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Anesthetic Protocols & Concerns in Planned & Emergent Cesarean Sections

Stephanie Krein, DVM, DACVAA, Angell Animal Medical Center, Boston, Massachusetts

Anesthesiology & Pain Management

|June 2021|Peer Reviewed

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Anesthetic Protocols & Concerns in Planned & Emergent Cesarean Sections

Designing and implementing safe anesthetic protocols and perioperative plans for both emergent and elective cesarean sections (C-sections) requires an understanding of maternal and fetal physiology and the changes associated with pregnancy. The goals of the anesthetic plan should be to allow the delivery of live and vigorous puppies/kittens, provide appropriate analgesia to the dam/queen, and simultaneously provide a rapid recovery from anesthesia. Prior studies have suggested that the mortality rate of puppies delivered via planned C-section is 6% to 11% and can be as high as 33% during dystocia.1 It is thus paramount that anesthesia time be kept to a minimum and performed as safely as possible.

History

A complete history and physical examination (including cardiovascular status, hydration status, and temperament) should be performed before an anesthetic plan is designed. Diagnostics should include abdominal ultrasonography (to assess fetal heart rate) and blood work, including electrolytes, glucose, total protein, and hematocrit. Blood volume, particularly plasma volume, is increased in pregnant patients; therefore, hematocrit may be overestimated in a dehydrated patient. In dystocia cases, the dam/queen may be in labor for a prolonged period of time, and clinical laboratory abnormalities (eg, hypocalcemia, hypoglycemia, dehydration) may be present and should be corrected prior to anesthesia if possible.2 It is also important to consider that pregnant patients can have delayed gastric emptying and increased intra-abdominal pressure that may lead to regurgitation and subsequent aspiration pneumonia.3 Functional residual capacity is also reduced, and these patients have a higher risk for desaturation, making preoxygenation necessary.

Pathophysiology

Changes in maternal physiology associated with pregnancy and fetal physiology should be thoroughly understood. The major body systems affected by pregnancy are the cardiovascular, respiratory, GI, and renal systems (Table 1). Drugs that cross the blood-brain barrier also cross the blood-placenta barrier and can cause physiologic changes to the fetus.4 The cardiovascular system is underdeveloped in the fetus, and the capability for increased contractility is thus reduced5; therefore, medication that may decrease the heart rate may also decrease cardiac output in the fetus and neonate. In addition, the enzymes responsible for hepatic metabolism are not active until 3 to 5 weeks of age, causing increased duration of action of anesthetic drugs in the fetus and neonate.6,7 Also, because the fetal oxyhemoglobin dissociation curve is shifted to the left, there is less unloading of oxygen to tissues.2,8

TABLE 1

MATERNAL PHYSIOLOGIC CHANGES & ANESTHETIC CONSIDERATIONS4,8

Body System Changes During Pregnancy Anesthetic Considerations
Cardiovascular
  • Blood volume increases ≈40% with larger increase in plasma volume; relative anemia can develop.
  • Cardiac output increases due to increased heart rate and stroke volume.
  • Right shift of oxyhemoglobin dissociation curve facilitates oxygen delivery to the fetus.
  • Myocardial work increases and cardiac reserve is reduced; patients that are very sick or have underlying disease/comorbidities are incapable of mounting a significant response to cardiovascular stressors.
  • Hypotension is common in patients in dorsal recumbency because venous return is compromised by the pressure of a large uterus on the vena cava.
  • Following removal of the uterus, abdominal vessels may dilate, leading to systemic hypotension.
  • Judicious use of IV fluids ± vasopressors is recommended unless there is risk for congestive heart failure.
  • Patients with pre-existing myocardial dysfunction can decompensate and develop heart failure.
Respiratory
  • Oxygen consumption increases by ≈20% due to the developing fetus, placenta, uterine muscle, and mammary tissue.
  • Functional residual capacity and total lung capacity are reduced.
  • Increased tidal volume and respiratory rate result in increased minute ventilation.
  • Patients are predisposed to hypoxemia; preoxygenation is imperative.
  • Increase in alveolar ventilation and reduced functional residual capacity can cause reduced minimum alveolar concentration (MAC) requirements and lead to a more rapid uptake of inhalant anesthetics. Although the mechanism is not fully understood, MAC reduction observed during pregnancy is thought to be influenced by progesterone levels and endorphins.
  • Partial pressure of carbon dioxide is reduced (general range, 30-33 mm Hg; normal range, 35-45 mm Hg).
GI
  • Positioning of the uterus and increased progesterone result in reduced gastric emptying and reduced gastric motility.
  • Risk for regurgitation and aspiration is increased, especially in brachycephalic breeds.
  • Rapid sequence induction and intubation are needed to quickly protect the airway.
  • Metoclopramide (0.2-0.5 mg/kg SC) ± an H2-receptor antagonist or proton pump inhibitor (famotidine, 0.5 mg/kg IV; pantoprazole, 1 mg/kg IV) should be considered.
Renal
  • Renal blood flow and glomerular filtration rate increase.
  • Patients often have low or low–normal BUN and creatinine.
  • Elevated renal values may suggest dehydration or underlying kidney disease.
  • Presurgical IV fluid administration and adjusted fluid therapy/use of vasopressors during anesthesia are necessary to maintain kidney perfusion.

Anesthetic Protocol

The ideal anesthetic protocol for patients requiring C-section provides adequate analgesia, optimal operating room conditions, rapid recovery in the dam/queen, and minimal fetal depression (Table 2). Protocols for emergent and scheduled C-sections may be the same, but maternal and neonatal mortality rates are higher with emergent procedures9; this can be reduced by avoiding placental hypoperfusion and hypoxemia and providing adequate care for the neonate.

Dystocia

Patients with dystocia are typically calm and easy to handle, allowing for IV catheter placement and clipping and prepping of the abdomen while the patient is awake and prior to administration of anesthetics. Preanesthetic medications should be avoided unless the patient cannot be handled or is fractious/aggressive. If premedication is necessary, it should be short-acting, be fully reversible, and provide adequate analgesia to minimize maternal stress and cardiovascular depression.

TABLE 2

ELECTIVE & EMERGENT CESAREAN SECTION PROTOCOL SUGGESTIONS

Species Anesthetic Protocol Analgesia
Dogs
  1. Preoxygenation, clipping, and preparation
  2. Propofol (4-6 mg/kg) or alfaxalone (2-3 mg/kg) IV, titrated to effect
  3. Maintenance on isoflurane or sevoflurane
  4. Balanced crystalloid IV fluids at (5-10 mL/kg/hour; adjust for patients with pre-existing heart disease)
  1. Line block with bupivacaine 0.5% (1 mg/kg) or lidocaine 2% (2 mg/kg)
  2. Buprenorphine (0.01 mg/kg IV) or hydromorphone (0.05-0.1 mg/kg IV) after removal of neonates; if no line block is performed, these agents should be given with premedication.
  3. Single dose of carprofen (4.4 mg/kg SC) or meloxicam (0.1 mg/kg SC)
Cats
  1. Preoxygenation, clipping, and preparation
  2. Propofol (4-6 mg/kg) or alfaxalone (2-3 mg/kg) IV, titrated to effect
  3. Maintenance on isoflurane or sevoflurane
  4. Balanced crystalloid IV fluids at (5-10 mL/kg/hour; adjust for patients with pre-existing heart disease)
  1. Line block with bupivacaine 0.5% (1 mg/kg) or lidocaine 2% (2 mg/kg)
  2. Buprenorphine (0.02 mg/kg IV) after removal of neonates; if no line block is performed, these agents should be given with the premedication.
  3. Single dose of meloxicam (0.1 mg/kg SC) or robenacoxib (2 mg/kg SC)

 

Premedication

Premedication crosses the blood-placenta barrier; thus, the lowest effective dose should be given to minimize the effect on the fetus.

  • Full µ opioids (eg, methadone, morphine, hydromorphone) can be used but may cause bradycardia in the fetus; therefore, naloxone should be readily available for neonatal administration.
  • Fentanyl is a short-acting, full µ-opioid agonist normally administered IV; thus, it may not be good in aggressive or fractious patients that do not have a catheter in place.
  • Midazolam is a fully reversible benzodiazepine that can be added to an opioid to provide sedation in older or debilitated patients. This sedation can be unreliable in alert or aggressive patients. If midazolam is used, the antagonist flumazenil should be readily available for neonatal administration.
  • Acepromazine is a good sedative but is long-acting, depends on hepatic metabolism (which is lacking or has reduced capacity in the fetus), and leads to vasodilation and possible hypotension, which may reduce blood flow to the placenta. Acepromazine is not reversible.
  • α2 agonists are usually avoided due to increased fetal mortality associated with xylazine administration as part of premedication,10 but the results of a recent study support medetomidine (another α2 agonist) as part of premedication in planned C-sections.11 Cardiovascular depression associated with medetomidine was not associated with reduced Apgar scores or puppy or maternal survival rates. This may be because medetomidine is more α2 specific than xylazine, which affects α1 and α2 receptors similarly.11 Medetomidine should not be used in debilitated or sick patients. If an α2 agonist is used, the antagonist atipamezole should be readily available for neonatal administration. Although this study suggested medetomidine may be an option, further research is needed before this drug can be recommended for use during C-sections.

Induction Agent

Anesthetic induction agents should be short acting, be rapidly metabolized, and cause minimal maternal cardiovascular depression. Patients should be preoxygenated for at least 5 minutes and induced in the operating room when possible. The primary determinant of fetal viability is the time from induction to delivery, with a target of <15 minutes.1 Propofol and alfaxalone are the induction agents of choice because they enable smooth induction, have a short duration of action and rapid clearance, and minimize fetal depression. Several studies compared these drugs and demonstrated that either is appropriate for use with dystocia and elective C-sections.12,13 Recent studies have shown improved Apgar scores in neonates in the first 60 minutes following delivery when alfaxalone induction was used as compared with propofol induction,12,14 but survival to 3 months of age was similar between the groups.13

Anesthesia Maintenance

Maintenance of anesthesia can be performed with either sevoflurane or isoflurane. The use of total IV anesthesia with propofol or alfaxalone is not recommended because metabolic capability of neonates is reduced, leading to lower Apgar scores and longer recovery time in dams/queens.7 Pregnancy-induced changes reduce maternal anesthetic requirements. Occasional small boluses of propofol or alfaxalone can be administered if the patient’s depth suddenly lightens, and local anesthetics can be used to provide multimodal analgesia.

It is important to avoid hypotension, reduced perfusion to the uterus, and hypoxemia during anesthesia for dystocia and C-section patients. Crystalloid boluses can be used to improve blood volume and venous return. Vasopressors should be used when the patient’s blood pressure is not responsive to IV fluid boluses. Manual or mechanical ventilation may be needed to ensure proper expansion of the lungs against an enlarged abdomen and to prevent hypoventilation.

Analgesia

A line block using lidocaine or bupivacaine alone or in combination can be performed prior to surgery. After the neonate is delivered, an opioid and antibiotic can be administered to the dam/queen if indicated. Buprenorphine (a partial μ agonist) is recommended, as it causes minimal sedation and respiratory depression but allows for adequate analgesia. A full μ opioid (eg, hydromorphone, methadone) can be administered, but a lower dose should be used to minimize cardiovascular and respiratory depression and the level of sedation. Providing analgesia to the dam/queen is key, as the adverse effects of pain can affect both the mother and neonate. Epidural analgesia can be performed using morphine alone or morphine and lidocaine in combination. It is recommended to administer the epidural postoperatively due to the time it takes to perform. If an epidural is performed, the pet owner should be made aware of the potential for urinary retention and pelvic end weakness. A long-lasting (ie, 72 hours) local anesthetic containing liposomal bupivacaine can be injected in the incision at closure. A single dose of an NSAID can be considered postoperatively in patients with normal blood pressure and adequate hydration perioperatively.15 NSAIDs should not be administered continuously in the postoperative period because it is excreted in maternal milk.

Neonatal Care

Neonatal management and resuscitation begin with one staff member dedicated to each neonate if possible. Early and frequent rubbing and drying of the neonate helps stimulate respiration and keeps the neonate warm. A bulb syringe should be used to suction secretions from the oral cavity, oropharynx, and nose. Swinging the neonate is not recommended, as this has been shown to result in cerebral hemorrhage.16 One drop of naloxone should be administered sublingually if the neonate shows signs of depression (eg, bradycardia, reduced respiratory rate, lack of vigor) and an opioid was used during anesthesia. A neonate that is thriving can be placed in an incubator or kept warm with a convective temperature management system or heat lamp for heat support until the dam/queen recovers. A neonate that is not thriving and shows signs of distress (eg, bradycardia, cyanosis, very low respiratory rates) should undergo continued stimulation, and ventilation should be provided because it allows for anesthetic gas elimination and aids in increasing heart rate, thus avoiding hypoxia-induced bradycardia.16-18 If necessary, a small IV catheter can be used as an endotracheal tube, or a small endotracheal tube can be placed to allow manual ventilation. A 25-gauge needle can be inserted in the nasal philtrum to stimulate ventilation by activating acupuncture point GV26. Oxygen supplementation can be provided via mask or intubation if necessary. Asystole is the most common arrest rhythm for neonates and should be treated with one unit (0.01 mL) of epinephrine (1 mg/mL) in the umbilical vein or intrahepatically.

Conclusion

Despite increased risks, anesthesia can be safely performed for both planned and emergent C-sections. Thorough history, physical examination, and diagnostics are important to correct any underlying dehydration or electrolyte abnormalities and to allow for the design of a safe anesthetic protocol. It is also vital to provide adequate analgesia and cardiovascular and respiratory support throughout the procedure and to be prepared to resuscitate the neonate.

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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