Medical management involves using ecbolic drugs (ie, agents that induce uterine contraction) and, less commonly, digital manipulation and removal of a fetus lodged in the birth canal. Malpresentation or malposition of the fetus can be corrected via careful and well-lubricated digital manipulation, as long as the fetus is of normal size.3 (See Figure 3.) Medical management of dystocia is pursued only when the bitch is healthy, the cervix is dilated, fetal size and positioning are appropriate for vaginal delivery, and fetal heart rate is normal.8 Common ecbolic drugs include oxytocin (0.25 units per dog IM or SQ q1h, to a maximum of 4 units per dog) and 10% calcium gluconate (0.5 mL/kg IV diluted 1:4 in sterile saline delivered over 20 minutes with continuous ECG monitoring). Oxytocin and calcium gluconate are typically administered concurrently.8,11-13 Hypoglycemia, although an uncommon cause of difficulty during whelping, should be aggressively treated with 50% dextrose (0.5-1.0 mL/kg IV diluted 1:4 in sterile saline).13 Ecbolic drugs are contraindicated in cases of obstructive dystocia.8
More than 60% of dystocia cases require surgical intervention, and cesarean delivery should be performed immediately if the fetal heart rate remains <150 bpm during a 3-minute ultrasonographic evaluation.3 Uterine rupture or torsion are absolute indications for cesarean delivery, and surgical intervention should be strongly considered for patients with obstructive dystocia, fetal stress indicated by heart rates 160 to 180 bpm, and primary or secondary uterine inertia.3
While planned cesarean deliveries carry a low risk and a favorable outcome, the risk to bitch or offspring increases when the procedure is performed as an emergency.3 Anesthetic protocols should minimize the time from induction to delivery, provide adequate maternal cardiovascular stability and analgesia, and minimize fetal depression. Fetal mortality increases with hypoxia and cardiopulmonary depression. Fetal blood pressure and perfusion are heart-rate dependent, so anticholinergic drugs should be part of the maternal premedication protocol to prevent fetal bradycardia3 and decrease vagal tone induced by intraoperative uterine traction.