1)     RECOMMENDATIONS

a)      General

i)        Total volume of 0.1 ml/kg for average case

(1)   Many set a maximum volume is 0.2 ml/kg; some will go up to 0.3 ml/kg injected very slowly to achieve higher effect for thoracic or foreleg surgeries

(a)    If using high volume, do not use local anesthetic unless you are planning extended mechanical ventilation

(2)   Q.s. with lidocaine, bupivacaine, ropivacaine or 0.9% saline if needed

ii)       20 - 22 gauge spinal needles are used @ 1.5” to 3.0” length

b)      Indications

i)        Useful to reduce systemic anesthetic need in older or debilitated patients

ii)       To provide substantial, long term analgesia without major systemic effect

c)      Procedure

i)        Remember spinal cord ends at L5-6 to L6-7 in dogs and L7-S1 in cats

ii)       Place patient in sternal recumbancy with rear legs pulled forward

(1)   Lateral recumbancy for certain fracture cases or if personal preference

iii)     Clip and prep area as you would for surgery

iv)     Use sterile gloves +/- sterile drape

(1)   If a drape is not used, the prepped area must be larger

v)      Draw up sterile saline in a “test” syringe

(1)   Assistant handles fluid bag

(2)   Volume should be different, smaller volume than medication syringe

(3)   Leave an air bubble in syringe to help in judging proper placement at injection

vi)     Draw up medication aseptically in second syringe

(1)   Assistant handles vial

(2)   If using glass ampoules, consider using a sterile filter straw to remove glass particle contaminants

(3)   Make sure volume in syringe is clearly more than test syringe

(4)   Leave an air bubble in syringe to help in judging proper placement at injection

(5)   Some prefer to use different size syringes to decrease likelihood of switching the syringes in error

(6)   Some prefer to use same size syringes to provide the exact same feel as the test syringe but test syringe volume must be significantly less than medication containing syringe

vii)   Palpate the wings of the right and left ileum – the dorsal spinous process of L7 should be even with an imaginary line drawn across the dorsoiliac wings but can be just cranial or caudal to this line

(1)   The needle should introduced just caudal to L7

viii)  Place the needle through the skin first, then place saline in hub for “hanging drop” technique

ix)     Needle should encounter three fascial layers with the ligamentum flavum being the final and most distinct pop

x)      The saline in the needle hub should be pulled into the needle when the epidural space is entered

(1)   If the drop does not move but the feel suggests proper placement, proceed to test injection

xi)     Perform test injection with saline syringe

(1)   Aspirate before injecting

(a)    If blood is present withdraw needle, replace with new needle, reassess landmarks, and begin again

(b)   If spinal fluid is present, plan to reduce the epidural medications volume by 50%

(2)   Inject small amount of saline

(a)    Bubble in syringe should not compress during injection

(b)   There should be no significant resistance to the injection

xii)   Connect medication syringe

(1)   Reaspirate before injecting

(a)    If blood is present withdraw needle, replace with new needle, reassess landmarks, and begin again

(b)   If spinal fluid is present, plan to reduce the epidural medications by 50%

(2)   There should be no resistance to the injection

xiii)  Withdraw needle

d)      Analgesic Agents

i)        Buprenorphine

(1)   General

(a)    Similar to somewhat less effective when compared to morphine in its duration and analgesic effect

(i)       Duration (14 - 18 hours)

(2)   Dose

(a)    0.004 mg/kg

(b)   Q.s. to 0.1 ml/kg to 0.2 ml/kg with saline

(i)      If volumes over 6 cc are used (some will use 0.2 ml/kg without limit) give slowly over 1 to 2 minutes

ii)       Hydromorphone

(1)   General

(a)    Slower onset (30 - 40 minutes) than Oxymorphone but longer duration (10 - 15 hours)

(i)      Based on lower lipid solubility than Oxymorphone

(2)   Dose

(a)    0.04 to 0.10 mg/kg

(b)   q.s. to 0.1 ml/kg to 0.2 ml/kg with saline

(i)      If volumes over 6 cc are used (some will use 0.2 ml/kg without limit) give slowly over 1 to 2 minutes

(3)   Use a dedicated “Epidural” bottle

(a)    Label as “Epidural Use Only” and date vial

(b)   Decide how many uses and over what timeframe you will be using the vial

iii)     Morphine

(1)   General

(a)    Slower onset (40 - 60 minutes) than oxymorphone but longer duration (12 - 18 hours)

(i)      Based on lower lipid solubility than oxymorphone and hydromorphone

(2)   Dose

(a)    0.1 mg/kg

(b)   q.s. to 0.1 ml/kg to 0.2 ml/kg with saline

(i)      If volumes over 6 cc are used (some will use 0.2 ml/kg without limit) give slowly over 1 to 2 minutes

(3)   If preservative free Morphine is not available

(a)    Use a dedicated “Epidural” bottle

(i)      Label as “Epidural Use Only” and date vial

(ii)    Decide how many uses and over what timeframe you will be using the vial

(b)   Methylparaben is the preferred preservative

(c)    Formaldehyde containing morphine is not recommended

iv)     Oxymorphone

(1)   General

(a)    Faster onset (20 minutes) than morphine but shorter duration ( 8 to 12 hours)

(i)      Based on higher lipid solubility than morphine and hydromorphone

(2)   Dose

(a)    0.10 mg/kg

(b)   q.s. to 0.1 ml/kg to 0.2 ml/kg with saline

(i)      If volumes over 6 cc are used (some will use 0.2 ml/kg without limit) give slowly over 1 to 2 minutes

e)      Local Anesthetic Agents

i)        General

(1)   Causes peripheral vasodilation via sympathetic blockade leading to some degree of hypotension

(2)   May still have motor effects the next day

ii)       Bupivacaine

(1)   General

(a)    20 - 30 minute latent period before onset of surgical analgesia

(b)   Provides 4 -6 hours of surgical analgesia

(2)   Dose

(a)    1.0 ml of 0.5 % solution / 5 kg (maximum dose)

(i)      Reduce by 1/2 when added to 0.1 mg/kg morphine for 0.2 ml/kg total dose

(ii)    Total volume should not exceed 0.2 ml/kg. Some cap volume at 6 ml.

1.      Reduce bupivacaine dose accordingly when other agents are used

(b)   Sympathetic blockade can create hypotension

(c)    Great for perianal surgery

iii)     Lidocaine

(1)   General

(a)    Almost immediate effect - 5 minutes

(b)   Provides 60 - 90 minutes of surgical analgesia

(2)   Dose

(a)    1.0 ml / 5 kg to maximum of 20 ml total dose

(i)      Can be added to 0.05 mg/lb morphine

(ii)    Total volume should not exceed 0.2 ml/kg

1.      Reduce lidocaine dose accordingly

(b)   Sympathetic blockade can create hypotension

f)       General

i)        Use luer slip syringes

ii)       Cats have more angled dorsal spinus processes

2)     PRECAUTIONS

a)      Contraindications for Epidural

i)        Sacral fractures

ii)       Overlying skin disease

iii)     Bleeding disorder

iv)     Septicemia

v)      Hypotensive/Hypovolemic Patients

(1)   Avoid local anesthetics

b)      Analgesics

i)        Temporary urine retention can result

(1)   Check bladder carefully

(2)   Most likely with morphine

ii)       Some respiratory depression can occur

iii)     Some sedation can occur

iv)     Bradycardias can develop

v)      Pruritis can develop

vi)     Delayed hair regrowth

vii)   Neurologic deficits can be revealed the next day

(1)   Vague weakness

(2)   Usually resolves within 2 - 3 days

c)      Anesthetic Agents

i)        Cause peripheral vasodilation via sympathetic blockade

(1)   Avoid if hypotensive/hypovolemic

ii)       Can still have motor effects the next day

d)      Support

i)         Watch bladder for urine retention