Undiagnosed pleural effusion is a diagnostic dilemma especially in exudative pleural effusions (EPE). 20-40 % are unable to be attributed to a specific diagnosis, even after thoracentesis and closed pleural biopsy. Thoracoscopy has been demonstrated to increase the diagnostic yield in undiagnosed EPE. The diagnostic yield of thoracoscopy in malignant and TB pleural effusion ranges from 91% to 94% and 93% to 100%, respectively.

Rigid thoracoscopy has traditionally been the modality of choice. The recently introduced semirigid thoracoscope provides ease of handling like a flexible bronchoscope. However, there are concerns about the diagnostic yield of semi-rigid thoracoscopy when compared with rigid thoracoscopy. According to the available literature, the yield of semirigid and rigid thoracoscopy is almost similar if adequate pleural biopsy is obtained. However there are concerns that with semi-rigid thoracoscope, there might be greater incidence of inability to obtain adequate pleural biopsy. On the other hand, the use of conventional rigid thoracoscope may be associated with greater procedure related pain.Mini-Thoracoscopy is a newer rigid thoracoscopy instrument which is smaller in diameter (5.5 mm) and may allow pleural biopsy with a smaller incision. There is scant literature on its utility. The investigators hereby propose to undertake a randomized comparison of rigid 'mini thoracoscope' vs semi rigid thoracoscope in undiagnosed pleural effusions.

Patients meeting the inclusion criteria and giving prior consent for the study shall be randomised. The randomization sequence will be computer generated with variable block size and the assignments will be placed in opaque sealed envelopes. All patients will undergo hemogram, liver and renal function tests, coagulation profile, an electrocardiogram and Computed tomography (CT) of the chest before entering the study. Chest ultrasound will be performed in all patients to evaluate the rib spaces, amount of pleural fluid and for selection of the entry point.

Instruments The semi-rigid thoracoscope to be used is the autoclavable Olympus LTF-160 (Olympus, Tokyo, Japan) thoracoscope with 2.8 mm inner channel diameter and 7 mm outer diameter. The forceps is flexible forceps with alligator jaw with spike cusps, 2.8 mm of the outer diameter. The rigid mini thoracoscope is the Richard Wolf 5.5 mm operating endoscope with the working channel.

Thoracoscopy technique Thoracoscopy will be performed in the interventional pulmonology lab. Patients shall be fasting for solids for 8 hours and for liquids 6 hours. Patients shall be having continuous monitoring of blood pressure, pulse rate, and oxygen saturation.

Topical anesthesia will be achieved by infiltrating 2% lidocaine locally at the incision site. The procedure shall be performed under conscious sedation and analgesia using a combination of midazolam and intravenous fentanyl. An incision shall be made at the site of maximum fluid thickness as assessed by pre-procedural USG chest, with the patient in lateral decubitus position and involved side upward. After incision, the appropriately sized trocar shall be placed through the skin into the pleural space. The thoracoscope shall be inserted through the trocar. The pleural surfaces shall then be thoroughly inspected. A minimum of 6-8 pleural biopsy samples shall be obtained by semi-rigid thoracoscope and at least 4 with rigid mini-thoracoscope.

Samples shall be sent for histopathological analysis and mycobacterial cultures. At the end of the procedure, a chest tube shall be placed and removed subsequently.

All patients shall be followed up for a period of six months from the time of procedure if non-specific inflammation/ fibrinous pleuritis is the diagnosis or no definitive diagnosis is made during that time.

Statistical analysis:

Data shall be expressed as mean ± standard deviation (SD), or percentage. Differences in continuous variables between the two groups shall be compared using Student's t test (or Mann-Whitney U test); while differences in categorical data shall be compared using the chi-square test (or Fisher's exact test). A p value of less than 0.05 shall be considered statistically significant.

Inclusion Criteria:

• Age >18 years Presence of undiagnosed exudative pleural effusion as determined by the criteria detailed by Light et al where a specific diagnosis was not obtained after initial cytological and/or microbiological examinations.

Adequate rib spaces for successful performance of thoracoscopy as judged by clinical examination Adequate pleural fluid space as judged by pre-procedural USG chest

Exclusion Criteria:

1. Pregnancy
2. Coagulopathy (platelet count < 50000/mm3, INR > 1.5)
3. Unstable hemodynamic status ( SBP > 180, DBP> 100 or SBP< 90 mm Hg / heart failure
4. Myocardial infarction or unstable angina in the last 6 wk
5. Hypoxemia not correctable with low flow oxygen (SpO2 <90% despite low flow oxygen @ 1-2 l/min)
6. Extensive rib crowding as judged by clinical examination
7. Extensive adhesions and lack of pleural space on USG chest
8. Refusal of consent