Katie Bennett, DVM, DACVAA
The opioid crisis of 2017 is not far from our minds as our world again faces challenges in the midst of the COVID-19 pandemic. This makes opioid-free anesthetic techniques even more relevant, as opioids may become more difficult to keep in stock in many veterinary hospitals as they become widely used in human hospitals for ventilator cases.
Opioids are certainly not something we can do without for 100% of our anesthetic protocols, however we are able to select the appropriate patient population to provide adequate anesthesia and analgesia without the side effects and risks associated with opioid administration. Patients that benefit most from an opioid-free anesthetic technique include brachycephalic dogs and cats, patients with severe adverse effects to opioid administration, and patients belonging to clients that are unable to take home oral opioid medications.
Decreasing the use of opioids both in and out of the hospital will decrease the likelihood and incidence of adverse side effects, but will also allow for a greater margin of safety for the prescriber and the prescribing hospital against those individuals that are seeking easy access to narcotics. Consider opioid-free anesthesia to be a valid option for those patients that you wish to avoid or minimize your use of opioids.
Opioid efficacy in veterinary medicine is moderate at best – animals tend to require higher doses when compared to humans, which only propagates the likelihood of adverse side effects. Intravenous opioid administration will decrease MAC (minimum alveolar concentration) by up to 50%, while epidurally-administered opioids will decrease MAC by up to 40%. The bioavailability of intravenous drugs is 100%, but other routes tend to have much lower bioavailability (oral, oral-transmucosal, topical, rectal), usually due to how the drug is metabolized. Unfortunately, both intravenous and other routes still carry the high likelihood for side effects such as those previously listed.
The first, and likely most important, aspect of opioid-free anesthesia is the utilization of locoregional anesthetic techniques. A good local block can provide such profound MAC reduction where post-operative care requires minimal to no injectable drugs. Consider adding secondary agents to local blocks (such as ketamine, dexmedetomidine, buprenorphine, etc.) to enhance their efficacy and potentially extend the length of blockade with minimal systemic uptake of the adjunctive drug.
Additionally, drugs such as dexmedetomidine, ketamine, or lidocaine (depending on the species) can be given to patients via intermittent boluses or even as a CRI to provide a reduction in the amount of inhalant anesthetic required to keep a patient asleep while also providing incredible analgesia and smoothing recovery. Furthermore, do not underestimate the benefit of pre-procedure medications, such as gabapentin, maropitant, and NSAIDs – these medications all play a role in the pain pathway, and may serve to provide perioperative analgesia for the appropriate patient.
If you are to give per os medications pre-operatively, giving them at least 90 minutes to two hours prior to the procedure is suggested for optimal absorption. It is acceptable to use a small “meatball” of canned food or other treat to facilitate administration, if needed. Sometimes these medications can be prescribed prior to the patient’s appointment for surgery or anesthesia to be given the morning of the appointment by the owners before arrival to the hospital.
- Premedication: a-2 agonist (dexmedetomidine) 0.5-2 mcg/kg IV +/- acepromazine 0.01-0.02 mg/kg IV or IM
- Induction: alfaxalone or propofol IV to effect with the addition of a co-induction agent, such as midazolam (0.2-0.4 mg/kg) or ketamine (1-2 mg/kg)
- Maintenance: inhalant in oxygen
- Locoregional Anesthesia: dental blocks, ophthalmic blocks, auricular blocks, intercostal blocks, line blocks, ring blocks, RUMM blocks, LS epidural (0.2 mL/kg total volume = pelvic limbs and caudal; 0.3 mL/kg total volume = abdominal procedures and caudal), coccygeal block (tail, perineal area)
- Intra-op pain control: consider 0.5-1 mcg/kg dexmedetomidine boluses (warn your nurses about heart rate changes) or ketamine 0.5-1 mg/kg (may alter respirations and require some ventilatory assistance depending on dose and speed of administration)
|LS Epidural – Pelvis/HL||Bupivacaine 5%||0.5 mg/kg; total volume 0.2 mL/kg (dilute)|
|LS Epidural – Abdominal||Bupivacaine 5%||1 mg/kg; total volume 0.3 mL/kg (dilute)|
|LS Epidural – Thoracic||Bupivacaine 5%||1 mg/kg; total volume 0.4 mL/kg (dilute)|
|Coccygeal Epidural||Bupivacaine 5%||0.5 mg/kg; do not exceed 0.2 mL/kg total volume|
|Epidural Additive||Dexmedetomidine||1 mcg/kg or 1 mcg/mL of local anesthetic|
|Epidural Additive||Morphine||0.1 mg/kg|
|Epidural Additive||Buprenorphine||0.01 mg/kg|
- Post-op Pain Control: NSAID, gabapentin
|RUMM Block||Bupivacaine 5%||1-1.5 mg/kg (K9); 1 mg/kg (Fel)|
|Ring Block||Bupivacaine 5%||1-1.5 mg/kg (K9); 1 mg/kg (Fel)|
|Intercostal Block||Bupivacaine 5%||1-1.5 mg/kg (K9); 1 mg/kg (Fel)|
|Line Block||Bupivacaine 5%||1-1.5 mg/kg (K9); 1 mg/kg (Fel)|
|LRA Additive||Dexmedetomidine||1 mcg/kg or 1 mcg/mL of local anesthetic|
|LRA Additive||Morphine||0.1 mg/kg|
|LRA Additive||Buprenorphine||0.01 mg/kg|
|LRA Additive||Ketamine||0.5-2 mg/kg|
|Dexmedetomidine||0.5-3 mcg/kg bolus
|Premed; Sedation; Analgesia
MAC reduction CRI
|Acepromazine*||0.005-0.02 mg/kg||Premed; Sedation (*no analgesia)|
|Midazolam/Diazepam*||0.1-0.5 mg/kg||Co-induction; MAC reduction|
|Lidocaine||1-2 mg/kg (K9 only)
|Premed, Co-induction; Analgesia
MAC reduction CRI
|Propofol*||2-4 mg/kg||Induction (*no analgesia)|
|Alfaxalone*||1-3 mg/kg||Induction; Sedation (lower doses) (*no analgesia)|
|Co-induction; heavy sedative
MAC reduction CRI
Katie Bennett is an Anesthesiologist and Pain Management specialist at Veterinary Specialty Center.