Many of our canine and feline patients experience trauma resulting in wounds that cause them severe pain. Often, we find it difficult to control the patient’s pain with the standard modalities such as opiate and non-steroidal anti-inflammatory drugs. Pain control can be the limiting factor in a patient’s discharge from the hospital because painful patients often do not eat, are anxious and difficult to treat, and thus are poor candidates for treatment at home. Effective pain control with a local anesthetic is extremely efficacious and is commonly used in the form of epidurals and regional nerve blocks, with the drawback of requiring multiple injections and limiting the patient’s mobility via neuromuscular blockade. A bupivacaine infusion catheter allows us to use this modality when the wounds are located in an area not amenable to treatment with epidurals and nerve blocks or when a longer duration of anesthesia is needed.
An 8 year old, 7.3 kg, MN Miniature Pinscher was referred to DoveLewis with massive degloving wounds and deep muscle injury to the head and neck from a dog maul incident that had occurred four hours earlier. After stabilization and thorough physical and neurologic examination, the patient was started on a fentanyl CRI at 3 mcg/kg/hr for analgesia. NSAIDS were not given because the patient had received flucortisone and dexamethasone SP at the referring clinic during initial stabilization. Despite the fentanyl drip, the patient remained extremely painful and additional therapeutic intervention was needed. The patient was taken to surgery to decontaminate, evaluate and potentially close the wounds.
The injury was severe. The skin was avulsed from the dorsum of the skull to the level of the scapulae. The wound was deeply contaminated, the right ear and left submandibular salivary gland were torn from their attachments, and there was deep injury to the cervical musculature. The wound was extensively debrided and lavaged, then primary closure undertaken due to the deep, extensive nature of the wound. A large muscle defect remained on the right side of the neck due to partial loss of the brachiocephalicus, cervical trapezius, splenius muscles and semispinalis capitus muscles. Along with two Penrose drains, a local anesthetic infusion catheter was made and placed through a dorsal skin stab incision, leaving the fenestrated catheter sitting in the subcutaneous space over the dorsum of the skull and the muscular defect. The wound was successfully closed by transposing ventral cervical skin with the remaining viable flap. A bandage was placed and the patient moved to the ICU unit for recovery. Prior to cessation of general anesthesia, 5mg bupivacaine diluted in 1ml saline was injected into the catheter for local analgesia.
Post-operatively, the bupivacaine injections were continued every 6 hours until pain control appeared adequate with other means (2.5 days). Technicians caring for the patient noted that as the 6 hour interval between bupivacaine doses neared, the patient would become more anxious and painful. Five to fifteen minutes after the infusion of bupivacaine, the patient would become less anxious and appeared to be more comfortable.
The benefits of local anesthetic drugs used to augment post-operative analgesia are well known. Epidurals, lidocaine constant rate infusions, and nerve blocks have all been shown to decrease the need for opiates or other analgesics as well as decrease the inhalant anesthetic requirement when used intraoperatively ¹. Delivery of local anesthetic directly to a wounded area via an indwelling catheter is another effective way to improve pain control in post surgical patients ².
Commercial wound catheters are available but are expensive and designed predominately for continuous local infusion of lidocaine. Others have reported techniques for making wound catheters ² and at our hospital we have modified a sterile butterfly catheter to make a functional system for intermittent injection of bupivacaine.
Materials needed to make a wound infusion catheter include a 19 gauge butterfly catheter, a small hemoclip, a pair of sharp scissors, and a male adapter plug. The needle end of the catheter is removed and then the catheter is fenestrated with scissors to the desired length, ensuring that the holes made are less than 30 % of the diameter of the tubing. Two hemoclips are applied to the end of the catheter to seal it, and the adapter plug added for the injection port.
The catheter is placed through a dorsal stab incision and the fenestrations placed so that anesthetic is delivered close to severed nerves and muscles. The end is secured to the skin with a purse string and Chinese finger trap suture. The catheter can be used in combination with closed suction drains (suction is temporarily discontinued for 10-20 minutes when the infusion is given) or Penrose drains (provided the catheter is not in close proximity with the exits for the drains).
Recommended doses of bupivacaine through a wound catheter²for dogs is 0.25% bupivacaine at 1 mg/kg initial dose followed by 1 mg/kg every 6-8 hours. The drug can be further diluted as needed to a volume that will spread the solution throughout the wound area. The dose should be decreased by 50 % for use in feline patients. The patients should always be monitored closely for cardiac or neurologic side effects related to accumulation of the drug, although this has not been reported in the literature associated with a wound catheter ¹ ². The minimum amount of drug that is effective in providing analgesia should be used.
In limited reports available to date there does not appear to be an increased incidence of wound healing complications or infection in patients treated with this modality ¹ ². As a further precaution to prevent iatrogenic introduction of bacteria into the wound, a millipore filter can be added directly to the catheter setup to minimize the chance for accidental introduction of bacteria, or the drug to be infused can be drawn up with a bacterial filter each time. The catheter should stay covered under a bandage when possible to help shield the insertion site from ascending infection and protect it from damage by the patient. (Adhesive bandages can be used in areas difficult to wrap. The catheter is removed as soon as the patient demonstrates adequate pain control without the infusions.
Use of these catheters does appear to significantly improve patient comfort and mobility after surgery. A study conducted at North Carolina State University in cats with fibrosarcomas removed surgically showed that patients treated with intermittent bupivacaine infusions via a wound catheter had significantly shorter hospital stays². A bupivacaine infusion catheter can be made from materials found in most veterinary practices, and can be constructed and placed easily and quickly during the surgical procedure. The benefits of improved pain control with potentially decreased amounts of opiates and NSAID needed, as well as decreased hospitalization times make this catheter an important modality in the management of severe surgical or traumatic wounds.
We would like to thank the staff of Cowlitz Animal Clinic and Veterinary Emergency Clinic of Vancouver for referral of this patient.
1. Carroll, G. Perioperative multimodal analgesic therapy. In Fossum, T. (Ed), Small Animal Surgery Mosby, 2007 p. 136
2. Davis, K., Hardie E., Lascelles B., Hansen, B. Feline Fibrosarcoma: Perioperative management. Compendium Sm An Pract 29(12) 712-729.
How many of you are eager to try this on your next nasty laceration? How many of you are already incorporating this into your pain management routine?