Sixty to eighty percent of cases of dystocia in bitches and queens require surgery, the majority of which (60%) on an emergency basis, although in some cases scheduled for the management of an expected case of dystocia. The time and method of performing surgery strongly affect the probability of survival for both the mother and, above all, the foetuses. Numerous surgical and anaesthetic protocols have been reported in literature, but unfortunately there are no randomised prospective studies identifying the best approach. It has, however, been observed that dystocia lasting for more than 4.5-6 hours increases the risk of perinatal mortality (defined as the sum of stillbirths and neonatal deaths).
INDICATIONS
The main risk factors for dystocia include a breed predisposition to uterine inertia, giving birth for the first time after the age of 6 years, the presence of fewer than three or more than eight to 12 foetuses, depending on the breed, a personal past medical history or a maternal family history of dystocia or gestational disorders, structural anomalies of the birth canal, obstructive dystocia, torsion or rupture of the uterus, foetal macrosomia, the presence of malformations or foetal monstrosities, disproportion between foetal parts typical of some breeds, all abnormalities of presentation, position and posture and the detection of foetal stress. A Caesarean section must be performed in all cases in which medical treatment of the dystocia is not possible, or has been ineffective, or when manual obstetric assistance is contraindicated or inefficient.
One of the main indications for performing an emergency Caesarean section is a decrease in the heart rate of foetuses, a sign of hypoxic distress and an indicator of the risk of death of the foetuses. In dogs the normal foetal heart rate is 200-220 beats per minute (bpm); a decrease in heart rate indicates different degrees of hypoxia, which necessitate, with varying urgency, performance of a Caesarean section. When the heart rate is less than 150 bpm, foetal distress is severe and surgery must be performed immediately, when the heart rate is between 150 and 170 bpm, the foetal distress is moderate and the operation can be organized within 2-3 hours and when the heart rate is between 170 and 200 bpm, foetal distress is slight and the operation is required within 12 hours. Ultrasound evaluation of foetal heart rate must take into proper consideration the temporary decreases in heart rate attributable to the effect of uterine contractions. The foetal heart rate should, therefore, be monitored for at least 1 minute and then re-evaluated after 2-3 minutes to make sure that it truly reflects the state of the foetus and not the effect of uterine contractions.
In breeds and subjects at high risk of dystocia a Caesarean section can be scheduled based on the detection of particular clinical signs and on a precise as possible evaluation of the physiological term of the pregnancy. This latter aspect is important in bitches, since the predicted date of delivery depends on the method used to evaluate the duration of the gestation (days since mating, since ovulation or since the luteinizing hormone peak) or the ultrasound measurement of some foetal and extra-foetal structures. An incorrect evaluation of gestational age entails a high risk of foetal prematurity and haemorrhage of areas of placenta (not sufficiently mature) following a Caesarean section performed too early or, on the contrary, the risk of foetal distress and death when the operation is performed late. Traditionally, a scheduled Caesarean section is performed 62-63 days after ovulation, even if this peremptory time limit does not fully comply with the physiological characteristics of pregnancy in dogs. In fact, while gestation can end as early as 62-63 days after ovulation in some dogs, for others this presumed gestational age does not correspond to full foetal maturity. According to some authors, Caesarean sections could be performed more reliably on the basis of evaluation of blood progesterone levels, since the drop in the plasma concentrations of progesterone (<2 ng/ml) indicates the beginning of delivery. In this regard, the monitoring of blood progesterone levels could begin from the 61st day after ovulation, although it would be safer to start this monitoring earlier, measuring progesterone levels from the first finding of a significant lowering of rectal temperature. It is known that a drop in body temperature of around 1°C follows the drop in blood progesterone levels and occurs about 8-24 hours before the start of labour in over 90% of dogs. It should, however, be noted that body temperatures can be very variable at the end of gestation and changes must, therefore, be interpreted correctly.
A protocol has recently been proposed for Caesarean sections scheduled based on the date of ovulation: this protocol was designed in order to plan the Caesarean section before parturition begins, while guaranteeing the maturity of the foetuses. A progesterone antagonist is administered at 60-61 days after ovulation (10-15 mg/kg of aglepristone subcutaneously) in order to mimic the physiological drop in progesterone at the end of pregnancy; this is followed 12 hours after the treatment by the Caesarean section (in this writer’s opinion, it would be a good idea to verify the actual drop in progesterone before performing the operation). This protocol has led to a reduction in the mortality rate in the immediate neonatal period from the 8% reported in the literature to the 0.5% obtained by the authors, the absence of adverse effects, the presence of lactation in 90% of the cases and subsequent normal fertility. The only negative aspect worth noting is the greater tendency to bleeding following removal of the placentas, which consequently must be done very carefully. The possible use of ultrasound prediction of the date of delivery combined with evaluation of blood progesterone levels could provide a more precise method for determining the best time to perform a Caesarean section.
PREPARATION
In the case of an emergency Caesarean section the patient must be first stabilised (Fig. 1), with the correction of possible states of dehydration, electrolyte, biochemical or haematological alterations and, in the more severe cases, shock. In addition, in emergency cases, the patient often has not fasted and this increases the risk of regurgitation, bronchoaspiration and possible aspiration pneumonia. When the Caesarean section is performed in the course of an already advanced delivery, the females might have ingested placentas, and this will have to be taken into account during induction and tracheal intubation. In scheduled Caesarean sections, a pre-operative fasting period of 4-8 hours is prescribed, depending on the animal's size.
ANAESTHESIA AND ANALGESIA
The choice of the anaesthesiological protocol must take into account the particular requirements of a Caesarean section, which are a short induction time, brief interval between induction and removal of the foetuses, maintenance of adequate uterine blood flow, minimum depressant effect on the foetuses and possibility of counteracting the effect of the anaesthetics in the neonates. Prolonged induction leads to foetal hypoxia and depression. In addition, it should be considered that, in advanced gestation, gravid animals may exhibit physiological peculiarities that can affect the anaesthesia. These physiological peculiarities include increased maternal blood volume and cardiac output, reduced vascular resistance, residual capacity and expiratory reserve volume and increased inspiratory capacity, inspiratory reserve capacity, respiratory frequency, tidal volume, minute volume and alveolar ventilation. It should be noted that there is no ideal anaesthesiological protocol for either the mother or the foetuses.
When possible, premedication must be avoided or performed with short-acting opioids, which guarantee good maternal analgesia with minimal depressant effects on the foetuses (moreover controllable with opioid antagonists such as naloxone) while, for the post-operative analgesia, long-acting opioids can be administered to the puerpera, although it should be kept in mind that these drugs pass into the milk at concentrations very similar to those in the maternal blood, albeit with very limited effects on the neonates. The use of phenothiazines, such as acepromazine, should be avoided, because they are long-acting; the same holds true for diazepam, whose effects on foetuses have not yet been fully investigated. α2-agonists could be used for sedative purposes, also given the possibility of antagonising their effect both in the neonates, but their vasoconstrictive activity can be counterproductive. To prevent the risk of regurgitation, prokinetic antiemetics (metoclopramide) are useful before the induction. After shaving the animal and surgical preparation of the operating field, pre-operative oxygenation of the patient is advisable, as long as it does not cause hyperarousal (a quite frequent occurrence). The absence of premedication and the physiological peculiarities of the pregnant animal make anaesthesia management difficult, in view of its instability.
The drug of choice for the induction of anaesthesia when performing a Caesarean section is propofol. Indeed, in spite of the fact that it crosses the placenta and the limited metabolic capacities of foetuses/neonates, propofol guarantees a rapid and short induction without causing marked foetal/neonatal depression; repeated administrations of propofol are contraindicated for maintaining anaesthesia. Anaesthetic gases cross the placental barrier and can cause foetal respiratory depression, with the neonates developing prolonged states of apnoea which require neonatal assistance. The recommendation is, therefore, to administer oxygen alone until complete removal of the foetuses and then supply inhalation anaesthetics (isoflurane and sevoflurane) until the end of the surgical operation.
Before separation of the tissues a linear anaesthetic block may be useful, with subcutaneous and intramuscular infusions (2-5 mg/kg of lidocaine) in the area adjacent to the incision line; this block is in addition to general anaesthesia and makes it possible to maintain the anaesthetic plan with lower percentages of inhalation anaesthetics and to control postoperative pain (bupivacaine). Epidural anaesthesia (lumbosacral) (Fig. 2) on its own is rarely sufficient for performing surgery. Opioids are more indicated than local anaesthetics, because they can induce analgesia without blocking mobility and without causing hypovolaemia, thus aiding prompt motor recovery of the puerpera after surgery.
Post-operative sedation of the female should be avoided, in order not to interfere with normal maternal behaviour; sedation, in fact, could lead to dysphoria, confusion, clumsiness and altered maternal behaviour for more than 24 hours.
SURGICAL TECHNIQUES
First of all it is necessary to evaluate the possibility of performing a conservative or non-conservative Caesarean section with a concomitant ovariohysterectomy. The choice depends primarily on the condition of the uterus, but also on whether or not the owner wishes to maintain the animal’s reproductive capability.
In both cases, a coeliotomy (more rarely through flank laparotomy), with an incision that extends from the navel to the pubis, allows the gravid uterus to be visualised and externalised (Fig. 3). Hysterectomy techniques may vary, depending on different factors (presence of foetuses in just one horn or in both), but must always allow rapid removal of the foetuses (Figs. 4 and 5), with the fewest number of incisions, and limit the risk of injuries to the foetuses and placental or uterine lacerations. Once the incision has been made, the foetuses are gently pushed outside the uterine opening by “squeezing”, which also helps detachment of the placenta. When the placenta is firmly anchored to the endometrium and its removal could cause excessive bleeding, some authors suggest leaving it in place until it is expelled spontaneously (as long as the cervix is patent when the Caesarean section is performed) in conservative operations and, in the case of non-conservative Caesarean section, until it is removed together with the uterus. In conservative Caesarean sections, before suturing the uterus it is a good rule to make sure that it has been completely emptied, checking that there are no small mummified or macerated foetuses.
The uterine wall is reconstructed with a simple continuous suture, followed by an inverting suture (Cushing or Lembert) with USP 4-0/EP 1.5 or USP 3-0/EP 2 absorbable suture material. Burying the knots limits the peritoneal exposure of material, which could lead to the formation of adhesions. At completion of the suturing, intraparietal administration of oxytocin promotes the involution of the uterus, limits bleeding and aids the expulsion of any residual placentas.
In non-conservative Caesarean section, once the foetuses and their placentas have been removed, an ovariohysterectomy is performed following normal surgical practice (Fig. 6).
In both types of operations peritoneal lavage can be useful to remove fluids and tissue debris before reconstructing the abdominal wall, which is performed in accordance with surgical dictates and recalling that during a Caesarean section the linea alba is very thin because of the effect of relaxin and intra-abdominal pressure. Intradermal cutaneous sutures are useful, as the absence of external knots aids the prehension of nipples, facilitates the feeding of the neonates and limits the licking of the wound by the puerpera. It should be noted that ovariohysterectomy does not impair lactation, which depends on the production of oxytocin and prolactin and not on ovarian hormones. A reduced production of milk can instead be the effect of low blood pressure during the surgical operation or of inadequate post-operative analgesia, which delays water and food intake and hinders suckling by the neonates.
Suggested readings
- Levy X (2011) Cesareo - Cesareo programmato in razze a rischio (brachicefali, razze nane e toy) - Cesareo d’urgenza -Quale anestesia nel parto (programmato e d’urgenza)? - Quale anestesia per i cuccioli? Atti 68 Congresso SCIVAC, 14th EVSSAR Congress - Advances in Feline Reproduction - Milano 11-13 Marzo 2011.
- Evans KM, Adams VJ (2010) Proportion of litters of purebred dogs born by caesarean section. J Small Anim Pract, 51: 113-118.
- Traas AM (2008) Surgical management of canine and feline dystocia. Theriogenology, 70: 337-342.
- Hedlund CS (2004) Chirurgia dell’apparato genitale e riproduttore. Taglio cesareo. In: Fossum TW Chirurgia dei piccoli animali. Masson/Ev, Milano, Cremona 2nd ed.: 607-610.
- JohnstonSD, Root Kustritz MV, Olson PNS (2001) Canine parturition – eutocia and dystocia. In: Canine and Feline Theriogenology. WB Saunders, 3rd ed Philadelphia: 105-128.
- JohnstonSD, Root Kustritz MV, Olson PNS (2001) Feline parturition. In: Canine and Feline Theriogenology. WB Saunders, 3rd ed Philadelphia: 431-437.
- Moon PF, Erb HN, Ludders JW, Gleed RD, Pascoe PJ (1998) Perioperative management and mortality rates of dogs undergoing cesarean section in the United States and Canada. J Am Vet Med Assoc, 213: 365-369.