Page 997 - Small Animal Internal Medicine, 6th Edition

CHAPTER 55 Clinical Conditions of the Bitch and Queen 969

Stage II labor in the bitch is defined to begin when exter- inflammatory reaction, sepsis, and hypotension (due to
nal abdominal efforts can be seen, accompanying myome- hemorrhage or shock).
VetBooks.ir trial contractions to culminate in the delivery of a neonate. involve mismatch of fetal and maternal size, fetal anomalies,
Fetal factors contributing to dystocia most commonly
Presentation of the fetus at the cervix triggers the Ferguson
reflex, promoting the release of endogenous oxytocin from
tion with small litter size can cause dystocia due to an over-
the hypothalamus. Typically these efforts should not last and fetal malposition and/or malposture. Prolonged gesta-
longer than 1 or 2 hours between puppies, although great sized fetus(es). In one study, induction of parturition was
variation exists. The entire delivery can take from 1 to more successfully performed at gestational day 59 using aglepris-
than 24 hours, but normal labor is associated with shorter tone (15 mg/kg SC bid [Alzine, Virbac]); this could be used
total delivery time and shorter intervals between neonatal in bitches with small litters and anticipated delayed parturi-
births. Vaginal discharge can be clear, serous to hemorrhagic, tion (Baan et al., 2005). Fetal anomalies such as twinning,
or green (uteroverdin). Typically bitches continue to nest hydrocephalus, and anasarca similarly can cause dystocia
between deliveries and may nurse and groom neonates inter- (Figs. 55.17, 55.18). Fetal malposition (ventrum of fetus
mittently. Anorexia, panting, and trembling are common. proximal to the dam’s dorsum) and fetal malposture (flexed
Stage III labor is defined as delivery of the placenta. neck and scapulohumeral joints most commonly) promote
Bitches and queens typically vacillate between stages II and dystocia because the fetus cannot transverse the birth canal
III of labor until the delivery is complete. During normal smoothly.
labor, all fetuses and placentae are delivered vaginally, An efficient diagnosis of dystocia is dependent upon
although they are not be delivered together in every instance. taking an accurate history and performing a thorough phys-
The stages of labor in the queen can be similarly defined. ical examination in a timely manner. The clinician must
Stage I labor in the queen is reported to last 4 to 24 hours quickly obtain a careful reproductive history detailing breed-
and stages II and III from 2 to 72 hours, although completion ing dates, any ovulation timing performed, historical and
of delivery of neonates within 24 hours is expected with recent labor, as well as a general medical history. The physical
normal queening. examination should address the general status of the patient
and include a digital and/or vaginoscopic pelvic examination
DYSTOCIA for patency of the birth canal, evaluation of litter and fetal
Dystocia is difficulty with normal vaginal delivery of a size (radiography most useful), assessment of fetal viability
neonate from the uterus and must be diagnosed in a timely (Doppler or real-time ultrasound, ideally), and uterine activ-
fashion for medical or surgical intervention to improve ity (tocodynamometry most useful).
outcome. Dystocia results from maternal factors (uterine
inertia, pelvic canal anomalies, intrapartum compromise), TOCODYNAMOMETRY
fetal factors (oversize, malposition, malposture, anatomic The canine and feline uterus each have characteristic pat-
anomalies), or a combination of both. For effective manage- terns of contractility, varying in frequency and strength
ment, prompt recognition of dystocia and correct identifica- before and during different stages of labor. Serial tocodyna-
tion of etiologic factors are essential to making the best mometry in the bitch and queen permits evaluation of the
therapeutic decisions (Fig. 55.16). progression of labor (Fig. 55.19). During late term, the uterus
Uterine inertia is the most common cause of dystocia. may contract once or twice an hour before actual stage I
Primary uterine inertia results in the failure of delivery of labor is initiated. During stage I and II labor, uterine contrac-
any neonates at term and is thought to be multifactorial, tions vary in frequency from 0 to 12 per hour, and in strength
including metabolic defects at the cellular level. Intrinsic from 15 to 40 mm Hg, with spikes up to 60 mm Hg. Con-
failure to establish a functional, progressive level of myome- tractions during active labor can last 2 to 5 minutes. Recog-
trial contractility occurs. A genetic component could be nizable patterns exist during prelabor and active (stages
present. Secondary uterine inertia results in cessation of I-III) labor. Aberrations in uterine contractility can be
labor once initiated and consequential failure to deliver the detected during monitoring. Abnormal, dysfunctional labor
entire litter. Secondary inertia can be due to metabolic or patterns are often associated with maternal morbidity and
anatomic (obstructive) causes and is also thought to have a fetal distress (Figs. 55.20, A, 55.20, B, 55.21, A, 55.21, B).
genetic component when no contributory cause can be Completion of labor (or lack thereof) can be evaluated via
identified. tocodynamometry. Fetal viability is evaluated best by exter-
Birth canal abnormalities such as vaginal strictures, ste- nal doppler fetal heart rate monitoring or ultrasonography;
nosis from previous pelvic trauma or particular breed con- 180 to 220 beats/min are normal, persistent deceleration
formation, and intravaginal or intrauterine masses can cause (<180 beats/min) reflects stress (Fig. 55.22).
obstructive dystocia. In most cases, canal abnormalities can
be detected in the prebreeding examination and resolved or Medical Therapy
avoided by elective cesarean section (see Chapter 54). Medical therapy for dystocia, based on administration of
Causes of intrapartum compromise rendering the dam oxytocin and calcium gluconate, can be guided and tailored
unable to complete delivery include metabolic abnormali- by maternal and fetal monitoring. Oxytocin generally
ties such as hypocalcemia and hypoglycemia, systemic increases the frequency of uterine contractions, whereas