Anesthesia Management and Considerations for C-Section

Elizabeth M. Goudie-DeAngelis, DVM, MS, DACVAA

Management of the periparturant and neonatal patients during routine or emergent C-section requires a thorough understanding of the physiology and drug pharmacokinetics to ensure the smoothest and safest anesthetic episode for both dam and neonates.

The anesthetic management of a C-section requires that the anesthetist first understand the physiologic changes that occur during pregnancy.

Cardiovascular

During pregnancy blood volume increases significantly by about 40% but this increase is not with regard to cell mass and plasma volume and results in a lower PCV. Heart rate and stroke volume increase resulting in an approximately 40% increase in cardiac output. During labor this output can increase an additional 20%. There is a general increase in cardiac workload by the time of parturition which is exacerbated by labor.

Pulmonary

As pregnancy progresses, the dam becomes more sensitive to elevations in carbon dioxide at the respiratory center of the ventral medulla. At parturition the PaCO2 can decrease to 30 mmHg while oxygen consumption can increase by 20%. A gravid uterus decreases functional residual capacity (FRC). FRC is the air left in the lungs after a passive expiration; compliance is maximal and airway resistance is minimal and is the point at which an oxygen reserve is present. Therefore preoxygenation is paramount to allow for maximal oxygen reserve prior to induction of anesthesia resulting in hypoventilation. While not recommended, induction with inhaled anesthetics in a mask or induction chamber is more rapid than in non-gravid individuals.

Coagulation

There is a general increase in clotting ability at the time of parturition.

Gastrointestinal

In general gastric emptying is slowed during pregnancy; while the lower esophageal sphincter is more relaxed. The gravid uterus puts additional pressure on the stomach and uterine contraction can further worsen this pressure, there is an increased risk of regurgitation and many emergent C-section patients have eaten before presentation increasing the risk of aspiration pneumonia. Risk of aspiration can be treated with metoclopramide and antiemetics as well as rapid and smooth intubation to secure the airway. Suction should be available at induction and recovery.

Maropitant should be administered to the dam at the time of induction.

Careful maintenance of blood glucose should also be considered as the fetus’ gluconeogenesis ability is severely limited.

Renal

Gravid patients in general, have a lower BUN and creatinine than on-pregnant patients due to an increased GFR, an elevation in BUN or Crea should be evaluated carefully to determine if it is pre-renal or truly renal.

Pharmacokinetics

As previously mentioned, induction of anesthesia with inhaled anesthetics is not recommended, in general, a pregnant bitch or queen should be premedicated and induced in a calm and organized manner. Drug choices are based on three main goals; analgesia for the dam, rapid and smooth protection of the airway of the dam, and safest drug choices for the neonates.

Anesthetic Management

An ideal protocol avoids opioids until the neonates are removed, this means we rely on an efficacious epidural for analgesia.

1. Alfaxalone 2-4 mg/kg IV to effect (propofol is also an acceptable choice but a recent study exhibited improved puppy vigor with alfaxalone). A. Doebeli, et.al 2013

   1. In cats lidocaine on the larynx should be used to facilitate smooth intubation

2. Maintenance on inhaled anesthetics (remember inhalant requirement may be lower)

3. LS epidural

   1. This should be set up for in the OR

   2. Sterile gloves, scrub, and epidural needle

   3. Drugs

      1. Preservative free lidocaine 1 mg/kg

      2. Preservative free morphine 0.1 mg/kg

      3. Dilute with sterile saline to 0.2 mL/kg (epidurals travel more cranially in gravid animals than their non-pregnant counterparts)

4. Once neonates are removed a fentanyl bolus of 2-3 ug/kg and CRI can be initiated for closure.

   1. If epidural is unsuccessful fentanyl boluses can be used to provide analgesia

      1. Neonates will require naloxone post delivery (1 drop sublingual)

5. Post-operative analgesia can be provided with buprenorphine (10-20 ug/kg IV) and NSAID

   1. There is limited excretion of NSAID into milk and the use of NSAIDs in breast-feeding women is commonplace.

Initial assessment of the patient, including CBC, chemistry, TPR, and baseline blood pressure should be included along with history, physical examination, and ultrasound evaluation of fetal viability. Many dams will allow for IVC placement and shaving of the abdomen without premedication. Acepromazine and/or alfaxalone are good choices for IM sedation as needed. An initial fluid bolus of 5-10 mL/kg can be administered during preparation. A clinically ill dam may require more IVF resuscitation and norepinephrine should be considered for maintenance of blood pressure.

In all cases of anesthesia for a C-section the goal is to minimize the time under general anesthesia to improve neonatal survival.

1. All shaving should ideally be performed with patient awake

   1. Hold patient in an upright position and shave abdomen

   2. Shave for epidural site and Doppler site

2. Induction should be performed in the OR with the surgeon scrubbing while the patient is induced and positioned.
   

   1. ECG and baseline blood pressure should be obtained

   2. Patient is induced with rapid and smooth intubation

   3. LS epidural is performed and patient is flipped into dorsal recumbency

Complications

Bradycardia

This author incorporates atropine into her protocol when the dam is clinically bradycardic with the knowledge that the atropine traverses the placental barrier. Some clinicians avoid atropine and use glycopyrrolate for this reason as they are concerned an increased heart rate in the fetuses will increase their oxygen demand. Empirically, this author has had more bradycardic patients that do not respond rapidly to oxygen supplementation in the post-delivery period as opposed to cyanotic neonates whose dam has received atropine.

Hypotension

Bradycardia is treated as noted above, most of these patients are healthy and can tolerate 5-10 mL/kg fluid boluses. In human medicine the use of hypertonic saline boluses has improved hemodynamics with epidural anesthesia. Norepinephrine or phenylephrine can both be employed to maintain blood pressure and uterine blood flow, in human and veterinary studies norepinephrine may maintain cardiac output more than phenylephrine due to some Beta-1 receptor effects.

Pain

As mentioned previously, if the epidural was unsuccessful or could not be achieved, this author employs fentanyl boluses (2-3 ug/kg) followed by a CRI (5 ug/kg/hour). Buprenorphine IV can also be administered but this may not significantly decrease inhalant demands rapidly. This does require reversal of the opioid in the neonate as fentanyl has a significant and rapid placental transfer. In human medicine ketamine is used for emergent C-sections but readers should be aware that ketamine does have rapid placental transfer and there are reports of low APGAR scores (a measure of neonatal vitality including appearance, pulse, activity, and respiration) in neonates and low puppy vigor after ketamine administration. Lidocaine should be avoided intravenously as it can become ion-trapped significantly affecting the fetuses, this is due to a significant difference in pH between the maternal and fetal side of the placenta resulting in lidocaine moving across the placenta but not back to the maternal side. Medetomidine has been used in the pregnant bitch with no significant negative outcomes in the neonates, but alpha-2 use can be associated with uterine contraction and a decreased cardiac output which may result in decreased uterine bloodflow.

Finally, while not analgesic agents, benzodiazepines should be avoided due to their negative effects on neonatal survival.[

Puppy Resuscitation

●      Suction bulb

●      Oxygen with large oxygen mask

●      Towels and heating pad

●      Naloxone (atipamezole if any alpha-2 used)

●      Stethoscope

●      20 g IV catheters for possible intubation

●      Doxapram

●      25 gauge needle

Example setup used by the author for neonatal resuscitation

Neonate resuscitation requires at least one person not involved in the surgery or anesthesia. Warming the neonates is paramount, normothermia results in a normal heart rate and respiratory rate. If a puppy or kitten is bradycardic provide oxygenation and you may need to provide breaths by covering the nose and mouth with your mouth and providing gentle ventilation. If naloxone was used it should be reversed by applying 0.1 mg/kg under the tongue, IV, umbilicus, or IO. Doxapram is a respiratory stimulant that is controversial, stimulation of the nasal philtrum with a 25 gauge needle can stimulate ventilation. Neonates can be placed with heat under a large oxygen mask allowing for heating and oxygenation.

Using a facemask to provide an oxygen rich environment for a neonatal puppy

Nasal philtrum stimulation in a neonatal puppy

Nasal philtrum stimulation in a neonatal kitten

Neonates can be placed with the dam, she should be treated with an anti-inflammatory, which have a negligible transfer into milk. A dose of buprenorphine can also be administered (0.015-0.02 mg/kg IV) as this also has a low level in breast milk and poor bioavailability.