Conservative management of PE using a suction device suffered long periods of neglect before the efforts of E. Klobe in 1992 because of inadequate materials and relevant side effects 4. The newly designed vacuum bell consisted of a silicon ring with a transparent polycarbonate window instead of glasses which old style suction cups were made of 9.
Vacuum bell therapy has been successfully established as a conservative management for PE; however, there is a lack of information on precise clinical indications as well as assessment tools in estimating the treatment achievement, which limits its use by clinicians 10. Difficulties in clinical evaluations may be attributed to the application of vacuum bell therapy being largely dependent on a patient’s preference.
A prerequisite for vacuum bell therapy is a patient's desire for non-surgical corrections, despite all clinical evidence relating to beneficial patient characteristics including a mild degree of PE, symmetric deformities, sternal depth greater than 1.5 cm, or younger age than preadolescence 11. Clinicians cannot ignore the patients’ desire to avoid pain and possible complications caused by surgery even when their clinical experience suggests surgical solutions.
Similar to other studies that have attempted to identify indications or objective assessment tools, we aimed to evaluate suitable pre-treatment patient characteristics associated with successful treatment outcomes. We estimated changes in HI 1 year after treatment and traced the variables that were associated with changes in HI≥0.5. We found that the expected improvement in HI was profoundly correlated with the availability of vacuum bell therapy (Figure 4).
This observation appears to be associated with chest wall flexibility, which has been reported to be related to successful treatment of PE, either surgically or non-surgically 12. Patients with more flexible chest wall can be expected to achieve better treatment outcomes. Based on this factor, clinicians would be able to tell their patients how their chest deformities will change after 1 year of vacuum bell therapy. The expected CI or HI calculated using chest CT taken after applying a vacuum bell device and the expected improvement in sternal depth could be supplementary tools in predicting outcomes.
Unlike the other two thoracic indices associated with good treatment outcomes, AI was not correlated with the treatment response. Symmetry has been demonstrated to be related to improved therapeutic efficacy 11. Although we did not examine the effects of symmetry on vacuum bell therapy, we believed that the discordance between improvement in chest deformity (improvement in HI≥0.5) and expected AI would be reflected in the results.
A low BMI was associated with better outcomes after vacuum bell therapy (p=0.001), while other pre-treatment factors including sex, age, and AI with or without vacuum bell therapy demonstrated no statistically significant differences between the two groups (p=0.366 and p= 0.228, respectively). A low BMI is believed to be related to the effectiveness of sternal lifting 13.
Young age at the initiation of treatment was associated with good outcomes. Initiating the therapy before adolescence and age<12 years demonstrated significantly positive treatment results 11. Another study reported that age<18 years was associated with better effects than those after starting treatment at age>18 years 12. In our study, age was not significantly associated with improvements in HI (p=0.233, univariate analysis). This was probably due to the age distribution of our patients (mean age, 15.3±6.23 years; 95% confidential interval, 13.78–16.92). Age was not significantly different between the groups. Most of the patients were adolescents; therefore, we could not identify the actual effects of age on efficacy of vacuum bell therapy.
The initial depth of PE in Group 2 was significantly larger than that in Group 1, which was opposite to findings of other studies 3,11,12,14 that reported that less severe depth in PE was related to excellent outcomes. This might be related to chest wall flexibility; patients with a large depth of PE achieve excellent results if they have good flexibility. The depth of PE measured 1 year after vacuum bell therapy demonstrated no significant differences between the groups (Table 2).
Improvement in the depth of PE demonstrated a flattening tendency as the treatment periods passed more than 1-year in our study (Figure 5). We believe that this finding could support our study design of comparing pre-treatment variables based on the improvements at 1 year. We evaluated treatment efficacy using chest radiographs and physical examination and would recommend patients to undergo surgery if they had less improvements in HI (usually less than 0.5, according to our findings).
Our study had several limitations. First, we enrolled patients regularly followed according to our treatment strategy. Therefore, we believe that all patients received a relatively homogenous treatment course, which could partly explain the lack of statistical significance. The choice for vacuum bell therapy depended on the patients and not clinical data; patients who were expected to not benefit from non-surgical treatment could be included in our study. Pre-treatment characteristics, such as HI, demonstrated significant differences between the groups. This inclusion bias implies inevitable limitations.
Successful long-term treatment results have been seen with MIRPE for PE. It is important to assure patients that vacuum bel therapy is not a substitute for surgery. MIRPE has resulted in excellent clinical results without fatal complications in a majority of patients 15. Vacuum bell therapy could offer satisfactory treatment results with few minor complications and less discomfort, and clinicians should not disregard that enormous effort has to be made by the patients and their caregivers to maintain treatment effects of vacuum bell therapy since the hassle of constant devotion often trumps small period of suffering induced by surgery.
In conclusion, expected improvements in HI as well as CI based on pre-treatment chest CT after applying a vacuum bell device could be used in predicting treatment efficacy. Patients who demonstrated pliability with a vacuum bell were identified as suitable candidates.