Therapeutics and anaesthesia of the dam and neonates

• What are the anatomical changes during pregnancy?

  Increased size of the uterus -> cranial displacement of the stomach or altered position -> diaphragm pushed cranially.
• What are the physiological changes that occur during pregnancy?

  Increased gastrin production -> increased HCl secretion—> decreased stomach pH.

  Decreased gastric motility.

  Reduced oesophageal sphincter tone.

  Increased risk of regurgitation + aspiration pneumonia.
• What are the changes in the respiratory system in pregnant animals?

  Increased oxygen consumption and basal metabolic rate due to increased cardiac workload to meet the needs of the foetuses.

  Minute volume is increased due to increased tidal volume.

  Increased ventilation causes a respiratory alkalosis but blood pH remains normal due to renal compensation.

  Cranial diaphragm due to increased size of the uterus causes an in increase in negative pleural pressure leading to a reduced total lung capacity and early closure of the small airways (atelectasis)
• What are the changes in the cardiovascular system for pregnant animals?

  Possible position compression of the vena cava in dorsal recumbency.

  Increased cardiac output (CO):

  • Increased stroke volume SV) and heart rate (HR)
  • Increase in venous capacitance d/t decreased systemic vascular resistance (SVR) -> decreased reserve due to increased workload, oxygen demand and tachycardia.

  50% increase in blood volume
• uterine blood flow in pregnant animals?

  Uterine blood flow = 10% of cardiac output.

  Depends on the maternal cardiac output and uterine perfusion pressure.

  Minimal auto regulation.
• C-section patient - preparation

  Make a plan.

  Place an IV cannula

  Start IVFT

  Get everything ready before premed/ induction (including emergency drugs).
• C-section patient - pre-medication effects

  Use low end of the dose range (need up to 60% less)

  • Noting licensed in pregnant animals. As worried that it will have some effect on the foetus. Any drug that can cross the blood-brain barrier can cross the placenta
• What pre-meds do you use in the pregnant patient?

  Consider an opioid - methadone:

  • Give a lower dose in pregnant animals.
  • Avoid ACP as is long acting, and cause reduced blood flow.
  • Benzodiazipines rapidly cross the placenta and the foetus does not have the enzymes to metabolise the drug in the liver.
• C-section patient - preoxygenation

  Pregnant animals have a higher oxygen requirement and increase in minute volume.

  • Pre-oxygenate to prevent hypoxaemia (use a mask or the end of the ET tube in the mouth of panting patients.
  • Supplement oxygen during surgery.
• C-section patient - induction

  Risk of regurgitation and aspiration.

  • Prior to induction reduce the risk by considering omeprazole and maripotant or ondansetron.

  Prompt induction (propofol or Alfaxalone NOT ketamine)

  Raise head

  Intubate swiftly.

  Cuff tube with head raised.
• C-section patient - positioning

  Tilt the table and position carefully as this will reduce the pressure on the diaphragm:

  • Don’t tilt to much as this will compromise venous return.

  Avoids exacerbating reduction in FRC and associated atelectasis and V/Q mismatch.

  May reduce aortovenous compression

  Reduces the risk of regurgitation.
• C-section patient - maintenance

  Maintain with isoflurane or sevoflurane bit be aware that:

  • Minimum alveolar concentration (MAC) is reduced.
  • Higher cardiac output slows changed in depth initially.
  • Decreased FRC and increase Va results in quicker changes in depth.
  • Inhalation anaesthesia cause significant cardiovascular depression in both dam and neonates.
• C-section patient - monitoring with Capnography

  Normal ETCO2 may be lower due t progesterone causing sensitivity to CO2.

  May induce hypoventilation caused by cranial diaphragm -> assist with ventilation.
• C-section patient - monitoring with pulse oximetry

  Peripheral oxygen saturation.

  If low the consider positioning/ alveolar recruitment.
• C-section patient - monitoring with blood pressure

  Risk of positional hypotension, sepsis, blood loss.

  Placental blood flow is dependant n blood pressure (no auto regulation).

  Provide IVFT and treat hypotension.
• C-section patient - post-op

  Provide NSAID post-operative ly.

  Pain score and top-up opioid/ give buprenorphine if needed.

  Discharge as soon as possible.
• C-section patient - dealing with the neonates

  Prepare a warm box/ cage or incubator.

  Clear away any membranes and fluid from the mouth and nose.

  • Suction, cotton buds, bulb syringes.

  Rub vigorously (avoid swinging).

  Supplement oxygen and assist ventilation

  • Mouth to mouth, intubate and start IPPV, flow by oxygen.
  • Slow HR and RR indicates myocardial hypoxia (or hypothermia)
  • GV26 acupuncture pint (nasal philtrum).

  Consider naloxone if concerns regarding opioid administration
• What is a suitable choice of induction agent for a dog undergoing a C-section?

  1. Either propofol or ketamine
  2. Co-induction with Propofol & midazolam.
  3. Either propofol or alfaxalone
  4. Co-induction with propofol and ketamine.

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• In a pregnant animal, how might the reduction in FRC affect tissue oxygen delivery?

  1. Reduces oxygen delivery by reducing peripheral perfusion.
  2. Reduced oxygen delivery by causing ventilation/perfusion mismatch.
  3. Reduced oxygen delivery by reducing the oxygen affinity of haemoglobin.
  4. Increases oxygen delivery by increasing alveolar ventilation.
  5. Increases oxygen delivery by increasing th oxygen affinity of haemoglobin.

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• What primarily determines uterine blood flow in a pregnant patient?

  1. Placental auto regulation.
  2. Maternal blood pressure
  3. Residual volume
  4. Foetal demand

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