Soaker-type catheter placement

A soaker-type catheter, also referred to as a diffusion or wound catheter, is simply fenestrated tubing that is sterilely placed at a painful site for the continuous or intermittent administration of local anesthetics. Soaker-type catheters are easily placed during a surgical procedure, such as a limb amputation or large tumor resection, just before closure. In addition, they can be positioned nonsurgically at the site of a lesion that is painful but cannot be resected or when a course of palliative care has been chosen.

Efficacy and adverse effects. The veterinary literature regarding the use of soaker-type catheters is limited, but human medical experience is extensive and, for the most part, positive. A 2007 study demonstrated the viability of soaker-type catheters in postoperative pain management in dogs, cats, and goats.³⁶ In another veterinary study, continuous infusion of bupivacaine into normal dogs' stifles for eight hours demonstrated plasma concentrations well below the toxic dose.³⁷ Unfortunately, no studies have evaluated the efficacy of continuous infusion of local anesthetics in veterinary patients with surgical or traumatic wounds. Results from human trials are largely encouraging, with most showing an improvement in patient pain scores or a decrease in opioid requirements,^38-46 whereas others have not found a benefit.^47-50 Of great interest is the reduction in chronic pain in people a minimum of four years after bone graft harvesting with the use of continuous bupivacaine infusion at the graft site for 48 hours.⁵¹

Figure 4. A commercially available soaker-type catheter and drug reservoir; the catheter has been inserted into the soft tissue over the humerus of a dog with osteosarcoma to provide palliative analgesia.

Obtaining a catheter. Soaker-type catheters can be purchased commercially (Diffusion/Wound Catheter—MILA International; On-Q PainBuster Post-Op Relief System—I-Flow Corp) (Figure 4) or can be fashioned in a sterile manner from materials commonly found in the veterinary clinic. Commercial catheters are made of plastic tubing, often polyurethane, and typically range in length from 2.5 to 10 in. The fenestrated areas vary in length and are designed to spread local anesthetic over a predetermined area (5 to 22 cm).

How to make a soaker-type catheter

Figure 5. A red rubber soaker-type catheter in place, along with a wound drain, in a dog that underwent radical excision of a soft tissue sarcoma. Note that the catheter is placed dorsally in the wound. A tacking suture holds the catheter to the skin, and the catheter will be wrapped to further secure it to the dog. Bupivacaine (1 mg/kg) will be administered through the catheter every six hours.

Soaker-type catheter placement can be accomplished outside the operating room as well when a painful lesion is not to be surgically addressed. Commercially available catheters are advantageous in such situations because they have tear-away applicators that allow for minimal tissue trauma during placement. Homemade versions could also be placed in such a situation but would require some tissue dissection to appropriately localize the catheter. Tunneling the catheter some distance in the subcutaneous tissues before exiting the skin will help provide stability to the placement.

Elastomeric and electronic reservoirs that allow for continuous infusion of local anesthetic can be purchased from the same companies that supply commercial soaker-type catheters. Syringe pumps can also be used to provide continuous infusion. Lidocaine or mepivacaine are likely the safest choices for continuous infusion, and care should be taken to avoid toxic doses, especially in cats. Infusions of lidocaine or mepivacaine of 1 to 2 mg/kg/hr should be safe and effective in most cases. For intermittent administration, bupivacaine at 1 to 2 mg/kg is the best option because of its long duration of action (four to six hours). Catheters are typically left in place for one to three days, but can be left in longer if strict aseptic technique is followed.

SUMMARY

The techniques described above are easy to perform and require simple materials and drugs available in most small-animal veterinary practices. By providing preemptive and multimodal analgesia, reducing the need for systemic analgesics and anesthetics and the attendant side effects, and decreasing the perioperative stress response through the use of local anesthetic techniques, you can improve the overall quality of the analgesic care in your patients. Look for subsequent articles in this series throughout the year covering additional helpful and easy-to-perform anesthetic techniques.