Chp 39 Pregnancy Flashcards
What factors determine anesthetic transfer across placenta into fetal circulation?
- Maternal blood concentration determined by drug dose, location, route of inj, maternal metabolism/excretion
- Rate of placental transfer from the concentration gradient per Fick equation
What is the most critical factor under veterinarian control during a c section?
- Time from beginning administration of anesthetic to time of delivery of newborn
- Minimizing time from beginning of uterine exteriorization until delivery crucial for reducing period of decreased uterine blood flow
Fick Equation
- Q/t = KA (Cm-Cf)/D
- Amount of diffused substance per unit time
Fick Equation: Q/t
Amount of diffused substance per unit time
Fick Equation: K
Diffusion constant of a given substance which takes into account its pKa, molecular weight, lipid solubility, protein binding
Fick Equation: A
Surface area for diffusion
Fick Equation: Cm
Concentration in maternal uterine blood
Fick Equation: Cf
Concentration of substance in fetal blood
Fick Equation: D
Thickness of the placental membrane
How does pregnancy affect anesthetic requirement (MAC)?
- Assoc with 25-40% decrease in anesthetic requirement
- Thought to be related to circulating levels of progesterone
Newborns and MAC
- Decreased MAC reduction for first month after birth —> at which time MAC requirement will be at a maximum for that animal’s lifetime
- Also thought to be related to progesterone that has crossed placenta to fetal circulation
- MAC values tend to decrease gradually from one month of age until death
Physiologic changes altering response to anesthetics occur during pregnancy: HR
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: CO
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: blood volume
increased
Physiologic changes altering response to anesthetics occur during pregnancy: PCV
Decreased
Physiologic changes altering response to anesthetics occur during pregnancy: hgb
Decreased
Physiologic changes altering response to anesthetics occur during pregnancy: plasma protein
Decreased
Physiologic changes altering response to anesthetics occur during pregnancy: oxygen consumption
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: minute ventilation
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: FRC
Decreased
Physiologic changes altering response to anesthetics occur during pregnancy: gastric emptying time
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: gastric pH
Decreased
Physiologic changes altering response to anesthetics occur during pregnancy: GFR
Increased
Physiologic changes altering response to anesthetics occur during pregnancy: renal blood flow
Increased
Which physiologic changes altering the response to anesthetics increase during pregnancy?
HR CO Blood volume O2 consumption Minute ventilation Gastric emptying time GFR Renal blood flow
Which physiologic changes altering the response to anesthetics decreased during pregnancy?
PCV Hgb Plasma protein FRC Gastric pH
Discuss effect of pregnancy on epidural analgesic technique
- Preg: increased blood vol, increased shunting of abdominal blood to epidural tissues, increased epidural fat stores (during optimal nutrition)
- Factors increase volume of epidural blood vessels/fat —> decreases potential vol of epidural space
- Thus: volume of epidural analgesic injected in pregnant animal at term will migrate more rostrally than the same volume injected into non pregnant animal of similar size, conformation
How much should you decrease your epidural injectate volume in pregnant animals?
About 1/3 of patients at term
Important considerations for canine castrations
- Inhalant at low concentrations
- If opioids used prior to delivery, reversal in the newborn can be achieved by administering 3-4 drops naloxone sublingually
- IVF, monitoring important
Important considerations for feline c sections
Oxymorphone, hydromorphone dose in cats = 0.3mgkg
Can also use 0.3mgkg Butorphanol for less likelihood of an excitatory reaction
Important considerations for equine c sections
BW used for calculation of doses should be estimated no preg weight
precautions for anesthetizing pregnant mares: first and second trimester
Generally uneventful
Precautions for anesthetizing pregnant mares: third trimester
- Gravid uterus may compress VC —> hypotension when mare is positioned in dorsal recumbency
- Paramount to attention to monitoring CV function, maintenance of ABP and oxygenation
What drugs susceptible to “ion trapping” in the fetal circulation?
- Weak bases cross the placenta into fetal circulation as unionized molecules, enter fetal circulation
- fetal blood more acidic than maternal blood
- Drug ionizes in fetal blood, becomes trapped and unable to readily diffuse back across the placenta
What are the most commonly used drugs that are weak bases?
- Opioids
- Use of sublingual or IV injection of naloxone frequently effective in reversing depression in neonates that have been exposed to maternal administration of opioids
What precautions should pregnant women take when working near anesthetized animals?
- No convincing studies to document health benefits from reduced exposure to inhaled anesthetics
- Should use vigilant scavenging equipment, avoidance of areas with IgG anesthetic use, elimination of mask or chamber induction techniques , recovery of patients to their breathing circuit with oxygen attached and use of properly fitted personal face masks for the person equipped with filters effective against hydrocarbons
