Chapter 38
Anesthetic Considerations for Orthopedic Surgery
Give that dog a bone
Odette O
Ross University School of Veterinary Medicine, St. Kitts
- Q. What type of patient is most likely to need an orthopedic procedure?
- A. Most patients present with either a congenital or traumatic orthopedic injury. A retrospective study from the UK found the frequency of cranial cruciate rupture in dogs to be 1.19%, with Rottweilers, West Highland White terriers, and Yorkshire terriers being over-represented. In addition, females, obesity, and dogs over 8 years of age were more likely to suffer cranial cruciate ligament rupture [1]. Another author looked at over 1 million dogs within a 40-year timeframe and found both hip dysplasia and cranial cruciate ligament rupture to be increasingly common over the study period. Also, they found that large and giant breed dogs were at greater risk for either or both of these orthopedic conditions [2]. Both studies also found a higher risk of these orthopedic problems in neutered animals.
- Q. What are the most common orthopedic procedures performed in dogs and cats?
- A. As previously stated, cranial cruciate ligament rupture and hip dysplasia are the most common orthopedic issues in dogs [3]. Fracture or luxation repair after a traumatic event is another leading cause of patient presentation to veterinary hospitals for orthopedic surgery. For cats, trauma is the most common reason for an orthopedic repair. However, radiographic evidence suggests that hip dysplasia, patellar luxations, and degenerative joint disease are becoming increasingly common in cats [4].
- Q. How painful is an orthopedic problem and corrective surgery?
- A. Severity of lameness has not been found to correlate with radiographic signs [5], so pre- and post-operative analgesic considerations should be based on clinical pain assessments and response to treatment. In human subjects, orthopedic pain is widely accepted as severe, with the incidence of moderate to severe pain in hospitalized patients being up to 76% [6].
- Q. What type of pre-anesthetic workup is recommended for a patient before orthopedic surgery?
- A. Depending on case presentation, a patient-specific pre-anesthetic workup should be planned (see Chapter 1). For young, healthy patients a minimum database of packed cell volume (PCV), total plasma solids, blood glucose, and blood urea nitrogen (BUN) will help determine overall patient status. Ideally, patients with a history of underlying disease or trauma should be stabilized as much as possible prior to an orthopedic procedure. A study of 100 dogs showed thoracic abnormalities in 57% of dogs presenting with traumatic orthopedic injury. Interestingly, 79% of these dogs had no evidence of thoracic lesions based upon physical examination findings [7]. A more detailed workup including complete blood count (CBC), biochemical profile, serum electrolytes, urinalysis, thoracic radiographs, electrocardiogram, and/or blood gas analysis should be considered along with appropriate supportive care for any patients presenting with a history of significant trauma.
- Q. What are some general anesthetic considerations in patients presenting for orthopedic surgery?
- A. General concerns may arise from specific history, physical examination findings, hydration status, and concurrent medications. In addition, the location of surgery will influence intravenous catheter placement location and positioning of the patient. Patient preparation is usually fairly standard (see Chapter 3). Patient comfort in these cases is of paramount importance. Multimodal analgesia is important for both treating acute and preventing the development of additional chronic pain.
- Q. Should pre-anesthetic drugs be administered?
- A. Yes! Pre-anesthetic medications are often given by the intramuscular route when the patient does not have an IV catheter in place. Use of premedications provides pre-emptive analgesia and muscle relaxation, facilitates minimal restraint and IV catheter placement, decreases patient anxiety, and decreases the amount of induction agent and inhalant required (Chapters 5, 6, and 8). Based on the potentially intense level of pain in patients presenting for an orthopedic procedure and the surgery itself, a pure μ agonist opioid such as morphine (0.3–1 mg/kg), hydromorphone (0.05–0.2 mg/kg), oxymorphone (0.05–0.2 mg/kg), methadone (0.5–1 mg/kg), or fentanyl (2–5 mcg/kg bolus followed by a constant rate infusion at 5–20 mcg/kg/h) and/or a loco-regional block is recommended. Sedative type and dosing will depend on the patient’s signalment, history, and physical exam findings with most healthy, well hydrated, yet anxious patients benefiting from either acepromazine (0.01–0.05 mg/kg intramuscular) or dexmedetomidine (2–10 mcg/kg intramuscular). Benzodiazepines provide the least predictable sedation in many patients, and may best be reserved for calm patients or those cases where other sedatives are contraindicated.
- Q. Which induction agents are the most suitable?
- A. Depending on the patient’s signalment, history, and presenting complaint a number of induction agents may be considered (see Chapter 10). Recall that the level of sedation provided by pre-anesthetic medication is inversely proportional to the amount of induction agent required, that is a patient with more profound sedation from premedication will require less induction agent. Patients who are healthy other than their orthopedic presenting complaints can most likely be induced with any of the currently available agents. Those who have suffered a traumatic injury presenting for orthopedic surgery after a period of stabilization/hospitalization may benefit from inclusion of an NMDA-antagonist such as ketamine in the induction protocol. The exception may be traumatic head injury, where the use of ketamine is still controversial. NMDA-antagonist use may help prevent central sensitization, a phenomenon resulting in chronic pain [8]. Although the pre-emptive effects of ketamine in chronic pain have recently come into question, it is still used in the treatment of this type of pain and its role in multimodal analgesia can also help to lower opioid dosing and related side effects as well as help prevent opioid-related hyperalgesia [9]. Ketamine in combination with a muscle relaxant such as a benzodiazepine or propofol can be used for induction and then serves as a loading dose if a constant rate infusion of ketamine is planned for surgical analgesia (see Chapter 22
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- Q. How painful is an orthopedic problem and corrective surgery?
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