Surgical drains are indicated for the prophylactic or therapeutic removal of fluid, air or exudate accumulation within tissue and to obliterate ‘dead space’ left following surgery (Figure 1). The removal of these wound fluids and exudate accumulations are necessary for normal wound healing to occur (Pead and Langley-Hobbs, 2007) and therefore their removal can decrease the risk of wound infection and dehiscence (Ladlow, 2009). Unfortunately, the development of infection by ascending nosocomial pathogens is an associated potential complication with the use of such devices (Johnson, 2002) and it is therefore essential that barrier nursing (wearing appropriate personal protective clothing) is performed to reduce the aforementioned risk to patients with indwelling devices (Johnson, 2002; Andrews and Boag, 2008).

In addition to barrier nursing, during the post-operative period, an aseptic technique is vital when attending to wounds, catheters and surgical drains. With hand washing being the single most effective method of reducing nosocomial infections, a thorough hand washing protocol, such as that recommended by the World Health Organisation (2009), should be carried out prior to (and after) handling the patient and any invasive devices (Gregory, 2005) Hand washing should be performed (with an appropriate antibacterial handwash) even if sterile gloves are to be worn in case there is a break in asepsis (Baines, 1996). Instances of incorrect management and poor aseptic technique will readily negate the benefits of minimizing and preventing bacterial contamination during the pre- and operative stages (Baines, 1996).
Types of available wound drain systems
There are numerous types of wound drain systems available for use in small animal practice. Four of the most common types in use will be covered in this article: Penrose, Jackson Pratt, Redon and Redovac drains. These drains can be classified by their method of action as either passive or active. Passive drains use capillary flow, overflow and gravity to remove fluid from the wound and active drains are those with a vacuum assisted suction via a closed reservoir; usually a collapsible chamber with an intrinsic memory which produces a vacuum on reinflation (Ladlow, 2009). Each of the aforementioned drains will be briefly described and discussed and attention paid to the necessary details for each drain type.
Penrose drains
Penrose drains (Figure 2) are passive drains made from soft flexible latex rubber tubing that relies on capillary action, wound overflow and gravity to drain fluid out of tissues and dead space. It is important to note that passive drains must be placed exiting at the ventral site of the wound to allow for this gravitational pull to enable drainage. As Penrose drains are essentially open to the environment it is essential that they are protected from contamination and the risk of ascending infection reduced by covering them with an absorbent dressing; it may also be necessary to use an emollient cream to protect the skin from becoming inflamed/irritated by the fluid produced.

As stated, these drains are open to the environment and are therefore unsuitable for the removal of air and without a reservoir they should only be used when the volume of fluid produced is expected to be small. Without a reservoir, monitoring the volume of fluid produced is relatively subjective; a more objective method of measuring fluid drained is to weigh the protective dressing pre and post-absorption of fluid. This method of assessing fluid production is obviously limited and will not be wholly accurate.
These drains are available in a variety of widths (6–50 mm); as a rule, the wider the drain the more effective the drainage (Ladlow, 2009). Theye are suitable for use in, for example, bite wounds or abscesses that require further drainage following treatment.
Jackson Pratt drains
Jackson Pratt (grenade) drains are active suction drains comprising a fat internal silicone tube (with a number of fenestrations along its length to increase surface area through which drainage occurs and prevents blockages) (Figure 3) that exits the body and is attached to an external grenade-shaped reservoir (Figure 4) for the collection of fluid. To activate the vacuum the grenade is squeezed to evacuate the air and its plug closed, thus creating suction along the length of the tube and drawing fluid into the grenade reservoir. Any loss of this vacuum will result in a subsequent loss of suction.


The grenade bulb has an external measuring scale to allow for the volume within the reservoir to be recorded. The reservoir should be checked at regular intervals (for loss of vacuum) and can be emptied, as necessary, by opening the plug and squeezing out the contents into a container before resetting the drain. This drain reservoir has two channels at the top: one for attachment of the drain tubing, and a second allowing for the contents of the reservoir to be emptied while still in place (Figure 5).

This type of drain is suitable in a number of patients and circumstances, for example removal of a mass within the tissues in order to reduce ‘dead space’ and prevent the accumulation of air or fluid. They are available in a variety of tubing and grenade sizes (Ladlow, 2009).
Redon/Red-O-Pack drains
Redon/Red-O-Pack drains are active suction systems consisting of a plastic fenestrated tube (Figure 6) exiting the body and connecting to a cylindrical reservoir chamber which when charged collapses into a concertina formation (Figure 7); as the drain removes fluid, it expands in volume. Again, as with the Jackson Pratt drain it should be checked at regular intervals to measure volume of fluid in the reservoir and to ensure that the drain vacuum is still charged and functional.


Unlike the Jackson Pratt drain, to empty the drain the reservoir must be disconnected from the tubing as it does not have a separate plug for emptying. These are useful, for example, following the removal of a mass where air or fluid is expected to be produced or where tissues were not able to be fully apposed or following wound breakdown resulting in abscess formation.
Redovac drains
Redovac drains are completely closed active suction units. They consist of fenestrated drain tubing which connects into a large rigid plastic reservoir bottle (Figure 8). The reservoir bottle has a pre-established vacuum mechanism which should not be activated (by the release of gate clamps present along the length of the drain tubing) until a seal has formed around the exit site (4–6 hours post operatively) as the vacuum in these bottles cannot easily be recreated (Ladlow, 2009). If the bottle fills with air before a seal has formed, this bottle will need to be replaced or emptied of air using a suction unit or syringe.

These systems have a scale along the side of the bottle which allows for the volume of fluid to be measured accurately and there is also an indicator allowing for the presence of the vacuum to be checked; this is essential to determine the presence of a vacuum as the reservoir bottle does not change shape. These systems are not always suitable/tolerated in cats due to their large size but they have been successfully used in some cases, e.g. septic joint, large wound closure where there has been difficulty in reducing ‘dead space’ and apposing tissue layers, stick injury deep within the tissues and where a moderate to large volume of fluid or air is expected to be produced.
The exit site of all drains must be covered and the drain can be carried by the patient in a stockingette dressing (e.g. Surgifix, Smith and Nephew, London) for patient comfort or can be placed in a canine back-pack (e.g. Dog Packs, Ruffwear, Oregon, USA) which is well tolerated in the majority of cases.
Advantages/disadvantages of passive and active drains
There are advantages and disadvantages to both passive and active drainage system.
Passive drains
Advantages
Disadvantages
Active drains
Advantages

Disadvantages
How to manage wound drains
Drains in situ may generate some degree of irritation and discomfort therefore measures should be taken to prevent patient interference allowing for the drain to function effectively and to prevent the patient contaminating the area. Patients should be assessed for pain and analgesia provided as necessary to ensure they remain comfortable as the premature removal of drains by patients may in some cases be prevented by the provision of adequate analgesia (Bacon, 2007). Unless contraindicated Buster Collars should also be utilized to prevent contamination or early removal of the drain by the patient.
The key to effective management of wound drains is to ensure that equipment is prepared in advance and in an aseptic manner. Considering the type of drain and the intervention required will assist in the preparation of the correct materials needed.
Drain sites should be checked at least daily with full removal of all dressing material to allow thorough inspection of the wound and exit site before the application of a new dressing. Recordings should be regularly made of the volume and nature of the fluid produced allowing for trends and changes to be noted (Whiting et al, 2007). See the Step-by-step guide.
Removal of drains
The presence of a drain will produce an inflammatory response and cause fluid production. It is accepted that the volume of fluid produced is approximately 2–4 ml/kg/24 hours, therefore when production of fluid falls below this volume, the drain should be removed. Usually this occurs within 2–5 days. The removal of passive drains should occur following an improvement in the appearance of the exudate and a significant reduction in the volume produced (Ladlow, 2009).
When drains are removed, the stoma should be left open and covered with a small dressing until sealed (Bacon, 2007).
Conclusion
Wound drains play a significant role in small animal practice and it is essential that they are managed with appropriate care and attention to ensure that their effectiveness and assistance in the management of wounds is not annulled by poor management technique.