To our knowledge, this trial is the largest multicentre randomized controlled clinical trial concerning PSP that has been conducted to date. Our reason for performing this study was the introduction of digital drainage systems, which potentially have an advantage in treating PSP. Digital drainage systems have been extensively evaluated in patients who have undergone thoracic surgery, but not in patients with PSP [22-23].
In this randomized controlled trial comparing digital and analogue chest tube drainage systems in primary spontaneous pneumothorax patients, total duration of chest tube drainage and LOS were not different between both groups. However, after excluding those patients with prolonged air leak (i.e. those undergoing surgery, medical thoracoscopy and/or pleurodesis), duration of chest tube drainage and LOS were significantly shorter (median 1 vs 3 days) in patients randomized to digital drainage compared to analogue drainage. The use of digital drainage is safe when compared to the analogue system, since there was no significant difference in treatment failure between the groups.
For the whole group of PSP patients LOS was comparable between the analogue and the digital drainage group. However, the large majority of patients (83/102) was treated with drainage only (i.e. without thoracoscopy, surgery or pleurodesis); in these patients we observed a highly significant difference in LOS. Therefore, in the subgroup analysis of patients without persistent air leak, which we call uncomplicated PSP, digital drainage was shown to shorten LOS in the patients studied here. The fact that we did not find a difference in hospital stay between the two complete groups may be explained by the large effect exerted by those with a prolonged air leak, on a relatively small study population.
According to current guidelines, manual aspiration is regarded as first choice therapy in PSP. However, since the digital drainage system appears to have an advantage over analogue systems in uncomplicated PSP, it might be considered a practical alternative for manual aspiration: after insertion of a chest tube, the clinician connects it to a digital device instead of evacuating air manually. As soon as the digital device indicates that there is less than 15 ml air flow per minute and the chest X-ray shows no more than a small pneumothorax, the tube can be safely removed. The chance of treatment failure, if this procedure is followed, was 6% in our study, which is lower than the percentages found in trials on manual aspiration (manual aspiration success rates range from 30% to 80% [11], although the definition of success rate varies considerably between the various studies). One could hypothesize that if we set the air leak threshold lower than 15 ml/min, the failure rate could drop even further. It is noteworthy that there is no consensus between clinicians on airflow threshold values for chest tube removal [20].
Unfortunately, due to the large variability in clinical management despite the trial algorithm, we cannot make meaningful statements regarding the usefulness of performing a chest X-ray in the absence of air leakage or clamping the chest tube in the absence of air leakage.
A noteworthy finding is the follow-up chest X-ray and outpatient clinic appointment, which at present is common practice. It is questionable whether this is necessary, as only 4 of all study subjects (4%) had a recurrence of pneumothorax at this scheduled follow-up.
An interesting aspect of digital drainage, that was not been evaluated in the current study, is air leakage patterns, as suggested by Takamochi et al [17]. Patients who have a high, non-declining flow rate are likely to have a persistent pleural defect and to benefit from early referral for surgery.
Patients with a declining flow rate are likely to benefit from a conservative approach. Whether use of air leakage patterns indeed stratifies between patient groups is an important question to address in future studies. Another potential subject for research is outpatient treatment of PSP with digital drainage systems. Digital drainage could facilitate home treatment since flow rate can easily be assessed and reported by the patient. It may also be of interest to compare these management strategies with manual aspiration in future studies.
In our view, the main strength of this study is that it is a 'real life' study in a common but underresearched condition. It helps us to define how to implement digital drainage systems in our daily clinical practice, and to re-evaluate the way we approach patients with PSP. On the other hand, our study has some important limitations. First, we were unable to achieve the target sample size due to unexpectedly slow inclusion. Secondly, we have no reliable data on missed inclusions and therefore cannot exclude any bias. Furthermore, the use of different types of chest tubes (including different chest tube diameters) might have influenced the results.
In conclusion, although a difference could not be shown for the whole group of PSP patients, a significant reduction in length of hospital stay was shown in the patients with complicated PSP (not needing surgery due to prolonged air leakage) when using a digital drainage system.