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TECHNOLOGY, COMPUTING, AND SIMULATION

Hemispheric Synchronized Sounds and Intraoperative Anesthetic Requirements

Susan Dabu-Bondoc, MD^*, Jacqueline Drummond-Lewis, MD^*, Dorothy Gaal, MD^*, Maryanne McGinn, MA^*, Alison A. Caldwell-Andrews, PhD^*, and Zeev N. Kain, MD^*,,

Departments of *Anesthesiology, Pediatrics, and Child Psychiatry, Yale University School of Medicine and Yale-New Haven Hospital, New Haven, Connecticut

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{at}biomed.med.yale.edu

	Abstract

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Hemispheric synchronization is currently promoted as a treatment for preoperative anxiety and for reduction of intraoperative anesthetic and analgesic consumption. We designed this study to examine the effect of Hemisync® sounds on anesthetic hypnotic depth. After obtaining informed consent, we randomized subjects undergoing general anesthesia and outpatient surgery into two groups: the treatment group received Hemisync® sounds (n = 31), and the control group received a blank cassette tape (n = 29). Both groups received the intervention in the preoperative area and during the surgical procedure. Subjects underwent a propofol-based anesthetic regimen, and propofol doses required for the induction and maintenance of anesthesia were recorded. A bispectral index monitor was used to ensure that the hypnotic component of the anesthetic state was the same in all patients. We found no differences in the amount of propofol used during the induction of anesthesia (2.49 ± 0.59 mg/kg versus 2.60 ± 0.59 mg/kg; P = 0.48) or the maintenance of anesthesia (0.141 ± 0.02 mg · kg^-1 · min^-1 versus 0.146 ± 0.04 mg · kg^-1 · min^-1; P = 0.62) between the Hemisync® and control groups. We also found no differences between the Hemisync® group and the control group for participants with high state anxiety (P = not significant). We conclude that Hemisync® sounds do not reduce the hypnotic component of the anesthetic state of patients undergoing general anesthesia and surgery.

IMPLICATIONS: Hemisync®, a product marketed to reduce anesthetic consumption by synchronizing hemispheres of the brain, does not appear to reduce the anesthetic requirements of patients who undergo general anesthesia and surgery when depth of hypnosis is controlled by a bispectral index monitor.

	Introduction

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In 1839, Heinrich Wilhelm Dove (1) first described the phenomenon of binaural beats. These result from two similar auditory impulses that are presented to both ears simultaneously and that differ in frequency between 1 and 30 Hz (2–4). For example, if a tone of 370 Hz is presented to the right ear and a tone of 380 Hz is presented simultaneously to the left ear, the difference between the two tones (10 Hz) is perceived as a single auditory binaural beat. It is important to note that this binaural beat is not really heard and that these binaural beats are auditory brainstem responses that have been described to originate in the superior olivary nucleus of each hemisphere (2). These binaural beats are of interest because they have been thought to cause hemispheric synchronization. That is, they bring both hemispheres of the brain into unison, as demonstrated by computerized topographic brainwave maps (3).

Currently, hemispheric synchronization is heavily marketed in the United States via the Monroe Institute (Faber, VA; http://www.monroeinstitute.org). This institute combines hemispheric synchronization with positive verbal suggestions and markets their product (Hemisync®) as a treatment modality for stress reduction, pain control, immune disorders, and many other diseases. The Monroe Institute also promotes a series of tapes titled "Surgical Support Series." The Institute states, "This album’s effectiveness has been demonstrated in major hospitals and clinics. The reported benefits include reduced anxiety, stabilized blood pressure, minimized need for anesthesia and pain medication, and quicker recuperation" (Primary Caregiver Instructions, The Surgical Support Series, The Monroe Institute, 1995). A short search of the World Wide Web reveals that Hemisync® is available from multiple retailers around the world.

Interestingly, in 1999, Kliempt et al. (4) published a randomized trial in Anesthesia that compared the effects of Hemisync® with those of classical music and a blank tape. The investigators studied subjects undergoing general anesthesia and surgery and found that subjects who were exposed to Hemisync® sounds under general anesthesia needed significantly less fentanyl as compared with patients who were listening to classical music or a blank tape. Whereas Kliempt et al. (4) examined the effect of Hemisync® on analgesia, we designed the following study in a complementary manner to examine the effect of Hemisync® on the depth of hypnosis.

We therefore designed a randomized, controlled trial that compared Hemisync® sounds with a blank tape. To control for the depth of hypnosis, we used the bispectral index (BIS) monitor. This new monitor has been suggested to serve for measuring and monitoring the depth of the hypnotic component of the anesthetic state (5,6).

	Methods

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Consecutive outpatients aged 18–65 yr, ASA physical status I–II, scheduled to undergo general anesthesia and elective outpatient surgery were considered for enrollment in this randomized, controlled study. Subjects were excluded from participation if they had any history of chronic illness or were taking psychiatric medications. The IRB approved the study protocol, and informed consent was obtained from each subject.

Subjects were contacted the night before surgery, and initial telephone consent was obtained. On the day of surgery, after recruitment, detailed demographic data and state and trait anxiety (State Trait Anxiety Index; STAI) of each participant were obtained. The STAI is a widely used self-report anxiety assessment instrument (7). This instrument contains 2 separate 20-item subscales that measure trait (baseline) and state (situational) anxiety, and it has been used in >1000 studies published in peer-reviewed literature (7).

Next, subjects were randomized into two groups: the treatment group received Hemisync® music, and the control group received a blank cassette tape. In the preoperative holding area, the Hemisync® group listened to Hemisync® Tape 1 via a headset. The tape lasted 30 min. Patients in the control group were given a headset with a blank cassette tape and listened to the blank tape for 30 min. No sedative premedication was offered to any of the subjects.

In the operating room (OR), anesthetic technique was standardized for all participants. ASA standard monitors were applied to all subjects, and electroencephalogram was continuously recorded with an Aspect A1000 spectral electroencephalogram monitor (Aspect Medical Systems, Natick, MA). This instrument provides a single BIS value (0–100). A BIS number in the range of 40–60 indicates loss of consciousness and recall. Larger BIS values indicate more awake hypnotic states. We induced general anesthesia with propofol 1 mg/kg, followed by a single dose of alfentanil (20 µg/kg). After observing for clinical response and allowing for BIS equilibration (60 s), additional small incremental doses of propofol (20–30 mg) were given to reach a BIS value of 40–60. Vecuronium 1 mg/kg was given to facilitate endotracheal intubation. Anesthesia was maintained with oxygen/N₂O (1:2 L/min), and a propofol infusion was started at 140–160 µg · kg^-1 · min^-1 and thereafter adjusted to maintain BIS in the 40–60 range. At the conclusion of surgery, the propofol infusion was discontinued, and the neuromuscular block was reversed with neostigmine and glycopyrrolate. The induction and maintenance doses of all anesthetics and the length of infusion were recorded. The investigators also recorded the heart rate and blood pressure of all patients throughout the anesthetic procedure.

It is important to note that the anesthesiologist was blinded to group assignment. Because Hemisync® Tape 2 needed to be inserted into the portable tape player in the OR, to keep the anesthesiologist blinded, headsets from both groups of participants were removed briefly before the patients entered the OR. After the patient entered the OR, Hemisync® Tape 2 was inserted into the tape player for the Hemisync® group, and a blank tape was reinserted for the control group. Tapes were disguised so that all tapes looked the same. Tapes were restarted after the induction of anesthesia for all participants, and all patients were exposed to the intervention (Hemisync® versus blank tape) throughout the surgical procedure.

The primary end-point of this study was the amount of propofol used during the induction and maintenance of anesthesia. To control for the confounding effects of various types of surgeries, patients were yoked to control for surgical procedure.

Comparisons between groups were analyzed with ² analysis for categorical data and Student’s t-test for continuous data (STAI). Data are presented as mean ± SD. P > 0.05 was considered significant.

	Results

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We enrolled 60 patients in this investigation. Baseline demographic and personality characteristics are presented in Table 1. The two groups were similar with regard to variables such as age, sex, years of education, trait anxiety, and whether they had experienced a previous surgery. Participants’ weight, total time in surgery, and alfentanil doses did not differ between the groups. State anxiety levels, as measured in the holding area, were similar for both groups (Table 1). Surgical procedure types included gynecological procedures such as hysteroscopy, hysterectomy, and tubal ligation (60%); general minor surgeries, such as removal of lesions (20%); orthopedic procedures, such as repair of a tendon (10%); and other (10%). It is important to note that the two intervention groups were matched as to type of surgery.

The amounts of propofol used during the induction and maintenance of anesthesia were calculated by weight for each participant. Results showed that there were no differences in the amount of propofol used during the induction of anesthesia between the Hemisync® and control groups (2.49 ± 0.59 mg/kg versus 2.60 ± 0.59 mg/kg; P = 0.48). Similarly, there was no difference in the amount of propofol used during the maintenance of anesthesia between the two groups (0.141 ± 0.02 mg · kg^-1 · min^-1 versus 0.146 ± 0.04 mg · kg^-1 · min^-1; P = 0.62; Fig. 1).

View larger version (7K): [in this window] [in a new window]   Figure 1. Propofol (mg · kg-1 · min-1) amounts required by the Hemisync® group compared with the control group during the maintenance of anesthesia.

Adjusted total propofol ranged from 0.01 to 0.47 mg · kg^-1 · min^-1 (0.188 ± 0.066 mg · kg^-1 · min^-1). An independent samples Student’s t-test showed no differences between the control group and the Hemisync® group in the amount of adjusted total propofol received (0.185 ± 0.065 mg · kg^-1 · min^-1 versus 0.190 ± 0.069 mg · kg^-1 · min^-1, respectively; P = 0.76).

Intraoperative average heart rate did not differ significantly between the Hemisync® and control groups (73.03 ± 7.5 bpm versus 72.76 ± 9.6 bpm, respectively; P = 0.90). Similarly, average intraoperative blood pressure did not differ between the two groups (systolic: 121.5 ± 9.9 mm Hg versus 119.9 ± 10.4 mm Hg, P = 0.55; diastolic: 77 ± 7 mm Hg versus 75 ± 7 mm Hg, P = 0.25).

We next examined the effect of the Hemisync® intervention on participants with high state and high trait anxiety (upper 25%). We found no differences between the Hemisync® group and the control group in adjusted total propofol for participants with high state anxiety (0.16 ± 0.06 mg · kg^-1 · min^-1 versus 0.12 ± 0.07 mg · kg^-1 · min^-1, respectively; P = 0.26) or high trait anxiety (0.16 ± 0.06 mg · kg^-1 · min^-1 versus 0.19 ± 0.10 mg · kg^-1 · min^-1, respectively; P = 0.50).

The effect of overall state anxiety for all participants on adjusted total propofol was then examined. The most anxious participants (top 25% of STAI scores) were compared with less anxious participants (lower 75%). Participants with high anxiety required significantly more propofol than participants without high anxiety (adjusted total propofol, 0.20 ± 0.061 mg · kg^-1 · min^-1 versus 0.15 ± 0.065 mg · kg^-1 · min^-1, respectively;P = 0.005). In contrast, trait anxiety did not have an appreciable effect on the amount of adjusted total propofol received by participants (adjusted total propofol in highest trait anxiety participants [upper 25%], 0.172 ± 0.08 mg · kg^-1 · min^-1 versus 0.192 ± 0.06 mg · kg^-1 · min^-1 for less anxious patients; P = 0.34).

	Discussion

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Under the conditions of this randomized, controlled trial study, we found that Hemisync® sounds did not affect the hypnotic anesthetic depth of patients who underwent general anesthesia and surgery. Music has recently become a nonpharmacological modality grouped with many alternative medical therapies that have evolved into complementary medicine (8). Indeed, this modality is being currently promoted as a treatment for perioperative conditions such as postoperative pain and preoperative anxiety (9). An article published in JAMA (10), however, underscored the very strong need for measurable outcome data to establish the therapeutic efficacy of music. We believe that our investigation used sound scientific design and objective outcome measurement instruments.

The findings of this investigation provide an interesting parallel to the work of Kliempt et al. (4) and Lewis et al. (11). The earlier investigation of Kliempt et al. demonstrated that subjects who were exposed to Hemisync® sounds under anesthesia needed less fentanyl as compared with patients who listened to classical music or a blank tape. Lewis et al. randomized patients undergoing general anesthesia for either laparoscopic bariatric or lumbar surgery to listen to Hemisync® or a blank tape. They found that bariatric patients who listened to Hemisync® sounds were given significantly less fentanyl than who listened to a blank tape. Interestingly, they also found no difference in fentanyl requirements for patients undergoing lumbar procedures, regardless of whether they listened to Hemisync® sounds or a blank tape. We have to realize, however, that although both Kliempt et al. (4) and Lewis et al. (11) studied the effects of Hemisync® on analgesic requirements, our investigation studied the effect of Hemisync® on depth of hypnosis.

Kliempt et al. (4) indicated that future studies should incorporate better monitoring of consciousness levels under general anesthesia. We adopted their suggestion and monitored the level of consciousness of patients in our study by using BIS technology while we examined the effect of Hemisync® on hypnotic depth of anesthesia. We find it very interesting that Hemisync® affects analgesia but not hypnotic depth. Clearly, further investigation is required to clarify these issues.

We conclude that although Hemisync® sounds are currently promoted in the United States as having therapeutic qualities, we identified no such effect on the anesthetic requirements of adult patients undergoing general anesthesia. We further suggest that additional peer-reviewed research is needed to validate Hemisync® as an effective nonpharmacological therapeutic modality for indications such as stress reduction.

	Acknowledgments

 
Supported in part by Aspect Medical Systems (Boston, MA) and the Patrick and Catherine Weldon Donaghue Foundation for Medical Research (Hartford, CT).

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Dove H. Über die Combination der Eindrücke beider Ohren und beider Augen zu einem Eindruck. Berlin: Verhandlungen der Königlich Preussischen Akademie der Wissenschaften zu Berlin, 1841: 251–2.
2. Smith J, Marsh J, Brown W. Far-field recorded frequency-following responses: evidence for the locus of brainstem sources. Electroencephalogr Clin Neurophysiol 1975; 54: 465–72.
3. Atwater F. The Hemi-Sync® process. Faber, VA: The Monroe Institute, 1997.
4. Kliempt P, Ruta D, Ogston S, et al. Hemispheric-synchronisation during anaesthesia: a double-blind randomised trial using audiotapes for intra-operative nociception control. Anaesthesia 1999; 54: 769–73.[ISI][Medline]
5. Liu J, Singh H, White PF. Electroencephalographic bispectral index correlates with intraoperative recall and depth of propofol-induced sedation. Anesth Analg 1997; 84: 185–9.[Abstract]
6. Glass PS, Bloom M, Kearse L, et al. Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. Anesthesiology 1997; 86: 836–47.[ISI][Medline]
7. Spielberger CD. Manual for the State-Trait Anxiety Inventory. Palo Alto, CA: Consulting Psychologists Press, 1983.
8. Lipe A. Beyond therapy: music, spirituality, and health in human experience—a review of literature. J Music Ther 2002; 39: 209–40.[Medline]
9. Thompson JF, Kam PC. Music in the operating theatre. Br J Surg 1995; 82: 1586–7.[Medline]
10. Marwick C. Music therapists chime in with data on medical results. JAMA 2000; 283: 731–3.[Free Full Text]
11. Lewis A, Osborn I, Roth R. The effect of listening to hemispheric synchronization on the amount of intraoperative analgesia required [abstract]. Anesth Analg 2003; 96: A257.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999