When should parapneumonic pleural effusions be drained in children?

Abstract

Pneumonia is an important health problem in children, and parapneumonic pleural effusion (PPE) is a frequent complication. There is no standard strategy for treating PPE, reflected in the few international guidelines that have been published on the issue. Compared to adults, there is no consensus on the utility of pleural fluid analysis in paediatric PPE. This is because of the lack of good evidence either in favour or against it and the risks of procedural sedation for acquiring pleural fluid for analysis to guide management. In this paper we provide a succinct review of the different approaches to the management of PPE, including diagnosis, pleural fluid analysis (Light’s criteria) and treatment, both medical and surgical.

Introduction

The ancient aphorism “Ubi pus ibi evacua” still stands as a general guide for treating the presence of pus in the pleural space [1]. The key question that remains to be answered is which parapneumonic pleural effusions (PPE) will evolve into pus. Numbers vary, but the annual incidence of PPE has been increasing over the last twenty years, with cohorts reporting changes from 1 to 5 per 100,000 children in the USA [2] and 19 to 35 per 100,000 in Spain [3]. Reports from the UK suggests a doubling incidence of up to 3 per 100,000 [4], even though there had been a decrease in the incidence of both pneumonia and pleural effusion after implementing the pneumococcal vaccination [5]. Parapneumonic pleural effusions are common in paediatric pneumonia, with 5–40% of children having this complication [6]. However, the majority of effusions are small and don’t need further investigation or a therapeutic approach different than systemic antibiotics [7]. Contrary to what is reported in adults, pleural effusions in children, complicated or not, are rarely associated with non-bacterial pneumonia, and Streptococcus pneumoniae remains, worldwide, the most common bacteria causing PPE in children [8].

The diagnosis of PPE is usually based on clinical findings and consistent imaging provided by a chest X-Ray (CXR) initially and selectively with chest ultrasound (U/S) and Computed tomography of the chest [9]. CXRs are still the mainstay for the initial diagnosis, but adding U/S has the advantage of estimating the depth and location of the PPE and the presence of septation in the pleural space. This will influence the decision for additional treatment besides antibiotics. There is an increasing use of U/S in clinical settings for this purpose, as well as for accurately guiding thoracentesis [10], [11]. Nevertheless, as a highly operator-dependant technique, proper training should first be undertaken in the use of U/S undertaken to avoid potential diagnostic and therapeutic errors. Computed tomography of the chest is called upon in complex or difficult cases where a more detailed thoracic and pulmonary assessment is needed.

Light’s criteria have been used for decades, in children and adults to decide when is appropriate to drain the contents of the pleural space. They were devised to estimate the stage of the PPE which, in turn, would suggest if the effusion was complicated or non-complicated. Basically, a non-complicated PPE is characterized by a pH > 7.20, glucose > 40 mg/dL and Lactate Dehydrogenase [LDH] < 1000 U/L. In contrast, a complicated PPE is characterized by a pH ≤ 7.2, glucose ≤ 40 mg/dL and LDH ≥ 1000 U/L. PPE with pus (empyema) or bacteria identified in the pleural fluid should also be considered as a complicated PPE [12]. Non-complicated PPEs are treated with systemic antibiotics and complicated PPEs need drainage in addition to antibiotics. Nonetheless, it’s important to acknowledge that Light’s criteria were originally based on adult studies, and they have been applied in paediatrics without properly confirming its full validity in children [13]. However, time seems to have given enough credit to its implementation, as many hospitals worldwide still use them for decision making in paediatric PPE with good results [14], [15]. Our published data already showed that, in children, the sensitivity and specificity of pleural fluid pH and glucose were, respectively, high and similar to what has been found in adult studies regarding PPEs that needed drainage [14].

Certainly, the most important decision that clinicians face with PPE in children is whether it needs to be drained or not. If so, when is the right time to do it? [16], [17]. The majority of studies published have relied on Light’s criteria to decide upon surgical intervention. However, some prominent thoracic and surgical societies have publicly taken a stand against the value of these criteria and have recommended a more invasive approach. For instance, the guidelines from the British Thoracic Society [13] and the Thoracic Society of Australia and New Zealand [18] do not favour the use of pleural fluid biochemical analysis, claiming there is not enough evidence supporting its use in children (only in adults). However, there is no evidence against it either. The American Pediatric Surgery Association (APSA) does not recommend using Light’s criteria, but that recommendation was apparently based on a single observational study with questionable validity of results [19]. On the other hand, although the Pediatric Infectious Disease Society and the Infectious Disease Society of America PIDS/IDSA guidelines consider that evidence supporting the use of pleural fluid analysis is low-quality, they do recommend collecting the fluid, by means of a simple thoracentesis, to guide antibiotics and/or more invasive management [20]. The different management strategies are depicted in Fig. 1.