A cadaver based descriptive study was performed in Faculty of Medicine, Khon Kaen University, Thailand. Fresh cadaveric tissue dissection was conducted from February 2017 to December 2018. All fresh non-embalmed human bodies were kept in refrigerator at -20o C until 30 minutes before study, after that they were allowed to warm in room temperature. Age, sex, weight, height and BMI were collected for each cadaver. Any cadaver with chest wall abnormality was excluded.
From the Inaba et al4 study found that the mean thickness of chest wall at the intersection between 5th intercostal space and mid-axillary line in 20 cadavers is 3.5 cm. (SD 0.9 cm.) the SD 0.9 cm is used for calculating. And the pilot study in the computer tomography, we found that the mean thickness of chest wall from the 20 samples is 2.8 cm. (SD 0.9 cm). It difference from the previous study. we determine the precision(d) = 0.3 cm. And when the numbers are calculated in the formula. Therefore, sample size in the study had at least 35 positions, or at least 18 cadavers.
Chest wall of the cadavers was drawn anterior axillary line; mid axillary line; and midpoint between these lines, called anterior-mid axillary line in this study, intersect with 3rd to 7th intercostal space (Figure1). The thickness of chest wall is collected by sternotomy and enter to the pleural cavity, puncturing of 56 mm, 16G needle (Figure2) and clamp while seeing tip of the needle then measure with standard ruler and collect data in data record form. The measured values are recorded in millimeters (mm.) and one decimal place.
All of the thickness of areas of chest wall were collected. Continuous data wes presented in mean and standard deviation. Categorized data were presented in percentage.
The Ethic Committee of Khon Kaen University approved this study on October 19th, 2017 (reference HE601075)
Figure 1 The line over the cadavers chest wall
Figure 2 - 16G Punctured needle (56 mm. length)
Twenty cadavers (40 chest wall sides) was used in this study. There were 14 male and 6 female cadavers. The mean age was 73.6 years old (range from 58-91). The average BMI was 23.7 (range from 18.0 to 32.9) kg/m2.
The mean chest wall thickness within the safety triangle varies between 14 mm. and 25 mm. (Figure 3). The points on the anterior axillary line in each intercostal space were thinner than other locations. The thinnest point was the intersection of anterior axillary line the 7th intercostal space. the thickest points were on the mid-axillary line especially at 5th intercostal space.
Figure 3 - The mean chest wall thickness on safety triangle area
There were three extreme cases found in this study, the thinnest chest wall, the thickest chest wall and the highest BMI.
The thinnest chest wall cadaver was the 82 years old male with 185 cm. tall and 82 kg. in weight, the BMI was 24 kg/m2 (Figure 4). His chest wall was thinner than the others in all area and the thinnest area was 5mm. at the intersection of anterior axillary line with 7th intercostal space.
Figure 4 The thinnest chest wall cadaver, 82 years old man; body weight 82 kg, height 185 cm, BMI 24 kg/m2
The second case was 76 years old female cadaver with 150 cm. tall and 60 kg in weight, the BMI was 26.7 kg/m2 (Figure 5). She had the thickest chest wall in this study. The area thicker than 50 mm. was located on the intersection of anterior axillary line with 3rd intercostal space. The points on the anterior axillary line were thicker than other points in each intercostal level.
Figure 5 The thickest chest wall cadaver, 76 years old woman; body weight 60 kg, height 150 cm, BMI 26.7 kg/m2
The last case, 65 years old male cadaver who had the highest BMI in this study. He was 170 cm. in height and 95 kg. in weight, the BMI was 32.9 kg/m2 (Figure 6). Although he had a high BMI, he has chest wall close to average chest wall thickness in this study. His chest wall thickness was between 13 mm. to 22 mm.
Figure 6 The highest BMI cadaver, 65 years old man; body weight 95 kg, height 170 cm, BMI 32.9 kg/m2
The areas with more than 50 mm. thickness were mostly found in the mid-axillary line and two cadavers (54 and 56 mm.) in the 3rd intercostal space crossing with anterior axillary line.
From observation, we found that the intersection of anterior axillary line with imaginary nipple line be almost on the 5th intercostal space, in male cadaver. The intersection of mid-axillary line with imaginary nipple line be almost on the 6th intercostal space.
In this study, the average thickness of the chest wall at the intersection of 5th intercostal space with anterior axillary line (18-19 mm.) was less than other studies (31.6-39.9 mm.)4-7.
Kenji Inaba, et al.4 mentioned about cadaveric study, by requiring pre-hospital medical personnel performed needle thoracocenthesis. Then measure the chest wall thickness and success rate of procedure at 2nd intercostal space midclavicular line compared with 5th intercostal space anterior axillary line. There was statistical significant different in chest wall thickness of both locations, the 5th intercostal space was 1.2(1.5) cm., and the 2nd intercostal space was 3.1(1.7) cm. (p<0.001). The success rate of the procedure in 5th intercostal space anterior axillary line was 82.0% and in 2nd intercostal space midclavicular line was 22.0%.
Danuel V. Laan, et al7, performed a meta-analysis of 15 studies comparison of chest wall thickness in 3 locations, 2nd intercostal space midclavicular line, 4th-5th intercostal space anterior axillary line and 4th-5th intercostal space midaxillary line. The mean thickness of the chest wall were 42.79(38.78-46.81) cm., 34.33 (28.20-40.47) cm., and (28.70-51.00) cm. respectively.
Laws D., et al3, study the proper location to insert the intercostal drain called Safe triangle, which has boundaries are the anterior edge of latissimus dorsi muscle, lateral edge of pectoralis major muscle, superior to nipple level and below axilla level.
The recommended area for insertion the tube thoracostomy in male patient is intersection of anterior axillary line with imaginary nipple line (5th intercostal space).
The thinnest areas are on the 7th intercostal space, anterior axillary line but insertion tube thoracostomy below the 6th intercostal space should be dangerous because when fully exhale the highest diaphragm level could reach to 6th intercostal space. In this study, we found that the intersection of mid-axillary line with imaginary nipple line is 6th intercostal space. Thus, insertion tube thoracostomy below the nipple line must be careful.
The chest wall thickness is related to BMI5,6 but in this study found some of cadavers do not meet expectations. We found that not only the BMI can affect the thickness of the chest wall.
The limitation in this study was studying in the elderly cadavers. It cannot be represented the younger population. In the female cadaver, we did not retract the breast while measuring. It may explain that why some female has thicker chest wall on the anterior axillary line.
The chest wall thickness in this study is thinner than others. The area for insertion of the tube thoracostomy should be carefully selected, especially in woman and the obese patients. Insertion below 6th intercostal space should be avoided due to risk of peritoneal penetration.
Some areas in the safety triangle for tube thoracostomy insertion are more than 50 mm. in thickness. The area for insertion of the tube thoracostomy should be carefully selected, especially in woman and the obese patients.
1. Ronald M. Stewart, MD, FACS. Advanced Trdauma Life Support (ATLS) 10th Edition. Chicago, IL: American College of Surgeons, 2018.
2. Peter I Tsai, Matthew J Wall Jr, Kenneth L Mattox. Trauma Thoracotomy - General Principles and Techniques. In: Earnest E Moore, David V Feliciano, Kenneth L Mattox, Editors. Trauma 8th edition. New York: McGraw Hill, 2017: 473-478.
3. Laws D, Neville E, Duffy J. BTS guidelines for the insertion of a chest drain. Thorax. 2003 May; 58: 53-59.
4. Inaba K, Karamanos E, Skiada D, Grabo D, Hammer P, Martin M, et al. Cadaveric comparison of the optimal site for needle decompression of tension pneumothorax by prehospital care providers. J Trauma Acute Care Surg. 2015; 79: 10441048.
5. Chang SJ, Ross SW, Kiefer DJ, Anderson WE, Rogers AT, Sing RF, et al. Evaluation of 8.0-cm needle at the fourth anterior axillary line for needle chest decompression of tension pneumothorax. J Trauma Acute Care Surg. 2014; 76:10291034.
6. Inaba K, Ives C, McClure K, Branco BC, Eckstein M, Shatz D, et al. Radiologic evaluation of alternative sites for needle decompression of tension pneumothorax. Arch Surg Chic Ill 1960. 2012; 147: 813818.
7. Laan DV, Vu TDN, Thiels CA, Pandian TK, Schiller HJ, Murad MH, et al. Chest wall thickness and decompression failure: A systematic review and meta-analysis comparing anatomic locations in needle thoracostomy. Injury. 2016; 47: 797804.