Chest drainage in the dog and cat

The insertion of a chest drain is indicated on every occasion that a pathological accumulation of fluid or air occurs in the pleural space in order to restore normal negative intrathoracic pressure._¹

AETIOLOGY OF DISORDERS OF THE PLEURAL SPACE

There are various different factors that contribute to the formation and reabsorption of fluids in the pleural space: hydrostatic pressure, oncotic pressure, coefficients of filtration and lymphatic drainage. When the balance between these factors is altered, the formation and reabsorption of the fluid is modified leading to the possible development of an effusion in the pleural space.

Depending on the type of fluid forming the effusion, the following diagnostic hypotheses are favoured:

• pure or modified transudate: right heart failure, pericardial disorders, hypoalbuminaemia, neoplasia, diaphragmatic hernia,
• aseptic exudate: infective peritonitis, neoplasia, diaphragmatic hernia, lung lobe torsion,
• septic exudate: empyema,
• chylous effusion: chylothorax,
• haemorrhagic effusion: trauma, clotting disorders, neoplasia, lung lobe torsion._²

The following events can cause a collection of gas in the pleural space:

• fractures of the ribs, lacerations of the chest wall
• diaphragmatic hernia,
• blunt pulmonary trauma,
• pneumomediastinum,
• spontaneous pneumothorax,
• iatrogenic pneumothorax (thoracocentesis)._³

Pneumothorax can be classified into the following types:

• closed
• open
• tension.

Closed pneumothorax develops most frequently as a consequence of trauma to the chest which ruptures the lung parenchyma as a result of sudden distension and compression of the parenchyma, without there being an injury opening onto the chest wall. In contrast, in an open pneumothorax there is an aperture on the chest wall connecting the exterior and the lung parenchyma. In both closed and open pneumothorax an equilibrium between the pleural pressure and the pressure of the inhaled atmospheric air is quickly reached. In contrast, in tension pneumothorax the air can enter the pleural cavity but because of a valve effect cannot leave it; this leads to a progressive increase in the pressure within the pleural space (which is, therefore, greater than the pressure of the atmospheric air inhaled) causing the lung parenchyma to collapse. Tension pneumothorax, if not quickly recognized and drained, can lead rapidly to the death of the patient._⁴

SYMPTOMS

At clinical examination the patient usually has clear evidence of one or more of the following:

• respiratory distress, congested mucosae
• exercise intolerance,
• open-mouthed breathing,
• increased respiratory rate,
• decreased respiratory depth,
• reluctance to assume a lateral decubitus position, preferring sternal decubitus,
• cyanosis in the more severe and uncompensated cases.

At chest auscultation there is a decrease in inspiratory and expiratory sounds._⁵

RADIOGRAPHIC SIGNS

Chest radiography is the diagnostic investigation of choice: it shows into which hemithorax the drain should be inserted. In order to diagnose a pleural effusion (Fig. 1), at least two views of the chest are necessary: latero-lateral (L-L) and sagittal dorso-ventral (D-V) or ventro-dorsal (V-D). The presence of large amounts of fluid in the pleural cavity hampers the vision of the lung parenchyma in the V-D view, which is distributed over a larger surface than in the D-V view; in fact, in D-V projections, the fluid accumulates in the lowest and deeper part of the chest enabling a better view of the parenchyma. Double views (L-L, D-V) are useful for evaluating both the presence and movement of fluid within the chest cavity. The classical X-ray signs of intrathoracic fluid are:

• a widespread increase in the radio-opacity of the chest cavity,
• a decrease or lack of visibility of the cardiac shadow,
• a decrease in the depth of the costo-phrenic angles because of the accumulation of the effusion (in V-D and D-V views)

In pneumothorax (Fig. 2), the presence of gas in the pleural space separates the two pleura (visceral and parietal), causing collapse of the lung parenchyma  and increasing the radio-opacity of the margins of the lobes.

The most typical X-rays signs:

• elevated cardiac shadow (L-L view),
• increased radio-opacity of the lung parenchyma,
• retraction of the edges of the pulmonary lobes,
• loss of the vascular structure peripheral to the parenchyma.

It must be remembered that radiographic studies should only be carried out after the patient has been stabilised, which may require thoracocentesis, oxygen therapy and preventive pharmacological control in order that the respiratory symptoms do not worsen. The choice of X-ray projections must be made taking into consideration the respiratory distress produced by the patient’s position; sometimes the ideal position must be renounced because it impedes ventilation. When the patient demonstrates unrest and intolerance of the ideal position, the X-rays must be performed in the projection in which the patient feels most comfortable, postponing double projections until the patient has been sufficiently stabilised. Forcing a patient into the position necessary to obtain the best L-L and V-D views can lead to worsening respiratory distress which may even be fatal.

MATERIALS AND METHODS

The tubes used for chest drainage are made of polyvinylchloride or siliconated plastic, since these materials are well tolerated by the patient. There are three types of chest drain:

• a thoracic catheter on a stylet (Fig. 3),
• a Redon-type thoracic catheter (introduced into the pleural cavity with large haemostatic forceps or Carmalt forceps) (Fig. 4).
• a Seldinger-type catheter (Fig. 5)

The choice of the diameter of the first two types of chest drain is based on the general rule according to which the diameter of the drainage tube should be the same as that of the main bronchus (measured on a L-L film at the tracheal bifurcation). In the case of pneumothorax, a small bore catheter can be used; normal sized tubes are recommended to drain fluids, particularly if dense (for example, purulent material). The weight of the animal can also guide the choice of tube:

The ancillary equipment necessary to place a chest drain consists of:

• razor,
• sterile gloves,
• standard sterile surgical kit,
• scalpel blade (n 10),
• non-reabsorbable suture material 3-0,
• three-way valve,
• sterile syringes from 20-50 ml,
• material for a semi-occlusive dressing.

TECHNIQUE

In order to insert a chest drain, with the exception of a Seldinger-type tube, the patient needs to be sedated and given analgesic treatment. Prior to giving the sedative, the patient should be oxygenated for at least 5 minutes by administering a high flow of oxygen near to the nostrils (flow by). The sedation and analgesia can be achieved with opioids (for example, morphine or methadone 0.1-0.2 mg/kg i.m.) combined with benzodiazepines (midazolam or diazepam 0.3-0.4 mg/kg). Local anaesthesia is obtained with lidocaine 2% (about 1 ml) in the intercostal space in which it is intended to insert the drain. During the procedure the patient’s arterial oxygen and carbon dioxide levels, blood pressure and electrocardiograph should be monitored.

Once the hemithorax in which to introduce the drain has been chosen, the insertion site must be prepared as a normal surgical field (shaven, cleaned and disinfected). The length of the tube to introduce should correspond to the distance between the planned site of insertion and the manubrium of the sternum; this distance should be marked on the tube with an indelible pen, if the tube does not already have length marks. Before introducing the drain, the skin of the chest wall should be pulled cranially and incised at the chosen intercostal space (usually the dorsal third of the 7_^th -8_^th space). The drain can also be introduced without pulling the skin of the hemithorax cranially (when the procedure is performed by a single person); in this case the incision is made more caudally (in the 10_^th – 11_^th intercostal space) and then the haemostatic forceps, gripping the drain, are introduced through the skin incision previously made with a scalpel, and moved cranially through a subcutaneous tunnel of three or four intercostal spaces up to the point that the tube will be introduced into the thorax. Once the pre-selected point of insertion has been reached, the haemostatic forceps or stylet must be given a firm push to make it cross the intercostal muscle planes and the pleura. When the chest wall has been crossed, the resistance disappears, indicating that the tube has been correctly placed. Once the drain has been introduced into the thoracic cavity, the prongs of the haemostatic forceps are relaxed and the tube is pushed manually from the outside in a ventro-cranial direction until the mark previously made on the tube is reached.

A three-way stop-cock must be attached to the tube before it is inserted; in the case of drainage with a stylet, the stop-cock must be applied as soon as possible after the stylet has been removed in order to minimise the air introduced into the pleural space during the procedure. The drainage tube must then be fixed to the skin of the chest with a Roman sandal suture (Fig. 6).

Having inserted and fixed the drainage tube, a chest X-ray is performed to verify that the drain is correctly placed and is removing material from the pleural space (Figs. 7 and 8). In some cases the tube may be effective at removing the pleural contents, particularly air, even if it is not perfectly positioned. If the drain is not positioned perfectly but is nevertheless able to remove sufficient foreign material, it can be left in place until the problem is resolved. If, however, the drain is not effective, it must be removed and re-introduced, even through the same point of insertion. Finally, a layer of antibiotic cream and a semi-occlusive elastic dressing must be applied over the drainage insertion site (taking care not to subject the chest to forces)._⁶  The patient will require analgesic treatment until the drain is removed. Drugs that can be used for this purpose are morphine or methadone (0.2 mg/kg i.m. or i.v.), or buprenorphine (10 mcg/kg every 8 hours); bupivacaine 0.5% can be infused through the tube (1.5 ml every 6-8 hours).

ASPIRATION TECHNIQUES

Once the chest tube has been placed, the pathological material accumulated in the pleural space can be aspirated. The choice of aspiration method depends on the underlying pathological process and its severity. Intermittent aspiration (Fig. 9) is usually sufficient to resolve most cases. This technique is performed using a syringe; the time between two aspirations depends on the amount of the aspirate. If the accumulated material increases, the time between two aspirations should be decreased; vice versa if the amount of aspirate decreases, the time between the two aspirations is doubled.

Continuous or permanent drainage is used in particular circumstances such as in a spontaneous, tension pneumothorax or when the rate of accumulation of fluid or air in the thoracic cavity is so fast as to make intermittent aspiration ineffective. For continuous drainage an aspiration system with two or three bottles is used. The drain is attached to the first bottle, which contains 2-3 cm of sterile water, which in its turn is connected to a second bottle which is attached to a pump to create the vacuum and also contains the amount of water necessary to create the desired intensity of aspiration (Fig. 10).

The “Seldinger”-type drainage technique or insertion of a catheter over a guide-wire

Chest drainage has been easier and faster since the recent introduction of the Seldinger technique, in which a specific catheter and insertion kit is used. Sedation is not usually necessary when this method is used; a local anaesthetic (lidocaine 2%) at the site of insertion is sufficient. As in the previously described technique, a small skin incision is made with a scalpel blade in the dorsal third of the 7_^th to 8_^th intercostal space. A large bore needle, contained in the kit, is then introduced through the skin incision and across the chest wall until it reaches the pleural cavity. A specific guide-wire is passed through the lumen of the needle and the chest drain is then run over the guide-wire until it reaches the pre-measured point within the pleural cavity. Finally, the drain is fixed to the chest wall with a suture.

This method is very useful in cats and small dogs. Given the small bore of the drainage tube and its flexibility, the tube may become kinked and blocked in large dogs, preventing it from draining the accumulation. Nevertheless, this technique may be used in such patients in an emergency to ensure ventilation, because it is very simple to perform and does not require sedation; a subsequent evaluation can be made to determine whether it should be substituted by a larger drain that is more effective at removing air and fluids. Seldinger-type drainage is less painful and is well tolerated by patients.  

COMPLICATIONS

The wrong choice of entry site of the drain or its violent insertion can damage the lung parenchyma only when the technique using a stylet is employed. The risk of damaging the lung parenchyma increases if the region involved is not determined by chest X-ray prior to placement of the drain. Finally, the fluids should be drained gradually to avoid the formation of oedema which can occur following rapid expansion of the parenchyma.

REMOVAL OF A CHEST DRAIN

In the case of pleural effusion, the chest drain is removed when the volume of fluid drained is ≤ 2 ml/kg/die. In patients with pneumothorax, the chest drain can be removed when a negative pressure has been restored in the pleural cavity and maintained for at least 12 hours. The drainage tube is removed simply by pulling it out after having taken out the Roman sandal stitch; the access is then dressed. It is not necessary to suture the intercostal muscles, since these will heal spontaneously by second intention. It may, however, be necessary to use one or two skin stitches (performed with a stapler) at the entry site of the drain. The procedure is carried out without sedating the patient; the drain must be removed rapidly in a single movement.

References

1. Vigano’ F. In: Viganò F. Terapia intensiva nel cane e nel gatto. 1st ed. Milano: Elsevier, Mason; 2011, pp.149-169.
2. AndersonGI. Pulmonary cavitary lesions in the dog: a review of seven cases. J Am Anim Hosp Assoc 1987; 23:89-90.
3. Tseng LW, Waddel LS. Approach to the patient in respiratory di stress. Clinical techniques in small animal practice 2000; 15,2: 53-62.
4. Pawloski DR, Broaddus KD.Pneumothorax: a review. J Am Aninm Hosp Assoc2010 Nov-Dec;46(6):385-97.
5. Noone KE. Pleural effusions and diseases of the pleura. Vet Clin North Am Small Anim Pract.1985 Sep;15(5):1069-84.
6. Frendin J, Obel N. Catheter drainage of pleural fluid collections and pneumothorax. J Small Anim Pract.1997 Jun;38(6):237-42.