Part two of this series will cover when medical management is suitable or when surgical intervention is required.
To start with, a few things indicate an immediate caesarean section is required:
Generally, successful medical therapy is dependent on positive feathering response.
If strong contractions are occurring, oxytocin therapy can be trialled. Dosed at 0.5IU to 2IU IM or SC, this can be repeated up to three times per neonate. Oxytocin can result in decreased placental blood flow or premature placental separation, leading to fetal hypoxia, bradycardia, or death.
Repeated doses against a fetal obstruction can result in uterine rupture. Therefore, this medication is contraindicated if an obstruction is suspected, especially if radiology is not an option.
Administration of 10% calcium gluconate IM or IV can be used in conjunction with oxytocin. It can increase the strength of uterine contractions. Calcium may increase the strength of contractions so much that oxytocin may not be required. It can be repeated as often as every four to six hours to maintain stronger uterine contractions.
It is feasible to start with 10% calcium gluconate at 0.5ml/kg slow IV. If this does not result in an increase in contraction strength, oxytocin therapy can be used, as described above, and repeated up to 3 times, 30 minutes apart. If no fetuses are passed, this is an indication for caesarean.
Early recognition of dystocia can help improve the survival of fetuses, whether that is from educating owners so they know the warning signs, or veterinary staff training so they can confidently advise owners when to seek veterinary attention.
Understanding the reasoning behind diagnostic methods and the medical management options will empower veterinarians to confidently manage dystocia patients.
Prolonged hypoxaemia, hypotension, and hypoventilation are the top three causes of periparturient fetal mortality; for these reasons, all precautions must be taken to avoid it.
As soon as authorisation has been obtained to proceed with a caesarean section, the patient should be stabilised immediately. This includes having perioperative blood work performed, and clinical hypoperfusion (common in patients that have gone through prolonged stage two labour) and hypotension corrected as soon as possible, usually with fluid boluses.
While fluid deficits are being corrected, preoperative monitoring, and surgical site preparation (clipping and the initial stages of surgical scrub) can be performed with the patient still conscious. This will significantly reduce the time the patient is anaesthetised, as isoflurane potentiates hypotension.
A few physiological changes in periparturient patients must be considered before anaesthetising them.
1. Higher oxygen demand
Firstly, pregnant animals have a higher oxygen demand due to the developing fetuses. However, due to their large gravid uteruses, they have decreased functional residual capacity and total lung volume. This is further exacerbated when animals are placed in dorsal recumbency, with increased pressure on their diaphragms.
For this reason, pregnant animals should always be preoxygenated before induction, with as much of the patient preparation completed to reduce the risk of hypoxaemia. This is one of the main reasons the time from induction to delivery of the puppies should be as short as possible.
2. Sensitivity to anaesthetic agents
Secondly, pregnant animals have an increased sensitivity to anaesthetic agents. Blood volume and cardiac output also increase dramatically during pregnancy; therefore, if blood loss occurs and blood pressure is not maintained, significant hypotension can occur.
Any medication that crosses the blood-brain barrier will equally cross the placental barrier; therefore, the effect of medications can be reduced by a few things. Firstly, the use of local anaesthetics (such as epidurals) can be employed to minimise inhalation anaesthetics, thus their hypotensive effects. Always use minimal drug dosages that achieve the desired effect. Short-acting, rapidly metabolised drugs and reversible drugs should be used whenever possible.
3. Be mindful of your premedication
Recently the recommendation of withholding premedication of caesarean patients has come under questions. One thing that is strictly avoided at our hospital is the use of sedatives such as Acepromazine, which has a long half-life, cannot be reversed and can result in hypotension. The use of opioids prior to removal of foetuses is a contentious point as if used at high doses it can cause potent respiratory depressants in unborn fetuses as it crosses the placenta. Puppies and kittens born heavily narcotised or sedated will have bradycardia and may not take spontaneous breaths, further increasing the risk of mortality. If opioids are used then consider short acting eg. Fentanyl and low doses should be used and use Naloxone as part of the neonate resuscitation.
Once the patient has been induced, the speed of delivering the fetuses is of paramount importance. Inhalant anaesthetics causes maternal vasodilation and decreases uterine blood flow, as well as neonatal depression.
Making a large abdominal incision is highly advised, despite the fact it may take longer to close, as it enables faster and more gentle manipulation of a large fetus-filled uterus.
The traditional caesarean technique involves a single incision in the uterine body. Fetuses should be gently be milked towards the incision. In patients with many fetuses, especially large-breed dogs, making a single uterine body incision may significantly delay delivery of the fetuses. Concern also exists with excessive traction and manipulation of uterine blood vessels when trying to manipulate the fetuses to the uterine body incision. In these cases, additional incisions in the uterine horns can be made.
With this method, surgical time for closure will be longer and considered carefully in patients where future breeding is likely, as the risks of adhesions and uterine rupture in subsequent pregnancies increases compared to the single uterine body incision method.
Closure of the uterine wall should always be in two layers: firstly, an appositional simple continuous pattern; followed by a second inverting (Cushing or Lembert) pattern.
Once the fetuses have been removed, a few medications can be given safely intraoperatively.
If opioids have been withheld, then they can then be safely administered at this point in time. Rapid analgesia can be achieved when the opioid is given IV. Oxytocin can also be administered during this time but beware uterine involution and contraction will be immediate; therefore, close attention needs to be paid to the uterine sutures to ensure they have not become loose.
NSAIDs should be avoided in lactating queens and bitches, as most are excreted in the milk. Safety data has not been established in lactating animals, while previous animal studies have shown an adverse effect on the fetus. Although the administration of a single post-operative dose of an NSAID is frequently recommended on discussion boards.
Tramadol, a synthetic opiate-like (μ receptor) agonist can be used but its analgesic effects have come under scrutiny. Tramadol and its active metabolite are known to enter maternal milk, albeit at very low levels. No animal reproduction studies exist to establish its safety in use in neonates, but it is an analgesic considered safe to use in young animals.
Opioid based options include oral transmucosal buprenorphine, low dose range Fentanyl patches, or codeine could be considered.
Caesarean section is the one emergency surgical procedure where speed is of the essence.
With prompt stabilisation, pre-induction surgical preparation, fast delivery of fetuses, and avoidance of certain medications, the chances of survival of the already distressed fetuses can dramatically increase.