Toracocentesis

Also known as: Pleurocentesis

Toracocentesis en caballos

Introducción

La toracocentesis es la técnica que permite la extracción de líquido (derrame) o aire acumulados en el espacio pleural y que interfieren en la correcta función respiratoria. Para ello se requiere el uso de un catéter o cánula introducidos percutáneamente en la cavidad torácica y hacia el espacio pleural. La toracocentesis, en situaciones de derrame pleural, constituye una herramienta de gran valor diagnóstico y terapéutico.

Cuando los datos obtenidos a la auscultación y percusión nos sugieran la presencia de derrame pleural, la punción en tórax tendrá varios objetivos: 1) Confirmar la presencia del derrame; 2) Aportar muestras para el análisis laboratorial con el que poder obtener información acerca de su etiología y el plan terapéutico a adoptar; y 3) Aliviar la presión causada por la presencia del derrame y que, indudablemente afecta a la función respiratoria.

En ocasiones, al realizar la punción, el animal muestra signos de malestar cuando se le retiran grandes cantidades de derrame. Esto es así por el efecto compensatorio que su presencia ha causado sobre la función pulmonar durante el tiempo de permanencia. A pesar de ello, la toracocentesis mitigará la disnea existente al liberar al espacio pleural del material contenido en él. La colocación de drenajes torácicos tras la punción puede ser necesario, cuando las cantidades de líquido sean elevadas o se sospeche de neoplasia.

Material necesario

• Buena sujección mediante potro o torcedor. Suele ser necesaria la sedación, en caso de intranquilidad. Vigilar no obstante la función respiratoria.
• Peladoras y material necesario para realizar la limpieza y desinfección quirúrgica de la zona (torundas, gasas, povidona yodada, clorhexidina, etc.)
• Écógrafo (si se dispone) para realizar la punción eco-guiada
• Anestésico local y jeringa de 3 cm y calibre 23G
• Guantes estériles
• Aguja de bisturí
• Cánula intramamaria metálica estéril (6-10 cm de longitud) o catéter urinario metálico (26 cm). Las posibles laceraciones del pulmón son menos frecuentes si se emplean cánulas de punta roma.
• Llave de 3 vías y tubos de toracocentesis y drenaje (equipo infusor)
• Tubos para recogida de muestras: 1) Tubo con EDTA; 2) Tubo sin anticoagulante; y 3) Viales estériles para cultivos bacterianos (hisopos, placas de petri, etc.)

Metodología

El lugar apropiado para la punción se establece teniendo en cuenta algunas referencias anatómicas: 7-8 espacio intercostal por el lado izquierdo, o 6-7 espacio intercostal por el lado derecho; en ambos casos, a medio camino entre el hombro y el codo. Cuando se detecte la presencia de derrame bilateral, es interesante realizar la punción an ambos lados (en los caballos sanos suele existir comunicación de ambos hemitórax, sin embargo en casos de pleuroneumonía esta comunicación puede desaparecer y por lo tanto podemos tener 2 líquidos con diferentes características, Aguilera et al., 2009). Para una identificación más precisa del punto de punción puede emplearse el ecógrafo. Hay que tener en cuenta que los vasos y nervios discurren por el borde caudal de cada costilla, por lo cual la punción deberá realizarse en el borde craneal de la costilla para evitar el daño de las estructuras antes mencionadas.

Una vez el animal sedado, y la zona de punción desinfectada y acondicionada quirúrgicamente, se aplica anestesia local y que abarque la zona subcutánea, musculatura intercostal y pleura parietal ver Local anaesthetic para lo cual se empleará una aguja de 3 cm y 23 g de calibre. A continuación se realiza una incisión en la piel, mediante una aguja de bisturí.

A stab incision using a number 15 scalpel blade should be made through the skin. Prior to inserting the cannula, a three-way tap and extension set should be attached to it. Using moderate pressure, the cannula should be pushed through first the intercostal muscles and secondly through the parietal pleura in order to enter the thoracic cavity. Passage of the cannula through the parietal pleura is extremely painful to the horse if the area has not been fully desensitised by the local anaesthetic. A release in pressure should be felt when the cannula enters the thoracic cavity. The cannula can be manipulated and moved to collect as much fluid as possible.

Complications

Iatrogenic pneumothorax

Pleural Fluid Analysis

Analysis of the pleural fluid may in turn help you to determine the underlying disease process and develop a therapeutic plan.

Pleural fluid in healthy horses normally contains less than 5,000 nucleated cells/l and less than 25g/l total protein. Levels greater than 10,000 nucleated cells/l and 35g/l total protein should be considered abnormal.

Small Animal Thoracocentesis

Introduction

Thoracocentesis is a procedure which has both diagnostic and therapeutic value.

When the clinical history, presenting signs, thoracic auscultation and percussion of the animal suggest a pleural effusion, thoracocentesis can both confirm its presence and provide a specimen for examination. Ideally radiography (minimum of two views - lateral and dorsoventral) or ultrasound should be performed to confirm pleural space disease prior to thoracocentesis. However it can be particularly useful in the emergency patient (the dyspnoeic cat in particular) who is too unstable to undergo radiography or similar diagnostic tests as drainage of pleural fluid will both provide a preliminary diagnosis and improve clinical signs.

Equipment

• Clippers and materials to perform a surgical scrub
• Ultrasonography if available
• Sterile gloves
• Butterfly needle with incorporated extension set or sterile needle (1 inch with the smallest possible gauge) with extension set
• 20ml sterile syringe
• 3-way tap - if large volumes of fluid are anticipated, as this allows for multiple syringes of fluid to be removed safely under a closed system
• EDTA tube for cytology and plain tube for biochemistry and culture

Sedation is not generally required, especially in the dyspnoeic patient (however it can be used if necessary to prevent further stress to an excitable animal). The patient should be handled gently and the procedure performed in a quiet environment. It may be necessary to place the animal in an oxygen cage prior to the procedure as they often have a poor oxygen reserve.

Procedure

The site for thoracocentesis is between the 7th and 8th intercostal space. If fluid is suspected in the pleural space then the needle should be inserted 2/3rds of the way down the chest. If pneumothorax is suspected then the needle should be inserted more dorsally, approximately 1/3rd of the way down the chest. Local anaesthetic can be used if necessary.

Clip and scrub a generous area around the 7-8th rib space on both sides of the chest. Advance the needle slowly at a 45 degree angle in the middle of the 7th or 8th intercostal space into the pleural space. A small amount of negative pressure should be applied as the needle passes through the thoracic wall. The needle should be angled downward, parallel to the body wall. The fluid or air should then be aspirated. The needle may need redirecting to access pockets of fluid.

Up to 100mls of fluid per side can be expected in the cat. Removal of fluid should see an improvement in clinical signs.

Complications

Iatrogenic pneumothorax

Pleural Fluid Analysis

Analysis of the pleural fluid may in turn help you to determine the underlying disease process and develop a therapeutic plan. The following can be analysed: cytology, total cell count, differential cell count, total protein, bacterial culture ans sensitivity, gram stain and triglyceride and cholesterol levels (if chylothorax is suspected).

The types of fluid that may cause pleural space disease are:

1. Exudate
2. Modified Transudate
3. Transudate
4. Chyle

These can be identified by the protein and cellular content of the sample.

The fluid can give an indication of prognosis; in the cat prognosis is generally poor for all diagnoses except pyothorax (an exudate with degenerate neutrophils and intracellular bacteria). Therefore it is often useful to perform in-house cytology to give a preliminary diagnosis, which allows the owners to make an informed decision before proceeding with further treatment. Differential diagnosis in the cat include congestive heart failure, FIP, pyothorax, neoplasia, haemothorax and chylothorax. It should be noted that any pleural effusion may produce bizarre mesothelial cells which could be mistaken for neoplastic cells.

References

http://www.veterinaria.org/revistas/redvet - http://revista.veterinaria.org Adamantos, S (2011) Feline Respiratory Emergencies RVC Emergency Medicine and Critical Care Elective, Royal Veterinary College

Mair, TS & Divers, TJ (1997) Self-Assessment Colour Review Equine Internal Medicine Manson Publishing Ltd

RVC staff (2009) Respiratory System RVC Intergrated BVetMed Course, Royal Veterinary College

Rutgers, C H (1989) Thoracocentisis in the dog and cat In Practice 1989 11: 14-1

Copas, V (2011) Diagnosis and treatment of equine pleuropneumonia In Practice 2011;33:155-162

RVC staff (2011) A logical approach to clinical problem solving RVC Feline Medicine Elective, Royal Veterinary College

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