Effects of two fentanyl constant rate infusions on thermal thresholds and plasma fentanyl concentrations in awake cats

Intraoperative Isoflurane End-Tidal Concentration during Infusion of Fentanyl, Tramadol, or Fentanyl–Tramadol Combination in Cats

“…The end-tidal fraction of isoflurane during traction of both ovarian pedicles in cats receiving fentanyl and tramadol together was not different from that recorded during skin incision and suturing, indicating a beneficial effect of the drug combination. Our results are consistent with previous studies [ 5 , 19 , 25 , 42 ] showing that opioids reduce inhalational anesthetic requirements in cats with a plasma concentration and MAC-dependent effect [ 1 , 11 , 12 , 14 , 16 , 43 ]. It has also been reported in cats that the use of a fentanyl patch (25 or 50 µg/h) can reduce the requirement for isoflurane [ 7 ], while the administration of oral tramadol (8.6 to 11.6 mg/kg) can reduce the MAC of sevoflurane [ 44 ].…”

“…This result is consistent with other experimental studies in cats and other species that have shown statistically lower blood pressure in subjects treated with tramadol compared to those treated with other drugs [ 8 , 10 , 30 ]. Unfortunately, it was not possible to perform an invasive blood pressure measurement, which is considered the gold standard [ 19 , 46 , 47 ]. Before and during surgery, the cats were placed on a circulating blanket of warm water.…”

“…Although it has been reported that tramadol is eliminated more slowly in cats than in dogs [ 22 ], further studies are needed to investigate the trend of plasma tramadol concentrations in cats. Some authors agree on the preference of slow infusion of opioids alone or in combination with the use of boluses [ 19 , 58 , 59 ]. The combination of slowly infused fentanyl and tramadol can also be used to treat pain in conscious cats, providing continuous analgesia and avoiding the peaks, depressions, and breakthrough pain associated with intermittent boluses [ 19 , 24 ].…”

“…However, the distribution of opioid receptors in the feline central nervous system remains unclear [ 4 ]. It has been reported that the infusion rate of 3 to 5 μg/kg/h of fentanyl provides a rapid onset and good analgesic effect during the infusion period, which is rapidly lost when the infusion is stopped [ 19 , 20 ]. Tramadol and its active metabolite (M1 O-desmethyltramadol), bind to µ-opioid receptors in the central nervous system, activating the monoaminergic descending inhibitory pathway to the spinal cord and reducing noradrenalin and serotonin reuptake into the neuronal terminal responsible for pain relief [ 6 , 10 , 20 , 21 ].…”

Phenylpiperidine opioid effects on isoflurane minimum alveolar concentration in cats

“…Fentanyl, sufentanil, alfentanil, and remifentanil are phenylpiperidine opioids and agonists of the μ‐opioid receptor (MOR) through which they exert analgesic and anesthetic effects in humans and many animal species. In cats, MOR‐agonist opioids are effective analgesics (Carrozzo, Alcorn, & Ambros, 2018;Robertson, Taylor, Sear, & Keuhnel, 2005), but most exhibit little or no effect on the immobilizing potency of volatile anesthetics. Fentanyl doses producing analgesia (Yackey, Ilkiw, Pascoe, & Tripp, 2004) and remifentanil concentrations more than 20 times greater than needed for analgesia (Brosnan, Pypendop, Siao, & Stanley, 2009) do not decrease isoflurane minimum alveolar concentration (MAC) in cats.…”