Perioperative analgesia in dogs and cats

Doses on this pageEvery dose below is quoted from the cited source. Verify against the current label/formulary and the patient's full clinical picture.

Core principles

The ISFM guidelines build the analgesic plan on two ideas: preventive analgesia and multimodal analgesia (combining drug classes) [1]. The panel links untreated acute pain, which it calls oligoanalgesia, to peripheral and central sensitisation. These are lowered pain thresholds that can make normal touch painful [1]. The panel cites human data showing that poorly treated surgical pain can become persistent postoperative pain, and suggests a similar course may occur in cats [1].

Grubb and Lobprise make a related argument for local anaesthetics. Because the intensity and duration of acute pain may promote chronic pain, they favour longer-lasting analgesic techniques after surgery, while noting that no animal studies yet confirm the human finding [3]. Merck describes NSAIDs as appearing to act synergistically with opioids and possibly reducing opioid needs [2].

Pain assessment and team roles

The ISFM panel treats pain assessment as the first step of treatment and identifies failure to recognise pain as the likely main cause of undertreatment [1]. It recommends that the whole veterinary care team be trained in feline pain assessment. It also describes validated tools as a way for nurses and technicians to advocate for patients and to support the clinician's decisions [1].

The ISFM guidelines describe the following timing:

• Cats may first be assessed 30 to 45 minutes after surgery ends.
• Assessment then continues hourly in the early postoperative period, depending on the drugs used, until discharge [1].
• After a rescue intervention, the panel advises repeating the assessment after 30 to 45 minutes [1].

The panel recommends combining observation of the undisturbed cat with gentle palpation around the wound, since evoked pain may otherwise be missed [1].

The panel notes that a veterinarian may give rescue analgesia below the cut-off if the cat is thought to be in pain [1]. Merck takes a similar view, stating that "the most accurate way to determine whether a patient is in pain is to administer a dose of analgesic and monitor the patient's response" [4]. Merck also cautions that physiologic measures such as heart rate cannot reliably separate pain from fear or anxiety. It adds that a cat sitting quietly at the back of its cage after surgery may be painful [4]. The ISFM guidelines list ketamine-based protocols, sedatives, fear and residual anaesthetic effects as factors that can bias scores [1].

After discharge, the ISFM panel considers cat carers part of the team and notes that the Feline Grimace Scale can be used reliably by owners [1]. Owners in one cited study identified behaviour changes for up to 3 days after neutering [1].

Building the plan

The ISFM guidelines organise drug selection around the acronym TELLS [1]:

• Type of pain
• Expected duration
• Location of the stimulus
• Location of the patient (inpatient or outpatient)
• Severity

In the panel's examples, visceral pain from neutering may be managed with NSAIDs, opioids, alpha-2 agonists and local blocks. Orthopaedic, spinal or neuropathic pain may call for NMDA receptor antagonists such as ketamine, and gabapentinoids [1].

The panel also points out that clinics without overnight staff may depend on long-acting oral, sustained-release or transdermal drugs. Patients needing infusions and intensive monitoring should, where possible, be moved to clinics able to provide that care [1].

Opioids and NSAIDs

Opioids

Merck calls opioids "the cornerstone of effective pain management in veterinary medicine" [2]. The ISFM panel ties opioid choice to procedure, pain intensity, comorbidities, temperament and local availability [1]. Points the panel attaches to specific opioids in cats include the following [1]:

• Gastrointestinal adverse effects can be avoided by choosing methadone, fentanyl or buprenorphine.
• Buprenorphine is described as not sufficient for acute pain relief after major orthopaedic procedures, especially as a sole analgesic. Subcutaneous use of the standard formulation is not recommended.
• Butorphanol does not give adequate analgesia as the sole analgesic for routine surgery.
• Transdermal fentanyl patches produce highly variable plasma concentrations in cats.
• Kittens and young cats may need more frequent dosing.

Opioids also reduce inhalant requirements less in cats than in dogs. The panel cites a maximum isoflurane reduction of 25% with high-dose remifentanil in cats versus 79% in dogs [1]. Merck notes a delayed onset of fentanyl patch analgesia of 6-24 h in cats and 12-24 h in dogs [2].

Merck's dose tables give, for example, methadone at 0.1-1 mg/kg IM, SC, IV q 4-8 h in dogs and 0.05-0.5 mg/kg IV, SC, or IM q 4-6 h in cats [2]. The ISFM panel's feline methadone range is 0.2-0.6 mg/kg IV, IM or OTM [1]. The two sources differ in places. The ISFM panel describes its doses as suggestions and advises consulting drug labels where a veterinary product is available [1].

NSAIDs

The ISFM guidelines list contraindications to rule out first [1]:

• Gastrointestinal disease
• NSAID intolerance
• Unmanaged renal disease
• Hepatic disease
• Coagulopathy
• Hypovolaemia and hypotension
• Concurrent NSAID or corticosteroid use

The panel advises dosing on lean body weight in normovolaemic cats [1]. For the US-approved meloxicam injection dose of 0.3 mg/kg SC once in cats, the panel recommends using lower doses instead [1]. Merck notes a black box warning on US meloxicam products stating that repeated use in cats has been associated with acute renal failure and death [2].

On timing, the ISFM panel describes it as "a controversial subject." It states NSAIDs can generally be given preoperatively for routine neutering of healthy cats, especially if blood pressure is monitored and cats are normovolaemic [1].

Local and regional anaesthesia

Grubb and Lobprise describe local anaesthetics as unique because they stop nociceptive signals before they reach the central nervous system. They cite evidence that blocks reduce intraoperative inhalant needs and opioid requirements in dogs and cats [3]. Their review was funded by the maker of liposomal bupivacaine, a conflict the authors disclose [3].

Grubb and Lobprise state these are total cumulative doses to be divided among blocks [3]. Cautions in the sources include:

• Aspirating before injection to avoid intravascular delivery [1][3].
• Bupivacaine's greater cardiotoxicity [1][3].
• Intravenous lipid emulsion as a rescue for toxicity [1][3].

Among local anaesthetics, only lidocaine can safely be given intravenously, according to the review [3].

The ISFM panel lists incisional, intraperitoneal, intratesticular and dental blocks as practical feline techniques [1]. It advises performing intratesticular blocks under general anaesthesia or deep sedation and limiting infraorbital needle depth to 4-5 mm to protect the globe. It no longer recommends the maxillary nerve block [1]. Feline spinal anatomy makes accidental intrathecal injection more likely at the lumbosacral space than in dogs [1].

For liposomal bupivacaine, the review describes infiltration at wound closure with a 25-gauge or larger needle. It warns against mixing with lidocaine and states it is unlikely to work well as a splash block [3].

Adjuvant drugs and non-drug care

The ISFM panel's second step adds adjuvant analgesics [1]:

• Alpha-2 agonists are described as useful for premedication but not as stand-alone analgesics. They are reserved for cats with stable cardiovascular function, with atipamezole kept available [1].
• Ketamine at subanaesthetic doses is used for its anti-hyperalgesic and opioid-sparing effects [1].
• Gabapentin has limited evidence in acute pain, though the panel values it for reducing stress and fear [1].
• Tramadol carries serotonin toxicity risk with drugs such as trazodone or fluoxetine [1][2]. It has failed to produce clinical analgesia in some studies [1].

Merck describes maropitant as providing visceral analgesia in addition to its antiemetic use [2].

The ISFM guidelines also list non-drug measures: bandaging, cold therapy, positioning, fluids, nutrition, grooming, a calm and quiet environment, cat friendly handling, and housing away from dogs [1].

Where opioids are unavailable, the panel cites one study in which an opioid-free injectable protocol with intraperitoneal bupivacaine and meloxicam failed to give optimal analgesia in more than half of the cats. The study had no opioid comparison group, so the panel treats the question of opioid-free feline analgesia as open [1].

Species differences and comorbidities

The ISFM panel explains that cats eliminate drugs that depend on glucuronidation slowly, including carprofen, ketoprofen and morphine. Oxidised drugs such as meloxicam and buprenorphine are often cleared faster than in dogs [1]. Merck advises giving carprofen to cats as one dose only [2].

The panel notes up to 40% of cats over 10 years old have chronic kidney disease [1]. In some cases, for normovolaemic cats with stable IRIS stage I or II disease undergoing strongly inflammatory surgery, it states a minimum effective NSAID dose "can be considered." This applies once blood pressure is controlled and there is no risk of intraoperative haemorrhage, ideally after the cat is eating and drinking [1].

Before using any dose aboveVerify against the current label/formulary and the patient's full clinical picture.