara A. BSN†§

doi: 10.1097/00000539-200104000-00018
Pediatric Anesthesia: Research Report
Free
SDC

We assessed the effectiveness of a behavioral intervention aimed at reducing the anxiety of children undergoing anesthesia and surgery. The intervention consisted of dimmed operating room (OR) lights (200 Lx) and soft background music (Bach’s “Air on a G String,” 50–60 dB). Only one person, the attending anesthesiologist, interacted with the child during the induction of anesthesia. Children undergoing anesthesia and surgery were randomly assigned either to a low sensory stimulation group (LSSG, n = 33) or to control group (n = 37). By using validated behavioral measures of anxiety (mYPAS) and compliance (ICC), children were evaluated at the preoperative holding area and during the induction of anesthesia. On postoperative Days 1, 2, 3, 7, and 14, the behavioral recovery of the children was assessed by using the Post Hospitalization Behavior Questionnaire. We found that the LSSG was significantly less anxious compared with the control group on entrance to the OR (P = 0.03) and on the introduction of the anesthesia mask (P = 0.003). Also, the compliance during the induction of anesthesia was significantly better in children assigned to the LSSG (P = 0.02). The incidence of postoperative behavioral changes, however, did not differ significantly between the two groups (P = ns). We conclude that children who are exposed to low-level sensory stimuli during the induction of anesthesia and who are exposed to background music exhibit lower levels of anxiety and increased compliance.

Departments of *Anesthesiology, †Pediatrics, and ‡Child Psychiatry, and the §Children’s Clinical Research Center, Yale-New Haven Children’s Hospital and Yale University School of Medicine, New Haven, Connecticut

Supported in part by National Institutes of Health (R01HD37007-01), the Children’s Clinical Research Center grant MO1-RR06022, General Clinical Research Centers Program, National Center for Research Resources, NIH and the Patrick and Catherine Weldon Donaghue Medical Research.

December 18, 2000.

Address correspondence and reprint requests to Zeev N. Kain, MD, Department of Anesthesiology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510. Address e-mail to kain@biomed.med.yale.edu.

IMPLICATIONS: Children are less anxious and show increased compliance during induction when exposed to a single care-provider in a dimmed, quiet operating room with background music.

It is estimated that 50% to 75% of children undergoing surgery will develop extreme anxiety and distress during the perioperative period (1). This phenomenon is important not only because of the associated postoperative maladaptive behaviors, but also because of clinical outcomes and quality improvements efforts (2). Recently, a panel of 72 anesthesiologists ranked various anesthesia outcomes based on importance and frequency. The panel of anesthesiologists reached a consensus on which low-morbidity clinical outcomes are common and important to the patient. The five clinical outcomes with the high-est combined score were incisional pain, nausea, vomiting, preoperative anxiety, and discomfort from IV insertion (2). Thus, there is a consensus among anesthesiologists about the need to treat patient’s anxiety during the preoperative period.

Several methods are used to decrease the anxiety level of a child in the preoperative settings. These include parental presence during induction of anesthesia (PPIA), preoperative preparation programs, sedative premedicants, and a combination of the above. None of these methods is ideal. Experimental evidence does not support the routine use of PPIA (3,4), and both sedative premedication and preparation programs are associated with significant operational costs to hospitals and surgery centers. Considering these limitations, it is no surprise that while anesthesiologists consider preoperative anxiety an important phenomenon (2), surveys have reported that most anesthesiologists do not routinely use any of the above interventions (5,6). Thus, the search for a low-cost and easy-to-implement anxiolytic intervention for children undergoing surgery continues.

Based on behavioral and physiological measures of anxiety, the induction of anesthesia in children has been identified as the most stressful point during the preoperative period (1). The distress experienced during the induction period is related to separation anxiety, a threatening operating room (OR) environment (equipment, bright lights, high noise levels), and the presence of masked individuals interacting with the child (1). Hodge and Thompson (7) measured noise levels in the OR and reported overall high sound levels with loud intermittent noises up to 108 dB. Further, the investigators found that the loudest noises are present during the period of the induction of anesthesia (7). The stimuli of bright lights, loud noise, and multiple individuals addressing the child may result in sensory-overload, distress, and anxiety for the child (8).

Thus, it can be hypothesized that a decrease in the sensory input during the induction of anesthesia will result in a decreased anxiety and increased compliance in children undergoing induction of anesthesia. The intervention evaluated in this study consisted of dimmed OR lights (200 Lx) and soft background music (Bach’s “Air on a G String,” 50–60 dB). Only one person, the attending anesthesiologist, interacted with the child during the induction of anesthesia. Music was incorporated into the intervention studied to further reduce the sensory stimulation as music has been suggested to affect mood and relieve emotional distress (9–12). Further, music is now being used routinely to treat symptoms such as pain and anxiety. A recent article published in Journal of the American Medical Association called for more objective outcome data related to this modality (12).

Back to Top | Article Outline

Methods

Study Design and Outcomes

This randomized, controlled study was conducted with children undergoing general anesthesia and surgery. Consecutive outpatients age 2–7 yr old, ASA physical status I and II, scheduled to undergo general anesthesia and elective outpatient surgery (herniorrhaphy, orchiopexy, hydrocelectomy, tonsillectomy and/or adenoidectomy, and circumcision) were considered for enrollment. Children were excluded from participation if they had any history of chronic illness, prematurity, or developmental delay. All inductions were performed by a group of six anesthesiologists. The IRB approved the study protocol, and informed consent was obtained from the parents of each patient.

Back to Top | Article Outline

Outcomes and Study Interventions

The primary endpoint of this study was the anxiety manifested by children undergoing the induction of anesthesia. Secondary endpoints included children’s compliance and the incidence of postoperative maladaptive behavioral changes. Patients were randomly assigned to one of two study groups according to a computer-generated list created from a random numbers table: Control group (CG), no change in OR routine; Low sensory stimulation group (LSSG). The intervention consisted of several elements: a) The lights for the intervention group were fixed at 200 LX. Regular light intensity in the OR is approximately 1500 LX. Lights in the OR were adjusted based on an illuminometer (Sekonic Handy Lumni, Tokyo, Japan). The accuracy of this instrument is ±10% when tested by using a standard parallel-light tungsten lamp of color temperature 2854K. b) Bach’s “Air on a G String,” which was previously documented to decrease anxiety (13), was played on a CD player (Philips Magnavox, China). This CD player was always set at the same volume (50–60 dB) and the same distance from the child. To assure delivery of the same sound level, we used a sound level meter (Radio Shack, Fort Worth, TX). c) All personnel present during the induction of anesthesia were instructed to avoid any conversation during the induction process. Surgical instruments were not arranged or moved during this period. The attending anesthesiologist was the only individual that communicated with the child during the induction of anesthesia, although another anesthesiologist was always present. In addition, the alarms of monitoring instruments, such as the Spo2 monitor, was adjusted to a very low level.

PPIA and sedative premedicants were not allowed for either group. PPIA was used, however, as rescue therapy for both groups as detailed in the protocol below.

Back to Top | Article Outline

Study Protocol

Psychometric data regarding the behavioral assessment instruments that were used in this study are reported in Appendix 1. Details about the training of the psychologists that administrated these instruments are presented in the protocol below. The following behavioral instruments were used in this study.

Back to Top | Article Outline

Primary Outcome Assessment

Yale Preoperative Anxiety Scale (mYPAS).

This instrument contains 27 items in five categories indicating preoperative anxiety in children (activity, emotional expressivity, state of arousal, vocalization, and use of parents). The mYPAS has good to excellent reliability and validity (14,15).

Back to Top | Article Outline

Secondary Outcomes Assessment

Induction Compliance Checklist (ICC).

This observational scale was previously developed and validated by our study group to describe the compliance of a child during the induction of anesthesia. This scale was found to have very high interclass r within (0.998) and between observers (0.978) (4).

Back to Top | Article Outline

Post Hospitalization Behavioral Questionnaire (PHBQ).

This self-report questionnaire for parents is widely used in the medical literature and is designed to evaluate maladaptive behavioral responses in children after surgery (16).

Back to Top | Article Outline

Baseline Measures

Monitor Blunter Style Scale (MBSS).

This standardized instrument assesses coping styles in adults through four scenarios of stressful situations. The instrument was developed specifically for patients undergoing medical procedures and identifies information seeking, information avoiding and distraction coping styles (17).

Back to Top | Article Outline

EASI Scale of Child Temperament.

This parental report instrument assesses four temperament categories, emotionality, activity, sociability, and impulsivity in children and is widely used in the literature (18).

Back to Top | Article Outline

State-Trait Anxiety Inventory (STAI).

This self-report anxiety instrument contains two separate 20-item subscales that measure trait (baseline) and state (situational) anxiety, and has been used in more than 1000 studies published in peer-reviewed literature (19).

Back to Top | Article Outline

Study Protocol

Training of Assessors.

Before the beginning of the study, we established the inter- and intraobserver reliability of the two assessors (psychologists) who were part of this study. These two assessors examined videotapes of children undergoing the induction of anesthesia (n = 43). The videotapes were analyzed separately and independently by the two assessors. Reliability between and within the two assessors was assessed by using weighted Kappa statistics for overall chance-corrected agreement (Kw). Calculations were performed by using the computer program RATCAT (Rater Agreement Categorical Data) (DV Cicchetti, New Haven, CT) (20). In addition, this program assigns the appropriate clinical significance to individual weighted Kappa values: Kw below 0.40 = poor; 0.40–0.59 = fair; 0.60–0.74 = good; and 0.75–1.00 = excellent. In the preoperative holding area, separation to the OR and during the induction of anesthesia, the agreement between the two assessors ranged from 0.91 to 0.96 in the five categories. Intraobserver weighted Kappa agreement ranged from 0.88 to 0.93 in the five categories. The assessors also trained with the ICC using videotapes of children and their interclass r within (0.978) and between (0.991) was very high.

Back to Top | Article Outline

Patient Recruitment.

After recruitment, demographic data, temperament (EASI), trait anxiety (STAI), and coping style of the parent (MBSS), were obtained.

Back to Top | Article Outline

Day of Surgery, Preoperative Holding Area.

Anxiety of the child was measured by an assessor using the mYPAS. Parents rated their own anxiety using the STAI. Next, patients were randomly assigned to one of the two groups. Management of children in the holding area and on separation to the OR was per our routine in the surgery center.

Back to Top | Article Outline

Separation to the OR.

If a child exhibited extreme anxiety (as determined solely by the attending anesthesiologist who was blinded to group assignment), PPIA was offered as rescue therapy. Parental anxiety was assessed after the separation process (STAI).

Back to Top | Article Outline

Day of Surgery, OR.

Anesthesia was induced by using O2/N2O and sevoflurane administered via a scented mask. The child’s anxiety (mYPAS) during the induction was assessed at two time points: a) entrance to the OR until the anesthesia mask was introduced;, and b) introduction of the anesthesia mask until the child was induced. Compliance of the child during the anesthetic induction was also rated (ICC). Drugs such as ketamine or droperidol were not used. The assessor also noted the number of individuals who interacted with the children during the induction of anesthesia. It is important to note that the same assessor ranked the child’s anxiety at the various time points. Only one anesthesiologist was interacting with the child during the induction of anesthesia.

Back to Top | Article Outline

Postanesthesia Care Unit (PACU).

Incidence of adverse effects, time to discharge, and analgesic requirements were recorded. Fitness for discharge from the PACU was measured by using Steward’s recovery scale (SPRS) (21).

Back to Top | Article Outline

Postoperative Period.

The child’s behavior was evaluated by the parents at several time points: postoperative Days 1, 2, 3, 7, and 14. Parents were contacted on these days by telephone by a trained research nurse who was using a written script and who was blinded to group assignment. Parents were asked about any behavioral changes in their child (PHBQ). The telephone interview lasted 5–10 min. It is important to emphasize that parents were specifically instructed to indicate only new behavioral changes that occurred after surgery.

Back to Top | Article Outline

Statistical Analysis

Because no previous data are available regarding sensory overload in the OR, the sample size is based on investigations involving music and children (10,22). These investigations report a change of 25%–30% in the anxiety level of the children. Because we previously reported a mean anxiety score of 50 ± 12 (mYPAS score) during the introduction of an anesthesia mask in children undergoing the induction of anesthesia, we could expect a mYPAS score of 40 ± 9.4 in the intervention group. Thus, a sample size of 32 subjects in each group (64 total) is sufficient to detect a 25% difference in anxiety level with a power of 0.95 and an α of 0.05. Intention-to-treat analysis was used in this study.

To control for potential confounding variables, subjects were matched with a yoked design based on their age, type of surgery, and participation in the preoperative preparation program. For example, the first 5-yr-old child undergoing herniorrhaphy who underwent a preparation program was randomized (by using a randomization table generated from a random numbers table) to one of the two groups. The second 5-yr-old child undergoing herniorrhaphy who did not attend a preparation program was automatically allocated to the same group. Descriptive statistics provide an overview of the child and parent variables. Data that were normally distributed were presented as mean ± sd, skewed data as median and interquartile range (25%–75%). The χ2 test, Student’s t-tests, and a two-way repeated measures analysis of variance were used. Comparisons were considered significant if P < 0.05.

Back to Top | Article Outline

Results

Between January 1999 and March 2000, 70 patients were enrolled in this investigation. Child and parental baseline demographic and personality characteristics are presented in Table 1. The two groups were similar with regard to variables such as age, sex, temperament, parental coping styles, previous surgery, and participation in the voluntary preparation program. PPIA was used as a rescue therapy on separation to the OR 11 times (n = 11). There was no group difference in the use of this rescue therapy (5 vs 6). Interestingly, 90% of the subjects in the control group received sensory input from at least three different individuals (e.g., anesthesiologists, nurses, surgeons) during the induction of anesthesia. This is in contrast to the intervention group that received input from only one individual.

Table 1

Table 1

Back to Top | Article Outline

Primary Outcome

There were no differences in the child’s observed anxiety level (mYPAS) between the two groups in the preoperative holding area and on separation to the OR (Fig. 1). Using two-way repeated measures analysis of variance, we next analyzed changes in observed anxiety level along four time points, holding area (T1), separation to the OR (T2), entrance to the OR until the introduction of the anesthesia mask, (T3) and the introduction of the anesthesia mask until the child was induced (T4). We found that observed anxiety differed significantly between the two groups (F [1,67]=6.3, P = 0.014), and there was a significant Time x Group interaction (F = 6.7, P = 0.002). Post hoc analysis demonstrated that the intervention group was significantly less anxious as compared with the control group on entrance to the OR (P = 0.03) and on the introduction of the anesthesia mask (P = 0.003) (Fig. 1). Children’s anxiety did not differ based on the particular attending anesthesiologist or the parental coping style (P = ns).

Figure 1

Figure 1

Back to Top | Article Outline

Secondary Outcomes

As can be seen from Figure 2, the percentage of inductions in which compliance of the child was excellent (i.e., ICC score = 0) was significantly higher in the intervention group as compared with the control group (47% vs 21%, P = 0.02). When the incidence of new-onset postoperative negative behavioral changes was compared between the two groups, no group differences were observed. Behavioral changes did not differ based on the coping style of the parent. Parental anxiety did not differ between the two groups either at the holding area (41 ± 10 vs 42 ± 10) or after separation to the OR (44 ± 14 vs 46 ± 16).

Figure 2

Figure 2

No anesthetic complications, such as laryngospasm, occurred during any of the inductions. In the PACU, the incidence of nausea or vomiting (31% vs 30%, P = ns) and time to a score of 7 on SPRS (45 [37–75] min. vs 60 [45–75] min) was similar for the intervention and control groups.

Back to Top | Article Outline

Discussion

This study was performed to assess the effects of decreased sensory stimuli, single-care provider, and background music on the anxiety and compliance of children undergoing anesthesia and surgery. We found that children are less anxious and more compliant during the induction when exposed to a single care-provider in a relatively dark, quiet OR with background music. We also found that the incidence of postoperative behavioral changes at two weeks after surgery was not affected by the change in the sensory stimuli level.

The anxiolytic response manifested by children during the induction of anesthesia represents an interaction between the child’s related factors and the environmental conditions in the OR. Child-related factors include age and developmental maturity, previous experience with medical procedures and illness, individual capacity for affect regulation, trait anxiety, and parental trait anxiety (1). OR-related environmental factors include the intensity of lights, the level of noise produced by the staff and instrument preparation, and the number of medical personnel interacting with the child. The last is of particular importance as it is not infrequent that the surgeon, the circulating nurse, the anesthesia resident, and the anesthesia attending are all trying to help the child through the induction process. This may result in conflicting messages and increased anxiety for the child. In the present investigation, we sought to significantly manipulate the environment in the OR by reducing the noise the child is exposed to and allowing only the attending anesthesiologist to interact with the child during the induction of anesthesia. Background music was introduced as well. We hypothesized that these changes may result in the child’s decreased anxiety. The results indicate that this hypothesis is valid and that this low-cost sensory intervention could be used routinely in ORs. It is important to note that while pediatric anesthesia textbooks advocate the use of a “quiet” surrounding during the induction of anesthesia, this recommendation has not been anchored in the results of a clinical, randomized, controlled trial.

Previous studies that have assessed noise levels in the OR concluded that while overall sound levels are not excessive, loud noises up to 108 dB are present intermittently (7,23). Cohen (24) has classified noises as just-audible (10db), very quiet (50dB, light traffic at 30 miles/hour), moderately loud (70 dB, dishwasher), very loud (90 dB, food blender), and uncomfortably loud (130 dB, rock-n-roll band). The dropping of a surgical instrument into a bowl in the OR can produce noise levels of up to 80 dB. Further, sound is measured on a logarithmic scale, which means that additional sounds in the OR with similar intensity will not greatly increase the total sound level. But, a sudden noise with a level as little as 30 dB above the background noise (e.g., an Spo2 alarm) might cause an immediate startle response which is associated with an activation of the sympathetic system and an anxiolytic response (25). Thus, it is important to stop setting up the instruments during the induction of anesthesia and to not allow loud conversation among the staff members.

It is important to note that it is unclear which component of the intervention investigated in this study was the most effective. That is, was it the decreased sensory stimuli or the background music? Future investigations should address this point.

We conclude that children are less anxious and show increased compliance during the induction when exposed to a single care-provider in a “dimmed,” quiet OR with background music. The results of this study are of particular importance because the low cost of the environmental manipulations described can be easily adopted by numerous to the benefit of millions of children undergoing surgery.

Back to Top | Article Outline

Acknowledgments

The authors would like to thank Paul G. Barash, MD, for his critical review of this manuscript.

Back to Top | Article Outline

Appendix 1

Primary Outcome Assessment

Yale Preoperative Anxiety Scale (mYPAS) (14,15) : This structured observational measure of preoperative anxiety in children was developed and validated previously by our study group. This scale was validated for use at four points, holding area (T1), separation to the OR (T2), entrance to the OR until mask is introduced (T3), and after the mask is introduced until the child is induced (T4). The mYPAS consists of 27 items in 5 domains of behavior indicating anxiety in young children (activity, emotional expressivity, state of arousal, vocalization and use of parents). By using Kappa statistics, all mYPAS domains have good to excellent inter- and intraobserver reliability, and when validated against other global behavioral measures of anxiety, the mYPAS had good validity (14). The mYPAS is also validated against a self-report measure, the State Trait Anxiety Inventory for Children (STAIC) (15), and against physiological measures of anxiety (14).

Back to Top | Article Outline

Secondary Outcomes Assessment

Induction Compliance Checklist (ICC) (4) : This observational scale was previously developed and validated by our study group to describe the compliance of a child during induction of anesthesia. Using the computer program BIGRI (DV Cicchetti), this scale has very high interclass r within (0.998) and between (0.978) observers. The ICC score is the sum of the negative behavior items observed. For example, if the child did not exhibit any of these behaviors, it is a perfect induction and scored as a zero (0).

Post Hospitalization Behavioral Questionnaire (PHBQ) (16) : This questionnaire for parents is designed to evaluate behavioral responses and “developmental regression” in children after surgery. The PHBQ consists of 27 items frequently cited in the literature as common behavioral responses of children after surgery (16). This instrument shows good agreement with psychiatric interviews (r = 0.47) and was used in several investigations to document behavioral changes as a function of preoperative interventions (16).

Back to Top | Article Outline

Coping and Temperament Measures

Monitor Blunter Style Scale (MBSS) (17) : This standardized tool was developed for patients undergoing medical procedures and identifies information seekers (high monitor)/information avoiders (low monitors) and distracters (high blunters)/nondistracters (low blunters). The MBSS assesses coping style through four scenarios of stressful situations (i.e., you are on an airplane that is experiencing severe turbulence). A list of eight possible reactions to the situation are presented and the subject is asked to check each behavior in which they would engage in that situation (i.e., look for exits or watch the in-flight movie). Four of the reactions are of a monitoring or information-seeking variety and four are of a blunting or information-avoiding variety. This measure has excellent reliability and validity.

EASI Scale of child temperament (EASI) (18) : This is a standardized tool used to the various aspects of temperament in children and is widely used in the literature. This instrument includes 20 items in four behavioral categories: emotionality, activity, sociability, and impulsivity. A parent is presented with individual patterns of behaviors and responses to daily events and is asked to rate the child on a five-point scale. A score ranges from 5 to 25 for each category with higher scores indicating higher baseline emotionality, activity, sociability, or impulsivity. The instrument has good validity when compared with other measures of temperament for preschool children. Test-retest reliability of the EASI temperament tool was good when mothers rated their preschool children on adjacent months.

Back to Top | Article Outline

Anxiety and Compliance Measures

State-Trait Anxiety Inventory (STAI) (19) : This is a widely used self-report anxiety assessment instrument. More than 1000 studies involving research using the STAI have been published in peer-reviewed literature. The questionnaire contains two separate 20-item, self-report rating scales for measuring trait and state anxiety. Parents respond on a 4-point scale, total scores for situational and baseline questions separately range from 20 to 80 with higher scores denoting higher levels of anxiety. Test-retest correlations for the STAI are high and range 0.73 to 0.86. Validity of the instrument was examined in two studies in which the STAI was given under high- and low-stress conditions to large samples of students. The r value ranged from 0.83 to 0.94, suggesting very good validity.

Back to Top | Article Outline

References

1. Kain Z, Mayes L. Anxiety in children during the perioperative period. In: Borestein M, Genevro J, eds. Child development and behavioral pediatrics. Mahwah, NJ: Lawrence Erlbaum Associates, 1996: 85–103.
2. Macario A, Weinger M, Truong P, Lee M. Which clinical anesthesia outcomes are both common and important to avoid? The perspective of a panel of expert anesthesiologists. Anesth Analg 1999; 88: 1085–91.
3. Kain ZN, Mayes LC, Caramico LA, et al. Parental presence during induction of anesthesia: a randomized controlled trial. Anesthesiology 1996; 84: 1060–7.
4. Kain Z, Mayes L, Wang S, et al. Parental presence during induction of anesthesia vs. sedative premedication: which intervention is more effective? Anesthesiology 1998; 89: 1147–56.
5. Kain ZN, Mayes LC, Bell C, et al. Premedication in the United States: a status report. Anesth Analg 1997; 84: 427–32.
6. Kain Z, Ferris C, Mayes L, Rimar S. Parental presence during induction of anesthesia: practice differences between the US and Great Britain. Paediatr Anaesth 1996; 6: 187–93.
7. Hodge B, Thompson J. Noise pollution in the operating theatre. Lancet 1990; 335: 891–4.
8. Abel S. The extra-auditory effects of noise and annoyance: an overview of research. J Otolaryngol 1990; (Suppl 1): 1–13.
9. Cunningham MF, Monson B, Bookbinder M. Introducing a music program in the perioperative area. AORN J 1997; 66: 674–82.
10. Chetta HD. The effect of music and desensitization on preoperative anxiety in children. J Music Therapy 1981; XVIII: 74–87.
11. Koch M, Kain Z, Ayoub C, Rosenbaum S. The sedative and analgesic sparing effect of music. Anesthesiology 1998; 89: 300–6.
12. Marwick C. Music therapists chime in with data on medical results. JAMA 2000; 283: 731–3.
13. Barger DA. The effects of music and verbal suggestion on heart rate and self-reports. J Music Therapy 1979; XVI: 158–71.
14. Kain Z, Mayes L, Cicchetti D, et al. Measurement tool for pre-operative anxiety in children: the Yale Preoperative Anxiety Scale. Child Neuropsychol 1995; 1: 203–10.
15. Kain Z, Mayes L, Cicchetti D, et al. The Yale Preoperative Anxiety Scale: how does it compare to a gold standard? Anesth Analg 1997; 85: 783–8.
16. Vernon D, Thompson R. Research on the effect of experimental interventions on children’s behavior after hospitalization: a review and synthesis. Dev Behav Pediatr 1993; 14: 36–44.
17. Miller S. Monitoring and blunting: validation of a questionnaire to assess styles of information seeking under threat. J Pers Soc Psychol 1987; 52: 345–53.
18. Buss AH, Plomin R. Theory and measurement of EAS: temperament—early developing personality traits. Hillsdale: L. Erlbaum Associates, New Jersey 1984.
19. Spielberger CD. Manual for the State-Trait Anxiety Inventory (STAI: Form Y). Palo Alto, CA: Consulting Psychologists Press, 1983.
20. Heavens R, Cicchetti D. A computer program for calculating rate agreement and bias statistics using contingency table input. Proc Am Stat Assoc 1978; 366–70.
21. Steward DJ. A simplified scoring system for the post-operative recovery room. Can Anaesth Soc J 1975; 22: 111–3.
22. Robb SL, Nichols RJ, Rutan RL, et al. The effects of music assisted relaxation on preoperative anxiety. J Music Therapy 1995; 32: 2–21.
23. Shapiro R, Berland T. Noise in the operating room. N Engl J Med 1972; 1236–8.
24. Cohen A. Environmental noise problems in broad perspective. Proceedings of symposium on environmental noise: its human and economic effects. Chicago: Chicago Hearing Society, 1970.
25. Falk S, Woods N. Hospital noise-levels and potential health hazards. N Engl J Med 1973; 289: 774–81.
© 2001 International Anesthesia Research Society