Chapter 42
Anesthetic Considerations for Cats
An everyday challenge
Paulo Steagall and Javier Benito
Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Canada
- Q. Is anesthetic risk higher in cats than in dogs?
- A. The risk of anesthetic-related death in cats varies between 0.1 and 0.3%. A recent study in the UK reported a mortality rate of 0.24% in cats, which was higher than the 0.17% reported in dogs [1]. Poor health status (ASA status), age, extremes of body weight, endotracheal intubation, and the lack of anesthetic monitoring or fluid therapy are among risk factors that have been associated with peri-operative mortality in this species. Monitoring of anesthesia is associated with reduced anesthetic risk. Cats should have intravenous access and fluid therapy should be administered.
- Q. What are the key points about anesthetic premedication in cats?
- A. Sedation will decrease stress and anxiety to facilitate handling while possibly providing analgesia and reducing the requirements for general anesthetics. Sedation should not be considered safer than general anesthesia since some sedatives can cause significant cardiorespiratory depression. All of the beneficial aspects of anesthetic premedication (see Chapters 5, 6, and 8) apply to cats. Generally, a sedative drug is combined with an opioid for analgesia. The desired degree and choice of sedation should be evaluated on a case-by-case basis. Table 42.1 shows doses and routes of administration of sedative agents in cats. Table 42.2 shows doses and routes of administration for opioids in cats.
Table 42.1 Sedative and premedication drugs in cats.
Drug
Dosage regimens
Comments
Acepromazine
0.03–0.05 mg/kg IM, IV, SC
Mild sedation in cats.
Diazepam
0.1–0.5 mg/kg IV
Poor absorption after IM administration. Commonly used in combination with ketamine or propofol for anesthetic induction.
Midazolam
0.1–0.5 mg/kg IM or IV
Commonly used in combination with ketamine or propofol for anesthetic induction.
Xylazine
0.2–1 mg/kg IM, IV
Sedation when (dex) medetomidine is not available.
Dexmedetomidine
3–20 µg/kg IM, IV
Lower doses are used for neuroleptanalgesia while high doses are administered for anesthesia in combination with ketamine and opioid (“kitty magic”).
Medetomidine
6–40 µg/kg IM, IV
Same for dexmedetomidine.
Ketamine
3–10 mg/kg IM or PO
Ketamine may be used for sedation in cats when combined with midazolam and an opioid.
Table 42.2 Dosage regimens and routes of administration of opioid analgesics in cats.
Opioid analgesic
Dosage regimens
Comments
Butorphanol
0.2–0.4 mg/kg IM, IV
Synergistic sedation when given with the sedative drugs listed in Table 42.1. Poor and short-acting analgesic effects.
Buprenorphine
0.02–0.04 mg/kg IM, IV, PO
0.24 mg/kg SC (Simbadol® every 24h for up to 3 days)
Good analgesia for moderate pain when combined with NSAIDs. Euphoric behavior.
Hydromorphone
0.025–0.1 mg/kg IV, IM
Reliable pain relief. Possible vomiting.
Oxymorphone
0.025 – 0.1 mg/kg IV, IM
Same for hydromorphone. Expensive.
Meperidine
3–5 mg/kg IM
Do not administer IV. Short duration of action.
Morphine
0.1–0.3 mg/kg IM
Vomiting and salivation.
Methadone
0.1–0.4 mg/kg IM, IV, PO
Rarely causes vomiting.
Fentanyl (CRI)
2–3 µg/kg loading dose followed by 3–20 µg/kg/h IV
Dose-dependent analgesia. Possible post-operative dysphoria. See text. Transdermal patches are also available at 12.5 and 25 µg/h.
Naloxone
0.01–0.04 mg/kg IV, IM
Opioid antagonist. It can be diluted in 5 ml of saline 0.9% and given to effect to reverse agitation and respiratory depression.
Other drugs: ketamine (3–5 mg/kg) or alfaxalone (2–3 mg/kg) have been administered by the intramuscular route for premedication in the “difficult” cat. Ketamine (5 mg/kg) is combined with an opioid (e.g., buprenorphine 0.02 mg/kg) and midazolam (0.25 mg/kg), or acepromazine (0.05 mg/kg) to facilitate handling.
- Q. Does the route of administration impact analgesic efficacy of opioids in cats?
- A. Yes. The route of administration influences pharmacokinetics and analgesic effects of opioids. This has been clearly demonstrated with buprenorphine and hydromorphone. Subcutaneous administration of buprenorphine at the current dosage regimens (0.02 mg/kg) and concentrations available (0.3 mg/ml) may induce euphoric behavior and mydriasis but without effective analgesia. A clinical study showed that buprenorphine may produce better post-operative analgesia and lower requirement for rescue analgesia when administered by the intravenous or intramuscular route in cats when compared with the subcutaneous or the oral transmucosal routes [2]. However, this concept should not be applied with the new formulation of buprenorphine (Simbadol® 1.8 mg/ml) that is currently approved for subcutaneous administration in cats in the USA. An open-access review has published guidelines on the clinical use of buprenorphine in cats [3]. Similar findings have been reported with hydromorphone. The subcutaneous route of administration produced a higher prevalence of adverse effects such as vomiting, and shorter duration of analgesia when compared with the intramuscular or intravenous routes. Meperidine and morphine may cause histamine release and hypotension when given intravenously.
The oral transmucosal route has been used for opioid administration in cats. Buprenorphine is commonly given for post-operative pain by this route. However, recent studies showed a lower bioavailability and potentially more limited application than previously reported. Nevertheless, the authors still find it an adequate option for post-operative analgesia in cases of moderate pain, and when combined with an NSAID. Methadone may be an alternative option for transmucosal administration and post-operative analgesia with similar physicochemical properties to buprenorphine. However, further studies are required in order to provide clinical recommendations. Most importantly, dosages and intervals of administration should be individualized since opioid “non-responders” have been reported. A multimodal analgesic approach is recommended.
- Q. How about transdermal analgesia in cats?
- A. Transdermal patches of fentanyl have been reported to produce variable plasma concentrations and inconsistent analgesia in the clinical setting, however some patients respond well and this technique may be an option for “hands-off” analgesia in some cases. A new transdermal formulation of fentanyl (Recuvyra™) that can be administered topically in dogs is not approved nor recommended for use in cats. The transdermal patch of buprenorphine did not produce adequate analgesia in one study in cats and further clinical investigations are required before any recommendation [4].
- Q. There is a general fear of NSAID toxicity in cats. Is this a true concern or are NSAIDs actually an important tool in pain management in this species?
- A. Yes, clinicians should be aware of potential toxicity with NSAIDs in any species. However, if dosage regimens, intervals of administration, and contraindications are respected, NSAIDs may be administered safely to cats. These drugs play an essential role in pain management due to their anti-inflammatory, analgesic, and anti-pyretic effects
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- Q. Does the route of administration impact analgesic efficacy of opioids in cats?
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