Letters: A few clarifications on dystocia management

In the article "My approach to canine dystocia" in the December issue, Dr. Scott Shaw provided an experienced approach to dystocia management, but several points need clarification.

Gestation in the bitch is 64 to 66 days from the day of the luteinizing hormone surge, an event we extrapolate from the "initial rise" in progesterone, usually between 2 and 3 ng/ml. A level of 5 ng/ml (not 5 ng/dl as stated by the author) confirms that ovulation has occurred but is not the day of ovulation. Using the first day of cytologic diestrus (the first day vaginal cytology is < 50% superficial or cornified cells) to predict gestation length is also accurate; whelping should occur 56 to 58 days later.

The drop in body temperature to < 99 F (37.2 C) is associated with the decline in progesterone before labor but only can be documented in 60% of bitches. Thus, it is not a reliable predictor of first stage labor in all cases.1

Primary inertia is not a lack of abdominal press but is defined as a failure of normal uterine contractions to ever be initiated; the etiology is often not identified.1

Dr. Shaw's advice that prompt recognition and management of dystocia is critical is correct. He gave subjective criteria to diagnose dystocia. Critical evaluation of a bitch in labor for evidence of dystocia should be based on evaluation of uterine activity (tocodynamometry) and on how the fetuses are faring (fetal heart rate monitoring). Radiographs cannot determine fetal distress accurately unless postmortem changes are evident or gross mismatch of fetal to maternal size or malpositioning is evident. Ultrasonography provides much more information about fetal distress (fetal bradycardia; HR < 170 beats/min). Measuring serum BG and iCa+ is optimal, but the subcutaneous administration of 10% calcium gluconate (0.47 mEq/ml; 1 ml/4.5 kg subcutaneously, diluted 1:1 with saline solution) results in improved strength of myometrial contractions even in eucalcemic bitches and may make oxytocin use unnecessary.1-3

Dr. Shaw's advice that cesarean section is indicated when primary inertia is present is correct, but I disagree with the management of secondary inertia. The suggested doses of oxytocin for secondary inertia are excessive. Tocodynamometry studies have shown that the appropriate dose of oxytocin (10 U/ml) is 0.03 to 0.04 U/kg. Higher doses produce titanic, dysfunctional myometrial responses. Dr. Shaw is correct that oxytocin transiently compresses placental blood flow, potentially producing fetal hypoxemia that can be detrimental when fetal distress is present. Treatment with 10% calcium gluconate before oxytocin administration is advised to achieve improved strength (calcium) and frequency (oxytocin) of myometrial contractions.1,3

Dr. Shaw's advice concerning time management during cesarean section is excellent. I do not advocate using atropine as a premedication. It crosses the placenta; dosing of fetuses can be suboptimal. Glycopyrrolate (Robinul-V—Fort Dodge/Pfizer Animal Health) is an acceptable alternative anticholinergic as it does not cross the placenta. Anticholinergic use is indicated because of the marked vagal stimulation inevitable with manipulation of the gravid uterus.

Finally, studies have shown that 50% of bitches having undergone previous cesarean section can have successful vaginal deliveries with appropriate obstetrical monitoring, which permits earlier detection of dystocia and more timely medical intervention. Advocating the use of home uterine and fetal monitoring (Whelpwise—Veterinary Perinatal Services) in future pregnancies is indicated for bitches with a history of cesarean section.1

REFERENCES

1. Davidson A. Obstetrical monitoring in dogs. Vet Med 2003;98(6):508-517.

2. Davidson A, Eilts B. Advanced small animal reproductive techniques. J Am Anim Hosp Assoc 2006;42(1):10-17.

3. Copley K. Parturition management: 15,000 whelpings later; An outcome based analysis. Theriogenology 2009'(1)2:297-307.

Autumn Davidson, DVM, MS, DACVIM

UC Davis School of Veterinary Medicine

Davis, Calif.

Dr. Shaw replies: I appreciate Dr. Davidson's thoughtful comments on canine dystocia. I agree that fetal distress is best evaluated via ultrasonography and that ultrasonographic evaluation of fetal heart rate and motion is an important part of the diagnostic algorithm.

The evidence to guide pharmacological intervention during canine dystocia is somewhat limited. Dr. Davidson is correct that lower doses of oxytocin may be appropriate, and it is reasonable to try those doses as a first-line therapy. If calcium gluconate is to be used before oxytocin administration, I recommend diluting the calcium to a 1.25% solution. I have seen three cases in which subcutaneous calcium administration resulted in epidermal necrosis.

I typically choose atropine as a premedication for a cesarean section despite its impaired ability to enter fetal blood flow because of its immediate onset. Glycopyrrolate takes 15 to 20 minutes to achieve maximal effect, so if it is used it should be administered at least 15 minutes before induction.

Bitches with a prior history of dystocia can most certainly have subsequent normal vaginal deliveries. Owners must work closely with their veterinarians to monitor this group of dogs prepartum to minimize complications.

Scott Shaw, DVM, DACVECC

Department of Clinical Sciences

Cummings School of Veterinary Medicine

Tufts University

North Grafton, Mass.