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Anesthesia and Analgesia for the Cesarean Section

By Kate Cummings, DVM, DACVAA
angell.org/anesthesia
617-541-5048

 

 

Figure 1 – Successful delivery and survival following emergency C-section

In considering an anesthetic protocol for both emergent and elective cesarean section (C-section), it’s important to first understand maternal physiologic changes associated with pregnancy and fetal physiology considerations. Major body systems affected by pregnancy include the cardiovascular (CV), respiratory, gastrointestinal, and renal systems – all of which are equally important to consider during any anesthetic event. A brief summary of how these systems are impacted during pregnancy and anesthesia are outlined in Table 1. In regards to fetal physiology, it is imperative to know that drugs that cross the blood-brain-barrier also cross the blood-placental-barrier. Enzymes responsible for hepatic metabolism are ineffective until 3-5 weeks of age. Finally, the fetal oxy-hemoglobin dissociation curve is shifted to the left, meaning that there is less unloading of oxygen to tissues.1,2,3

Body
System

Changes During
Pregnancy

Anesthetic
Impact

Cardiovascular
  • Blood volume increases ~40% (with larger increase in plasma volume); thus relative anemia develops
  • Increased cardiac output (CO) due to increased heart rate and stroke volume
  • Right shift of oxy-hemoglobin dissociation curves facilitates oxygen delivery to fetus
  • Increased myocardial work and reduced cardiac reserve – susceptible animals incapable of mounting a significant response to CV stressors
  • Common to battle hypotension with patients in dorsal recumbency as venous return is compromised by pressure of large uterus on vena cava
  • Following removal of the uterus, abdominal vessels may vasodilate, leading to systemic hypotension
  • Judicious use of IV fluids recommended unless patient at risk for developing CHF +/- use of vasopressors
  • Animals with pre-existing myocardial dysfunction may decompensate and develop heart failure
Respiratory
  • Oxygen consumption increases by ~20% (due to developing fetus, placenta, uterine muscle, and mammary tissue)
  • Functional residual capacity (FRC) and total lung capacity reduced
  • Increased tidal volume and respiratory rate result in increased minute ventilation
  • Patients predisposed to hypoxemia – pre-oxygenation IMPERATIVE
  • Increase in alveolar ventilation and reduced FRC results in reduced MAC requirements
  • Reduced PaCO2, generally in the range of 30-33 mmHg
Gastrointestinal
  • Positioning of uterus and increased progesterone result in reduced gastric emptying and reduced gastric motility
  • Increased risk of regurgitation and aspiration
  • Higher percentage of brachycephalic breeds requiring C-section adds to this risk
  • Rapid sequence induction and intubation to quickly protect the airway
  • Consider use of metoclopramide and/or an H2-receptor antagonist
Renal
  • Renal blood flow and GFR increased
  • Patients often have low or low normal BUN and creatinine
  • Elevated renal values may indicate dehydration or underlying kidney disease
  • Pre-surgical fluid resuscitation and adjusted fluid therapy/use of vasopressors during anesthesia necessary to maintain kidney perfusion

  Table 1 – Maternal physiologic changes and their anesthetic impact1,2,3

An ideal protocol for C-section patients provides adequate analgesia to the mother, optimal operating conditions, rapid recovery, and minimal fetal depression (Table 2). It is important to note that maternal and puppy or kitten mortality increases with emergent vs. planned C-section.4,5 Fetal and neonatal mortality can be minimized by avoiding placental hypoperfusion and hypoxemia and providing proper neonatal care upon delivery.6,7,8 Prior to anesthesia, the mother should have a full physical exam, thorough history taking, and a minimum database of bloodwork (e.g. PCV/TP/Azo/iCa/Glu). In debilitated patients or those with comorbidities, a complete database of lab work should be performed prior to anesthesia. Correction of electrolyte and/or hydration/volume deficits should occur before induction.

Most dystocia patients are easy to handle and calm, allowing for IV catheter placement and initial abdominal clipping and prepping BEFORE administration of anesthetic agents. Preanesthetic medications can and should be avoided unless the patient is overly fractious or unmanageable. If dealing with an aggressive patient, consider short-acting and reversible drugs such as fentanyl and midazolam. Alpha-two adrenergic agonists, particularly xylazine, should be avoided as they have been linked to decreased survival in the neonate.4 All patients should be pre-oxygenated for at least five minutes and induced in the OR when possible. The primary determinant of fetal viability is the time from anesthetic induction to delivery, with a target of < 15 minutes.4,5,6,7,8 Propofol or alfaxalone are induction agents of choice, both short-acting and with similar CV and respiratory effects. Both drugs cross the placenta, but there is rapid clearance and minimal fetal depression. Newer studies have shown improved APGAR scores within the first 60 minutes following delivery in neonates with an alfaxalone induction compared to propofol.9,10 Survival out to three months was similar between groups however, indicating that either induction agent is appropriate.9

Following induction, maintenance can be achieved with isoflurane or sevoflurane, keeping in mind that maternal anesthetic requirements are often reduced due to pregnancy-induced changes. Occasional small boluses of propofol or alfaxalone can be used if patient depth suddenly lightens. Multi-modal analgesia is important and possible in the mother. Prior to surgery, a line block can be performed quickly with either bupivacaine or lidocaine. After delivery (Figure 1), an opioid and chosen intra-op antibiotic can be administered. Inhalants should be adjusted following removal of the puppies/kittens since the opioid effectively reduces anesthetic requirements. Buprenorphine, a partial mu agonist, is recommended as it results in minimal sedation and adequate analgesia. A full mu agonist (e.g. hydromorphone or methadone) can be used as an alternative, but lower doses are recommended to minimize CV and respiratory depression as well as limit the degree of sedation. An epidural can be considered post-operatively with morphine alone or morphine and lidocaine. If an epidural is performed, owners should be made aware of possible urinary retention and hind end weakness (short duration) if lidocaine is used.1,2,3 Finally, a single postoperative dose of an NSAID can be considered in patients with normal blood work and adequate intraoperative blood pressures (MAP > 65 mmHg).

Species

Anesthetic Protocol

Analgesia

 

Dog

  1. Pre-oxygenate, clip, and prep
  2. Propofol (4-6 mg/kg) or alfaxalone (2-3 mg/kg) titrated to effect IV
  3. Maintenance on isoflurane or sevoflurane
  4. Balanced crystalloid IVF at 5-10 mL/kg/hr (adjust if pre-existing heart disease)
  1. Line block with bupivacaine (1 mg/kg) or lidocaine (2 mg/kg)
  2. Buprenorphine (0.01 mg/kg) or hydromorphone (0.05-0.1 mg/kg) IV after removal of puppies
  3. Single dose of carprofen (4.4 mg/kg) or meloxicam (0.1 mg/kg) SC
 

Cat

  1. Same as above
  1. Same as above aside from these changes
  2. Buprenorphine (0.02 mg/kg) IV after removal of kittens
  3. Single dose of meloxicam (0.1 mg/kg) or robenacoxib (2 mg/kg) SC

Table 2 – Elective and emergent C-section protocol suggestions in dogs and cats

Neonatal management and resuscitation begins by having one person dedicated to each neonate when possible. Early and frequent rubbing to dry helps stimulate respiration and keep the neonates warm. A bulb syringe can be used to suction oral and airway secretions. Swinging the neonate is NOT recommended as this has been shown to result in cerebral hemorrhage.1,2,3,6,7,8 Neonates that are thriving can be placed in an incubator for heat support until the mother recovers. In neonates that may be struggling, ventilation is key as it 1) allows for elimination of gas anesthetics and 2) aids in increasing HR as bradycardia is caused by hypoxia.6,7,8 Attempts can be made to stimulate ventilation by activating the acupuncture point, GV26, with a small gauge needle inserted into the nasal philtrum. Oxygen supplementation can be provided via mask or intubation. The most common arrest rhythm for neonates is asystole and should be treated with basic life support measures, including epinephrine +/- atropine. Consider sublingual use of reversal agents (e.g. flumazenil, naloxone) if benzodiazepines or opioids were used prior to fetal delivery.

 

References

  1. Lumb and Jones’ Veterinary Anesthesia and Analgesia, 5th Grimm KA, Lamont LA, Tranquilli WJ, Greene SA, and Robertson SA. Wiley Blackwell; 2015.
  2. Small Animal Anesthesia and Analgesia. Carroll GA. Ames: Blackwell; 2008.
  3. Canine and Feline Anesthesia and Co-Existing Disease. Snyder LBC and Johnson RA. Wiley Blackwell; 2015.
  4. Perioperative risk factors for puppies delivered by cesarean section in the United States and Canada. Moon PF, Erb HN, and Ludders JW et al. JAAHA 2000, 36:359-368.
  5. Perioperative management and mortality rates of dogs undergoing cesarean section in the United States and Canada. Moon PF, Erb HN, Ludders JW et al. JAVMA 1998, 213(3):365-369.
  6. Resuscitation of canine and feline neonates. Traas AM. Theriogenology 2008, 70(3):343-348.
  7. Neonatal critical care. Moon PF, Massat BJ, and Pascoe PJ. Vet Clin North Am Small Anim Pract 2001, 31:343-367.
  8. Small Animal Neonatal Health. Wilborn RR. Vet Clin: Small Anim Pract 2018, 48(4):683-699.
  9. Apgar scores after induction of anesthesia for canine cesarean section with alfaxalone versus propofol. Doebeli A, Michel E, Bettschart R et al. Theriogenology 2013, 80(8):850-854.
  10. Alfaxalone for total intravenous anaesthesia in bitches undergoing elective caesarean section and its effects on puppies: a randomized clinical trial. Conde Ruiz C, Del Carro AP, Rosset E et al. Vet Anaesth Analg 2016, 43:281-290.
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