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There has been much debate over the preferred location for needle decompression of a tension pneumothorax.
Chest wall thickness (CWT) is related to BMI.
In overweight- and obese subjects, mean CWT is thinner in the 2nd intercostal space in the midclavicular line (ICS2-MCL) compared to the 4th/5th ICS in the anterior axillary line (ICS 4/5-AAL).
Theoretical changes of successful needle decompression of a tension pneumothorax using standard equipment are significantly higher in ICS2-MCL compared to ICS 4/5-AAL.
Tension Pneumothorax (TP) can occur as a potentially life threatening complication of chest trauma. Both the 2nd intercostal space in the midclavicular line (ICS2-MCL) and the 4th/5th intercostal space in the anterior axillary line (ICS 4/5-AAL) have been proposed as preferred locations for needle decompression (ND) of a TP. In the present study we aim to determine chest wall thickness (CWT) at ICS2-MCL and ICS4/5-AAL in normal weight-, overweight- and obese patients, and to calculate theoretical success rates of ND for these locations based on standard catheter length.
We performed a prospective multicenter study of a convenience sample of adult patients presenting in Emergency Departments (ED) of 2 university hospitals and 6 teaching hospitals participating in the XXX consortium. CWT was measured bilaterally in ISC2-MCL and ISC4/5-AAL with point of care ultrasound (POCUS) and hypothetical success rates of ND were calculated for both locations based on standard equipment used for ND.
A total of 392 patients was included during a 2 week period. Mean age was 51 years (range 18-89), 52% was male and mean BMI was 25.5 (range 16.3-45.0). Median CWT was 26 [IQR 21-32] (range 9-52) mm in ISC2-MCL, and 26 [21-33] (range 10-78) mm in ICS4/5-AAL (p<0.001). CWT in ISC2-MCL was significantly thinner than ICS4/5-AAL in overweight- (BMI 25-30, p<0.001), and obese (BMI>30, p=0.016 subjects, but not in subjects with a normal BMI. Hypothetical failure rates for 45mm Venflon and 50mm Angiocatheter were 2.5% and 0.8% for ICS2-MCL and 6.2% and 2.5% for ISC4/5-AAL (p=0.016 and p=0.052 respectively).
In overweight- and obese subjects, the chest wall is thicker in ICS 4/5-AAL than in ICS2-MCL and theoretical chances of successful needle decompression of a tension pneumothorax are significantly higher in ICS2-MCL compared to ICS 4/5-AAL.
Tension Pneumothorax (TP) is a threatening complication of chest trauma due to collapse of the lung and mediastinal shift away from the affected side, resulting in hypoxemia and a reduction in venous return [
]. This can ultimately result in respiratory- and cardiac arrest, and may develop quickly in ventilated patients. Immediate intervention is therefore warranted. Advanced trauma life support guidelines [
] advise needle decompression (ND) with a wide bore catheter as a temporizing treatment until definitive treatment, by insertion of a chest tube in the 5th ICS anterior to the mid-axillary line (MAL), is available.
There has been much debate however, over the preferred location for ND. Whereas the ATLS recommendations have changed in 2018 from the 2nd intercostal space in the midclavicular line (ICS2-MCL) to the 4th/5th intercostal space just anterior to the mid axillary line (ICS 4/5-MAL), other guidelines such as the ETC trauma guidelines [
One of the considerations for choosing the location for ND is the likelihood of penetration of the needle into the thoracic cavity. This likelihood depends on both patient- (chest wall thickness(CWT)) and equipment factors (needle length). Previous studies [
] investigating the relation between anatomical location and (hypothetical) success rate of ND were hampered by small sample sizes, single center- and/or retrospective designs, homogenous populations (some were performed exclusively in military personnel [
]. As a result, the quality of evidence for the best anatomical location to perform ND is low. Furthermore, although it is well known that CWT increases with BMI, it is unknown if the optimal place for ND may vary with BMI.
Therefore, in the present study we aim to determine CWT at various anatomical locations in normal weight-, overweight- and obese patients, and to calculate theoretical success rates of ND for these locations based on standard catheter length.
Patients and methods
Study setting and design
We performed a multicenter observational study of a convenience sample of patients presenting in the ED of 8 hospitals during a two-week period from June 11th-23rd 2019. Participating hospitals were university hospitals (n=2) or teaching hospitals (n=6) participating in the PRIDE POCUS consortium. Ethical approval was obtained from the ethical committee of the METC of the University Hospital Groningen, University of Groningen, protocol number 2018/270, UMCG research register number 201800322.
Selection of participants
All adult patients (>18 years) were eligible to participate if they presented to the ED of one of the participating hospitals (full list at affiliations) during the study period, and provided written consent for participation. Patients with (pre-existing) thoracic deformities, patients who were seriously ill requiring continuous urgent care and patients who were unable to provide consent were excluded from participation.
Following consent, each patient's sex, age, weight and height were recorded and Body Mass Index was calculated. Ultrasound of the chest was subsequently performed by 36 physicians certified in the use of point-of-care ultrasound for examination of lung and pleural space. Ultrasonographic examination of the chest was performed with the patient lying supine on the bed with the arm 90 degrees abducted and the elbow in flexion according to a standard protocol. Images were obtained with the linear high frequency probe (12-5 MHz) in small parts- pleural- or MSK pre-setting. Without any compression the probe was placed exactly perpendicular to the chest wall with the marker to the patients head. The CWT was measured from skin to pleural line at the 2nd intercostal space in the mid clavicular line (ICS2-MCL) and in the 4th/5th ICS in the anterior axillary line (ICS4/5-AAL) on both sides of the chest. Measurements were recorded on a paper CRF and subsequently entered in a dedicated electronic CRF (Castor EDC) by the investigators. Images were recorded for review. Quality control of measurements was performed at the coordinating central hospital site by an Emergency physician internationally certified in Point of Care Ultrasound by the Ultrasound Leadership Academy. A list of ultrasound machines used in this represented in Supplementary file 1.
Hypothesis and outcomes
Null hypothesis was that the CWT in ICS2-MCL was not thicker than ICS4/5-AAL (non-inferiority margin 2mm), and therefore would yield a similar hypothetical success rate for ND.
Primary outcome was defined as the difference in CWT as measured by ultrasound between ICS2-MCL and ICS4/5-AAL.
Secondary outcomes were the relation between chest wall thickness and BMI, and the hypothetical ND failure rate for each anatomical location based on the length of the standard 45- and 50 mm thoracocentesis devices used in normal practice.
The study was powered on the primary objective, e.g. the difference in CWT between ICS2-MCL and ICS4/5-AAL. Based on a non-inferiority design with a power of 90%, an alpha of 0.05 and a non-inferiority margin of 1 mm, under the assumption that mean CWT is 30 (SD4) mm [
] for patients with a normal BMI (<25), the required sample size was calculated to be n=275 per anatomical location. To account for patients with higher BMI's and missing data it was decided to recruit at least 350 patients. The distributions of chest wall thickness are summarised by the median, quartiles and range. However, parametric tests of significance (paired and independent t-tests) are applied to the measurements, as there are large sample sizes and the Central Limit Theorem ensures normality of the means. Hypothetical failure rates of standard 45- and 50 mm ND equipment on different anatomical locations were compared using McNemar's test. Pearson correlation coefficients were calculated for the association between BMI and CWT on various locations. Chest-wall thickness was compared across different BMI groups using ANOVA with post-hoc Tukey comparisons. A p-value <0.05 was considered statistically significant. All statistical analysis were conducted with SPSS 26.0 software, SPSS, USA)
During the study period, 392 patients were screened, and CWT was measured and recorded in 390 patients presenting to the ED (in 2 patients images were accidentally not stored) in one of the 8 participating hospitals. Mean age was 51 years (range 18-89), and 204 (52%) were male. Mean BMI was 25.5 (range 16.3-45.0).
Results of CWT measurements stratified by location of measurement and gender are represented in Table 1.). Median CWT was 26 [IQR 21-32] (range 9-52) mm in ISC2-MCL, and 26 [21-33] (range 10-78) mm in ICS4/5-AAL (p<0.001). Female patients had a slightly thicker chest wall than males, both in the 2nd and 4/5th ICS, although the differences did not reach statistical significance.
Table 1Median chest wall thickness in mm, stratified by gender in a heterogeneous population of patients visiting the ED (n=390).
25 [20-32] (9-57)
26 [19-32] (9-52)
25 [21-32] (10-57)
26 [21-31] (8-57)
26 [21-32] (8-49)
25 [20-31] (10-57)
26 [21-32] (9-52)
26 [20-32] (9-51)
26 [22-32] (11-52)
26 [21-32] (10-76)
27 [20-31] (10-61)
25 [21-32] (11-76)
26 [21-35] (9-79)
27 [21-34] (9-56)
26 [21-35] (12-79)
26 [21-33] (10-78)
26 [21-32] (8-49)
25 [22-34] (12-78)
Legend Table 1. Represented are Median [IQR] (range). ICS-2MCL, 2nd intercostal space, midclavicular line; ICS4/5-AAL, 4th/5th intercostal space anterior axillary line.*Independent t-test for difference between males and females.
The median CWT in the ICS2-MCL was 22 [18-27] (range 9-41) mm in lean subjects, 27 [23-31] (range 12-47)mm in overweight subjects (BMI 25-30) and 35 [30-40] (range 21-52) mm in obese subjects (BMI>30), p<0.001). A similar increase in CWT with increasing BMI was present for the ICS4/5-AAL: 22 [19-26] (range 10-53) mm in lean-, 29 [25-34] (range 13-51) mm in overweight- and 39 [31-45]] (range 23-78) mm in obese subjects (p<0.001). Overall there was a moderate correlation between BMI and CWT in both ICS2-MCL (r=0.64, p<0.001) and ICS4/5-AAL (r=0.67, p<0.001). The difference in mean chest wall thickness between the 2nd and 4th/5th ICS was BMI dependent: Whereas thickness was not significantly different between the 2nd and 4th/5th ICS in lean subjects, chest wall was significantly thicker in the 4th/5th ICS compared to the 2nd ICS in overweight and obese subjects (Table 2, Fig. 2).
Table 2Chest wall thickness on different anatomical locations stratified by BMI (n=390).
Mean diff [95% CI]
BMI <25 (n=188)
22 [18-27] (9-41)
22 [19-26] (10-53)
BMI 25-30 (overweight) (n=136)
27 [23-31] (12-47)
29 [25-34] (13-51)
BMI> 30 (obese) (n=66)
35 [30-40] (21-52)
39 [31-45] (23-78)
Legend table 2. Represented are median [IQR] (range). ICS-2MCL, 2nd intercostal space, midclavicular line; ICS4/5-AAL, 4th/5th intercostal space anterior axillary line.*paired t-test for comparison ICS2-MCL and ICS4/5-AAL.
CWT in relation to (un)successful needle thoracocentesis
Hypothetical failure rates of standard equipment available to perform needle thoracocentesis based on the observed chest wall thickness in various locations are represented in Table 3. Failure rates range from 0.8% for 50 mm Angiocatheters placed in the ICS2-MCL to 6.2% for a 45mm 14 or 16G IV catheter placed in the ICS4/5 AAL. When a minimal penetration depth of 5 mm in the thoracic cavity to prevent dislodgement was set as a prerequisite, failure rates increased significantly (Table 3). Hypothetical failure rates for both 45 mm IV catheters and 50 mm angiocatheters were significantly higher in the 4th/5th ICS
Table 3Hypothetical failure rates of standard equipment available to perform needle thoracocentesis based on chest wall thickness measurements in a heterogeneous population of patients visiting the ED (n=390).
ICS2- MCL failure rate n (%)
ICS4/5-AAL failure rate n (%)
45 mm IV catheter (tip at pleura)
45 mm IV catheter (tip ≥5mm in chest)
50 mm Angiocatheter (tip at pleura)
50 mm Angiocatheter (tip ≥ 5 mm in chest)
Legend table 3. ICS-2MCL, 2nd intercostal space, midclavicular line; ICS4/5-AAL, 4th/5th intercostal space anterior axillary line.*McNemar test for difference between ICS-2 and ICS4/5.
Of the 24 patients in whom a 45 mm IV catheter would not have penetrated the pleura in the ICS4/5-MCL, a subsequent attempt in ICS2-AAL would have been successful in 18 patients (Fig. 1). There were no patients in whom a 50mm Angiocatheter would not have penetrated the pleura on both ICS2-AAL and ICS4/5MCL.
In a heterogeneous cohort study of patients attending the ED, we demonstrate that the chest wall in ICS4/5-AAL measured with POCUS is significantly thicker than in ICS2-MCL in overweight- and obese subjects, and that theoretical failure rates of standard equipment to decompress a tension pneumothorax are lower for ICS2-MCL compared to ICS 4/5-AAL.
These findings are in sharp contrast to the latest treatment recommendations of the Advanced Trauma Life Support (ATLS), wherein placement in the ICS4/5 just anterior to the MAL is advocated [
] demonstrating a lower CWT for ISC2-MCL compared to ICS4/5-AAL. The reported heterogeneity most likely not only originates from differences between study populations, but also from differences in measurement of CWT. Several studies were exclusively performed in military personnel, consisting mostly of young men [
]. As young males often have well-developed pectoral muscles, findings may not be representative of the general population. This is confirmed by a previous study on chest wall thickness performed in elite rugby players [
]. Although cadavers are often used to practice invasive procedures as (needle) thoracostomies, we don't know how post-mortal changes in tissue composition and density influence thoracic wall composition and resultant measurements. Finally, CT-scanning was used in almost all non-cadaveric studies to estimate CWT. As arm-positioning during CT-scanning (erect or compressed against the chest wall) likely influences CWT, this is a potential confounder not accounted for.
We found not only that CWT was lowest at the ICS2-MCL, but, also that hypothetical failure rates of standard equipment used to decompress a tension pneumothorax were lowest at this anatomical location. We report a hypothetical failure rate of 2.5% for 45 mm IV catheters, and only 0.8% for a standard 50 mm Angiocatheter at ICS2-MCL, which is low compared to previous cadaveric, radiographic, and clinical studies [
], these differences may be explained by the lower average BMI in our study population compared to previous studies. BMI in our population however, equals the average for the Dutch population, and is in line with previously reported values for western populations [
Although hypothetical failure rates for needle thoracostomy in our study were low both for ICS2-MCL and ICS 4/5AAL, we demonstrate that the difference in CWT between both anatomical locations increases with increasing BMI in favor of ICS2-MCL (Fig. 2). Therefore, this seems the preferred anatomical location for chest decompression for overweight- and obese subjects.
When ND is warranted in a patient with rapidly deteriorating haemodynamics and a presumed tension pneumothorax, there is no time to use ultrasound to establish the optimal location for ND. When there is time to use ultrasound, ND is usually not the treatment of choice. Therefore, based on our study results, we recommend to perform a ND in ICS-2 MCL with a 50mm (or longer) angiocatheter as a temporizing measure in haemodynamically compromised patients when a tension pneumothorax is suspected, and when a finger thoracostomy cannot be performed immediately due to restricted (prehospital) access to the patient, or when personnel trained to perform a finger thoracostomy is not present
Our study has several limitations. First, although the study was performed in a heterogeneous cohort of ED patients, patients with acute pathology warranting immediate treatment were excluded from our study. Second, we cannot exclude that compression of the chest wall by the ultrasound probe may have influenced CWT measurements on certain instances. Third, CWT may vary between various study populations. In countries with a higher average BMI, hypothetical failure rates for needle decompression of the chest with a 5 cm needle are likely higher, warranting adaptations to standard equipment (e.g. using an 8 cm instead of 5 cm Angiocatheter needle). However, as we demonstrate that differences in CWT between ICS2-MCL and ICS 4/5 AAL increase with increasing BMI, this will likely not influence the preferred anatomical site for needle decompression. Furthermore, in our study we studied hypothetical failure rate. True failure to decompress a tension pneumothorax however, may also be present due to other factors than CWT in relation to needle length, such as catheter diameter, obstruction by blood or tissue, and/or kinking- or dislodgement of the catheter, which may be related to the anatomical site chosen [
]. Although we have not quantified this in our study, we assume that placement in the ICS2-MCL will leave the catheter less prone to obstruction by blood (as patients are usually treated supine) and/or dislodgement due to arm movements. In addition, ICS 4-/5-AAL is more difficult to access during transport in ambulance or helicopter, when abduction of the arm might be difficult to achieve. A theoretical disadvantage however, is that ICS2-MCL is harder to define anatomically, and therefore a catheter inserted here may not go in where intended. Finally, our findings cannot disprove ATLS recommendations, as we measured CWT in ICS 4/5-AAL and not just anterior of MAL. However, it is unlikely that our results would have been different for ICS 4/5 MAL, as a recent meta-analysis [
] demonstrated that the average CWT was thicker in ICS 4/5 MAL compared to AAL.
In overweight- and obese subjects, the chest wall is thicker in ICS 4/5-AAL than in ICS2-MCL and theoretical changes of successful needle decompression of a tension pneumothorax are significantly higher in ICS2-MCL compared to ICS 4/5-AAL.