Vet Tips

Facilitating Cesarean Section in Dogs: Epidural Anesthesia/Analgesia
12/10/2008

Concerns often arise regarding the “best” or “least depressant” anesthetic protocols to administer to dogs requiring a cesarean section. All drugs routinely used to produce surgical anesthesia in dogs cross the placenta and have the potential to produce fetal depression. The inhalant anesthetics, thiopental and propofol are particularly notorious in this regard and cross into the fetus almost as fast as they are administered to the dam. The goal, therefore, is to design an anesthetic protocol that uses drugs that cross the placenta slowly or to anesthetic/analgesic techniques that reduce the need for injectable or inhalant anesthetics thereby reducing the potential for fetal depression. Most pregnant dogs respond favorably to lower doses of preanesthetic medications. Low doses of acepromazine (0.02 mg/kg) and opioids (0.1 mg/kg butorphanol or 0.05 mg/kg hydromorphone) generally provide good to excellent stress reduction and analgesia. Midazolam (0.2 mg/kg, IV) – propofol (2 mg/kg. IV) usually provides rapid and safe induction to anesthesia. Propofol, however, as stated above rapidly crosses the placental barrier but is rapidly redistributed and cleared from the plasma. Ketamine (3-5 mg/kg, IV) and diazepam (0.2 mg/kg, IV) administered sequentially or together can be administered to induce anesthesia in sick pregnant dogs or cats and crosses the placenta more slowly than propofol. Although once popular the epidural administration of larger doses of local anesthetics is no longer advocated for analgesia, primarily due to the loss of motor function (hind limb paralysis, loss or rectal sphincter tone) and the high incidence of maternal stress or fear during recovery from anesthesia. Current epidural formulas are formulated around opioids, generally preservative free morphine. Many contain lower doses of bupivacaine in order to avoid loss of motor function or paresis. Some include alpha-2 agonists (medetomidine, dexmedetomidine) in or order to extend the duration of analgesia from 4-6 hours to up to 18-24 hours. The epidural can be combined with a 2% lidocaine (1-2 ml lidocaine diluted in 0.9% NaCl to 10 ml) local anesthetic line block. The dog is intubated and administered oxygen from a circle anesthetic system. Once the fetuses are removed the inhalant anesthetic can be turned on.

Epidural Cocktail:
0.1 mg/kg morphine
0.2 mg/kg bupivacaine
0.002 ug/kg (2 ug/kg) medetomidine or dexmedetomidine
Dilute all drugs in 0.9 % NaCl to a volume of 0.3 ml /kg and administer into the lumbo-sacral (L7-S1) junction using a spinal (Touhy) needle (ReCathCo, LLC; www.recathco.com).

Submitted by:
William Muir, DVM, PhD, ACVA, ACVECC, VCPCS
338 West 7th Avenue
Columbus, Ohio 43201