Decompression of tension pneumothorax in children is a rare but life-saving procedure that usually has to be performed under pressure. Due to the tiny spatial relationships, it carries a significant risk of injury to intrathoracic structures, especially in smaller children. Knowledge of chest wall thickness and width of the intercostal space enables the provider to choose the optimal decompression needle regarding length and bore but has only been investigated by few studies so far [2,3,4, 9]. Especially the correlation of age and body dimensions with these values has not been well investigated. Knowledge of these correlations could therefore assist in predicting the needed depth of insertion for decompression and minimize the risk of injury to intrathoracic structures and the intercostal vessels and nerve.
Chest wall thickness and width of the intercostal space
In this study, we only found moderate correlations between measures of the chest wall relevant for needle decompression and body dimensions like age, weight and height. For chest wall thickness, the highest correlation was found with weight of the children (2nd ICS MCL r = 0.57, 4th ICS AAL r = 0.64). BMI also correlated well with CWT at 4th ICS AAL (r = 0.60) but not at 2nd ICS MCL (r = 0.44). Correlation for Broselow categories (2nd ICS MCL r = 0.42, 4th ICS AAL r = 0.38) and height (2nd ICS MCL r = 0.42, 4th ICS AAL r = 0.40) were lower and the lowest correlation was found for age (r = 0.38 at both insertion sites). Hossain et al. investigated CWT in a convenience sample of children presenting to the emergency department using ultrasound. Their results for correlation of CWT with weight (2nd ICS MCL: r = 0.55; 4th ICS AAL: r = 0.58) are comparable to ours. Correlation of CWT with age, height, BMI and Broselow color, however, was not investigated. Mandt et al. in a CT-based evaluation, also found the highest correlation between chest wall thickness and weight (2nd ICS-MCL: r = 0.53; 4th ICS-AAL: r = 0.45) and reported a lower correlation with height-based Broselow categories . In most adult studies however, BMI, followed by weight, showed the strongest correlation with chest wall thickness [10,11,12]. In multivariable regression analysis in this present pediatric study, weight had the greatest influence on the children’s CWT, with a more pronounced influence at 4th ICS AAL. However, the effect size was low with a partial R2 ranging from 0.31 to 0.4. Both our own previous data as well as Mandt’s data showed a large variability of CWT within an age group [2, 3]. Given the at most moderate correlation of CWT with anthropometric data, the low effect size in multivariable regression analysis and the large variability within age groups, one seems to be able to roughly guess CWT from patient characteristics, but accurate prediction of the required insertion depth does not seem possible.
One of the many possible complications of needle thoracostomy that has previously been described in adults is laceration of the intercostal vessels . The width of the intercostal space has, to the knowledge of the authors, not received any attention in adult studies and, even though injury appears much more likely in pediatric needle thoracostomy, was only investigated in one pediatric CT-based study . The results of this study match very well with the results of the ultrasound measurements presented here. Previously recommended bore sizes for decompression in infants vary from 22 to 14G. The margin of safety the provider has when using a 14G needle in an infant is extremely small. One might even encounter an infant in which the use of a 14G needle unavoidably leads to laceration of the intercostal vessels. The mean diameter of the 4th ICS at AAL was 5.3 mm in this study, the outer diameter of a common 14G needle is 2 mm. This leaves a mean safety margin of 3.2 mm. Even a slight deviation from the correct angle of insertion in direction towards the upper rib might therefore lead to vessel injury. With an 18G or 22G needle the difference between the outer diameter of the needle and the width of the ICS is still small with 4 mm and 4.4 mm but increases by 25% or 37.5% compared to the 14G needle. Width of the ICS was moderately correlated with age, weight, height and Broselow color (r = 0.58–0.71). There was no correlation with BMI. For all variables, except BMI, correlation was higher at 2nd ICS then at 4th ICS. Multivariable regression analysis showed height being the only factor with significant influence on width of the ICS. This influence was more pronounced at 2nd ICS (R2 = 0.47–0.50) then at 4th ICS (R2 = 0.31–0.37). To our knowledge, there are no other studies investigating influences on width of the ICS in children or adults to which these findings could be compared.
Reproducibility of the measurements
We found an excellent intra-rater agreement with an overall ICC of 0.93 (0.92–0.94). Mean intra-rater difference between left- and right-sided measurements was remarkably small (< 1 mm) at all insertion sites. To our best knowledge, no other studies examining intra-rater reliability of measurements of CWT or width of the ICS exist. Nanikawa et al. assessed intra-rater reliability of sonographic measurements of the thickness of the lateral abdominal wall muscles and found normal to excellent reliability of the measurements (ICC = 0.74–0.96) . Keshwani et al. reported ICCs > 0.9 in measurements of inter-rectus distance in women with rectus diastasis . These reports of high reliability of ultrasound measurements of the abdominal wall match well with our findings of good to excellent intra-rater agreement of sonographic assessment of CWT and width of the ICS.
Vital structures were only detected in children younger than 5 years of age and significantly more often at the 2nd compared to the 4th ICS. The only structures identified by ultrasound were the heart and the thymus gland, large vessel were not detected. In children, different from adults, risk of injury to intrathoracic structures by the decompression needle seems to be a clearly bigger concern compared to insufficient needle length for decompression [1, 3, 16]. Nevertheless, failure of the procedure remains a problem. Quinn et al. report on 10 needle thoracocenteses performed prehospitally, of which 30% failed . If this was due to inadequate insertion depth or other reasons like kinking of the catheters remains unclear. In their further course, all children required mini-thoracostomies for sufficient relieve of tension physiology. The authors therefore question the use of needle decompression in general and favor mini-thoracostomies [17, 18]. Up to the age of 10 years the intercostal width hardly exceeds 10 mm in the AAL . Due to the small intercostal spaces, finger thoracostomy seems to be difficult in children, so a modified technique, e.g., with forceps, has to be used. It will however be hard to establish widespread sufficient training for this in children quite demanding procedure. Needle decompression therefore remains the technique of choice for many providers. The data from this study show that neither CWT nor width of the ICS can be accurately predicted from patient characteristics like age, weight or height. The rather high periprocedural risk of needle decompression in children in combination with the paucity of data has, in recent years, led to studies investigating this topic. As a result, current pediatric trauma guidelines recommend the 4th or 5th ICS AAL as the preferred insertion site together with the use of age appropriate decompression needles to reduce the risk of injury to vital structures . Another possibility to reduce risk of injury and increase decompression success is using ultrasound. Extended Focused Abdominal Sonography for Trauma (eFAST) is an easy to learn and nowadays standard investigation in trauma care in all age groups and includes assessment of pleural sliding to rule out pneumothorax [20, 21]. Measurement of CWT and width of the ICS as well as recognition of vital structures close to the insertion site can easily be incorporated into ultrasound assessment of respiratory failure and preprocedural planning. One can then tailor the choice of needle size, especially diameter, and insertion depth to the individual patient and thereby increase decompression success and reduce risk of injury.
When ultrasound is not available, the provider has to keep in mind that age and height are rather poor predictors of CWT. The best, yet only moderate correlation was found for weight. As a rule of thumb, CWT only increases very little in the first 5 years of life and is slightly bigger at the anterior insertion site. Width of the intercostal space shows a more linear increase and is also bigger at 2nd ICS MCL.