Wound catheters are a perfect method of delivering local anaesthetic directly to the surgical site.
Local anaesthetics are a key component of multimodal, preventive analgesia. The wound catheter is laid directly onto the wound bed prior to final closure of the incision. Catheters are structured with a section with pores which the local anaesthetic comes out of as well as a section for tunnelling without any pores. In the image below the pores start at the black mark and run distally.
Catheters are manufactured specifically for dogs (Mila and Vygon) but can also be home made in the low-resource setting by sealing the end of a soft urinary catheter and creating pores in the catheter.
Limb amputations are perfect examples of where wound catheters play a huge role. Amputation is often undertaken as a result of a painful condition such as extensive fracture or neoplasia. In such cases controlling the pre-existing pain in a multimodal fashion is important.
Protocol for limb amputation:
A full mu opioid agonist in the premed, ideally with an alpha 2 agonist for the analgesic properties.
NSAID to reduce peripheral sensitisation, administered once we are certain there is no further risk of haemorrhage or hypotension.
A continuous rate infusion of ketamine to deal with any central sensitisation related to pre-existing pain.
Pelvic limb: either an epidural injection of morphine and bupivacaine or a peripheral nerve block.
Thoracic limb: cervical paravertebral, or infusion of the surgical site.
A wound catheter laid in the wound bed prior to closure. Bupivacaine 0.5% 1mg/kg or ropivacaine 0.75% 1.5mg/kg can be administered at the end of the procedure and repeated every 6 hours. In our experience this dramatically reduces the opioid requirement. We recommend using validated pain scoring tools such as the Short Form of the Glasgow Composite Pain Scale, which is available for both dogs and cats. Catheters are typically left in situ for 24-48 hours.
Tumour resection can create extensive surgical wounds and wound catheters allow excellent analgesia for these patients. Remember that in many of these cases a surgical drain will be present so ensure you do not infuse the local anaesthetic and drain it straight out of your active suction drain!
In these cases the wound catheter is used in a similar fashion as for limb amputation.
One study looked at using wound catheters connected to a CRI of lidocaine to give continuous infusion. Realistically we find this difficult as our patients like to move around and disconnection becomes an issue. In our experience either bupivacaine or ropivacaine every 6 hours gives excellent analgesia.
If you would like to share your experiences of wound catheters just drop us a message via our Facebook page or through the contact box on this site.
This post was written by Matt Gurney.
Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Anderson Moores Veterinary Specialists. Matt is Vice-President of the European College of Veterinary Anaesthesia & Analgesia.
Matt & Carl established Zero Pain Philosophy to provide educational resources to veterinary professionals enabling optimal management of pain.
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