In this VETgirl online veterinary continuing education blog, Dr. Garret Pachtinger, VMD, DACVECC addresses anesthesia for the C-section veterinary patient! Anesthesia can be a scary thought for any patient, let alone when you are performing anesthesia on a patient that is pregnant!  Simply put, we know there are a multitude of physiological and hormonal changes that occur during pregnancy and what happens to the pregnant patient also happens to the fetus.

There are many important physiologic alterations induced by pregnancy (Tranquilli WJ, et al. Veterinary Anesthesia and Analgesia 4th, ed. Blackwell, 2007: 956):

  • Increase in:
    • Heart Rate
    • Cardiac output (30-50%)
    • Blood volume (40%)
    • Plasma volume
    • Minute ventilation
    • Oxygen consumption (due to increased metabolic demand from the fetus)
    • Gastric emptying time/intragastric pressure (increased the risk for regurgitation)
    • Renal plasma flow and GFR
  • Decrease in:
    • Packed Cell Volume (PCV)
    • Hemoglobin
    • Plasma protein
    • PaCO2 (Progesterone increases sensitivity to CO2)
    • Functional residual capacity
    • GI motility
    • Gastric pH
    • BUN, Creatinine

As such we need to recognize, understand, and prepare for anesthesia in our pregnant patients.

Prior to anesthesia and the c-section, the clinician should perform a thorough physical examination as well as important pre-operative tests.

    • Blood work – importantly we want to assess for underlying co-morbidities as well as electrolyte derangements including the calcium level, ideally ionized calcium
    • Radiographs to assess the number of fetuses present as well as abdominal ultrasound to assess fetal heart rates, which is particularly important with an emergency C-Section as opposed to a planned C-Section.

 

Once the clinician and nursing team are satisfied with the examination and preoperative testing, the team performs as many pre-surgical tasks prior to drug administration with the goal of reducing anesthesia time.

  • Clip and initial scrub of the abdomen (a more thorough scrub is required prior to surgery for a true aseptic procedure).
  • Intravenous fluid therapy if required (e.g. dehydration, hypovolemia).
  • Pre-oxygenation
  • Maropitant, 1mg/kg IV prior to anesthesia can also be considered to reduce the risk of vomiting / regurgitation
  • Set up neonate resuscitation station
    • Suction bulbs
    • ET tubes or catheters
    • Naloxone
      • Reverse Opioids
    • Epinephrine
      • If they are bradycardic
      • Atropine can also be considered as epinephrine can result in marked tachycardia
    • O2
      • Pediatric/Exotic Face Masks – once the puppies are resuscitated placing them in a plastic box with oxygen can be considered (similar to the box used in the past to box down a cat)
    • Heat support
    • Towels

Ideally, during patient preparation by the nursing team, the surgeon should be preparing for the procedure including scrub, gowned/gloved and preparing their instrument table so everything is ready prior to patient being induced.

Regarding medications, we have to remember that anything the patient receives, the fetus is likely to receive as well.  Most sedation / anesthesia medications cross the placenta.  Below is a recommended drug protocol for a c-section.  NOTE: this may not be safe for ALL patients and therefore it is recommended to create a plan for YOUR patient that is determined to be safe and effective.

  • Drug Protocol for C-section
    • Premedication(Short acting opioids)
      • Fentanyl 5 mcg/kg IV – fentanyl has a fast onset of action, 1-2 minutes and a quick elimination (approximately 30 minutes). During this time the patient should receive supplemental oxygen for the pre-oxygenation period.
      • Butorphanol 0.4 mg/kg IV – this can be considered instead of Fentanyl based on availability or patient requirements. For example, butorphanol is less likely to induce vomiting and may be beneficial for brachycephalic patients.
    • Inductionto effect – Similar to premedication, often ONE of the following are used, not in combination with each other)
      • Propofol 4-8 mg/kg IV – propofol does cross the placenta, but fortunately is rapidly cleared.
      • Alfaxalone – this may be a more optimal choice for patients with cardiac disease as compared to propofol
        • 2 mg/kg IV dogs
        • 5 mg/kg IV cats
      • Line block – Following induction, a line block over the linea alba can be considered to reduce the requirement for intraoperative as well as post-operative medications.
        • Lidocaine 2 mg/kg
        • Bupivacaine 1 mg/kg (Nocita may be considered as well)
      • Maintenance – inhalant anesthesia
        • Noted above, we are limiting the use of other medications which may be part of your normal pre-operative agent arsenal (e.g. benzodiazepines). As such, the patient will likely require inhalant delivered at higher rate than expected.
        • A side effect of higher inhalant rates includes hypotension.
        • If hypotension is noted, fluid boluses can be considered.
        • If they are hypotensive and bradycardic, Glycopyrrolate can be considered. Glycopyrrolate does not cross placenta
        • If hypotensive with normal heart rate, Ephedrine can be considered. Ephedrine does not easily cross through the placenta.
        • A dopamine CRI can be considered for longer surgeries. Dopamine will cross over the placenta barrier but should have minimal impact.
        • Re-dose fentanyl after fetuses are out if more than 30mins from the last dose.
        • Consider Buprenorphine administration at the end of the procedure so it is on board once they are awake.
      • Epidurals can also be considered, notably for a planned c-section, as they can significantly reduce systemic drug requirements.
        • Use 2% Lidocaine (1ml/10kg) +/- opioid
        • If fetus is in distress and/or dam has been in labor for extended period of time, then time should not be wasted trying to perform epidural.

While the above protocol can be considered, there are anesthesiologists that do not premedicate patients.  An alternative approach would be to have the patient clipped and prepped (initial scrub). The patient is then induced in the OR with the surgeon scrubbed and ready, pre-oxygenation during this process.  The patient is induced with propofol or alfaxalone and then receives inhalant anesthesia (isoflurane or sevoflurane).  This protocol limits the medication the fetus (e.g. puppy) receives and there is no concern / requirement to reverse any puppies.  If elective and they are not distressed, they are more likely to be alert and moving following delivery.  Once puppies are out, the patient receives hydromorphone (0.1 mg/kg).

  • Recovery
    • Buprenorphine 0.02 mg/kg IV
    • Single dose of NSAID
      • 4 mg/kg Carprofen dogs
      • Limited levels in milk
    • Oxytocin
      • 5-20 units titrated to effect
    • Heat support
    • O2 support if needed
    • Return neonates to dam as soon as she is awake (If they are still sedate, there is increased risk for accidental trauma to the newborn)
    • Encourage nursing
  • Regarding neonate resuscitation, considerations / preparations include:
    • Clear airway
    • No swinging neonates (risk of coup contrecoup injury)
    • Dry vigorously to maintain heat and stimulate breathing
    • Hypothermia associated with high morbidity/mortality
    • HR should be >180bpm, if <180bpm, the concern is myocardial hypoxia.  Another reason to provide supplemental oxygen listed above during stimulation post-delivery.
    • Intubate if necessary
    • VETgirl Pearl: you can provide suction by cutting the needle off of a butterfly catheter and the line connects to a syringe and then can safely suction the airway.
  • Of note, medications that should be avoided include:
    • Benzodiazepines, Alpha 2 agonists, and Dissociatives
    • Masking down was previously thought to be optimal as inhalants such as isoflurane do not last long and minimizes exposure of drugs to the fetus. However, masking down increases patient stress, requires high levels of  isoflurane, and increased the risk for complications such as hypotension and aspiration pneumonia.

Dr. Garret Pachtinger, DACVECC

References

  • Brock N. Anesthesia for canine caesarian section. Can Vet J Volume 37, Feb 1996: 117-118.
  • Metcalf S, et al. 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;92:333–338.
  • Luna SPL, et al. Effects of four anaesthetic protocols on the neurological and cardiorespiratory variables of puppies born by caesarean section. Veterinary Record (2004)154: 387-389
  • Moon PF, et al. Perioperative Risk Factors for Puppies Delivered by Cesarean Section in the United States and Canada. J Am Anim Hosp Assoc 2000;36:359–68.
  • Moon-Massat PF, Erb HN. Perioperative Factors Associated With Puppy Vigor After Delivery by Cesarean Section. J Am Anim Hosp Assoc. January/February 2002, Vol. 38; 90-96.
  • Ryan SD, Wagner AE. Cesarean Section in Dogs: Anesthetic Management. Compendium 2006: 44-57.
  • Traas AM. Surgical management of canine and feline dystocia. Theriogenology 70 (2008) 337–342.

  1. Good information. Haven’t done a c-section in over a year but looking forward to using this information in the future.

  2. Great read, Dr. Pachtinger! I commenced my career under the direction of a board certified Theriogenologist and his paradigm was pretty much spot-on with these guidelines. He went more of the way of pre-O2, skip PA, straight to Sx-he was very conservative with meds because most of his C-secs were A.I. P’s of show quality with breeders/owners always present during Sx/recovery.

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