Pleural disease is common, affecting around 360 patients per 100,000 each year globally. It is estimated that approximately 1.5 million individuals will develop pleural effusion in the USA alone [1]. Nonmalignant pleural effusion, including parapneumonic and cardiac effusion, remains the most common cause of pleural disease in the developed world, followed by metastatic pleural malignancy [1].

Malignant pleural effusion (MPE) is associated with a poor prognosis in most cases and often aggravates the performance status, mainly due to the associated dyspnoea [2]. Definitive management with talc pleurodesis or indwelling pleural catheter with or without pleurodesis is therefore recommended by current guidelines [2]. Although no pleural procedure prolongs life in a patient with MPE, the aims of these interventions are to relieve the dyspnoea and to increase exercise capacity to improve the quality of life and potentially improve the performance status to the point where the patient qualifies for modern, individualised oncological modalities.

Pleurodesis and indwelling pleural catheters are not universally available nor necessarily the preferred interventions, particularly in benign disease or in patients with MPE with a very limited anticipated survival or very poor performance status. In these settings, therapeutic thoracentesis (TT) may be offered [3]. Complications associated with the procedure including infection and loculations and predicting the rate of recurrence may be challenging [3]. Furthermore, benign effusions may resolve after one or two therapeutic thoracenteses. Regardless, a significant proportion of patients may require repeated interventions at variable time intervals depending on the underlying aetiology.

There is a paucity of good-quality evidence on the rate of recurrence of a symptomatic plural effusion and thus the time to next TT. Evidence has suggested that large effusions on chest radiography, the drainage of a large volume, high pleural fluid lactate dehydrogenase, and malignant disease are all associated with rapid reaccumulation [4-6]

In the current edition of Respiration, Fjaellegaard et al. [7] report an ambitious attempt at predicting the time to next TT and identification of risk factors of rapid pleural fluid recurrence. In a prospective, observational study, the investigators aimed to evaluate the ability of the patient and physician to predict the time to next TT and to identify characteristics associated with rapid pleural fluid recurrence. Patients’ and physicians’ predictions deviated by 6 days from the actual number of days to repeat TT. On multivariate analyses, factors associated with an increased hazard risk of pleural fluid recurrence included the volume of daily fluid production and large effusion size. Septations were associated with a decreased hazard risk. The authors concluded that both patients and physicians were equally unable to predict the time to next TT and that the three main findings may be used to predict when to expect the need for a next TT.

The investigators’ findings emphasise that “pre-booked repeated thoracenteses” is not an ideal approach to TT and that there is no reliable “prediction model” to calculate when a patient will need their next TT. Did Fjaellegaard et al. [7] achieve what was suggested by the title “Prediction of time to next therapeutic thoracentesis and identification of risk factors of rapid pleural fluid recurrence”? Unfortunately, the answer is “no.”

There findings are still, however, highly significant. Both patients and physicians were using “educated guessing,” which was clearly shown to be inaccurate. This is unfortunately not unique to pleural disease, as nonevidence-guided “guesswork” is still used in many fields of medicine to pre-book procedures which can potentially be detrimental to patient care [8, 9]. Based on their findings, an “open door” policy for symptom-guided TT should be followed, particularly in malignant disease, where improving the quality of life and limiting the time spent in hospital are paramount [2].

Proposing and validating a model for prediction of time to next TT may in fact not be a realistic goal, given the heterogeneity of the underlying pathological processes, the efficacy of any other medical interventions, and various comorbidities. At least for now, it is safe to paraphrase the song from U2 (the Irish rock band from Dublin) that as far as the prediction of time to next TT is concerned, “we still haven’t found what we’re looking for.”

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