Page 73 - BSAVA Guide to Pain Management in Small Animal Practice

BSAVA Guide to Pain Management in Small Animal Practice

VetBooks.ir intraoperatively as part of a balanced which can result in remodelling of the central
Low-dose intravenous infusions are useful
nervous system and ultimately alter the animal’s
perception of future painful and non-painful
anaesthesia technique to reduce anaesthetic
requirements and postoperatively to provide stimuli (central sensitization). Drugs that
titratable sedation and analgesia. antagonize NMDA receptors are analgesic and
exmedetomidine infusion 1 g kg hour has can also help prevent central sensitization,
been shown to be as e ective to a morphine secondary hyperalgesia and chronic pain.
infusion .1 mg kg hour for providing
analgesia following major surgery in dogs Ketamine
without adverse e ects Valtolina et al., 9 . Ketamine is a dissociative anaesthetic and
Dogs receiving dexmedetomidine in this study analgesic that antagonizes NMDA receptors in
had lower heart rates and higher diastolic blood the central nervous system. It also acts at other
pressure than dogs receiving morphine, but receptors including opioid receptors, and
these were still within acceptable ranges. The inhibits serotonin and dopamine reuptake.
cardiovascular e ects of an infusion are less etamine is now a Schedule Controlled rug
severe than those that occur following in the UK and must be kept in a locked
intravenous or intramuscular injection of a bolus cupboard with detailed records of its acquisition
dose. Suggested doses for clinical use are 1 and use.
g kg hour for medetomidine and . g
kg/hour for dexmedetomidine, although the Effects: Ketamine’s properties and uses vary
dose can be adjusted to achieve the desired with dose. At doses greater than mg kg
e ect. o achieve an appropriate plasma intravenously or intramuscularly it can be used
concentration of the drug quickly, an initial to induce dissociative anaesthesia, at lower
intravenous bolus is usually recommended. The doses it can be used as part of a sedation
aim should be a calm patient that can still protocol, and at very low doses . 1 mg kg it
function normally, i.e. eat, drink and ambulate, is an e ective somatic analgesic. Because of its
unless more profound sedation is required. adverse e ects dysphoria, excitement,
Volumes used are very small so the solution increased muscle tone, seizures in dogs),
must be diluted carefully, and an infusion pump ketamine should not be used alone except at
or syringe driver should be used. very low doses, and it is usually combined with
In locoregional anaesthesia, addition of an alpha agonist or ben odia epine for this
alpha agonists to the local anaesthetic reason. It can cause increased salivation and
solution signi cantly prolongs the duration of nausea. etamine has several bene cial e ects
e ect. or example, a techni ue for sciatic and compared with other induction agents: it
femoral nerve blocks using dexmedetomidine maintains cardiac output and blood pressure
.1 g kg for each block combined with due to its sympathomimetic e ects with little
bupivacaine has been described (Bartel et al., e ect on blood vessels. It also causes
16 . nly preservative free solutions should bronchodilation, preserves laryngeal re exes
be used for epidural or spinal anaesthesia. and patients usually breathe well. However,
ketamine increases cerebral blood ow and
NMDA receptor antagonists cerebral oxygen demand, which may result in
N-methyl- -aspartate (NMDA) receptors are increased intracranial pressure. Used alone, it
located in the brain and spinal cord. Activation increases intraocular pressure. In dogs,
occurs after repeated or widespread input from ketamine is metabolized in the liver
a erent neurones carrying nociceptive signals (norketamine is an active metabolite) and
(temporal and spatial summation). NMDA excreted in urine; in cats, it is mostly excreted
receptor activation results in prolonged unchanged in urine and therefore its
depolarization of second order dorsal horn e ects may be prolonged in cats with
neurones, a phenomenon known as ‘wind-up’, renal insu ciency.

68

Ch05 Pain Management.indd 68 19/12/2018 10:36