Page 24 - BSAVA Guide to Pain Management in Small Animal Practice

3 | Acute and perioperative pain

VetBooks.ir the fentanyl is more commonly to provide the anticipated pain level after surgery, with
Postoperative opioid selection depends on
sedation while limiting adverse events on the
cardiovascular system rather than to provide
severe pain and buprenorphine reserved for use
analgesia. If analgesia is re uired it must be methadone the drug of choice for moderate to
remembered that the duration of action of in patients experiencing mild pain or moderate
fentanyl is short after a single dose 1 pain if a multimodal approach to analgesia has
minutes and further top ups will be necessary been adopted. If analgesia with methadone is
to provide sustained analgesia. insu cient, a fentanyl CRI can be considered
he use of opioids need not be con ned to 1 g kg h , with the rate ad usted according
use in premedication; further opioids may be to pain score.
re uired to treat poorly controlled
intraoperative nociception, recogni ed as Local anaesthetics
di culty in controlling depth of anaesthesia Local anaesthetics can be utili ed as part of a
even with relatively high concentrations of local or locoregional techni ue, or lidocaine can
inhalant agent. ethadone, administered as be used systemically.
top ups .1 mg kg i.v. , fentanyl administered Local anaesthetic techni ues form a
as a bolus dose 1 g kg or continuous valuable ad unct to perioperative analgesic
rate infusion CRI 1 g kg h will provide regimens and their use is encouraged whenever
additional analgesia during invasive surgeries possible. Using a local anaesthetic techni ue
and will allow the concentration of inhalant can decrease the re uirement for systemic
agent re uired to maintain anaesthesia to be analgesia for the duration of the block, which
reduced Sim es et al., 16 . osing accuracy can be particularly advantageous in reducing
is important and a CRI should be given using the dose of systemic opioid re uired for
controlled infusion apparatus. Care must be ade uate analgesia. An e ective block may
taken to support the respiratory system obviate the need for systemic opioids
following intraoperative methadone or fentanyl completely; for example administration of
administration, and it is recommended that epidural morphine and bupivacaine for pelvic
respiratory function be monitored with surgery may prevent the need for systemic
capnography and ventilation supported with opioids for the rst 4 hours after surgery. Local
intermittent positive pressure ventilation if anaesthetic blocks will also decrease the dose
necessary. he other ma or side e ect of re uirement for the inhalant agent during
methadone or fentanyl to be aware of following anaesthesia, i.e. exert a AC sparing e ect,
intraoperative administration is bradycardia, which can be advantageous for the
which can be managed by the administration of cardiovascular system. A large number of
an anticholinergic if the low heart rate is having di erent local anaesthetic blocks are described
a negative impact on blood pressure. dependent on the site of surgery. See Appendix
Buprenorphine has a longer onset of action for more details about the di erent local
than methadone and is not ideally suited to anaesthetic techni ues and appropriate drug
intraoperative administration for providing choices and drug doses for blocks relevant for
additional analgesia. hether full mu agonists di erent types of surgery.
such as methadone should be administered Lidocaine is a reversible blocker of sodium
after partial mu receptor agonists such as channels and has been used for many years to
buprenorphine remains contentious; however, provide analgesia as part of local anaesthesia
recent evidence in humans ifa et al., 9 techni ues. owever, more recently it has been
and dogs unt et al., 1 has challenged the administered systemically to provide analgesia,
concept of a negative interaction between full although the mechanisms by which analgesia is
and partial mu agonist drugs suggesting that provided are not fully understood Lui and Ng,
methadone administered after buprenorphine 11 . Similarly to the other ad unctive agents
is e cacious. there is a limited evidence base to support

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