Pain control without opioids
NSAIDs are an important part of managing peri-operative pain and should be given preoperatively to manage inflammatory pain.
In an interesting lecture at the BSAVA Congress in Birmingham, Karen Walsh from the Willows Veterinary Centre, looked at alternative methods of analgesia to opioids. She said that post surgical pain occurs in up to 50 per cent of human patients. It is not unreasonable to assume that the picture is similar in dogs and cats and surgical pain will certainly affect their quality of life.
NSAIDs are an important part of managing peri-operative pain and should be given preoperatively to manage inflammatory pain. There are concerns about side effects with NSAIDs, 64 per cent of which are gastric in nature. It is important to use licensed veterinary products appropriate for the species being treated.
Karen emphasised that it is possible to minimise the side effects of NSAIDs by taking a good history, not using them concurrently with corticosteroids, and monitoring patients closely for side effects – something that is especially important to emphasise with clients. It is also critical to optimise dosing, use gastro-protective agents and monitor blood biochemistry.
Paracetamol should be used at 10mg/kg every 12 hours in dogs. The licensed product name is Pardale V. Use it in patients that don't tolerate NSAIDs or in addition to manage chronic pain. Paracetamol should not be given to dogs with hepatic disease and must not be given to cats.
Local anaesthetic techniques should not be overlooked for pain control. Although unlicensed specifically for veterinary use, mepivacaine, lidocaine, bupivacaine and ropivacaine can be used, especially for incisional infiltration. There are also 'soaker catheter' techniques using catheters placed deep in the wound, and intraperitoneal infusion and regional nerve blocks can be successfully employed in a range of situations.
The use of constant rate infusions is gaining in popularity. In this instance, it is vital to use the appropriate agent and monitor cases closely, including the total fluid intake. Catheter care is essential because they are technically challenging owing to the need for drivers and pumps. It is important to take into account their contribution to anaesthesia.
Alpha2 agonists produce analgesia by modulating pain at the spinal level. Their major side effects are sedation, depression and hypotension and bradycardia.
Ketamine is very useful substitute for opioids and NSAIDs, especially in the control of somatic and neuropathic pain, rather than visceral pain. It is a Schedule 2 controlled drug and has analgesic effects at sub-anaesthetic doses. Give 0.5 - 1mg/kg intramuscularly or intravenously to provide analgesia for about 20 minutes. This can be followed up constant rate infusion at much lower doses, watching for excitatory side effects.
Lidocaine is useful for managing ocular, visceral and pancreatic pain. Side effects include vasodilation, sedation and neurotoxicity. It is possible to use a combination of morphine, lidocaine and ketamine to control extreme pain, especially associated with cancers.
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