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246 Section IV: Postoperative Care and Rehabilitation

calculating fluid rates. Daily maintenance fluid requirements are surgery should be opioids. The selection of opioid will depend on
calculated as (BW × 30) + 70 (mL per day). For animals weighing the type of surgery performed, the availability of opioids, and level
kg
less than 2 kg or more than 50 kg an alternative calculation should of postoperative care that is available in your practice. Postoperative
be used: (BW kg 0.75 ) × 70. analgesia is typically provided by a continuous‐rate infusion of opi-
Spinal patients often fail to maintain adequate fluid intake prior oids (Table 28.1). For patients undergoing craniotomy, bolus dosing
to surgery due to stress, pain, or lack of mobility and may be mildly of opioids such as morphine and hydromorphone should be used
to moderately dehydrated on presentation. For acute spinal cord with caution, as vomiting can be associated with its administration,
injuries, fluid therapy is indicated as hydration of the spinal cord which may increase intracranial pressure [3,4].
and prevention of hypotension is thought to be an important com- Alternatively, intermittent use of longer‐acting opioids can be
ponent in the health and recovery of neurons [1]. Intraoperative used effectively (Table 28.2). Methadone is also an appropriate
blood losses can be significant, especially in small‐breed dogs, and choice for analgesia, when available. Methadone is a μ‐receptor ago-
need to be considered when assessing a patient’s fluid requirements. nist that has 10 times the potency of morphine but is also an N‐
The venous sinuses run along the ventral aspect of the spinal col- methyl‐d‐aspartate (NMDA) receptor antagonist that reduces
umn and can be disrupted during hemilaminectomy, mini‐hemi- reuptake of norepinephrine and serotonin, which may make it ideal
laminectomy, corpectomy, or ventral slot procedures. During for neuropathic pain [5,6].
craniotomy, there can be blood loss from compromise to the dorsal Adjunctive analgesics that can also be used based on response to
sagittal and transverse sinuses. If greater than 10–15% of blood vol- opioids include continuous‐rate infusions of ketamine (an NMDA
ume is lost intraoperatively or packed cell volume is below 22%, use receptor antagonist), lidocaine (local anesthetic), or dexmedetomi-
of replacement blood products is indicated [2]. dine (an α agonist that provides both analgesic and sedative effects)
2
Specific blood products can also be indicated for thrombocyto- (Table 28.1).
penia (platelet‐rich concentrate), prolonged clotting times as with Several recent studies have evaluated the use of topical analgesia
von Willebrand disease (cryoprecipitate, fresh frozen plasma, and following hemilaminectomy with either morphine alone [7] or
DDAVP or desmopressin acetate), and hypoalbuminemia (fresh morphine and dexmedetomidine administered using gel foam as a
frozen plasma). Alternatives to increase oncotic pressure include carrier [8]. Both studies concluded that the topical use of analge-
colloids such as Pentaspan® and Voluven®. Blood typing should be sics reduced the need for systemic administration. However, tem-
performed prior to transfusion and cross‐matching should occur if porary loss of nociception has been reported following topical
the patient has previously received blood products to prevent acute intrathecal morphine administration using gel foam as a carrier
transfusion reactions. [9]. Further studies comparing the use of directly applied analge-
sics versus those administered in a carrier and their long‐term
safety are required.
Analgesia
Postoperative pain associated with surgery is typically controlled NSAIDs versus Corticosteroids
with multimodal analgesia protocols. A large number of neurologi- The use of corticosteroids in spinal surgery and in most cases of
cal patients will present having already received either nonsteroidal intracranial surgery has shown no benefit and may possibly be
antiinflammatory drugs (NSAIDs) or corticosteroids, which may detrimental. A large proportion of neurosurgical patients present-
affect the options for postoperative analgesia (see discussion below). ing to referral centers for surgery have already received NSAIDs or
The mainstay of postoperative pain management following neuro- corticosteroids. The decision is then whether to continue with the
current protocol or stop it and use alternate drugs.

Table 28.1 Continuous‐rate infusion doses for analgesics commonly used in dogs Corticosteroids
and cats. There is little evidence to support the use of corticosteroids in
intervertebral disc (IVD) surgery. The previously recommended
Drug Dose
protocol of methylprednisolone sodium succinate 30 mg/kg
Fentanyl 2–6 μg/kg per hour within the first 6 hours followed by 15 mg/kg every 6 hours for
Morphine 0.1–0.2 mg/kg per hour 24–48 hours may provide some benefit in neurological recovery,
Butorphanol 0.1–0.4 mg/kg per hour although recent evidence suggests that there is no difference in
Ketamine 0.1–2.0 mg/kg per hour outcome [10]. In addition, using this protocol greater than 8 hours
Lidocaine* 20–80 μg/kg per min after the initial spinal injury has been shown to have a detrimental
Dexmedetomidine 0.5–1 μg/kg per hour
effect in humans [11].
* Care when using with cats as increased risk of toxicity. The use of corticosteroids may also predispose nonambulatory
Source: Doses modified from Plumb’s Veterinary Drug Handbook [20]. dogs undergoing neurosurgery to urinary tract infections (UTIs),

Table 28.2 Opioid doses that can be administered intermittently in dogs and cats.
Drug Dose Frequency Route
Hydromorphone 0.025–0.05 mg/kg 4–6 hours IV, IM, SC
Morphine 0.2–1.0 mg/kg 3–4 hours IV, IM, SC
Methadone 0.1–0.5 mg/kg 4–6 hours IV, IM, SC
Buprenorphine 0.01–0.03 mg/kg 6–8 hours IV, IM, buccal

Source: Doses modified from Plumb’s Veterinary Drug Handbook [20].