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Analgesia for a pyometra

Updated: May 17, 2023

Pyometra is one of those often emergency surgeries where having a pre-determined plan can be a real help. Thinking along the lines of our mainstays of analgesia being the opioids, NSAIDs and local anaesthetics, which do we incorporate into our plan?

The severity of pyometra can vary from the dog being relatively healthy, through to a septic case. This work shows that a closed pyometra is more often associated with severe illness.

In a healthy case I would not hesitate to use all three of our analgesic mainstays. I’m hesitant when we have a query over whether the bitch is perhaps septic – and of course I’m talking about withholding the NSAID here. What do I always say – we should use an NSAID unless we can find a very good reason not to! And sepsis or any doubt, is one of those very good reasons.

Talking with reference to a recent case, there was indeed a question over the dog’s clinical signs and we sat on the side of caution with avoiding the NSAID. Of course, we can reappraise the health status in the coming days and use that NSAID once we are satisfied with progression.

For me, an opioid is my first line drug here. I choose methadone at 0.2-0.3mg/kg. We know that methadone is superior to buprenorphine in dogs – and we also have the advantage of a rapid onset of around 5 minutes – whether given IV or IM. For more understanding on the use of methadone, join our webinar here. Would you combine this with your normal sedative agent? If the pet is cardiovascularly stable, you can certainly use either acepromazine or an alpha-2-agonist – depending on your preference. Remember that the alpha-2-agonists also confer analgesia.

How do we incorporate local anaesthesia? There are several options here. This capsule review from BSAVA covers the topics of intraperitoneal and incisional anaesthesia. I’m a huge fan of an incisional block. You can see in this video how easy it is to perform. The aim is to deliver the bupivacaine (onset 15mins, duration 8hrs) subcutaneously to lie on top of the linea alba. I calculate 2mg/kg which gives me plenty of local, within a safe dose. We see very little response to surgical incision and a comfortable patient. Need a little more understanding on local anaesthesia? Try our free webinar called ‘Let’s add local’. Another option is an epidural – which would be an effective long-lasting block for up to 24hrs. Join our Epidural Masterclass webinar to learn how.

As with all surgery involving traction on the ovaries, we expect to see nociception. We detect this by a 20% increase above baseline of either heart rate, respiratory rate or blood pressure. In this particular case we gave 1mg/kg ketamine IM prior to surgery to attempt to minimise this response. We did see a mild reaction – involving just an increase in respiratory rate. Our response to this was to administer 1mcg/kg fentanyl IV. Another option if you don’t have fentanyl is 0.1mg/kg methadone IV or 0.5mg/kg ketamine.

Given our reluctance to use an NSAID at the surgical stage, we elected to use paracetamol IV at 15mg/kg. You can read about the use of paracetamol in this pain update or understand the rationale behind this in our webinar.

This pain update was written by Matt Gurney.

Matt & Carl established Zero Pain Philosophy to provide educational resources to veterinary professionals enabling optimal management of pain.

Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Anderson Moores Veterinary Specialists. Matt is President of the European College of Veterinary Anaesthesia & Analgesia.

Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is President of the Association of Veterinary Anaesthetists. Carl works at Anderson Moores Veterinary Specialists.

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