Uterine Rupture and Septic Peritonitis Following Dystocia and Assisted Delivery in a Great Dane Bitch

Introduction

Periparturient uterine rupture is an uncommon complication in the dog. Reference texts suggest that preparturient rupture in dogs is sometimes associated with external trauma such as road traffic accidents;¹ however, rupture during or after birth is thought to most likely occur when the uterine wall is compromised (such as in the presence of infection, a dead fetus, uterine torsion, or from inappropriate obstetrical technique).^1–3 Excessive doses of oxytocin are also suggested as a potential cause of uterine rupture, but this is a controversial issue.² Canine uterine rupture has been reported previously secondary to pyometra-endometritis complex, obstruction, and trauma.^3–11 A large retrospective study of 652 dogs with pyometra identified uterine rupture in only 3.2% of cases.¹¹ To date, no reports of uterine rupture associated with manually-assisted whelping are available, and only one case report involved administration of oxytocin.³ The dog discussed herein was administered large doses of oxytocin and was manually whelped. This report discusses the risks involved in this approach.

Case Report

A 2-year-old, intact female Great Dane weighing 57 kg was presented to the primary veterinarian because of owner-perceived dystocia. A normal, first-stage labor on day 63 of pregnancy was followed by the birth of one live and one dead puppy. A 2-hour period followed without the birth of any more puppies and with no visible straining. A presumptive diagnosis of primary uterine inertia was made, and five doses of oxytocin^a were administered intramuscularly (IM), totaling 38 IU over a period of 5 hours (0.67 IU/kg). Four grams of calcium borogluconate^b (70 mg/kg) were also administered subcutaneously (SC) for presumptive hypocalcemia, although serum calcium concentration was not assessed. During the period of medical therapy, seven puppies (six live and one dead) and seven placentae were delivered. Six hours after the initiation of stage 2 labor (and 4 hours after the first dose of oxytocin), abdominal contractions ceased. Manual examination of the vagina and uterus revealed additional fetuses, and three additional puppies (but no placentae) were delivered with manual assistance and without the use of whelping forceps. The referring veterinarian reported manipulating fetuses beyond the level of the uterine bifurcation. In total, 10 live puppies, two dead puppies, and nine of the 12 placentae were delivered.

Postwhelping, the dog was treated with intravenous (IV) balanced electrolyte fluid therapy (Hartmann’s solution),^c buprenorphine^d (10 μg/kg SC once), and clavulanate-potentiated amoxicillin^e (12.5 mg/kg SC once). Two further doses of oxytocin (7 IU each, 0.13 mg/kg) were administered IM to aid placental expulsion. The dog was discharged 8 hours after the last puppy was delivered. She was cardiovascularly stable, mentally alert, and appeared to have adequate milk production.

Fifteen hours after discharge, the dog was presented again to the primary veterinarian because of marked clinical deterioration, and the dog was referred for further evaluation. On presentation to the referral institution, the dog was mentally depressed and reluctant to stand. Cardiovascular assessment revealed a tachycardia of 200 beats per minute with poor pulse quality and pale mucous membranes and a prolonged capillary refill time of 2.5 seconds. Examination findings were consistent with severe hypoperfusion. The dog was also tachypneic at 42 breaths per minute and pyrexic at 40.7°C. Abdominal palpation did not elicit any signs of pain. A small amount of milk was present in the cranial mammary glands only.

Venous blood gas analysis on presentation revealed a pH of 7.406 (reference range 7.360 to 7.470), bicarbonate (HCO3) of 14.8 mmol/L (reference range 20.8 to 24.2 mmol/L), and partial pressure of carbon dioxide (pCO₂) of 23.4 mm Hg (reference range 33 to 52 mm Hg), indicating a mixed acid-base disorder resulting from metabolic acidosis and respiratory alkalosis. A hyperlactatemia of 4.2 mmol/L (reference range 0.6 to 2.5 mmol/L) and a moderate hyponatremia of 137 mmol/L (reference range 40 to 153 mmol/L) were also identified. Hematology revealed a degenerative left shift with a neutrophil count of 5.32 × 10⁹/L (reference range 3 to 11.5 × 10⁹/L) and 54% bands, supportive of a marked inflammatory process. A lymphopenia of 0.43 × 10⁹/L (reference range 1 to 4.8 × 10⁹/L) was also present. Serum biochemical analysis revealed a moderate hypoalbuminemia of 1.82 g/dL (reference range 2.8 to 3.9 g/dL), a mild hyperbilirubinemia of 0.31 mg/dL (reference range 0 to 0.14 mg/dL), and an elevated creatine kinase of 447 U/L (reference range 61 to 394 U/L). Abdominal radiography and ultrasonography revealed ascites, presence of gas within the uterine horns, and pneumoperitoneum compatible with uterine wall rupture [Figures 1, 2]. The uterine wall was assessed as abnormally thickened on ultrasonographic examination. Cytological analysis of fluid obtained by abdominocentesis revealed a septic inflammation characterized by neutrophils and a mixed population of both intra- and extracellular bacteria.

The dog required aggressive fluid therapy during the above investigations. Therapy consisted of 5 L of balanced isotonic crystalloid solution^f (88 mL/kg), 300 mL of hypertonic saline^g (5.3 mL/kg), and 500 mL of pentastarch^h (17.5 mL/kg) to improve the cardiovascular parameters. Once abdominocentesis had been performed and septic peritonitis was confirmed, the dog was prepared for emergency surgery. Broad-spectrum antibiotic therapy also consisted of IV metronidazoleⁱ (10 mg/kg), and IV clavulanate-potentiated amoxicillin^j (22 mg/kg) was initiated.

Anesthesia was induced with IV fentanyl^k (5 μg/kg) and IV midazolam^l (0.4 mg/kg), and the dog was maintained on inhalant isoflurane^m in oxygen and a constant-rate infusion (CRI) of fentanyl^k (0.15 μg/kg per minute). The dog was hypotensive during anesthesia and required multiple fluid boluses in addition to Hartmann’s fluid administered at 20 mL/kg per hour. Inotropic and vasopressor support with an IV CRI of dopamineⁿ (6 to 10 μg/kg per minute) was also required. Exploratory celiotomy was performed. Purulent fluid (4 L) along with two free-floating placentae were present in the abdomen. Two full-thickness tears were identified in the uterus: one in the right horn and one in the body. The uterus appeared grossly erythematous and swollen and was noted to be friable. Ovariohysterectomy was performed, and a gastrotomy tube was placed in the pyloric antrum for nutritional support and gastric decompression postsurgery (if required). Histopathology was not performed.

Due to the gross peritoneal contamination and septic inflammation, the cranial two-thirds of the abdominal incision was left open to allow continual peritoneal drainage. To achieve this, loose, simple continuous sutures were placed in the external rectus sheath using size 0 (3.5 metric) polyamide 6^o and leaving a gap of approximately 3 cm between the edges of the body wall. Multiple, large sterile swabs were placed over the incision line and were bandaged to the trunk using conforming and cohesive bandages. The dog was continued on IV potentiated amoxicillin^j q 8 hours and metronidazoleⁱ q 12 hours postsurgery for 3 days. Hartmann’s fluid therapy was continued at a rate of 5 mL/kg per hour. Analgesia was provided with morphine^p (0.2 mg/kg IV q 4 hours) for 60 hours and then with buprenorphine^d (0.02 mg/kg IV q 8 hours until discharge).

Mild peripheral edema developed over the following 12 hours, prompting treatment with a CRI of pentastarch^h (1 mL/kg per hour IV) and furosemide^q (0.1 mg/kg per hour IV). Every 24 hours, the abdominal bandages were changed in a sterile manner while the dog was conscious, and a sample of abdominal fluid was examined cytologically each time. After 48 hours, cytological examination of the abdominal fluid revealed nondegenerate neutrophils and no bacteria. At 52 hours after the first surgery, the dog was anesthetized as described herein, and the abdominal cavity was lavaged with warm, sterile saline and closed in a routine manner.

The dog was discharged 5 days after admission and surgery. The only noted clinical abnormality at the time of hospital discharge was a slightly decreased appetite. Culture of the abdominal fluid obtained on initial abdominocentesis yielded growth of Escherichia coli and Proteus spp., both of which were sensitive to enrofloxacin and metronidazole. The potentiated amoxicillin^j therapy was stopped on the third day following surgery; therefore, the dog was continued on oral enrofloxacin^q (5 mg/kg) q 24 hours and oral metronidazole^r (10 mg/kg) q 12 hours for 10 days.

Reexamination was conducted at the referral hospital 9 days after discharge. The dog was assessed to be consuming adequate amounts of food, and the gastrotomy tube was removed. Long-term telephone follow-up 1 year postdis-charge revealed the dog had made a full recovery.

At the time the dog was admitted to the referral hospital, the puppies were weaned because of the severity of the dam’s condition and the concern regarding the increased energy requirements associated with nursing. The puppies were hand-reared, but, unfortunately, all puppies died between 1 and 2 weeks of age.

Discussion

This case report describes uterine rupture in a large-breed bitch in which manual whelping was physically possible. This method was chosen with drug therapy rather than a surgical approach when the dog failed to whelp naturally. The oxytocin therapy or the manual method could have ultimately been responsible for uterine rupture or a combination of the two.

Oxytocin is a hypothalamic nonapeptide that is stored in the posterior pituitary after production in the supraoptic and paraventricular nuclei of the hypothalamus. Secretion of oxytocin is stimulated by vaginal and cervical stretch. Oxytocin acts to increase sodium permeability in the uterine myofibrils, resulting in uterine contraction. The threshold for contraction is reduced as pregnancy progresses because of the increased number of oxytocin receptors in the myometrium. Oxytocin also facilitates milk ejection. When administered IM, oxytocin induces uterine contraction within 3 to 5 minutes and has a 20-minute duration of action. Oxytocin is rapidly metabolized by the liver and kidneys via the circulating enzyme, oxytocinase.¹²

When used at recommended doses, oxytocin rarely causes significant adverse reactions. Most adverse effects have been reported when the drug is used at excessive doses or when used inappropriately, as in cases of birth canal obstruction.¹² Repeated bolus doses of oxytocin have been reported to cause uterine cramping and discomfort.¹² Overdosage is said to lead to hypertonic or tetanic contractions, which can lead to “tumultuous labor,” uterine rupture, and fetal injury or death.¹² The recommended dose in dogs varies from 1 to 5 IU to 3 to 20 IU IM at intervals no more frequent than 30 minutes. If no progress in whelping is noted after three doses, then a cesarean section should be performed.^12–15 A recent review has suggested that much lower doses of oxytocin (0.5 to 2 IU) could be used with equal effect.¹⁵

Based on the recommended doses described,^12–15 the dog of this report did not receive an overdose, as 7 to 10 IU oxytocin was administered IM at frequencies of not <1 hour. Progress was noted after oxytocin administration, with one to two puppies delivered per dose until the delivery of the ninth puppy. After this, only one further dose of oxytocin was administered, and subsequent puppies (the final three) were manually delivered.

Uterine rupture in women has been extensively studied. Most cases of uterine rupture reported in developed countries result from rupture of a previous cesarean section scar during a subsequent labor. In developing countries, uterine rupture is most commonly reported in obstructed labor, multiple gestations, high parity, and abnormal fetal position that is not detected and treated.^16,17 The role of oxytocin has been debated as a potential risk factor for uterine rupture in humans.¹⁸ A recent meta-analysis evaluating the risk factors for uterine rupture in women who have had a previous cesarean section found insufficient evidence to make a reliable estimate of the risk of uterine rupture when oxytocin is used during labor.¹⁸ Two case-control studies identified a two- to fourfold increase in the risk of rupture;^19,20 however, prospective cohort studies have not corroborated these results.^21–25 No studies have evaluated oxytocin use and risk of uterine rupture in women without histories of previous cesarean section. Nonetheless, extrapolation of findings in humans to dogs is of limited use given the differences in anatomy, etiology (no previous uterine scar tissue), and dose and route of oxytocin administration.

Although “inappropriate obstetrical technique” is suggested as a potential cause of canine uterine rupture in textbooks, no cases of manual intervention during whelping associated with uterine rupture in dogs have been reported in the veterinary literature.

Anecdotal reports suggest manual intervention, particularly with the use of whelping forceps, as a cause of canine uterine rupture. Forceps were not used in this case. In most dogs, manual intervention is not possible because of size constraints. Manually assisting the delivery of larger veterinary species (such as sheep, cows, and horses) is commonplace. In these larger species, poor obstetrical technique can lead to uterine rupture.³ Manual intervention is suspected to be at least a contributing factor, if not the cause, of uterine rupture in the case described herein (particularly given the location of the ruptures that correspond well with the level of manual intervention reported by the referring clinician). The rapid onset of clinical signs following parturition is consistent with reports of uterine rupture in other species and other reported cases in dogs.^3,4,26

Open peritoneal drainage was used in this case because of the presence of septic inflammation and gross peritonitis. Management of open peritoneal drainage cases can be challenging, particularly in giant-breed dogs. Complications commonly encountered include hypoalbuminemia, persistent fluid loss, weight loss, adhesions of viscera to the bandage, and contamination of the peritoneal cavity with cutaneous organisms. Nonetheless, open peritoneal drainage has been suggested to improve the animal’s metabolic condition by facilitating drainage, decreasing the risk of adhesion formation, and by allowing access for repeated exploration and inspection of the abdomen.²⁷

Conclusion

This report is a novel presentation of canine uterine rupture and septic peritonitis suspected to have resulted from manual intervention during parturition. The role of oxytocin in uterine rupture remains unknown. Although digital manipulation of the fetus in the vagina and vulva can be used successfully to manage dystocia secondary to fetal obstruction of the birth canal,^14,15 we recommend against manual evacuation of the puppies from the uterus in cases of suspected primary uterine inertia. Instead, surgical intervention should be considered. This report illustrates the importance of recognizing early signs of obstetrical-related complications in ensuring a successful outcome for the bitch and the puppies.