In my last post, I reviewed a large prospective series comparing smaller (28-32 Fr) to larger (36-40 Fr) chest tubes for management of pneumothorax. The authors did not detect any significant difference because the study was underpowered given the incidence of the adverse events examined.
Today, I’ve chosen a more recent paper that attempts to do the same thing. Interestingly, it cites the previous paper as a good example showing no differences! This one is from an emergency medicine group in Fukui, Japan. It is a retrospective review of seven years worth of patients who had a chest tube inserted for hemothorax only.
Here are the factoids:
- Small bore tubes were 20-22 French, and large bore tubes were 28 French (huh?)
- The tube selection was made (once again) at the discretion of the attending physician
- Demographics and injury data from the two groups were equal
- A total of 124 tubes were placed in 116 patients, 68 small bore and 56 large bore
- Empyema occurred in 1% in each group
- Retained hemothorax occurred in 2% of small tube patients and 3% of large tube patients
- An additional tube was placed in 2% of small tube patients and 7% of large tube patients (p = 0.41)
- Pain was not evaluated
The authors concluded that “emergent insertion of the small-bore tubes had no difference in efficacy of drainage, complications or need for additional invasive procedures.”
Bottom line: Huh? Once again we have an inferior design (retrospective review) and huge potential for selection bias (no criteria or randomization for tube size). But in this case, the tube sizes are very similar! The difference in diameter between a 20 Fr tube and a 28 Fr one is only 2.5mm! Reason #1 for no apparent differences.
For reason #2, look at the sample size. First of all, this hospital placed only 124 tubes in 7 years. That’s a one tube every three weeks. Is there that little chest trauma, or is a chunk of data missing? This sample size is less than half of that in the previous post, so the statistical power is far weaker. Look at the stats above for additional tube placement. A 3.5x change was not even close to being statistically significant. In fact, this sample size would not show a significant difference for retained hemothorax until one group had nearly 8x the number! No wonder the authors assumed there was no difference. The study was not designed in such a way that it could ever show one!
So throw this study in the trash bin, too. I’ll continue my search for a more convincing “size matters” paper in my next post.
And if you think you’ve got one, send it my way so I can have a look!
Reference: Small tube thoracostomy (20-22 Fr) in emergent management of chest trauma. Injury 48(9):1884-1887, 2017.