Anaesthesia for Caesarian Section: An Evidenced Based Approach to Choosing Drugs
Professor, Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Argentina
Anesthesia goals for cesarean section should be focus in:
1. Deliver viable puppies with the least amount of depression.
2. Keep the mother as awake as possible with the least amount of depression.
3. Return the mother and the youngsters to their own environment as soon as possible.
Preoperative tests depend in part on the age and general condition of the patient.
With regards to blood work, at a minimum, PVC, TP and blood glucose should be measured.
In older or sick animals it may be necessary to perform a more complete approach that depends on the overall health of the patient at the time of anesthesia.
Twice of the blood loss may occur with a cesarean section as with normal parturition resulting in blood volume loss and hypotension.
All preanesthetic and anesthetic drugs cross the placenta to some degree and therefore can affect the newborn. The drugs used in anesthesia are highly lipid-soluble and of small molecular size and, therefore, readily cross the placenta.
Drug that are highly protein-bound do not cross the placenta as rapidly.
Neuromuscular blocking agents are about the only drugs that may be used in anesthesia that do not cross the placenta.
Analgesic agents, alone or in combination with sedative, should be use to avoid pain and to reduce the stress. A good combination with a very small impact over the newborn is tramadol (2 mg/kg) plus acepromazine (0.01 mg/kg) by intravenous route.
Atropine can be used to prevent an excess of vagal tone during the uterus manipulation. Fetal cardiac output is dependent on fetal heart rate, and it is mandatory to prevent bradycardia by administering an anticholinergic. Atropine crosses the placenta and increase fetal HR, glycopyrrolate does not.
Fluids via an intravenous catheter should be administered overall in dehydrated patients.
The preanesthetic use of metoclopramide and cimetidine may be indicated to treat nausea or increases the gastric pH.
Propofol is the agent of choice because of rapid clearance, minimal hepatic metabolism, and minimal cardiac depression. Propofol must be administered tapering its dosage with a very slow rate, not less than 5 minutes.
Important: If local anesthesia is used; propofol should be titrated to promote sedation instead of anesthesia (Propofol 1-2 mg/kg very slowly).
In animal with air way obstruction or brachycephalic patients (e.g., Bull Dogs) an endotracheal tube must be used. Generally a topical administration of lidocaine over the larynx is enough to perform the intubation maneuvers. If necessary, 1 mg/kg of propofol can be used. To improve oxygenation laryngeal mask or a simple face mask can be used.
Epidural anesthesia is the best option because of the small depression in the newborn. This technique is the election when the puppies are compromised or in those cases in which the mother is exhausted. To perform a c-section with an epidural anesthesia, a level up to T5 is needed. To achieve the optimal cephalic migration, 0.1 mL per each centimeter of occipito-coccygeal length should be used. With a small volume, you'll achieve an incomplete blockade and, if the animal is merely sedated, the procedure shall promote vomit, discomfort and, probably, pain. For technical details see lecture "Epidural anesthesia and analgesia. Clinical technique and surgical applications", in this proceeding.
All inhalant agents cross the placenta. The most rapidly acting agents are preferable. Isoflurane and sevoflurane are preferred over halothane. A good practice can be to maintain the alveolar concentration of volatile in a 70% of the MAC concentration (Isoflurane: 0.8 vol%; sevoflurane: 1.6 vol%) during the "delivery" and increase the alveolar concentration, if necessary, at the synthesis time.
This protocol can be dangerous when the newborn have breathing and hemodynamic compromise because, although the volatile are not metabolized, they need the ventilation and the circulatory mechanism to be depurated from the puppy's body. If the muscular relaxation is deficient, because of the anesthesia level, neuromuscular agents (e.g., rocuronium, atracurium) can be used. Those agents do not affect the newborn and its effect disappear very quickly. During the time of action of neuromuscular drugs, patient must be ventilated.
Mostly, the pregnant animals develop atelectasis because of the intraabdominal pressure. There is usually a decreased tidal volume owing to anterior displacement of the abdominal viscera by the gravid uterus. This displacement puts pressure on the diaphragm and prevents maximal expansion of the thoracic cavity. In these patients, mechanical ventilation will improve the gaseous interchange, incrementing the mother blood oxygenation and, therefore, the fetus oxygenation, protecting it from a slow reaction after delivery.
Do not hurry to extract the puppies! If you have sedated the mother with drugs, you should wait until they are metabolized, as, unlike the puppies, the bitches are able to metabolize the anesthetic agents. While the placenta is attached, the fetuses can stay in the uterus without aggravation of its condition. It is a much worse option to count on the metabolic capacity of the newborns.
1. Skarda RT, Tranquilli WJ. Local and regional anesthetic and analgesic technique: dogs. En Lumb & Jones', Veterinary Anesthesia, by JC Thurmon, WJ Tranquilli and GJ Benson, 4a edition, Williams & Wilkins, Waverly Company 2007b; 561-594.
2. Paddleford RR. In Cap. II, Manual of Small Animal Anesthesia, second edition, 1999. W. B. Saunders Company.
3. Otero P. Administración epidural de analgésicos. En Dolor. Evaluación y tratamiento en pequeños animales. Intermédica, Argentina, 2004; 333-353.