Over the next few days I will be reviewing a number of papers that try to determine whether the dogma that bigger chest tube size is better is actually true.
Here are the questions that need to be answered when reading each one to determine if it’s worth its weight:
- How good is the study design? Obviously, prospective is better than retro. How did the authors decide to put in a small vs a large tube? Were there enough subjects to achieve any meaningful statistical significance?
- Were the tubes used actually different? If the small bore tubes are 30 – 32 French and the large tubes are 36 – 40 French, would that make a difference?
- What were the outcomes studied? Mortality and complications like pneumonia and empyema are too crude and uncommon to detect a difference. But what about incidence of retained hemothorax, accidental removal, subjective pain, or clotting?
- Did the authors identify and acknowledge any limitations in their study?
- Do the conclusions match up with the actual results?
Let’s kick off the chest tube size debate with an oldie but goodie. The first paper I’ll review was published back in 2012 by a busy LA trauma center. They performed a prospective, observational study of their experience with two tube size ranges inserted for hemo- and pneumo-thorax over a three year period. The size ranges were 28-32 for small and 36-40 for large. The size selected was based on the discretion of the attending physician.
A total of 353 chest tubes were placed during the study period. This analysis will only dissect the 275 that were inserted for hemothorax.
Here are the factoids:
- Pertinent demographics were identical for the large and small bore tube patients
- Pneumonia occurred in about 5% of both groups, and empyema in about 5% of both
- Retained hemothorax occurred in 12% of small tubes and 11% of large tubes
- Duration of tube placement was about 6 days in each
- Additional procedures such as thrombolysis, additional chest tubes, VATS, or thoracotomy were 3-6% in both groups and were not statistically different
- Pain scores could only be performed on about 45% of patients, and were not different between the two groups
The authors concluded that there were no differences in complications, tube reinsertion, or need for invasive procedures based on tube size. They also concluded that choice of tube size did not impact outcomes.
Bottom line: The authors seem to be saying that the choice of tube size is not important. And if you only read the abstract or conclusions of this study, you might actually believe it. But wait, the authors end the paper with this telltale sentence:
“Further evaluation of percutaneously placed drainage systems is warranted”
This is code for: “this paper isn’t very good and shouldn’t change your practice; it needs further verification.”
So what are the issues?
- There is huge potential for selection bias since the choice of tube size was based on personal preference. For example, the attending could look at the chest x-ray, see a lot of blood, and decide to use a big tube in that patient. No guidelines or randomization were used.
- The authors did not acknowledge any limitations of the study in their discussion.
- The only outcomes that really counted in this study were incidence of retained hemothorax (which was not very well defined) and additional procedures required. However, if you take the incidence of retained hemothorax in the large bore tube patients and do an analysis of the statistical power of the study, you run into a major problem. Given the number of patients in each of the two groups, this study would only be able to show statistical significance if the number of retained hemothoraces in the small chest tube group doubled! Anything short of 25% retained hemothorax in the small tube group would not be significant. Thus, the authors’ findings that there was no difference between the groups was entirely expected based on sample size.
So this paper does not really say that there is no difference in using a small vs a large chest tube. It says that it was not sufficiently powered to detect anything but a massive difference. Many more patients (thousands) were needed to answer the question.
So the question remains, does (chest tube) size matter? More in the next post.
Reference: Does size matter? A prospective analysis of 28-32 versus 36-40 French chest tube size in trauma. J Trauma 72(2):422-427, 2012.