Transthoracic Ultrasonography in Predicting the Outcome of Small-Bore Catheter Drainage in Empyemas or Complicated Parapneumonic Effusions

Abstract

Thoracic sonography has been advocated as being complementary to small-bore catheter drainage in pleural effusions. However, it is not known whether the initial sonographic appearances of empyemas or complicated parapneumonic effusions (CPPEs) can predict the outcomes of small-bore catheter drainage for these pleural insults. This retrospective study investigated the outcomes of patients who had been diagnosed with empyema and CPPE and had received ultrasound-guided small-bore catheter (size from 12F to 16F) drainage in a tertiary university hospital from September 2005 to August 2007. Patients were excluded when empyemas or CPPEs were traumatic, they were less than 18 years old or their charts were incomplete. We evaluated 141 small-bore catheters in 70 patients with empyemas and 71 patients with CPPEs over a two-year period. The mean age was 58 ± 15 y and the male gender was more frequent (112 men, 79%). The overall successful rate of small-bore catheter drainage in empyemas or CPPEs was 63% (89/141). The sonographic appearances of these empyemas or CPPEs exhibited a complex septated pattern in 57% (81/141) of patients and a complex nonseptated pattern in 43% (60/141) of patients. The success rate in a complex nonseptated sonographic pattern was significantly higher than in a complex septated sonographic pattern (48/60, 80% vs. 41/81, 51%, respectively; p = 0.001). Moreover, patients with complex septated sonographic patterns also had higher intensive care unit admission rates compared with nonseptated sonographic patterns (22/81, 27%, vs. 8/60, 13%, respectively; p = 0.0047), as well as infection-related mortality rates (17/81, 21% vs. 4/60, 7%, respectively; p = 0.018). The appearance of sonographic septation is a useful sign to help predict the outcome of small-bore catheter drainage in cases of empyemas or CPPEs. Patients with a complex septated sonographic pattern have a poorer prognosis for a successful outcome, higher ICU admission rate and a higher mortality rate.

Introduction

Adequate antibiotics accompanied by a tube thoracostomy are now the standard medical treatments for pleural effusions such as empyema and complicated parapneumonic effusion (CPPE) (Light 1995). Although early surgical intervention such as video-assisted thoracic surgery (VATS) has its advocates (Landreneau et al. 1996), it is invasive and has potential morbidity and mortality. Thoracostomy with conventional large-bore chest tubes probably remains the most widely used for empyema and CPPE. However, the success rate for tube drainage is lower than VATS, possibly because of the blind insertion of the chest tube (Wait et al. 1997). In recent years, image-guided percutaneous small-bore drainage, especially when using thoracic ultrasound, is a simple and effective examination that allows for real-time monitoring of the drainage procedure and results in the rapid and accurate placement of the drainage catheter (O'Moore et al. 1987). However, there is a continuing debate regarding the effectiveness of small-bore catheters in the setting of documented empyemas or CPPEs, with several authors not advocating their use at all (Horsley et al. 2006; Hyde et al. 1997).

Sonographic examination has been helpful in evaluation of the disposition of fibrin clot and fibrin membranes of the pleural cavity, in addition to gaining information on the nature of the effusion (Yang et al. 1992). As far as we know, more fibrin and debris in the pleural effusion may cause the tube to become occluded and thus cause treatment failure. However, we seldom use sonography to detect the characteristics of pleural effusion, and more study is needed to determine if the initial sonographic characterization of empyemas or CPPEs can predict the patient outcome in these pleural diseases when managed with small-bore catheter drainage.

The purpose of this study was to retrospectively review all patients presenting with empyemas or CPPEs treated by ultrasound (US)-guided percutaneous small-bore catheter insertion to determine the success rates and outcomes of small-bore catheter drainage. Our aim was to determine whether the appearance of sonographic septations can predict the outcome of small-bore catheter drainage in cases of empyema or CPPE.

We retrospectively collected and carefully reviewed the medical records of patients who had empyemas or CPPEs and received US-guided small-bore catheter drainage between September 2005 and August 2007 (24 mo) at the China Medical University Hospital (CMUH), a 2,062-bed tertiary medical center located in central Taiwan. The internal review board of the hospital approved this study and waived the requirement of informed consent. During this two-year period, 263 patients with empyemas or CPPEs were admitted to CMUH. Patients were excluded from the study for the following criteria: the empyemas or CPPE were traumatic; the age of the patients was <18 y; or the chart was incomplete (Fig. 1). Of the included patients, 70 patients were diagnosed with empyema and 71 patients were diagnosed with CPPE.

Percutaneous pigtail catheters (SKATER, PBN Medicals, Stenlose, Denmark) sized 12–16F were placed using a modified Seldinger technique in connection with a one-way valve drainage bag. A chest US was performed for guidance before patients underwent tube insertion. We defined the symptomatic resolution of empyemas or CPPEs as being characterized by improvement in the effusions, including clinical and radiographic findings, and the absence of other required surgical intervention. Clinical findings included fever subsiding, no leukocytosis, improved signs of sepsis, etc. Radiographic findings were evaluated by chest X-ray scoring, which was estimated by using the erect posteroanterior CXR film, and determined by the largest lateral linear dimension of pleural effusion or thickening in millimeters (Andreas et al. 2004). Surgical interventions included VATS with decortication, open thoracostomy or inserted large-bore chest tube.

The following data were collected for each patient: age, gender, underlying disease, initial hemogram, serological results, treatment strategies, surgical interventions and outcomes. The characteristics of the pleural effusion including gross appearance, cell counts, levels of glucose, protein, lactate dehydrogenase (LDH) and bacterial culture findings were also recorded.

Based on Light's criteria and the literature (Light 1995), a CPPE was defined as a pleural fluid LDH level >1000 IU/L (normal range in our hospital is from 98 to 192 IU/L), or a glucose level <40 mg/dL or a positive Gram stain or culture. Pleural empyema was defined as pleural fluid that contained frank pus. Hospital-acquired infections related to pleural empyema were defined as infections that occurred >48 h after admission, with no evidence of infection upon admission. Patients with pneumonia were defined clinically and were characterized by a febrile state with purulent sputum, leukocytosis and a new onset of pulmonary infiltrates upon chest X-ray or computed tomography. A bacteriologic diagnosis based on the microbiological examination of the pleural fluid and other samples was also made. The bacteria found in the pleural effusion were classified as follows: aerobic Gram-positive, aerobic Gram-negative, anaerobic or polymicrobial bacteria. A polymicrobial infection was defined as the isolation of more than one strain of pathogen on the pleural effusion culture. Treatment failure was defined as mortality caused by infection or radiographic or sonographic evidence of a loculated pleural effusion with poor drainage, whereby the clinical condition suggested the presence of persistent sepsis and the need to receive VATS.

On the first day of admission, all patients underwent a chest sonographic examination with an Aplio-80 sonography machine (Toshiba Medical Systems Co., Ltd, Tokyo, Japan) equipped with a 3.75-MHz convex transducer under fixed parameters such as the power settings, a gain setting of 80 dB and a transmitted focal depth of 6 cm. We used tissue harmonic imaging for improvement in contrast and reduction of side lobe artifact, with enhanced visualization of the pleural effusion. The patients were examined in the supine or sitting positions, as clinically appropriate. The chest US was performed by a well-trained and experienced pneumologist, and the sonographic images were recorded regularly on the hard disk of the commercial US machine.

The sonographic appearances of empyemas or CPPEs have been defined in previously published literature with the following criteria (Tu et al. 2004): (i) anechoic pattern—no echogenic scatterers within the effusions; (ii) complex nonseptated pattern—complex appearances on the internal echo image, but with no evidence of fibrin strands or septal formation in the pleural cavity; (iii) complex septated pattern—presence of strands (hyperechoic lines within the effusion) suspended inside the pleural space, which form weblike or branching patterns; and (iv) homogenously echogenic pattern—with echogenic material distributed evenly within the effusion (Fig. 2).

To obtain interpretations of the sonographic appearance of the pleural effusions and interobserver agreement, three experienced and well-trained pulmonologists, without knowing the results with the effusion, independently interpreted all the sonographic appearances on the recorded hard disks. The final interpretations had the concordant agreement of at least two physicians.

The data were compiled and analyzed using commercial statistical software (SPSS for Windows, version 10.0, Chicago, IL, USA). All continuous variables were reported as the mean ± standard deviation (SD) and were compared using a two-tailed Student's t-test. Categorical variables were reported as the number of patients and percentages. Differences in categorical variables were examined using Fisher's exact test. All tests of significance were two sided and a value of p ≤ 0.05 was considered to be statistically significant.