Acute Pain Management

Originally created by Alex Terreros, DMV, IPSAV, ACVS

Edited and presented by Mathew MacCormick, DVM & James Gant, DVM

PATHOPHYSIOLOGY

What is pain and why does it even exist?

• Nervous system detects and interprets various thermal and mechanical stimuli
• Nociception: creation and transfer of signals after activation of nerve endings by a stimuli
• The ability to detect noxious stimuli is essential to an �organism’s survival.

​

The importance of treating pain

• The 5th vital sign
• Detrimental to overall healing process and well-being
• Length of hospitalisation in humans and animals
• Hypothesis that better management of the acute pain will help to prevent the development of chronic pain
• Oh, also, it’s inhumane to not treat pain… Be nice to your patients!!

Clinical impact of pain

• Trauma leads to hypothalamic stimulation which triggers a cascade of reactions leading to stress response
• Activation of sympathoadrenal and corticomedullary systems = catecholamine release
• Catecholamines induce increased cardiac output through increased stroke volume and heart rate.
• Increased Myocardial work (metabolic rate and O2 consumption)
• Can predispose to Arrhythmias or prevent resolution when present
• Splanchnic vasoconstriction= ileus, nausea or vomiting
• Pain induced reluctance to move, walk or breathe
• Atelectasis, hypoventilation, suppression of cough= predisposing to pneumonia

​

​

Clinical Impact of Pain: by systems

Classifying pain

• Acute vs. Chronic
• Acute pain occurs in response to physical damage and resolves after days/weeks
• Chronic pain: definition is arbitrary, clinical pain persisting more than 3 months could be considered chronic

​

• Chronic pain is a separate entity, should be considered as a disease state

​

• Pain types:
• Nociceptive (or physiologic)
• Inflammatory
• Neurogenic
• Cancer (typically combines inflammatory + neuropathic pain)

Pathophysiology

• Unlike other senses, receptors do not return to pre-stimulus state after activation

​

• sensitivity of nerve endings after injury and synaptic connections to CNS may be modified or reorganized.

​

• Plasticity

​

Steps leading to perception

• Transduction
• Peripheral nerve fibers, nociceptors, termed A Delta afferents and �C-Fiber afferents, perceive noxious thermal, mechanical or �chemical stimuli

​

• Transmission (action potential)
• Impulse conducted through fibers Adelta rapidly and Cfibers slowly; �

Steps leading to perception

• Modulation
• Fibers enter spinal cord through dorsal nerve root mostly, synapse �to interneurons which can regulate and modify information before� relay to projection neurons.

​

​

​

• Projection
• Projection occurs along noxious-specific neurons in pathways �(‘’tracts’’) to thalamus and reticular formation

​

​

​

• Perception
• Sensory-discriminative (where, how intense) occurs in Thalamus
• Brainstem: poorly localized pain
• Descending pathways are then able to modulate pain responses

​

Peripheral sensitization

Plasticity of nociception and pain: Inflammatory soup

• Neurotransmitters:
• Glutamate
• Peptides
• Substance P
• Calcitonin
• Gene-related Peptide
• Bradykinin
• Serotonin (mast-cells)
• Histamine (mast-cells)
• Eicosanoids
• Lipids
• Prostaglandins
• Thromboxanes
• Leukotrienes
• Endocanabinoids

• Neurotransmitters:
• Glutamate
• Peptides
• Substance P
• Calcitonin
• Gene-related Peptide
• Bradykinin
• Serotonin (mast-cells)
• Histamine (mast-cells)
• Eicosanoids
• Lipids
• Prostaglandins
• Thromboxanes
• Leukotrienes
• Endocanabinoids

​

​

Effect= Directly activate or sensitize

nociceptors to different stimuli

​

​

Plasticity of nociception and pain:

• Upon injury, sympathetic nerve fibers release substances (catecholamines, neuropeptide Y) that potentiate inflammatory mediators
• Other substances are produced by p.nerves (substance p, somatostatin, cholecystokinin, etc.)
• Many of these chemicals act on G-coupled proteins, this then activates intracellular signaling pathways that actually modify nociceptor thresholds and kinetics (by way of phosphorylation of receptors and ion-channels).
• Prostaglandins = prototypic nociceptor sensitizers
• PGE2 can causes changes in TRPV1 by phosphorylating it, thus drastically reducing it`s thermal threshold (activation of cAMP-dependent protein kinase A (PKA) and CA2+-dependent protein kinase C (PKC).)

Central Nervous System Changes/Sensitization

Central nervous system changes (spinal cord)

• Inputs from periphery can, via activation of receptors (principally NMDA), produce changes in the way nociceptive signals are processed in the Spinal Cord.
• Frequent or severe peripheral nociceptor input can lead to central release of neurotransmitters that modulate response (such as Substance P)
• Substance P:
• Removes the magnesium block of NMDA receptor
• Without magnesium block, Glutamate is allowed to activate NMDA receptors
• NMDA receptor
• With repeated stimulation, it can produce prolonged depolarisation of dorsal horn neuron
• Termed WINDUP, this leads to central sensitization.

​

Central Sensitization

• Wind-up can be self-propagating and hyperexcitable states can result in changes in genetic expression
• Cells function changes over time and lead to the development of ``pain memory``
• Clinical effect:
• Hyperalgesia (exaggerated pain response to painful stimulus)
• Allodynia (pain with non painful stimulus)
• Spontaneous pain
• Neuroplasticity (phantom limb pain)

​

Treatment strategies

Pre-emptive Analgesia: �

• an ounce of prevention is worth a pound of cure�
• Hypothesis: preventing nociceptive input to the central nervous system may prevent establishment of central sensitisation, thus improving post-op comfort

​

​

• Few studies have evaluated this concept in Veterinary medicine

​

​

• Humans studies have shown:
• Less wind-up
• Reduced overall need for analgesia
• Reduced need for rescue analgesia

​

Treatment Strategies: Veterinary Medicine

​

• In Veterinary Medicine, pre-emptive analgesia is a pretty well accepted concept, especially for NSAIDs and Opioids.

​

​

• Relevant veterinary studies have:
• Shown that pre-operative administration of Carprofen (vs. post-op and placebo) was more effective at preventing hyperalgesia
• Shown that Opioid use (meperidine) prior to surgery prevented development of allodynia post-operatively
• Shown that pre-op or post-op Ketamine administration decreased and delayed onset of wound hypersensitivity

​

​

Treatment strategies

Multimodal (balanced) analgesia

​

• Great benefit can be derived from combining drugs that have different mechanisms of action
• Why? Decreased side effects while attaining increased efficacy

Assessment of pain

​

​

• Our patients…

​

• Observation is key

​

• Methods available:
• Subjective evaluations: Scales using descriptors, numeric scales, etc.
• Objective evaluations: Heart rate, respiratory rate, blood pressure, etc.*

​

• Expected pain severity according to medical condition

​

• The need for post-operative pain assessment using a comprehensive approach lead to the development of multiple validated pain scales

​

​

Surgical Technique and Influence on pain

• Human medical literature has clearly shown surgical technique influences pain
• Technique (MIS vs. Open)
• Skill of surgeon

​

• Canine literature
• Lap-Spay vs. Open-OHE
• Overall message is that laparoscopic techniques were associated with lower post-op pain scores
• Less requirement for additional pain medication
• Less pronounced cortisol response
• Increased activity in post-operative period for Lap-spay groups

​

PAIN IN THE ER

Concerns of treating pain in emergency patients ?

​

• Analgesics ``mask`` physiologic indicators (HR, RR, etc)

​

• Potential Toxicity or Adverse effects of drugs

​

• Alteration of consciousness/neurological impairment

Withholding analgesia?

Evidence exists in human literature, and has also been an observation in veterinary medicine, that analgesics do not mask the signs of patient deterioration and should not be withheld for that reason

​

​

• Even when large doses of opioids are used as a CRI to treat pain, compensatory response of the body to hypotension, hypoxia, hypovolemia or hypercarbia is still high
• If you treat the pain; then the changes in HR will be assumed secondary to deterioration!

​

Study performed in hypovolemic dogs (30%) confirmed that hydromorphone does not result in hemodynamic deterioration. (Machado CEG, DVSc thesis 2002)

​

​

​

​

What about side effects?

• These effects, primarily Opioids, seem to be overemphasized

​

​

• Ventilation: opioid administration after a traumatic incident may improve rather than impair ventilation

​

​

What are your options?

AAHA guidelines

SPECIFIC CONDITIONS/ SITUATIONS

Major Chest Trauma

• Oxygen !

​

• Analgesia/Sedation is required to:
• Reduce animal movement and secondary pain
• Allow manipulation of chest

​

• Methadone, Fentanyl vs. Hydromorphone according to severity of trauma
• Slow IV route preferred, if RR increases, administration can be stopped before panting

​

• Local analgesia may supplement your protocol (Intercostal or Splash block)

​

FLAIL CHEST

• Definition: Freely movable segment of the �Thoracic Wall secondary to fractures of consecutive� ribs

​

• Consequence: respiratory compromise, pain, trauma to lungs, pneumothorax, decreased ventilation

​

• Stabilization:
• Standard triage procedure: Provide O2, acquire IV access, determine need for resuscitation
• Monitoring: pulse oximetry, blood gases, End tidal CO2 if intubated
• Diagnostics: T-Fast, X-rays, Diagnostic Thoracentesis
• Therapeutic thoracentesis: if 2 or more required, thoracostomy tubes should be placed
• Chest wrap over flail segment and around chest

FLAIL CHEST

• Chest wrap Benefits:
• decreased motion of flail segment = reduced pain
• Decreased motion = less risk for lung and intercostal vessel laceration

​

• Open wound care
• Clip and cleaned
• Cover wound with sterile dressings
• Broad spectrum antibiotics (eg. amoxiclav, unasyn.)

​

Other Trauma cases

• Lacerations and fractures obviously require analgesia

​

• Drug and dose determined according to severity and instability of the �injury

​

• Immobilisation is required, no drugs will stop the pain produced by �fractured bones grinding together

​

• NSAID therapy is appropriate IF:
• No concerns with hypovolemia
• No ongoing hemorrhage
• Bloodwork shows no concerns for kidney, liver or coagulation issues

​

• Contusions/muscular damage is painful as well! If no fracture is identified, remember muscles can hurt!
• Icing trauma area can provide additional analgesia

Cardiovascular compromise

• This situation you must avoid unnecessary sedation/anesthesia
• Doses selected should be low and titrated to effect
• Any opioid is safe, if needed midazolam/diazepam is safe as well
• If bradycardia and cardiac output decrease occurs
• For sedation: Butorphanol works very well, low risk, even with higher dosage
• For Anesthesia premedication (if necessary)
• Fentanyl (remifentanil or similar) bolus + CRI
• Hydromorphone + Midazolam acceptable alternative
• Induction: Propofol does induce hypotension, Alfaxalone may be superior choice?
• In dogs ASA III-IV, a dose of 1-2 mg/kg IV over 60 seconds was shown to be acceptable induction agent with smooth recovery when compared to fentanyl/diazepam induction + Propofol

GI pain - GDV/FB/Etc

• Full mu agonist; titrated to effect is recommended for this condition as a starting point

​

• Postoperative management with Fentanyl CRI

​

• We already discussed the beneficials roles of Lidocaine in GDV
• Antiarrhythmic drug
• Analgesic drug
• Free radical Scavenger

Pancreatitis and Peritonitis

• Condition can cause moderate to excruciating pain.
• Moderate pain:
• Butorphanol 0.4 mg/kg q2-3 hours or CRI may be sufficient for dogs
• Buprenorphine 0.015mg/kg q8 hours may be sufficient for cats�
• Excruciating pain:
• Opioids: Hydromorphone, Fentanyl, etc
• Lidocaine/Ketamine CRI may be considered
• Epidural Analgesia/Anesthesia

SPECIFIC DRUGS

Opioids - General

Mechanism of action - agonists or antagonists of the opioid receptors

• Mu (most important for pain), Kappa, Delta

​

Dose

• Varies based on potency of the opioid you are planning on using

​

Uses - almost any procedure has a use for an opioid

• Analgesia
• Sedation
• Euphoria
• Antitussive
• Antidiarrheal

​

Good combo drugs - everything!

​

Reversal - Naloxone

Opioids - General

Side effects

• Dysphoria - can happen with large doses of opioids, relatively common following anesthesia
• Can be treated with either sedatives - I commonly reach for acepromazine or very low dose dexmedetomidine
• Can be treated with reversal - either naloxone, or if a full mu you are trying to reverse, can use butorphanol (ideal if you don’t want to take away all of your pain management)
• Cardiorespiratory and other effects
• Increase vagal tone – reduced heart rate that is most pronounced with mu agonists that is exacerbated by inhalant anesthetic
• Can sometimes see an AV block, particularly with boluses of fentanyl
• Can prevent with anticholinergic - theoretically, but I have not experienced that in practice
• Does not cause clinically significant respiratory depression at the doses they should be used
• Only worry in sick animals when combined with other drugs
• This is what happens with an opioid overdose
• Gastrointestinal
• Increases segmentation, but decreases propulsion 🡪 leads to constipation
• Increases bile duct sphincter constriction
• Stimulation of the chemoreceptor trigger zone will induce vomiting
• Hyperthermia in cats

Butorphanol

Mechanism of action - functional mu antagonist, kappa agonist

​

Dose - 0.1-0.5 mg/kg (I generally use 0.1-0.2)

​

Uses - sedation, antitussive, visceral pain via CRI?

• Great for non-painful procedures/diagnostics
• Great for sedation for respiratory cases

Buprenorphine

Mechanism of action - partial mu agonist, kappa antagonist

​

Dose - dogs 0.01-0.04; cats 0.01-0.03 (may want higher like 0.05 for OTM)

• Cats SQ Simbadol - 0.12-0.24 mg/kg SQ for the 24 hr dose

​

Uses - pain management for medium pain procedures/trauma

• Do not administer if planning on doing surgery on a patient
• Due to the partial mu agonism and a very high binding affinity it will block other full mu agonists

Hydromorphone

Mechanism of action - full mu agonist

​

Dose - 0.05-0.2 (I generally don’t go above 0.1 - I see more dysphoria, panting, etc., sedation if using it in an awake dog for pain)

​

Uses - Pain management for invasive procedures/trauma, sedation for painful procedures

​

Side effects - more vomiting and panting than other opioids

Methadone

Mechanism of action - full mu agonist, NMDA antagonist

​

Dose - 0.2-0.5 (I like 0.2, find it is effective and well tolerated)

​

Uses - Pain management for invasive procedures/trauma, sedation for painful procedures

​

Side effects - I find less side effects than hydromorphone, but same things can happen

Fentanyl

Mechanism of action - very potent full mu agonist

​

Dose - give a bolus, and then if need it any more than about 10 minutes, need to use as a CRI

• 2-10 mcg/kg/hr (can theoretically go up to 50, I have not…)
• I often run 3-4 mcg/kg/hr on an awake patient
• I usually run 4-10 mcg/kg/hr on an anesthetized patient
• ​

Uses - pain and sedation

Lidocaine

• Sodium Channel blocker
• CRI use
• Alleviates neuropathic pain and hyperalgesia
• Decreases opioid requirements post-operatively
• Species
• Cats: Few studies, contradicting recommendations in literature.
• Most quoted study concerning lidocaine in cat: bolus administration induced hypotension,
• CRI are not studied but have been used at ½ rate of dogs without major side effects. Must be careful with toxic dose (3 mg/kg over 24h)

​

Analgesia - Mechanism of Action

The systemic analgesic effects are not well understood and likely via several mechanisms

• reducing ectopic activity of damaged afferent neurons
• action at different molecular sites
• Na⁺ channels
• Ca₂⁺ channels
• K⁺ channels
• N-methyl-D-aspartate (NMDA) receptors

Multimodal Analgesia doses - Dogs

Lidocaine/dexmedetomidine

• Lidocaine 2 mg/kg IV with dexmedetomidine 2 µg/kg IV
• Then lidocaine 3 mg/kg/hr with dexmedetomidine 3 µg/kg/hr IV CRI during surgery

Lidocaine/ketamine

• Lidocaine 1.5 – 2 mg/kg with ketamine 0.5 – 3 mg/kg IV
• Then lidocaine 25 – 100 µg/kg/min with ketamine 0.03 – 0.1 mg/kg/min IV CRI

Lidocaine/dexmedetomidine/ketamine

• Lidocaine 2 mg/kg with dexmedetomidine 1 µg/kg and ketamine 1 mg/kg IV
• Then lidocaine 100 µg/kg/min with dexmedetomidine 3 µg/kg/hr and ketamine 40 µg/kg/min during surgery
• Rates were reduced post-op to lidocaine 25 µg/kg/min, dexmedetomidine 1 µg/kg/hr and ketamine 10 µg/kg/min IV CRI

Lidocaine/fentanyl/ketamine

• Lidocaine 3 mg/kg/hour combined with fentanyl 3.6 µg/kg/hour and ketamine 0.6 mg/kg/hour IV CRI

Multimodal Analgesia doses - Cats

Morphine/lidocaine/ketamine (MLK) combination

• To a 500 mL bag of LRS add:
• morphine sulfate 10 mg
• lidocaine 120 mg
• ketamine 100 mg
• Infuse at a rate of 10 mL/kg/hr IV CRI
• (will provide morphine at 0.2 mg/kg/hr, lidocaine 40 micrograms/kg/minute, and ketamine 2 mg/kg/hr)

Systemic lidocaine infusion as an analgesic for intraocular surgery in dogs: a pilot study Smith et al

Anesthesia with acepromazine, propofol, and isoflurane

• 3 groups each receiving a bolus followed by an infusion
• Saline
• Morphine
• Lidocaine (1.0 mg/kg then 25 mcg/kg/ min
• Rescue morphine was administered if the subjective pain score > or =9 (maximum=24), and the dog was excluded from further data analysis

​

Results:

• Incidence of treatment failure was 100% in saline-treated dogs and 50% in morphine- or lidocaine-treated dogs

Evaluation of a constant rate infusion of lidocaine for balanced anesthesia in dogs undergoing surgery Ortega et al

Premed with acepromazine and buprenorphine, induced with propofol and midazolam; maintained with iso

• Group A received 2 mg/kg IV lidocaine then a CRI at 50 μg/kg/min; increased as needed for reactivity up to 200 μg/kg/min
• Group B received an equivalent volume of saline instead of lidocaine

Comparison of postoperative effects between lidocaine infusion, meloxicam, and their combination in dogs undergoing ovariohysterectomy Tsai et al

Three groups:

• Meloxicam bolus
• Lidocaine bolus and CRI
• Meloxicam and Lidocaine bolus with subsequent CRI

​

Results:

• There were no significant differences in subjective pain scores, serum cortisol, and glucose concentrations between the three groups

Postoperative analgesic effects of either a constant rate infusion of fentanyl, lidocaine, ketamine, dexmedetomidine, or the combination lidocaine-ketamine-dexmedetomidine after ovariohysterectomy in dogs Gutierrez-Blanco et al

Multiple groups:

• Control/torb; Fentanyl; Ketamine; Lidocaine; Dexmedetomidine; LKD

​

Results:

• No dogs in LKD and fentanyl groups received rescue analgesia.
• Control/torb pain scores were significantly higher at 1 hour than fentanyl, dexmedetomidine and LKD; but not than ketamine or lidocaine
• Fentanyl and LKD sedation scores were higher than Control/torb at 1 hour

Antinociceptive and analgesic effect of continuous intravenous infusion of maropitant, lidocaine and ketamine alone or in combination in cats undergoing ovariohysterectomy Correa et al

70 healthy cats undergoing OVH received acepromazine and morphine, propofol, and isoflurane then one of 7 treatments:

• control (CG), maropitant (MG), lidocaine (LG), ketamine (KG), maropitant + lidocaine (LMG), maropitant + ketamine (KMG), and maropitant + lidocaine + ketamine (LKMG)

​

Results:

• Adverse effects related to maropitant, lidocaine and ketamine infusion were not observed
• Pain scores were lower in the MG, KG and LG groups when compared to the CG group using both scales
• Although pain scores were also lower in all combination groups than CG, more animals in these groups required rescue analgesia compared to MG

Ketamine

Mechanism of action - NMDA antagonist

​

Dose - high in Plumbs - practical doses - 0.5 mg/kg for analgesia as a bolus, or use CRI, higher doses 1-2 mg/kg for sedation

​

Uses - is a dissociative anesthetic

• Dream-like state of pseudo-unconsciousness - Eyes open, swallow reflex intact, can hear normally, intense muscle rigidity, hallucinogenic, disconnected from surroundings and pain
• Can spray this into the mouth of an aggressive animal - mix with dexmedetomidine

Ketamine

Side effects

• Generally minimal at low doses
• Sympathomimetic - increases heart rate, blood pressure, sympathetic nervous system stimulation
• If critically ill, cannot mount the sympathetic response - therefore the body does not show the above, instead you will see the opposite - bradycardia, hypotension, depression
• Muscle spasticity

​

Contraindications

• Increased intraocular pressure, shouldn’t use it alone for anything, heart disease, hypertension, uncontrolled hyperthyroidism, careful with hepatic and renal dysfunction

​

Good combo drugs

• Pretty well anything
• recommend adding muscle relaxant when administering to help with rigidity - i.e. benzodiazepine

​

Reversal - None

Ketamine

Use of ketamine as an adjunctive analgesic has been shown in multiple studies in veterinary medicine to improve:

• Improved pain management following major trauma
• Immediate perioperative pain management
• Post-operative pain management
• Decreased use of systemic anesthetics
• Decreased reliance on high doses of opioids

​

Suspected but less proven benefits:

• Preventing wind of up and chronic pain from major surgical procedures
• TECA
• Mastectomy
• Amputation
• Pelvic trauma

​

A large (> 4,000 patients) prospective 5-year study named The ROCKet trial (Reduction Of Chronic post-surgical pain with Ketamine is underway right now

Ketamine

Dogs – chronic pain:

• Recommended treatment protocol for intravenous ketamine infusion
• Loading dose: 0.2-0.5 mg/kg
• Infusion: 8 microg/kg/minute
• Duration: 4 hours
• Treatment schedule: Day 1, 15 and 29, or based on response to treatment.

​

Low dose subcutaneous ketamine?

• 0.5 mg/kg SC
• Anecdotal really, but seems promising

​

NSAIDS AND THE ER

• Potential for side effects (Kidneys, Liver, Coagulation, GI tract, etc.)�
• NSAIDS should be withheld until the volume, cardiovascular and renal status of the patient is determined to be WNL

​

• No use or very cautious use in patients with
• AKI
• Hepatic Insufficiency
• Dehydration, Hypotension or low ``effective circulating volume``
• Coagulopathies
• Evidence of Gastric Ulceration or GI disorders of any kind…�
• NEVER/CONTRA-INDICATIONS:
• Patients in Shock
• Trauma cases on presentation
• Patients with evidence of Hemorrhage

NSAIDS AND THE ER

Adjuvant Drugs: Gabapentin

• Anti-epileptic drug Used for the management of neuropathic pain in humans (Allodynia)

​

• Conditions where Gabapentin are indicated
• Cervical or Thoracolumbar disk disease
• Pelvic trauma
• Can be useful in animals that are restless, disoriented, vocalizing or manic post-seizure or CPA (Karol Matthews)
• Remember that patients with this type of pain may need weeks to months for resolution of pain.

​

• Consideration:
• Excreted by Kidneys; animals with CKD may require less frequent dosage
• Nephrotoxicity not an issue

Adjuvant Drugs: Amantadine

• NMDA- antagonist
• Advocated in use of acute and chronic neuropathic pain
• Limited studies but frequently used
• Typical dose used in dogs and cats 3-5mg/kg
• High safety profile with low reported side effect
• ​

Adjuvant Drugs: Acetaminophen

Mechanism of action is unknown - suspected to be central blockage of COX-3 +/- serotonin receptor agonist +/- cannabinoid receptor agonist +/- TRPV1 receptor

​

Tolerated well at appropriate dosage in dogs, NEVER IN CATS

​

Non-inferiority studies comparing pain management to NSAIDs have been positive

​

Contraindications

• Severe hepatic impairment
• Severe active hepatic disease
• Advanced stages of chronic kidney disease

​

​

Adjuvant Drugs: Tramadol

May be a useful analgesic in cats, but evidence of analgesia for dogs is conflicting

• M1 is an active metabolite that is what interacts with opioid receptors
• Dogs seem to mostly form the inactive metabolite M2 instead
• Cats produce lots of M1

​

Dosage information is limited for cats, wide range for dogs

​

Well tolerated in both species but cats hate the taste. Possible side effects include:

• CNS (eg, excessive sedation, agitation, anxiety, tremor, ataxia)
• GI (eg, hypersalivation,13 inappetence, vomiting, constipation, diarrhea)

​

Need to watch out for serotonin syndrome as tramadol will also act on the serotonin and adrenergic receptors not just opioid receptors

Nocita (Liposomal Bupivicaine)

• Local anesthetic that has up to 72 hour duration of effect

​

• Be kind to the Liposomes
• ​

Cerenia?

LOCAL ANESTHESIA

Epidural Anesthesia

• Indications:
• Surgeries of hindlimbs, penis, vagina, tail, abdomen, etc
• Use for thoracotomies reported as well (modify protocol)
• Common conditions: Orthopedic sx, urethrostomy, C-section�abdominal sx�
• Contra-indications:
• Skin Infection, Sepsis
• Allergies to drugs used
• Coagulopathy*
• Heart Disease, pre-existing hypotension (increased risk of hypotension)
• Trauma to injection area (pelvic fractures)
• Pre-existing neurological deficits

​

Epidural

• Technique:
• Use sterile technique
• Insert needle perpendicular to skin surface while the index is palpating L-S intervertebral space
• As needle advances through the ligamentum flavum a ‘‘pop’’ can be felt
• Hanging drop technique helps confirm location
• Check for blood (venous sinus) or CSF prior to injection
• If blood or CSF, retract/start again
• Intrathecal inj. is not recommended

Epidural Anesthesia

• Complications:
• Hypotension (2nd to sympathetic blockade by Local Anesthetic)
• Respiratory arrest (rare; 2nd to local anesthetics)
• Bradycardia (rare)
• Infection, Hemorrhage
• Delayed Hair Regrowth
• Urinary Retention�
• Drugs:
• Preservative free* Morphine (1 mg/ml): 12 hour effect
• Dosage of 0.1 ml/kg
• Bupivacaine (0.25% or 2.5 Mg/ml): 6-8 hour effect
• Dosage of 1ml/10 pounds (0.05 ml/kg)

Sacrococcygeal block

• Great for cats with
• Dose: 2% preservative free lidocaine at 0.1-0.2 ml/kg
• Technique:
• use sterile technique
• palpate the space between the sacrum and first coccygeal vertebra
• A 25 gauge, 1 inch needle is inserted at a 30 to 45° angle at the midline of the sacro-coccygeal space (While advancing the needle, a characteristic “pop” can be felt.
• After entering the epidural space, a syringe is attached and gentle negative pressure applied. If blood or cerebrospinal fluid is obtained, retry

Maxillofacial blocks

1. Maxillary (caudal maxillary)

​

2. Infraorbital (rostral maxillary)

​

3. Mental or alveolar (rostral mandibular)

​

4. Mandibular (Inferior alveolar - caudal mandibular)

WHAT WE FORGET

Alternative modalities

• Cryotherapy (ice)
• Much of the analgesic properties of cold is considered to be due to inactivation of sodium channels
• Animal studies provide evidence that there is an effect of cryotherapy on inflammatory mediator production
• Effect is however temporary
• Certain level of controversy on the rise in human sports medicine
• Laser Therapy
• TENS
• Acupuncture

Alternative modalities

• EMLA cream
• Stands for Eutectic Mixture of Local Anesthetic (Lidocaine 2.5% & Prilocaine 2.5% + thickening agents to form an emulsion)
• Not sterile
• Use: blood draw, catheter placement, blood collection, lumbar puncture or minor superficial procedures.
• Drawback: once applied, occlusive dressing should be placed for 20 minutes or longer for optimum effect

Nursing care

• Cold, Damp, Dirty or Noisy environment contributes to anxiety and sensitizes to pain
• Tender loving care!

References

Textbooks:

• Tobias K, Johnston SA, eds. Veterinary Surgery: Small Animal. St Louis, MO: Elsevier Saunders; 2012:1752.
• McKune, C et al. Chapter 29: Nociception and Pain. In: Kurt A. Grimm, Leigh A. Lamont, William J. Tranquilli, Stephen A. Greene, Sheilah A Robertson eds. Veterinary Anesthesia and Analgesia: The Fifth Edition of Lumb and Jones. Ames, Iowa: John Wiley & Sons, Inc; 2015.�
• Lee, L and Seddighi, R. Chapter 14: Management of Surgical Pain. In: Griffon, D, Hamaide, A, eds. Complications in Small Animal Surgery 1rst Ed. John Wiley & Sons, Inc; 2016�
• Pigott, A. Chapter 19: Pain Management. In: Kirby, R and Linklater, A eds. Monitoring and Intervention for the Critically Ill Small Animal: The Rule of 20. John Wiley & Sons, Inc; 2016

​

Lectures

• Robertson, Sheilah. The Central Role of Ketamine in Pain Management
• Robertson, Sheilah. Is There a Place for Acetaminophen in Canine Pain Management?

​

Websites

• Plumb’s online: Tramadol drug page; accessed 6/22/2026
• Lee, Justine. Vet Girl: Coccygeal epidurals for feline urethral obstruction. Accessed 6/22/2026

​

References

​

Articles:

• Psatha E, Alibhai HI, Jimenez‐Lozano A, Armitage‐Chan E, Brodbelt DC. Clinical efficacy and cardiorespiratory effects of alfaxalone, or diazepam/fentanyl for induction of anaesthesia in dogs that are a poor anaesthetic risk. Veterinary anaesthesia and analgesia. 2011 Jan 1;38(1):24-36.
• Berry SH. Analgesia in the perioperative period. Veterinary Clinics: Small Animal Practice. 2015 Sep 1;45(5):1013-27.
• Dyson DH. Analgesia and chemical restraint for the emergent veterinary patient. Veterinary Clinics of North America: Small Animal Practice. 2008 Nov 30;38(6):1329-52.
• Quandt J. Analgesia, anesthesia, and chemical restraint in the emergent small animal patient. Veterinary Clinics: Small Animal Practice. 2013 Jul 1;43(4):941-53.
• McCarthy D, Darrow BG, Tobias KM, Evans H, Williams D, Monahan C, GeFellers NF. Flail Chest: Diagnosis & Bandaging. Clinician's Brief. 2015\
• Bruchim, Yaron, et al. "Evaluation of lidocaine treatment on frequency of cardiac arrhythmias, acute kidney injury, and hospitalization time in dogs with gastric dilatation volvulus." Journal of veterinary emergency and critical care. 22.4 (2012): 419-427.
• Valverde A. Epidural analgesia and anesthesia in dogs and cats. Veterinary Clinics of North America: Small Animal Practice. 2008 Nov 30;38(6):1205-30.
• Tsai TY, Chang SK, Chou PY, Yeh LS. Comparison of postoperative effects between lidocaine infusion, meloxicam, and their combination in dogs undergoing ovariohysterectomy. Vet Anaesth Analg. 2013;40(6):615-622
• Gutierrez-Blanco E, Victoria-Mora JM, Ibancovichi-Camarillo JA, et al. Postoperative analgesic effects of either a constant rate infusion of fentanyl, lidocaine, ketamine, dexmedetomidine, or the combination
• Smith LJ, Bentley E, Shih A, Miller PE. Systemic lidocaine infusion as an analgesic for intraocular surgery in dogs: a pilot study. Vet Anaesth Analg. 2004;31(1):53-63
• Ortega M, Cruz I. Evaluation of a constant rate infusion of lidocaine for balanced anesthesia in dogs undergoing surgery. Can Vet J. 2011;52(8):856-860
• Corrêa JMX, Niella RV, Oliveira JNS, et al. Antinociceptive and analgesic effect of continuous intravenous infusion of maropitant, lidocaine and ketamine alone or in combination in cats undergoing ovariohysterectomy. Acta Vet Scand. 2021;63(1):49

​