1)     RECOMMENDATIONS

a)      General Information

i)        Opioids are excellent agents for a variety of perioperative purposes.

(1)   Their general reversibility makes them especially attractive in higher risk cases

ii)       Opioid uses:

(1)   Pre-anesthetic sedative-analgesics

(2)   Induction agents

(3)   Anesthetic maintenance

(4)   Analgesics

(a)    Can be given as oral tablet, intermittent injection, constant rate infusion, transdermally, or epidurally

(b)   Can be combined with lidocaine and bupivacaine for extended duration local analgesia ^1,2

iii)     Their expense varies.

(1)   Inexpensive – fentanyl injectable, hydromorphone, morphine

(2)   Moderately expensive – butorphanol and buprenorphine at lower dose range

(3)   Expensive – duragesic patches, oxymorphone, butorphanol and buprenorphine at higher dose range

iv)     Their duration of effect varies.

(1)   Very short (30 minutes) - fentanyl injectable

(2)   Moderately short (3/4 to 1.5 hours) - butorphanol

(3)   Medium (3 to 6 hours) – oxymorphone, hydromorphone, morphine sulfate, buprenorphine at lower dose range

(4)   Moderately long (6 to 8 hours) – buprenorphine at moderately high dose

(5)   Long (10 to 12 hours) - buprenorphine at higher dose

(6)   Very long (12 to 18 hours) – epidural morphine, epidural buprenorphine, epidural oxymorphone, epidural hydromorphone

(7)   Many days (3 to 5 days) – fentanyl transdermal patch

v)      Categorization

(1)   Pure mu agonists – fentanyl, hydromorphone, morphine sulfate, & oxymorphone

(2)   Partial mu agonist – buprenorphine

(3)   Mixed – butorphanol (controversial – mainly kappa agonist, may have partial mu agonistic activity at very low doses and has mu antagonist properties at higher doses)

b)      Pre-anesthetic Medications

i)        The following opioids are preanesthetic options:

(1)   Butorphanol

(2)   Buprenorphine

(3)   Fentanyl – injectable and duragesic patches

(4)   Hydromorphone

(5)   Morphine Sulfate

(6)   Oxymorphone

ii)       Usually combined with other medications

(1)   Benzodiazepines (diazepam IV or midazolam IM)

(a)    Well suited to older or more debilitated patients

(2)   Acepromazine

(a)    Best suited to younger and middle age pets in good to excellent category

iii)     Sedative effect

(1)   When used alone, only morphine has a consistent sedative effect

(a)    Hydromorphone and oxymorphone have less sedative influence

(2)   When used with Acepromazine:

(a)    Buprenorphine has the least sedative effect

(b)   Hydromorphone and oxymorphone have moderate sedative effect

(c)    Butorphanol and morphine have greater sedative synergism

c)      Induction

i)        Fentanyl, oxymorphone, or hydromorphone combined with diazepam or midazolam

ii)       Most effective for dogs

iii)     Usually requires some additional agent for inducing cats

(1)   Ketamine

(2)   Propofol

(3)   Etomidate

(4)   Isoflurane/sevoflurane mask

d)      Maintenance

i)        Oxymorphone or hydromorphone alternated with diazepam or midazolam

ii)       Most effective for dogs

e)      Support

i)        Respiratory depression and bradycardia are the two most predictable negative consequences when utilizing opioids

(1)   ETCO2, Pulse Oximetry, and Blood Pressure monitoring help guide the anesthetist regarding anticholinergic use and ventilatory assistance

(2)   Hydromorphone and oxymorphone are less likely to cause any significant respiratory depression or significant bradycardia

(a)    Even with lower heart rates, there is rarely a significant decrease in blood pressure.

(3)   Morphine, especially when given IV, is more likely to cause a transient decrease in blood pressure.

(a)    This is caused by histamine release

2)     PRECAUTIONS

a)      General Information

i)        Respiratory depression and bradycardia are the two most predictable negative consequences when utilizing any opioids

ii)       Buprenorphine has an extremely high mu receptor affinity which makes it difficult to effectively reverse with opioid antagonists

(1)   Adverse effects are highly unlikely however

iii)     Vomiting usually occurs with IM or SubQ use of morphine and hydromorphone

(1)   Vomiting is less frequent with oxymorphone but may still occur

iv)     Morphine sulfate

(1)   Commonly causes defecation and vomiting

(2)   IV use associated with histamine release and transient drop in blood pressure

(a)    IM use minimizes this effect

v)      Oxymorphone

(1)   May sensitize patients to loud noises

vi)     Panting is commonly seen with hydromorphone and oxymorphone

b)      Pre-anesthetic Medications

i)        Morphine's strong synergism with acepromazine requires lower acepromazine doses

c)      Induction

i)        Opioid based induction techniques do not allow for rapid airway control

ii)       This is of much more limited use for cats

(1)   Requires some additional agent (ketamine, propofol, etomidate, isoflurane or sevoflurane mask)

d)      Maintenance

i)        This is not a practical option for use with cats

e)      Support

i)        Monitor ventilation adequacy and insure proper blood pressure maintenance

ii)       Heart rate values can be deceiving if interpreted alone. Use blood pressure values to help determine when anticholinergics are needed for cardiovascular support.