Notes supplied by Nadja Sigrist, DrMedVet, FVH(Small Animals), DACVECC.

Introduction

Dystocia is defined as the inability of the dam to expel the fetus without assistance through the birth canal. Knowledge of normal physiology, a thorough history and clinical examination, and appropriate medical or surgical treatment based on the findings are mandatory for a good outcome in both dam and offspring.

Physiology of Normal Parturition

In bitches, normal gestation length is 63 +/- 7 days from the first breeding, 65 +/- 1 day from luteinising hormone (LH) peak or 57 +/- 3 days from first day of dioestrus.

Predictors of labour are a measured drop in progesterone, temperature drop of 1–1.7°C, 6–18 hours prior, mammary development with onset of lactation, vulvar enlargement, mucous vaginal discharge, decrease in appetite and nervousness. The three stages of labour can be seen for each fetus born: cervical dilation (6–12 hours), delivery of the fetus (2–6 hours) and placental passage (5–15 minutes).

Aetiology

Dystocia may be caused by maternal or fetal factors and/or ineffective uterine contractions. Maternal factors may be metabolic (hypoglycaemia, weakness, etc.) or anatomical (narrow birth canal, old pelvic fractures). Oversized puppies are the most common fetal causes but malformations, malpresentations and dead fetuses may also cause dystocia. Primary uterine inertia (complete or partial) and uterine fatigue leading to secondary uterine inertia are causes of ineffective uterine contractions.

History, Clinical Examination and Diagnostic Approach

A thorough history should be collected. The clinical examination includes a general examination as well as an obstetric examination, including digital vaginal exploration and vaginoscopy (sterile). 'Feathering' of the dorsal vaginal wall should trigger straining if the dam is in labour and excludes uterine inertia as a cause of dystocia. If the cause of dystocia cannot be determined by palpation, diagnostic imaging provides further information. Both lateral and dorsoventral (or ventrodorsal) abdominal radiographs should be taken and will give information regarding the number of fetuses, the developmental stage, abnormal presentations, position or posture and fetomaternal proportion. To determine fetal viability, fetal heart rate can be evaluated ultrasonographically. Blood samples should be evaluated for anaemia, hypoproteinaemia, hypoglycaemia and hypocalcaemia among other parameters necessary based on the history of the patient.

Indicators

Knowledge of normal gestation and parturition is essential for the identification of problems associated with birth. Indicators of dystocia are:

 Illness in the full-term female (fever, seizures, vomiting, shock, etc.)

 More than 68 days from day of last breeding in the bitch

 > 24–36 hours since temperature drop with no signs of impending parturition

 > 30 minutes of persistent abdominal straining (stage II) without delivery of a puppy

 > 2–4 hours of intermittent abdominal straining (stage II) before first neonate

 > 1 hour of active labour between birth

 Constant unrelenting unproductive straining

 Palpation of a stuck puppy in the birth canal

 Abnormal vaginal discharge: haemorrhagic, foul smelling, green (before delivery of first puppy)

 Labour seems to have stopped before entire litter is delivered

 Known anatomical predisposition

Management of Dystocia

Depending on the underlying cause, dystocia is treated medically or surgically. If no 'true' dystocia is present, time and rest will enable normal parturition. In other cases, obstetrical manoeuvres or medical treatment is possible, but 60–80% of cases will require surgical intervention.

Medical Treatment

Medical treatment includes correction of underlying medical problems of the mother (hypocalcaemia, hypoglycaemia, shock), oxytocin administration and calcium gluconate. Most patients also benefit from fluid therapy with lactated Ringer's solution (10 ml/kg/hr) with glucose added in small breeds.

Medical treatment should only be considered if the dam and offspring are in good general condition (fetal heart rate > 180 bpm) and if the birth canal is fully dilated (including the cervix) and fetal malpositioning, fetal oversize and birth canal obstruction can definitely be ruled out. Otherwise, there is a risk of uterine rupture with administration of oxytocin.

Oxytocin may be tried with secondary uterine inertia, dead fetuses or primary uterine inertia (often unresponsive). Pretreatment with glucose and/or calcium and a tocolytic agent may be considered. Oxytocin (1–2 IU/kg, do not exceed 20 IU/animal) is administered intramuscularly 20 minutes later. Some authors describe concurrent instillation of warm fluid (volume should not exceed estimated volume of one fetus) into the uterus using a soft rubber catheter. If effective, oxytocin can be given every 30 minutes until all fetuses are delivered. If no contractions can be seen, the dose (care maximum dose) can be repeated once after 45 minutes. If two applications are not effective, Caesarean section should be initiated. Oxytocin may lead to uterine spasm, increasing hypoxia in the already stressed fetuses.

Caesarean Section

Surgical intervention is mandatory if relative or absolute fetal oversize, uterine torsion or rupture, or obstruction of the birth canal is present, and also if medical therapy fails. It may be the safer approach in primary and secondary uterine inertia, maternal or fetal illness/stress and a previous history of dystocia.

Anaesthesia of the dam should be as short and as superficial as possible. Preoxygenation of the mother will reduce hypoxia in the newborn. The anaesthetic protocol should include both analgesics and anaesthetics, medications should be antagonisable (mu-agonists, benzodiazepines), or have a short half-life (propofol, isoflurane), and have no or little influence on the circulation.

Prior to surgery, it has to be decided whether or not ovariohysterectomy of the dam will be carried out. Caesarean section is performed through the linea alba. The abdominal incision should be large enough to ensure good visibility. With ovariohysterectomy, the uterus may be resected en bloc. Otherwise, the uterus is incised at the uterine bifurcation and one fetus after the other is delivered. Good preparation, knowledge of the anatomy, enough assistants and a fast but confident delivery of the fetuses are keypoints. For a detailed description of the surgical approach please refer to a surgical textbook.

Postoperative analgesia is best accomplished with buprenorphine (0.01 mg/kg q8h) as buprenorphine is not readily released into the milk. Maintenance fluid therapy is indicated until the dam voluntarily eats and drinks.