THE USE AND ABUSE OF SURGICAL WOUND DRAINS STEVE MEHLER, DVM, DACVS
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Some suction sources apply a fixed amount of pressure (grenades, bulbs, vacuum containers) or to a suction device in which a prescribed pressure can be selected. Active drain collection canisters usually lose their suction when are about 50% full. Drainage lines, if possible, and collection canisters should be completely replaced every 48-72 hours to reduce drain related infections. Active drains can be open or closed. Open active drains have an air vent into the wound (sump) but there is significant danger of retrograde contamination of the wounds through the vent. Passive drains have no suction and work according to the differential pressure between body cavities and the exterior environment or rely partially or exclusively on gravity to remove fluid from a wound or body cavity. The most commonly used passive drain in veterinary medicine is the Penrose drain and it should only be utilized to drain the subcutaneous space. Penrose drains are used exclusively in clean wounds and only when the exposed end can be covered at all times by a bandage. They should exit the skin at least 1 cm from the incision and be place at the most gravity dependant location. Most commercial drains are made from silastic or rubber. Silastic drains are relatively inert and induce a less severe tissue reaction compared to rubber drains. Some forms of rubber, like red rubber drains, can induce an intense tissue reaction, and should be avoided. 3 REMOVAL Generally, drains should be removed once the drainage has significantly
decreased, ceased completely due to malfunction or blockage of the drain, or becomes less than about 1-2 mls/ kg/day. Consider sedating the patient or providing analgesia as there may be some discomfort when the drain is pulled out. Place a dry dressing over the site where the drain was removed as temporary continued drainage is expected. 4 EVIDENCE AND CONTROVERSY Despite the paucity of clinical evidence demonstrating any benefit supporting their use, drains continue to be placed frequently in wounds in dogs and cats. Drains must not be used as a substitute for aggressive surgical debridement. The only proven benefit of surgical drains is to remove fluid from a wound that otherwise would lead to complications associated with healing. In regards to active drains, a recent study concluded that closed active suction drains can be used with low risk of major complications, but they lead to a high rate of infection in clean surgeries in dogs. It is recommended that such drains are kept in place for the shortest time possible and that strict asepsis is adhered to both during placement and management. In a recent study evaluating different types of active drains, the drainage systems varied widely in their initial suction and rate of loss of suction during filling. However, grenade-type compressible suction drains appear to perform in a safe, predictable, and consistent manner and operate with a lower amount of suction. An increased rate of wound infection or inflammation in association with the use of surgical drains has been documented in a prospective study of surgical site
infection in dogs and cats. The use of active suction drains reduces surgical site infection, compared with the use of open passive drains. The constant negative pressure generated by the system minimizes the potential for retrograde flow of bacteria and fluid. 5 DISADVANTAGES OF DRAINS Drains serve as a retrograde conduit for skin and environmental contaminants to enter the wound. All drain materials impair the local tissue environments resistance to bacterial colonization and infection by 10,000 fold. Drains made from latex or rubber incite more inflammation than those made of silicone. Vacuum assisted closure has been shown to be effective in the treatment of traumatic and chronic wounds. The therapy decreases interstitial edema, increase perfusion to the wound and periwound, and the mechanical strain on the fibroblasts appears to increase proliferation and collagen synthesis. Its use in veterinary medicine is extremely promising, with one of the advantages being prolonged time between dressing changes (up to 72 hours). This modality was evaluated in a controlled, experimental setting on open wounds as well as free skin grafts and demonstrating the beneficial and potentially negative effects of vacuum assisted closure. 6 NEGATIVE PRESSURE WOUND THERAPY (NPWT)
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