Equine Health Update EHU Vol 20 Issue 03 - Page 37

CPD Article | EQUINE Pleural effusion is present if there is more than 3.5cm fluid identified in the ventral part of the thorax 15 . Lung ultrasound evaluation is limited to superficial lesions or peripheral lung fields and the pleural space 3 as parenchymal lesions overlying aerated lung tissue will not be detected 3 15 . With the presence of pleural effusion confirmed, thoracocentesis 5 should be ideally performed as the next diagnostic procedure to obtain a pleural fluid sample prior to administration of anti-microbials 9 , although this may not always be practical. The caudal mediastinum is fenestrated, however this fenestration may be blocked with fibrin deposition 3 or cellular debri 2 therefore a sample from each hemithorax should be obtained in cases where bilateral effusion is identified 2 11 . Thoracentesis may be both diagnostic and therapeutic as once a chest drain is placed, large volumes of effusion can be drained, thus reducing respiratory distress 11 and allowing for lung re expansion 3 . Samples must be submitted for aerobic and anaerobic culture and sensitivity 6 . A drop of the pleural effusion can be smeared, air dried and gram stained 9 for immediate evaluation. The resultant cytological staining may give an indication of causative organisms 9 and help guide appropriate antimicrobial therapy pending culture results9. Gas detected in the pleural effusion on thoracic ultrasound imaging may indicate that anaerobic bacteria are present 9 . Pleural Fluid Analysis: Normal pleural fluid 3 1 Nucleated cell count: ≤8 000 cells/ul TSP ≤2.5g/dl Clear – light yellow fluid No smell Abnormal pleural fluid 3 Nucleated cell count: ≤10 000 cells/ul (+90% neutrophils) TSP ≥2.5g/dl Cloudiness or colour change evident Foetid odour Thoracocentesis is performed at the level of the costochondral junction in the 7th and 8th intercostal space 11 . For sample collection or small volume drainage, a blunt teat cannula can be used 3 . A 24 -32 Fr chest tube with a 1 way valve (e.g. a condom witht he tip cut open or Heimlich valve) can be inserted and left as an in dwelling drain for continuous fluid drainage 3 . The type of drainage used – single, intermittent or continuous is determined by the volume and character of the pleural effusio 13 . With severe effusions, between 30 -50 L can be drained from the pleural space 11 . Thoracocentesis or chest drain placement should be performed under ultrasound guidance 3 to ensure accurate placement. Possible complications arising from thoracocentesi s11 are: pneumothorax, lung laceration, haemothorax, cardiac arrhythmias, organ puncture (heart / liver) and a localized cellulitis 3 . A TTA sample often yields the causative organism and therefore should always be performed 3 7 especially if there is not a large pleural effusion volume evident. It also allows other potential causes of pleural effusion to be excluded 10 . Chest radiographs 13 can be performed after drainage of the pleural effusion to evaluate the extent of the pneumonia 10 , assess the mediastinal structures 13 , detect the presence and severity of a pneumothorax 13 and examine possible deep leions 11 . • Volume 20 Issue 3 | October 2018 • 37