Anesthesia Considerations & Techniques for Caesarian Section
World Small Animal Veterinary Association World Congress Proceedings, 2015
S. Robertson, BVMS (hons), PhD, DACVAA, DECVAA, DACAW, DECAWBM (WSEL), Specialist in Welfare Science, Ethics and Law, MRCVS
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA

Caesarean sections (C-sections) are performed for many reasons and may be an elective or emergency procedure. The outcome for both the dam and the offspring should be positive if you are well prepared, understand the physiologic changes related to pregnancy and their impact on anesthetic management, and have a neonatal resuscitation protocol in place. A successful C-section is a team effort and should be a rewarding experience rather than a stressful ordeal. Mortality rates for dams and offspring have decreased over the years due partly to improved anesthetic management and the introduction of new anesthetic agents.

Physiologic Changes During Pregnancy

The physiologic changes that occur during pregnancy are well documented in humans1 and these changes are assumed to occur in dogs and cats but not are documented.

Hematologic system: In women red cell production increases but does not match the increase in plasma volume resulting in "anemia of pregnancy."1 Similar changes have been documented in dogs.2 The mean packed cell volume (PCV) in Labrador Retrievers fell from 0.50 L/L in week one of gestation to 0.38 L/L at week eight and the magnitude of the changes correlated with the number of puppies. The clinical significance of this is that if the PCV is normal at term the dam may be dehydrated and should be further assessed.

Cardiovascular system: Up to 25% of the cardiac output (CO) during pregnancy goes to the uterus and placenta. CO increases by 30–50% in response to increased blood volume and decreased afterload and is achieved by an increase in heart rate and stroke volume. There is a hormone mediated decrease in peripheral vascular resistance but the mean arterial pressure is usually well maintained. Probst and others3 reported no differences in blood pressure under general anesthesia in Golden Retrievers at term compared to post-weaning, but did report lower systolic blood pressures in small to medium sized (9–16 kg) bitches at term. In women, the supine position results in compression of the vena cava and aorta by the gravid uterus and a significant drop in cardiac output and blood flow to the uterus.1

In Beagles and Golden Retrievers undergoing C-section no differences in blood pressure were reported between lateral, a 10 or 15 degree lateral tilt or dorsal recumbency.3,4 The gravid horns of the bitch's uterus likely lie on either side of the major vessels during surgery, but it should not be assumed that supine hypotension cannot occur in giant breeds or when a large number and/or oversized fetuses are present.

Respiratory system: Metabolic rate and oxygen consumption increase during pregnancy requiring an increase in minute ventilation. A decrease in functional residual capacity (FRC) occurs in women due to increased abdominal mass and pressure pushing on the diaphragm and similar changes likely occur in dogs and cats. This decrease in FRC in the face of increased metabolic rate and oxygen demand increases the risks of hypoxemia.

Gastrointestinal system: The expanding uterus displaces the stomach and intestines and combined with hormonal changes results in delayed gastric emptying and increased gastrointestinal transit times. Although most bitches and queens usually stop eating before going into labor, the stomach may not be empty at the time of surgery. Aspiration pneumonitis is well documented in women and preventative measures include administration of antacids, H2 antagonists and anesthetic techniques that allow rapid control of the airway. Moon and colleagues reported pneumonia as a cause of death in bitches.5

Brachycephalic dog breeds have the highest C-section rate.6

Pedigree cats have a higher prevalence than mixed breeds, with conformation (dolicocephalic and brachycephalic) increasing the likelihood of a C-section. Historically a wide range of maternal death rates have been reported but recent data suggests a zero mortality rate is possible.10 Survival rates in offspring have increased over the years and are higher if the C-section is planned and the dam is not a brachycephalic breed.

Anesthetic Management

A checklist is recommended so that all goals, concerns and plans are communicated in advance. As with all surgery patients a thorough history, physical examination and appropriate blood work are required.

Drugs that cross the blood brain barrier cross the placental barrier; therefore, all perioperative drugs can affect the neonate. The need for premedication will depend on the status and temperament of the dam. Alpha-2 adrenergic agonists should be avoided unless dealing with feral or fractious animals. A C-section is a major surgery and analgesia is required. The advantage of administering opioids prior to, or at, induction of anesthesia is that they will reduce the requirements for induction and inhalant agents resulting in greater hemodynamic stability. In many cases they may be withheld until after delivery of the offspring but should be given prior to recovery. Infiltration of local anesthetics prior to incision and at closure is easily and quickly performed. Non-steroidal anti-inflammatory agents can be used in stable patients, but should not be used in dehydrated or hypotensive animals.

Preoxygenation (for 3 minutes by face mask) prior to induction is recommended. Mask induction with an inhalant agent should be avoided as this is associated with greater mortality and increases the risk of aspiration. With good planning, puppies and kittens will be delivered within 5 to 15 minutes after induction of anesthesia; therefore, it is important to know the impact of injectable anesthetic agents on the offspring. Ketamine has been linked to neurologic depression in puppies and should be avoided.7

Propofol has been widely used and associated with better neurologic scores in puppies when compared to the use of thiopentone.7

More recently, alfaxalone has been compared with propofol as an induction agent in dogs undergoing C-section.8,9 Compared to propofol Apgar scores were higher at 5, 15 and 60 minutes after delivery in puppies whose dams received alfaxalone. Based on the available evidence alfaxalone is the agent of choice in bitches and although there is no published data for cats, it is also recommended for feline C-sections.

Epidural administration of a local anesthetic agent alone provides sufficient analgesia to perform a C-section but does not guarantee that the patient will be unresponsive to pressure, traction or manipulation. Drawbacks to this technique including technical challenges especially in overweight animals, residual motor deficits following the procedure, hypotension and the need to induce general anesthesia if the patient becomes restless. Another concern is that the airway is unprotected in patients that are at high risk for aspiration due to positioning, their conformation (brachycephalic breeds) and the physiologic changes related to pregnancy.

Depth of anesthesia should be closely monitored. A pulse oximeter provides continuous information on pulse rate and oxygenation status. It is important not to over-ventilate a pregnant patient as hypocapnia reduces placental blood flow, therefore access to a capnograph is ideal. Maintaining normal body temperature of the dam should be a high priority. Hypothermia increases bleeding, delays recovery and results in shivering, increased oxygen demand and discomfort. Criteria for discharge will differ between individual cases but the aim should be to discharge the dam and offspring as soon as possible so they can return to their home environment.

References

1.  Tan EK, Tan EL. Alterations in physiology and anatomy during pregnancy. Best Pract Res Clin Obstet Gynaecol. 2013;27(6):791–802.

2.  Allard RL, Carlos AD, Faltin EC. Canine hematologic changes during gestation and lactation. Compan Anim Pract. 1989;19:3–6.

3.  Probst CW, Broadstone RV, Evans AT. Postural influence on systemic blood pressure in large full-term pregnant bitches during general anesthesia. Vet Surg. 1987;16(6):471–473.

4.  Probst CW, Webb AI. Postural influence on systemic blood pressure, gas exchange, and acid/base status in the term-pregnant bitch during general anesthesia. Am J Vet Res. 1983;44(10):1963–1965.

5.  Moon PF, Erb HN, Ludders JW, Gleed RD, Pascoe PJ. Perioperative management and mortality rates of dogs undergoing cesarean section in the United States and Canada. J Am Vet Med Assoc. 1998;213(3):365–369.

6.  Evans KM, Adams VJ. Proportion of litters of purebred dogs born by caesarean section. J Small Anim Pract. 2010;51(2):113–118.

7.  Luna SP, Cassu RN, Castro GB, Teixeira Neto FJ, Silva Junior JR, Lopes MD. Effects of four anaesthetic protocols on the neurological and cardiorespiratory variables of puppies born by caesarean section. Vet Rec. 2004;154(13):387–389.

8.  Doebeli A, Michel E, Bettschart R, Hartnack S, Reichler IM. Apgar score after induction of anesthesia for canine cesarean section with alfaxalone versus propofol. Theriogenology. 2013;80(8):850–854.

9.  Metcalfe S, Hulands-Nave A, Bell M, Kidd C, Pasloske K, O'Hagan B, Perkins N, Whittem T. Multicentre, randomised clinical trial evaluating the efficacy and safety of alfaxalone administered to bitches for induction of anaesthesia prior to caesarean section. Aust Vet J. 2014;92(9):333–338.

10. Lever W, Ayres S. A retrospective study on the effect of anaesthetic protocol during caesarean section on bitch survival and puppy morbidity and mortality from 1999–2009. In: Proceedings from the Association of Veterinary Anaesthetists Spring Meeting; April 23–26, 2014; Nottingham, UK.

  

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Sheilah Robertson, BVMS (Hons), PhD, DACVAA, DECVAA, DACAW, DECAWBM (WSEL), MRCVS
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
Michigan State University
East Lansing, MI, USA


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