ORIGINAL ARTICLE
A novel structural risk index for primary
spontaneous pneumothorax: Ankara
Numune Risk Index
Yucel Akkas
a,*
, Neslihan Gulay Peri
a, Bulent Kocer
a,
Tevfik Kaplan
b, Aslihan Alhan
c,da
Department of Thoracic Surgery, Ankara Numune Research and Training Hospital, Ankara, Turkey
bDepartment of Thoracic Surgery, Ufuk University Faculty of Medicine, Ankara, Turkey c
Department of Statistics, Ufuk University Faculty of Arts and Science, Ankara, Turkey
Received 30 July 2015; received in revised form 11 September 2015; accepted 16 September 2015
Available online 14 November 2015
KEYWORDS
primary spontaneous pneumothorax; Ankara Numune Risk
Index;
body mass index; chest height; structural factors
Summary Background: In this study, we aimed to reveal a novel risk index as a structural risk marker for primary spontanoeus pneumothorax using body mass index and chest height, struc-tural risk factors for pneumothorax development.
Methods: Records of 86 cases admitted between February 2014 and January 2015 with or without primary spontaneous pneumothorax were analysed retrospectively. The patients were allocated to two groups as Group I and Group II. The patients were evaluated with regard to age, gender, pneumothorax side, duration of hospital stay, treatment type, recurrence, chest height and transverse diameter on posteroanterior chest graphy and body mass index. Body mass index ratio per cm of chest height was calculated by dividing body mass index with chest height. We named this risk index ratio which is defined first as ‘Ankara Numune Risk Index’. Diagnostic value of Ankara Numune Risk Index value for prediction of primary spontaneous pneumothorax development was analysed with Receiver Operating Characteristics curver. Results: Of 86 patients, 69 (80.2%) were male and 17 (19.8%) were female. Each group was composed of 43 (50%) patients. When Receiver Operating Characteristics curve analysis was done for optimal limit value 0.74 of Ankara Numune Risk Index determined for prediction of pneumothorax development risk, area under the curve was 0.925 (95% Cl, 0.872e0.977, p< 0.001).
Conflicts of interest: The authors declare no conflicts of interest.
* Corresponding author. Department of Thoracic Surgery, Ankara Numune Research and Training Hospital, Ankara, Turkey. E-mail address:y.akkas@yahoo.com(Y. Akkas).
d Akkas Y: Conception and design of study, acquisition of data (clinical), data analysis and interpretation, drafting of manuscript and
critical revision, approval of final version of manuscript. Peri NG: Conception and design of study. Kocer B: Conception and design of study, acquisition of data (clinical), approval of final version of manuscript. Kaplan T: Data analysis and interpretation. Alhan A: Data analysis and interpretation.
http://dx.doi.org/10.1016/j.asjsur.2015.09.004
1015-9584/ª 2015 Asian Surgical Association and Taiwan Robotic Surgical Association. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Available online atwww.sciencedirect.com
ScienceDirect
Conclusions: Ankara Numune Risk Index is one of the structural risk factors for prediction of primary spontaneous pneumothorax development however it is insufficient for determining recurrence.
ª 2015 Asian Surgical Association and Taiwan Robotic Surgical Association. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Spontaneous pneumothorax is defined as air accumulation in the pleural space without the presence of trauma. Spontaneous pneumothorax is classified as primary spon-taneous pneumothorax (PSP) in the absence of an
under-lying pulmonary disease and secondary spontaneous
pneumothorax (SSP) in the presence of an underlying pul-monary disease.1,2 PSP is mostly seen as the result of
rupture of the subpleural bullae in the 2nd and 3rd de-cades.3,4
The incidence of PSP is 7.4e18/100,000 in males and 6/100,000 in females.5There are many risk factors for the development of spontaneous pneumothorax, including male sex, smoking, low body weight, tall height, low body mass index (BMI), meteorological factors, and toxic metals.6e9
In this study, we aim to reveal a novel risk index as a structural risk marker for PSP using BMI and chest height, structural risk factors for pneumothorax development.
2. Material and Methods
Ethics committee approval was obtained from Ankara Numune Research and Training Hospital prior to the study (date/number: 08.04.2015/E-15-468). Records of 86 cases admitted between February 2014 and January 2015 with or without PSP were analyzed retrospectively. The patients were allocated to two groups as Group I (admission due to PSP) and Group II (admission due to trauma or mediastinal mass lesion). The patients were evaluated with regard to age, sex, pneumothorax side, duration of hospital stay, treatment type, recurrence, chest height (CH), and trans-verse diameter on posteroanterior (PA) chest radiograph, and BMI.
BMI was calculated as kg/m2 using weight and height data in the files. PA radiographs of the chest were obtained from the same distance on discharge of the patients and CH was calculated by measuring the distance between apex and costophrenic angle, transverse chest diameter was calculated by measuring lateral distance of bilateral ribs 6, and a picture archiving and communication system was used for measurements (Figure 1). BMI ratio per cm of CH was calculated by dividing BMI by CH. We named this value the risk index ratio, which is defined as the Ankara Numune Risk Index.
The SPSS, version 18.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. Categorical variables were evaluated with Chi-square test. Student t-test was used for determining the difference between average values of the variables between the two groups (Group I and Group II). A
p value < 0.05 was accepted as statistically significant. Diagnostic value of Ankara Numune Risk Index value for prediction of PSP development was analyzed with receiver operating characteristic (ROC) curve. Sensitivity, speci-ficity, and positive predictive and negative predictive values of these limits were calculated in the presence of valuable limit values. In assessment of the area under the curve, the diagnostic value of the test was interpreted as statistically significant if the Type 1 error level was< 5%.
3. Results
Of 86 patients, 69 (80.2%) were male and 17 (19.8%) were female. Each group was composed of 43 patients (50%). In Group II, 27 patients (62.8%) were admitted with blunt trauma, 15 (34.9%) with penetrating trauma, and 1 (2.3%) with mediastinal mass lesion. Of the patients in Group I, 37 (86%) were male and 6 (14%) were female. Mean age was 24.9 6.36 years (16e40 years) in Group I and 30.4 6.81 years (18e40 years) in Group II. Mean duration of hospital stay was 5.98 1.74 (3e9) days in Group I and 5.58 6.08 (1e40) days in Group II. In Group I, while 11 (25.6%) pa-tients underwent video-assisted thoracoscopic surgery, 29 (67.4%) underwent tube thoracostomy and 3 (7%) received observational therapy. In Group II, 17 patients (39.5%) un-derwent tube thoracostomy, 24 (55.8%) unun-derwent obser-vation, 1 (2.3%) underwent urgent thoracotomy, and 1 (2.3%) received VATS. In Group I, pneumothorax was on the right in 21 patients (48.8%), on the left in 21 (48.8%), and as bilateral pneumothorax in 1 (2.3%). There was recurrence
Figure 1 Chest height and transverse diameter measure-ment on posteroanterior chest radiography.
in 11 patients (25.6%) in Group I and 9 (81.8%) were male (Table 1). Mean BMI was 19.9 1.66 (16.6e24.8) kg/m2and 24.9 4.32 (16.7e35.1) kg/m2 in Group I and II,
respec-tively. Mean CH was 32.02 2.96 (26.73e37.34) and
28.65 3.08 (21.97e35.34) cm in Groups I and II,
respec-tively. Transverse thorax diameter was 28.90 2.20
(24.14e32.82) cm in Group I and 28.43 2.38 (23.71e33.63) cm in Group II. Mean BMI/CH was 0.627 0.08 (0.487e0.887) in Group I and 0.881 0.20 (0.593e1.498) in Group II (Table 2).
A statistically significant relationship could not be found between Group I and Group II (pZ 0.279).
A statistically significant relationship was not found
be-tween recurrence and mean CH (pZ 0.767), mean
trans-verse diameter (p Z 0.311), mean BMI (p Z 0.404) and
Ankara Numune Risk Index (pZ 0.463) (p > 0.05). In Group
I, a statistically significant difference was found between recurrence and mean age (pZ 0.022) (p < 0.05). Recur-rence increased with age in Group I.
The difference between Group I and Group II with regard to mean CH (pZ 0.000), mean BMI (p Z 0.000) and Ankara Numune Risk Index (pZ 0.000) was found to be statistically significant (p < 0.05). Although mean CH was higher in Group I compared with Group II, mean BMI and mean Ankara Numune Risk Index were lower in Group I compared with Group II. A statistically significant difference was not found between groups with regard to mean transverse diameter (pZ 0.344) (p > 0.05) (Table 2).
When ROC curve analysis was carried out for optimal limit value 0.74 of Ankara Numune Risk Index determined for prediction of pneumothorax development risk, the area under the curve was 0.925 (95% confidence interval [CI], 0.872e0.977, p < 0.001). 0.74 is the cut off value for Ankara Numune Risk Index. Sensitivity and specificity values for Ankara Numune Risk Index were 0.9302; 95% CI (0.8139e0.9760) and 0.7674; 95% CI (0.6226e0.8685) (k 0.698; p< 0.001). Positive and negative predictive values for limit value of Ankara Numune Risk Index were 0.8000; 95% CI (0.6971e0.8756) and 0.9167; 95% CI (0.8318e0.9626) (Figure 2).
4. Discussion
Pneumothorax was first reported by Itard in 1803 and its clinical findings were first described by Laennec in 1819.10 12Kjaergard reported that PSP was different from
tuberculosis pneumothorax in 1931. Later, Devillier
explained the pathophysiology secondary to subpleural bulla.13Structural factors such as thorax measurements and BMI also play a role in the development of subpleural bullae.
Ample amounts of studies are available in the literature investigating the role of structural factors in PSP develop-ment. Peters et al14reported that CH/transverse diameter ratio was high in male patients with PSP, anteroposterior diameter decreased in female patients, and the shape of the thorax played a role in pneumothorax development depending on stress distribution in the lungs. However, Kawakami et al15 reported that stress distribution in the
lungs is not a major risk factor because they could not find a difference between patient and controls with regard to chest height in PSP patients. Casha et al16reported that low thoracic index leads to high apical stress and they increased pleural pore and bulla development and although this stress
Table 2 Comparison of body mass index, chest height, transverse chest diameter and body mass index/chest height (Ankara Numune Risk Index) of both groups.
Group I Group II p
BMI 19.9 1.66 (16.6e24.8) 24.9 4,32 (16.7e35.1) 0.000 CH 32.02 2.96 (26.73e37.34) 28.65 3.08 (21.97e35.34) 0.000 Transverse chest diameter 28.90 2.20 (24.14e32.82) 28.43 2.38 (23.71e33.63) 0.344 BMI/CH (Ankara Numune Risk Index) 0.627 0.08 (0.487e0.887) 0.881 0.20 (0.593e1.498) 0.000
BMIZ body mass index; CH Z chest height.
Table 1 Patient demographic characteristics. Group I (nZ 43, 50%) Group II (nZ 43, 50%) All (nZ 86, 100%) Age 24.9 6.36 (16e40) 30.4 6.81 (18e40) 27.7 7.12 (16e40) Sex Male 37 (86%) 32 (74.4%) 69 (80.2%) Female 6 (14%) 11 (25.6%) 17 (19.8%) Disease PSP 43 (100%) d 43 (50%) Blunt trauma d 27 (62.8%) 27 (31.4%) Penetrating trauma d 15 (34.9%) 15 (17.4%) Mediastinal mass d 1 (2.3%) 1 (1.2%) Hospital stay (d) 5.98 1.74 5.58 6.08 5.78 4.45 Treatment Oxygen therapy 3 (7%) 24 (55.8%) 27 (31.4%) Chest tube 29 (67.4%) 17 (39.5%) 46 (53.5%) VATS 11 (25.6%) 1 (2.3%) 12 (14%) Thoracotomy d 1 (2.3%) 1 (1.1%) Site NE Right 21 (48.8%) Left 21 (48.8%) Bilateral 1 (2.3%) Recurrence 11 (25.6%) NE
NE Z nonexamined; PSP Z primary spontaneous pneumo-thorax; VATSZ video-assisted thoracoscopic surgery.
decreases in women and the elderly, it increases in the young. Chang et al17 reported that CH and upper chest width measurements increase in adolescents (12 years and older) differently from the normal population and thereby thorax measurements are a structural risk factor. Saita et al18 reported that PSP patients had subclinical chest
deformity based on the tomography of thorax images, and this condition was related to subpleural bleb formation through leading to alveolar pressure heterogeneity.
BMI is the measurement of obesity found by dividing body weight (kg) by the square of height (m2), which was defined by Adolphe Quetelet in 1832.19In the literature, BMI of PSP patients is reportedly lower than that of normal patients and this is a structural risk factor for
PSP.6e8 Case reports are available in the literature
reporting that PSP develops as the result of sudden increased intra-alveolar pressure due to vomiting as lung elasticity decreases as a result of impaired nutrition in patients with a low BMI.20
In the literature, we can see that various radiological sizes of the thorax are used for investigating the structural properties of PSP. Peters et al14investigated CH/transverse
diameter ratio and anteroposterior diameters on chest graphs. Casha et al16 measured apical stress with apical
measurements of the lung using computed tomography of the thorax and evaluated the relationship between them by finding thoracic indices with Bellemare’s method. Saita et al18investigated the structural relationship by measuring asymmetry ratios of anteroposterior and transverse di-ameters on computed tomography of the thorax of PSP patients. Chang et al17evaluated CH by measuring from the
apex to the costodiaphragmatic sinus in the right lung on a PA chest radiograph, and transverse diameter by measuring from rib levels 2, 6, and 9 on PA chest radiograph. We carried out our measurements in the manner described by Chang et al,17 but we only used rib level 6 for transverse
measurement.
We did not use transverse diameter averages because we did not find a statistically significant difference between groups (p> 0.05). Instead, we used BMI and CH ratios that showed a statistically significant difference between groups (p < 0.05). In our study, BMI ratio per cm of CH was
calculated by dividing BMI/CH when determining the pneu-mothorax risk index. This showed us that structural char-acteristics in asthenic patients were directly proportional with BMI and inversely proportional with CH. This formula, which determines PSP risk, was first described by us and named the Pneumothorax Risk Index (Ankara Numune Risk Index). Ankara Numune Risk Index averages were found to be significantly different between groups (p < 0.05). We found a cut-off value of 0.74 for Ankara Numune Risk Index. According to this information, we identified values< 0.74 as a risk factor for PSP development.
In the literature, although some authors consider that detection of bullous lesions on high-resolution computed tomography obtained at the first exacerbation is a risk factor for prediction of ipsilateral recurrence, some others consider the opposite.12,21 We could not find a significant difference between recurrence and CH, BMI, and Ankara Numune Risk Index in Group I patients (p > 0.05). Therefore, we considered that the Ankara Numune Risk Index is insufficient for prediction of recurrence.
Where to use the new structural index is an important topic of discussion. This index is one of the primary struc-tural risk factors that can predict the risk of spontaneous pneumothorax. Therefore, it may be useful in the recruit-ment medical examination used for professions with a high risk of pneumothorax, such as pilots or divers.
5. Conclusion
There are many structural, congenital, and environmental risk factors for PSP development. Ankara Numune Risk Index is one of the structural risk factors for prediction of PSP development. However, it is insufficient for deter-mining recurrence; however, the Ankara Numune Risk Index could give direction to the discovery of new structural indices for the prediction of the recurrence of PSP in future studies.
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