Department of Small Animal Medicine and Clinical Biology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
Drains evacuate fluids (blood, serum, pus) and/or air from tissues or body cavities. They are used with curative intent to drain existing accumulations or are placed prophylactically to prevent the built-up of secretions and obliteration of dead space after surgery.
Drains typically are made up of latex rubber, red rubber, polyethylene, polyvinyl chloride, or silicone rubber. As foreign material, drains induce an inflammatory response and decrease tissue resistance to bacterial colonization. Red rubber and latex cause a marked inflammatory response, polyethylene, polyvinyl chloride and silicone rubber are fairly inert. Selection of a more comfortable and less reactive material is of importance when long-term drainage is expected. Also, softer tubes appear less likely to cause tissue damage or to compress underlying structures.
Wound drains are placed in a surgical created wound for several reasons. Accumulations of serum or blood create a media for bacteria not readily accessible to the immune system or antibiotics. Also, fluid built-up can lead to increased pressure that can compromise tissue perfusion and can cause pain. The early evacuation of mediators that can perpetuate tissue compromise (inflammatory mediators, bacteria, necrotic tissue, and foreign material) leads to swift wound healing. As a general principle drains should not exit through the main incision line. In case of a passive drain the exiting fluid would compromise tissue healing at the incision site and when an ascending infection occurs along the drain exit point, this would migrate along the incision line and cause wound dehiscence with potential herniation.
The most commonly used drain in wounds is the open suction or passive Penrose drain. This is a soft collapsible, radiopaque, latex rubber tube, where exudate flows down the surface of the drain and is collected in a bandage. The mechanism of drainage is passive, which means it relies on capillary action, gravity, body movements creating fluctuation of pressure, and overflow. The amount of fluid flowing along a Penrose drain is proportional to its surface area. Because drainage occurs on the outside it is especially suited to drain thick, viscous exudate (abscess, salivary mucocoele) that would obstruct drain types which evacuate fluids through their lumen. The proximal end of the Penrose drain is placed in the deepest aspect of the tissue to be drained. The exit hole is placed in a more ventral position because of reliance of gravity. The skin incision is made larger than the drain circumference so the egress of fluid is not blocked. The drain is kept in place by two percutaneous sutures at its exit hole. A complication seen with this type of drain when used in the inguinal or axillary region is the creation of subcutaneous emphysema when the drain acts as a one-way valve that draws in air during movement. Increased chance of infection occurs with so-called ingress-egress drains (when both ends of the skin exit on different sides of the suture line). And placing a fixating suture through the most proximal end of the drain risks the drain to tear, and leave a fragment behind, when it is pulled. Maintenance consists of regular chances of the absorbent dressing, protecting the skin with petrolatum based ointments and removing any obstructions at the skin-drain interface (blood cloths, crusts).
Closed suction or active drains consist of a fenestrated tube placed in the wound, attached to a suction device. The vacuum pulls fluid through fenestrations at the end of the tube into the tube lumen and down the tube into an external reservoir. In surgical wounds suction helps skin flaps adhere to underlying tissue, seals off leaking lymphatics, and reduces seroma and hematoma formation. The closed system decreases the risk of infection compared with open drains and prevents skin dermatitis around the exit point.
Butterfly catheters can be converted into a closed active suction drain by cutting of the syringe adaptor and make multiple holes, measuring less than 1/3 the diameter, in the free end of the catheter. The fenestrated part is passed through the skin and placed in the deep part of the wound. The catheter is fixed to the skin and the wound sutured close. Inserting the butterfly needle in a blood collection tube (vacutainer) generates suction. This device is suited when small amounts of non-viscous exudate are expected. Commercial active drains are available in different tube diameters and reservoir types. They typically consist of a multi-fenestrated circular polyvinyl chloride or polyethylene tube and the often used Redon drain, they may have a trocar attached to easily create a tunnel from the wound to the exit point in the skin. These can be used in wounds where larger volumes of fluid are expected (i.e., oncologic surgery, thoracic bite trauma). Manually compressible collection chambers (corrugated or grenade-like) have an inherent tendency to reinflate and this generates a vacuum, typically around 60–125 mm Hg. Because suction is rapidly lost as they fill to 20–30% capacity, they should be emptied whenever the reservoir is half full. Rigid reservoirs connected to wall sources create stable pressures adjustable between 10–360 mm Hg. Complications of active suction drains are air leakage through the incision site or the drain opening, obstruction of the drain lumen by cloths or plugs, disconnection, accidental incorporation of the drain in closing sutures.
The most commonly used tube for abdominal drainage is the Jackson-Pratt drain. The flat, white, silicone part is specifically designed to prevent occlusion of the fenestrations by abdominal structures (i.e., omentum). Before drain placement the abdomen is copiously lavaged. Larger dogs may require the placement of two drains. The drain tube is exited through the abdominal wall and skin via a hole adjacent to the incisional wound. It is then anchored in place by a purse-string suture extended into a modified Chinese fingertrap pattern. Complications consist of metabolic derangements due to loss of electrolytes and/or proteins in drained fluids, ascending infections, pain, subcutaneous fluid collection, and drain failure (inadequate diameter, kinking or disconnection).
Thoracostomy tubes are placed to remove fluid or air from the thoracic cavity of patients; instead of repeated thoracocentesis and also for monitoring hemorrhage, fluid, or air accumulation after thoracic surgery. Commercially available thoracostomy tubes are flexible, yet resistant to collapse, have multiple fenestrations identified with a radiopaque marker line and come with a trocar for thoracic wall penetration and intra-thoracic orientation during placement. Tube diameter is chosen based on the size of the patient and the type of fluid expected: 10–16 Fr for pneumothorax and 16–36 Fr for liquothorax. Thoracostomy tubes are tunneled subcutaneously so that the skin exit point is around the 10th or 11th intercostal space while the tube enters the thoracic cavity in the 7th or 8th intercostal space. The tube is inserted in the dorsal third and advanced in a craniomedial direction. Length of the tube is chosen to avoid entering the most cranial extent of the mediastinum. Percutaneously placed tubes should be radiographically checked for correct intrathoracic position. Thoracostomy tube drainage may be intermittent, for non-life threatening air or fluid, or continuous. Commercially available systems for continuous drainage consist of three compartments: a collection tube, a water seal to avoid air entry during inspiration and to visualize evacuated air in the form of air bubbles, and a chamber to down-regulate negative pressure to between 5 and 10 cm H2O. Complications of thoracic drains occur in 22% of patients and consist of peristomal discharge, accidental removal or disconnection, pneumothorax, blockage and subcutaneous emphysema.
The decision to remove a drain is based on the quantity and quality of the fluid and ongoing drain function. Drains should be removed as soon as possible since the risk of bacterial colonization increases with the length of time. Fluid production will never be zero because a drain is foreign material and induces fluid production. Furthermore active drains induce fluid by altering the balance between hydrostatic and oncotic pressures. The decision is made when fluid steadily decreases and reaches a plateau, while turning increasingly serosanguineous. Serial cytology can also be performed to evaluate cellular characteristics. Closed suction drains in wounds are removed when fluid production is < 0.2 ml/kg/hour. Thoracic drain removal is typically performed when production is around 3 ml/kg/day (dog) and 5 ml/kg/day (cat).
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