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DUNKEL
FIGURE 4 To drain a pleural effusion, a thoracic drain is inserted through a skin and muscle incision at the cranial edge of the rib (a) into the pleural space and secured with a purse- string suture and roman sandal pattern (b) before a Heimlich valve is attached (c) to prevent aspiration of air.
marked systemic inflammation with tachycardia and tachypnoea and the overall picture is very much that of acute distress. In countries where long- distance travel is common, such as the USA and Australia, pleuropneumonia is the most common cause of pleural effusion while in the United Kingdom, almost 40% of cases are secondary to neoplasia (Johns et al., 2017 ). Haemothorax is very rare but can occur after trauma, rodenticide or warfarin toxicity or, very rarely, systemic phenylephrine administration for the treatment of nephrosplenic en- trapments or haemangiosarcoma (Frederick et al., 2010 ). Although a diagnosis can sometimes be made by auscultation alone, ultrasonogra- phy is essential to determine the extent and character of the effusion, assess concurrent pulmonary damage and choose the best location for thoracocentesis. There are no strict guidelines when drainage of pleural fluid is necessary to alleviate distress. Thoracocentesis might be indicated for diagnostic and therapeutic purposes if the fluid vol- ume is greater than 3 cm in depth (Davis, 2018 ). It is prudent to place an intravenous catheter prior to the procedure and consider admin- istration of IV fluids if drainage of a large volume is anticipated as rapid drainage can cause hypotension and re- expansion pulmonary oedema in people. Both complications appear to be rare in horses despite the fact that sometimes very large volumes, up to 30–96 L, are recovered (Arroyo et al., 2017 ; Camacho- Luna et al., 2021 ; Johns et al., 2017 ). To the author ' s knowledge, only one case of re- expansion pulmonary oedema has been reported in horses and this was in as- sociation with tissue plasminogen activator administration (McGorum et al., 2018 ). Large volume thoracic effusions are more common in cases of thoracic neoplasia than infectious pleuropneumonia and the volume and character of the fluid can be helpful in distinguishing both (Johns et al., 2017 ). The tube should be placed on the side with the larger effusion first, as ventral as possible and at the cranial edge of the rib while still avoiding the heart, diaphragm and lateral thoracic vein. Frequently, this is just above the costochondral junction of the seventh or eighth intercostal space (one hand ' s width caudal to the olecranon and one hand ' s width above the lateral thoracic vein). If
extensive fibrin accumulation is present, aiming for a large fluid pocket might achieve the best drainage. After clipping and sterilely preparing, the site is infiltrated with 10–20 mL of a local anaesthetic before a stab incision is made with a scalpel blade through the skin and muscle. A 16 – 32 Fr blunt trocar is then pushed through the intercostal muscles which might take considerable force (Figure 4a ). Holding the trocar firmly close to the tip avoids accidentally puncturing the lung. Once in the thoracic cavity a sudden release of resistance is often felt and fluid can be seen exiting between stylet and trocar. The trocar is then removed, a Heimlich valve or punctured condom secured at the end to avoid air aspiration and the tube is secured in place with a purse- string and Roman sandal suture (Figure 4b,c ). Additional treatment with anti- microbials, anti- inflammatories and intranasal oxygen is also required.
CONCLUSIONS
History and physical examination can often give sufficient clues to identify the cause of respiratory distress and initiate emergency treatment. Upper respiratory tract obstruction, tension pneumo- thorax and occasionally pulmonary oedema can be rapidly fatal and require immediate intervention.
FUNDING INFORMATION There are no funders for this review article.
CONFLICT OF INTEREST STATEMENT No conflicts of interest have been declared.
ETHICS STATEMENT No approval required for this review article.
ORCID Bettina Dunkel
https://orcid.org/0000-0003-2041-2144
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