Page 1001 - Small Animal Internal Medicine, 6th Edition

CHAPTER 55 Clinical Conditions of the Bitch and Queen 973

crosses the placenta (can exacerbate fetal myocardial hypox-
emia) and causes relaxation of the lower esophageal sphincter
VetBooks.ir making maternal aspiration more likely. However, an anti-
cholinergic is indicated for the dam because of the anticipated
vagal stimulation during manipulation of the gravid uterus.
Glycopyrrolate (Robinul [AH Robins] at 0.01-0.02 mg/kg
SC) does not cross the placenta and is preferred. Most dams
are tractable or exhausted and do not need preanesthetic
tranquilization, which has a depressant effect on the fetuses.
Phenothiazine tranquilizers are transported rapidly across
FIG 55.22 the placenta and are depressants. α 2 -adrenoceptor agonists
Fetal heart rate (HR) monitoring in an Airedale bitch during
the eighth week of gestation. Normal fetal HR should be such as dexmedetomidine and xylazine are contraindicated
over 180 beats/min. because of their severe cardiorespiratory depressant effects.
Similarly, the respiratory depressant effect of opioids makes
them unpopular before removal of the fetuses. If tranquil-
ization is necessary with an intractable dam, narcotic seda-
tives are preferable because their effects can be reversed (IV
or IM naloxone, 1-10 µg/kg) during neonatal resuscitation.
Metoclopramide (0.1-0.2 mg/kg) can be administered sub-
cutaneously or intramuscularly to the dam before induction
of anesthesia to reduce the risk of vomiting during the proce-
dure. Dissociative induction agents such as ketamine and the
barbiturates are best avoided because they produce profound
depression of the fetuses. Propofol (Rapinovet [Bayer Animal
Health] at 6 mg/kg IV to effect) appears to be the most
useful induction agent; because of its rapid redistribution it
has a limited effect upon the neonates. Alfaxalone (Alfaxan
[Jurox]) at 2 mg/kg IV (canine) and 5 mg/kg IV (feline)
is an alternative. Mask induction actually produces more
maternal and fetal hypoxemia than IV propofol induction.
For maintenance of anesthesia, volatile agents are prefer-
able, especially those with low partition coefficients, such as
isoflurane and sevoflurane. These agents show rapid uptake
FIG 55.23 and elimination by the animal and may have a better cardio-
Uterine torsion diagnosed preoperatively with vascular margin of safety than the more soluble agents (e.g.,
tocodynamometry. Immediate cesarean section resulted in halothane). Nitrous oxide may be used to reduce the dose
preservation of the uterus and survival of all fetuses. of other anesthetic agents. It is transferred rapidly across the
placenta, and although it has minimal effects upon the fetus
fetal size, or fetal malposition or malposture incompatible in utero, it may result in a significant diffusion hypoxia after
with vaginal delivery), or if aberrant contractile patterns are delivery. Using a local anesthetic (bupivacaine 1-2 mg/kg,
noted by uterine monitoring (Fig. 55.23). If fetal heart rates lidocaine (canine only) up to 2 mg/kg diluted to necessary
decline in response to administration of calcium or oxytocin, volume) line block in the skin and SC tissues before incising
further medical management is contraindicated. Well- permits more rapid entry into the abdomen while the dam
orchestrated cesarean sections result when anesthetic and is making the transition from propofol induction to inhalant
neonatal resuscitative protocols are established and coordi- maintenance, and helps with postoperative discomfort. Care
nated, and the preoperative preparation of the dam opti- must be taken not to inadvertently administer bupivacaine
mized. The dam can be debilitated and require careful or lidocaine into a mammary vessel. Local (epidural) anes-
anesthetic management, there often is be little time for thetic techniques require expertise and monitoring for severe
routine preanesthetic preparation, and the dam might have hypotension. Sedatives could still be required to enable posi-
been fed recently. Minimally, the hematocrit, total solids, tioning for surgery. Epidural lidocaine is preferable (bupiva-
serum calcium, and glucose concentrations should be evalu- caine has too long a duration of action and is a more potent
ated preoperatively. IV fluid support at an operative rate is negative inotrope) at 2 to 3 mg/kg, not to exceed a maximum
indicated (5-10 mL/kg/h). volume of 6 mL; adding epinephrine 5 µg/mL intensifies and
Preoxygenation by mask (5-10 minutes) is always indi- prolongs the block achieved. Inadvertent penetration of the
cated. Initial preparation of the abdomen (clipping and first dura mater can occur.
scrubbing) can be undertaken during this time. Atropine is Ovariohysterectomy at the time of cesarean section is an
undesirable as a premedication anticholinergic because it option for the surgeon and owner but results in longer