Study Design

This was a prospective, randomized, double-blind, controlled trial involving treatment in parallel groups for 4 weeks. Active treatment was hyperbaric treatment at 1.3 atm and 24% oxygen for 40 sessions lasting 1 hour each at pressure ("treatment group"), whereas the control treatment consisted of slightly pressurized room air at 1.03 atm and 21% oxygen for 40 sessions lasting 1 hour each at pressure ("control group"). Comparison of the clinical effects of parallel treatments for 4 weeks was the primary objective of this study. The number of treatments (40 sessions) and the overall treatment period (4 weeks) were chosen because these were previously shown to be safe in two other studies of hyperbaric treatment in children with autism [7, 17].

Participants: Eligibility Criteria and Recruitment

This study was approved by the Liberty Institutional Review Board and enrolled children, 2 to 7 years of age, who had a diagnosis of Autistic Disorder and had not previously received any type of hyperbaric treatment. All children met the DSM-IV criteria for Autistic Disorder [1] and this diagnosis was also corroborated by psychologists using the Autism Diagnostic Interview–Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS). Children with PDD-NOS, Asperger syndrome, seizure disorder, current ear infection, uncontrolled asthma, inability to equalize ear pressure, fragile X syndrome, and ongoing treatment with chelation medication were excluded from participation in this study. Written informed consent was obtained from the parents and, when possible, the child. Sixty-six children were evaluated for inclusion in the study from six clinics throughout the U.S. Four children were excluded from participation because the diagnosis of Autistic Disorder could not be corroborated by ADI-R and ADOS. Therefore, the recruitment process yielded 62 eligible participants, who were randomized as depicted in Figure 1.

Figure 1 Consolidated Standards of Reporting Trials (CONSORT) flow diagram. Full size image

Interventions

The active treatment was hyperbaric treatment at 1.3 atm and 24% oxygen in a monoplace hyperbaric chamber for 60 minutes at this pressure per session (this length of time did not include approximately 10–15 minutes for pressurization and depressurization). Oxygen flowing at 10 liters per minute from an oxygen concentrator was mixed with room air and pumped into the chamber following a protocol previously described [7]. This resulted in a final chamber oxygen concentration of approximately 24% as measured by an oxygen monitor. This treatment was given twice a day separated by a minimum of 4 hours, 5 days per week, for 4 consecutive weeks, for a total of 40 treatments per child.

Control treatment consisted of slightly pressurized room air (1.03 atm and 21% oxygen) in a monoplace hyperbaric chamber for 60 minutes at this pressure per session (this length of time did not include approximately 10–15 minutes for pressurization and depressurization). This treatment was given twice a day separated by a minimum of 4 hours, 5 days per week, for 4 consecutive weeks, for a total of 40 treatments per child. For blinding purposes, participants underwent a brief compression to 1.1 atm at the beginning of each treatment. The chamber was then slowly decompressed from 1.1 to 1.03 atm where the pressure stayed for the remainder of the treatment. No oxygen was added to the chamber and thus the chamber was pressurized with room air (approximately 21% oxygen). The children in the control group remained in the chamber for the same length of time as children in the treatment group. At the end of each treatment, the pressure was slowly increased to 1.1 atm over about 5 minutes and then the chamber was depressurized. Procedures were developed and applied to mimic, for the control group, the experience of hyperbaric treatment at 1.3 atm, and thereby to keep participants and parents unaware of the nature of the intervention. These procedures included covering control switches, inflating and deflating the chambers to simulate pressure changes, and masking the sounds from the chambers. To further mask the group assignments, the equipment (including chambers) used for the control group was indistinguishable from the equipment used for the treatment group. Moreover, the same type of equipment was used at each study site. A pressure of 1.03 atm (with increases to 1.1 atm for several minutes at the beginning and at the end of the treatment) was chosen for the control group because this pressure represented the lowest that could be applied and still effectively simulate hyperbaric treatment at 1.3 atm. To verify its effectiveness, prior to beginning the study, this pressure protocol was tested in six adult individuals who were randomly and repeatedly exposed to both the treatment group pressure (1.3 atm) and the control group pressure (1.03 atm with short increases to 1.1 atm) and none of these individuals were able to reliably distinguish between the two pressures. At each study site, the primary investigator (DAR) visited and trained each hyperbaric technician to ensure that the same protocol was followed to minimize variances between study sites. An analysis performed after the study was finished demonstrated no significant differences (p = ns) between the six study sites for age, initial autism severity, and initial and final scores on all of the scales used in this study (this analysis can be found in the results section).

Initial screening for this study included medical history taking and a physical examination by one of the study physicians. This included examination of the ears and tympanic membranes. Throughout each treatment, children were closely monitored by a hyperbaric technician for any signs of ear pain or other problems, and parents were instructed on how to recognize ear pain in their child. In both groups, in order to facilitate treatments, a parent or primary caretaker accompanied the child into the chamber as it was deemed that the children were too young to enter and remain in the chamber alone for the duration of each treatment. Children finishing more than one full session were included in the final analysis in an intention-to-treat manner. Daily treatment logbooks for each child were maintained by the hyperbaric technician and any side effects during treatment were recorded. At the end of the study, all children assigned to the control group were offered 40 hyperbaric treatments at the treatment pressure (1.3 atm and 24% oxygen) if the parents desired (all parents chose this option; treatments were provided without charge). During the study period, children in both groups were not allowed to begin any new therapies or stop any current therapies, including medications and nutritional supplementation. At the onset of the study, the use of nutritional supplements, medications, and applied behavioral analysis (ABA) therapy was similar in both the treatment and control groups (p = ns), see Table 1.

Table 1 Initial characteristics of children in the treatment and control groups Full size table

Randomization and Allocation

From the 62 children who were enrolled in the study, 33 were randomly allocated to the treatment group and 29 were randomly allocated to the control group. To achieve this allocation, a random allocation sequence (1:1) was generated and stratified on both the participant's group (treatment or control) and center, and this sequence was equilibrated every eight patients. The allocation sequence remained concealed to all investigators, study participants, parents, nursing staff, and all other clinic staff. The only person at each center who was aware of the group assignment for each particular child was the hyperbaric technician, who had no input in the evaluation (outcome measures) of the child. The hyperbaric technician was specifically instructed not to discuss the treatment nature or group assignments with anyone else in the clinic, including participants, parents, psychologists, and physicians. It was not possible to blind the hyperbaric technician due to the nature of the study (the technician had to know the group assignment in order to adjust the chamber to the correct pressure for treatment). However, all individuals involved in evaluating the child (parents, physicians, and psychologists) remained blinded to the group assignment for each child throughout the entire study period. In hyperbaric treatment studies, the study is considered double-blinded if the study participants and the evaluators of outcome measures are both blinded to group assignment (as they were in this study), even though the hyperbaric technician is aware of the assignment [37, 38]. After the study was completed, parents in both groups were surveyed to determine the effectiveness of the blinding process, and there was no significant difference between groups in their ability to determine which group their child had been assigned (p = ns).

Outcome measures

The primary outcome measures were changes compared to baseline observed after 4 weeks (40 sessions) of treatment, in parallel groups, on (1) Aberrant Behavior Checklist–Community (ABC) total score and subscale scores, based on the parent's or primary caretaker's rating, (2) Autism Treatment Evaluation Checklist (ATEC) total score and subscale scores, based on the parent's or primary caretaker's rating, and (3) Clinical Global Impression–Improvement (CGI) scale for changes in overall functioning and subscales, as rated by the parent or primary caretaker and also as rated separately by the treating physician (without knowledge of the parental ratings).

Previous studies of hyperbaric treatment in children with autism have utilized the ABC and/or ATEC [7, 17]. The ABC is a 58-item questionnaire that assesses communication, reciprocal social interaction, play, and stereotypical behaviors [39]. It is used to evaluate the effectiveness of medications and other therapeutic interventions and is scored from 0 ("not at all a problem") to 3 ("problem is severe in degree"). For this study, a total score was calculated as well as scores in 5 subscales: irritability, social withdrawal (also termed lethargy), stereotypy, hyperactivity, and inappropriate speech. The ABC was administered immediately prior to beginning the study (to determine baseline scores) and immediately after finishing 40 sessions. Lower scores on the ABC indicate lower autism severity.

The ATEC is a questionnaire developed by the Autism Research Institute to evaluate treatment efficacy in individuals with autism. It consists of four subscales: Speech/Language/Communication, Sociability, Sensory/Cognitive Awareness, and Health/Physical/Behavior. The scores are weighted according to the response and the corresponding subscale. The higher the subscale and total scores, the more impaired the subject. A split-half reliability analysis on 1,358 checklists indicated high internal consistency among the questions within each subscale [40]. The ATEC is designed to allow evaluators to assess outcomes of certain treatments commonly used in individuals with autism. In this study, scores were calculated for the total score and the four separate subscales. The ATEC was administered immediately prior to beginning the study (to determine baseline scores) and immediately after finishing 40 sessions. Due to an administration error, the baseline ATEC was not performed at one of the study centers, and thus data was available for analysis for 23 children in the treatment group and 21 children in the control group.

Scores for the CGI scale were obtained immediately after 40 sessions. The CGI scale gives an impression of global changes in certain areas for each child compared to baseline [41]. A total score for change in overall functioning was rated by a parent or primary caregiver and separately by the treating physician (the same physician who initially evaluated the child) using the following ratings: 1 ("very much improved"), 2 ("much improved"), 3 ("minimally improved"), 4 ("no change"), 5 ("minimally worse"), 6 ("much worse"), and 7 ("very much worse"). Children who received a score of "very much improved" or "much improved" on the physician CGI overall functioning score were considered to be "good responders" to treatment. Data was also collected from parents and physicians as to whether or not there were improvements in the following CGI subscales: receptive language, expressive language, sleep pattern, attention span, activity level, bowel movement pattern, self-stimulatory behavior, social awareness/alertness, social interaction, play skills, self-injurious behavior, eye contact, mood, anxiety level, aggression, general health, gross motor skills, and fine motor skills.

Analysis

All data were prospectively collected and analyzed using StatsDirect statistical software (version 2.7.2) and are presented as mean ± SEM (standard error of the mean). Data analysis was based on an intention-to-treat approach on all participants who finished more than one treatment or control session.

Power Calculations

Because this was the first controlled study of its kind, power calculations were based on the closest comparable study that had outcome data available at the time of this study design [17]. Analysis of this data demonstrated a medium to large effect size, depending on the scale examined (Cohen's d = 0.44 to 0.77) [42]. Using the most conservative effect size (d = 0.44), a power calculation using G*Power 3 [43] indicated that a total sample of 43 children would achieve a power of 80% with alpha set at 0.05 (two-tailed).

Planned Comparisons

Planned group comparisons were performed on the primary outcome measures. The normal distribution of data was checked using the Kolmogorov-Smirnov test. In parameters with normal distribution, comparisons were analyzed using the Student's t test. When normality was not present and equal variance could not be assumed, nonparametric tests (Mann-Whitney and Wilcoxon signed rank tests) were used. The Pearson's chi-square (χ2) test with Yates' correction or the Fisher's exact test (when subgroups contained less than 10 children) was applied to assess differences in the percentage of children responding to treatment in each group. In all analyses, a p-value less than 0.05 (two-tailed) was considered significant.