Case discussions of perioperative concerns in pain management-renal, hepatic, heline, c-section, trauma (Proceedings)

General and specialty practice provide a number of analgesia challenges: those cases that don't fit the simple mold of opioids and NSAIDs.  The practitioner must be sufficiently knowledgeable in the pharmacodynamics and kinetics of drugs in order to provide appropriate comfort without causing adverse events.  Additionally, the practitioner must be familiar with nonpharmacologic alternatives.  The following cases present interesting analgesic challenges with some considerations and some potential options.

1.  Acute disc disease in a dog with separation anxiety

·         Signalment: 7 yrs old MC dachshund

·         History:  Has been undergoing treatment for separation anxiety and interdog aggression with fluoxetine for 2 years.  Presented with acute back pain; has had 2 other episodes that resolved.

·         PE: Ambulatory x 4, kyphosis, hypertonicity in the TL region.  Pain on palpation neurologic exam is within normal limits.  Screening radiograph reveals mild narrowing at T11-12. No other findings.  Client does not want to do advanced imaging and wants to avoid surgery if possible. 

Analgesic considerations 

o    Suspected nerve origin pain

o    Concurrent use of SSRI (fluoxetine)

Analgesic action items

o    Avoid use of tramadol if possible:  potential for serotonin syndrome

o    Careful consideration to use of NSAIDs vs. steroid

o    Consider non-pharmaceutical therapies as well

Plan

o    Methocarbamol 15-20mg/kg TID

o    Prednisone 0.5mg/kg BID and taper as soon as possible using alternatives

o    Amantadine 3mg/kg q 24hr

o    +/- gabapentin 10+mg/kg TID-QID (caution with fluoxetine… )

o    Acupuncture, Massage, Rehabilitation

 2. Cranial Cruciate Ligament Rupture in a dog undergoing chemotherapy for lymphoma

·         Signalment:  8yrs old FS Golden Retriever

·         History:  undergoing chemotherapy for lymphoma; cranial cruciate ligament rupture yesterday. 

·         PE:   Grade 2/5 lameness right pelvic limb. Effusion, medial buttress, no evidence of meniscal injury

Analgesic considerations

o    Immunosuppression (not a candidate for surgery right now)

o    Prednisone (not a candidate for NSAIDs right now)

o    Joint injections:  risky in the immunocompromised

Analgesic action items

o    Do not use strict cage rest as this leads to muscle atrophy and weight gain

o    Do use a comprehensive, integrative plan

Plan: 

o    Pharmaceutical options

ü  Acetaminophen 10-15mg/kg BID for 3-5 days

ü  Tramadol 3-5mg mg/kg TID-QID

o    Rehabilitation (immediate): 

ü  Controlled daily exercise (not cage rest)

ü  Joint mobilization exercises

ü  Icing

ü  Passive range of motion

ü  Myofascial triggerpoint therapy and massage

o    Orthosis  (knee brace)

ü  External coaptation using force coupling to limit cranial tibial translocation and tibial internal rotation

ü  Orthosis specific rehabilitation to increase weight bearing and improve gaiting.

ü  Will not improve weight bearing or comfort significantly if the meniscus is damaged:  partial menisectomy will be needed in addition to orthosis.

o    Joint supplements may provide a modest contribution over time.  Caution is warranted in selecting brands. Select among:

ü  Omega 3 fatty acids

ü  Adequan

ü  Microlactin

ü  Glucosamine/chondroitin with avocado/soy unsaponifiables

o    Acupuncture and LASER

o    Surgical stabilization if appropriate/needed after chemotherapy is complete

3.  Traumatic fracture of the mandible in a dog

·         Signalment:  5 yrs old SF terrier mix

·         History:  presented on emergency after having jumped out of a moving car

·         PE:  HR 200, RR panting, mm pale, CRT 1 sec, lacerated tongue, degloving injury chin, suspected fracture of the right mandible, PLR's normal, pupils equal though dilated.  No other injuries noted.  Anxious, normal thoracic excursions as best can be noted while panting and struggling. 

Anesthesia and analgesic considerations

o    Address emergency issues (resuscitatition, hemostasis, multiple injury assessment, etc)

o    Do not increase intracranial pressure until head trauma assessment is cleared

o    Do not induce vomiting

o    Do not induce cardiovascular distress (hypertension, hypotension, brady/tachycardia)

o    Do not induce respiratory depression until thoracic trauma is fully characterized

o    Do not risk renal compromise until resuscitation is complete

Anesthesia and analgesia action items

o    Avoid ketamine (increases intracranial pressure)

o    Use lower dose opioid  or methadone (hydromorphone or morphine can cause vomiting)

o    Avoid dexmedetomidine; it decreases cardiac output by increasing vascular resistance (hypertension), causing reflex bradycardia, and resulting in late phase vasodilation

o    Avoid NSAIDs in shocky patients because decreased renal perfusion may increase potential for renal injury.

Plan:

o    Immediate

ü  Resuscitation with fluid therapy and oxygen

ü  Anxiolysis:  Low dose acepromazine 0.0025 -0.005 mg/kg IV titrate small doses to effect; NOT analgesic but IS antiemetic

ü  Analgesia options:   low dose opioid (avoid vomiting)

§  buprenorphine causes less frequent vomiting compared to hydromorphone and morphine

§  methadone causes less frequent vomiting; not as powerful mu agonist, but also an NMDA agonist

§  hydromorphone (vomiting may be offset by acepromazine)

ü   Icing if patient will tolerate

o    Perioperative options

ü  Premedication any opioid continue to avoid vomiting +/- acepromazine or dexmedetomidine.  The latter 2 will depend on stabilization

ü  Intraoperative: 

§  0.5-1 mg/kg ketamine in induction (if no evidence of intracranial pressure increase)

§  regional blockade of the mandibular nerve branches (myohyoid, inferior alveolar and lingual.

§  MLK or FLK or HLK (see analgesia balancing acts for dosing)

§  fentanyl bolus prn to maintain level of anesthesia (5 ?g/kg IV)

§  Post operative options

§  Assess for comfort, opioid induced dysphoria, anxiety, combination

§  Be prepared to micro dose (titrate) to effect

¯         Opioid

¯         Naloxone 1-2mg/kg IV repeat to effect to control dysphoria (no more than 2-3 doses so as not to reverse analgesia

¯         Acepromazine 0.5-1mg/kg IV repeat to effect (wait between doses)

¯         Dexmeditomidine 0.25-0.5mg/kg IV repeat to effect

§  If needed continue lower dose MLK or FLK or HLK  +/-dexmedetomidine

§  Icing if patient will tolerate

§  NSAID:  if blood pressure adequately maintained perioperatively and no corticosteroids administered during emergency treatment

§  Tramadol 2-5mg/kg TID-QID

§  Acetaminophen 10-15mg/kg BID-TID for 3-4 days (if hepatic function ok)

4.  Portal vein hypoplasia/microvascular dysplasia in a dog:  multiple dental extractions

·         Signalment:  5 year old MC Yorkshire terrier

·         History:  Diagnosed with PVH/MVD as 1 year of age, managed medically with lactulose, lower protein diet, and metronidazole; doing well.

·         PE:  Severe dental disease.  Several extractions anticipated.

Anesthesia and analgesia considerations:   

o    Hypoglycemia risk                                     

o    Potential seizure risk (hypoglycemia and hepatic encephalopathy)

o    Hypoproteinemia

o    Hepatic function for drug clearance compromised

Analgesic action items:

o    Decrease dose of highly protein bound drugs (NSAIDs)

o    Decrease dose of hepatically metabolized drugs (e.g. opioids, gabapentin, NSAIDs, dexmedetomidine, tramadol)

o    Avoid non reversible drugs (e.g. ketamine, acepromazine) in favor of reversible (e.g. opioids, dexmedetomidine, midazolam)

Plan: 

o    Routine lab screening pre-op to include pre-op blood glucose (treat prn with CRI)

o    Premedicate with lower end dosing of opioid (e.g. hydromorphone) and midazolam SQ

o    Regional analgesia (dental blocks) to minimize reliance on perioperative opioids

o    LASER has been used in periodontal disease therapy in people

o    Dispense:   tramadol low dose 0.5-2mg/kg BID-TID or buprenorphine 15-30?g/kg TID transbuccal). +/- NSAID lower dose depending on protein levels and hepatic function

5.  Cesarean section

·         Signalment:  3 yrs old F English bulldog

·         History:  Routine planned cesarean section

·         PE:  Significant brachycephalic conformation, panting, mildly cyanotic when she gets excited

Anesthesia and analgesia considerations:

o    Abdominal distension and brachycephalic conformation

ü  increase risk of aspiration

ü  cause respiratory compromise

o    Many drugs cross placental barrier causing sedation and cardiac depression in neonate

o    Epidural space (fat and vasculature) is altered in pregnancy

o    Many drugs are excreted into milk

Analgesic action items

o    Avoid drugs that induce vomiting perioperatively (e.g. hydromorphone, morphine)

o    Avoid drugs that must be metabolized by the pups (e.g. ketamine, benzodiazepines)

o    Avoid overstressing the dog (i.e. masking down is not advised)

o    Decrease dose of epidurally delivered drugs by 50%

o    Decrease dose of local analgesic in epidural to decrease motor blockade

o    Avoid drugs that are excreted in milk (NSAIDs) or decrease dose (opioids).     

Plan

o    Oxygen by mask throughout pre-operative preparation

o    Atropine in premedication if maternal heart rate is normal to decreased.  Atropine intraoperatively if the pups or dam are cardiovascularly compromised

o    Very low dose opioid followed shortly (minutes) by propofol induction to effect

o    Morphine epidural (0.05mg/kg) +/-bupivicaine 0.2mg/kg

o    Delay in surgery for this procedure is acceptable because it gives propofol a chance to redistribute out of the pups =  more alert pups

o    Consider additionally opioid (e.g. hydromorphone 0.05mg/kg IV after pups removed.  Naloxone for pups as needed.

o    Incisional blockade with bupivicaine up to 2mg/kg.

o    SLOW recovery; leaving ET tube in as long as possible to ensure airway control

o    Acetaminophen post op 10-15mg/kg BID for 3-5 days

6.  Perineal urethrostomy (PU) for chronic urethral obstruction in cat with chronic renal failure

·         Signalment:  10 years old MC DSH

·         History:  Has obstructed multiple times in the past 2 years. Decision to proceed with PU.  Patient has mild chronic renal failure with persistent azotemia (BUN 70mg/dl, creatinine 3.0mg/dl), isosthenuria, mild hyperkalemia (5.5).  No evidence of hyperphosphatemia.  HCT 37%

·         PE:  Obese, stabile for anesthesia; not currently obstructed (urinary catheter in place)

Anesthesia and analgesic considerations

o    Hyperkalemia associated with urethral obstruction: implications for anesthesia safety

o    Positioning for PU (head down)) decreases lung compliance due to compression

o    Renal status concern for anesthesia and analgesia: acute on chronic renal failure risk

o    ANY cause for inappetance post op is a concern for development of hepatic lipidosis (e.g. uncontrolled pain, adverse pharmaceutical events, anxiety)

Anesthesia and analgesic action items

o    Monitor potassium: should not be an issue since obstruction resolved

o    May require ventilation support intra-operatively; at the very least deliver a deep breath up to 20cm water pressure every 5-10 minutes.

o    Maintain normotensive status during anesthesia (judicious use of balanced anesthesia to decrease cardiovascular depression, fluid therapy, dopamine or dobutamine)

o    Judicious choice of analgesics that are minimally cleared by the kidneys

o    Monitor appetite post-operatively:  consider placing an esophageal feeding tube or use of appetite stimulants prn.

Plan:

o    Premedication with an opioid (e.g. hydromorphone, buprenorphine, etc)

o    Preoxygenate and deliver a fluid bolus immediately prior to induction

o    Pre-instrument: immediate blood pressure monitoring (Doppler, always a good choice!)

o    Induction:  propofol to effect along with 1mg/kg ketamine and midazolam 0.2mg/kg

o    Morphine epidural (0.1mg/kg) +/-bupivicaine (0.2-0.5mg/kg)

o    Incisional analgesia:  bupivicaine up to 1mg/kg

o    Post-operative analgesia:  opioid based on clinical assessment (buprenorphine 15-30?g/kg TID-QID)

o    Home care:  buprenorphine transbuccal  (15-30?g/kg TID-QID) or SR (0.12mg/kg) SQ*

o    efficacy of Buprenorphine SQ  or Buprenorphine SR is not fully characterized