Chp 39 Pregnancy

Question 1

What factors determine anesthetic transfer across placenta into fetal circulation?

Answer 1

• 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

Question 2

What is the most critical factor under veterinarian control during a c section?

Answer 2

• 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

Question 3

Fick Equation

Answer 3

• Q/t = KA (Cm-Cf)/D

- Amount of diffused substance per unit time

Question 4

Fick Equation: Q/t

Answer 4

Amount of diffused substance per unit time

Question 5

Fick Equation: K

Answer 5

Diffusion constant of a given substance which takes into account its pKa, molecular weight, lipid solubility, protein binding

Question 6

Fick Equation: A

Answer 6

Surface area for diffusion

Question 7

Fick Equation: Cm

Answer 7

Concentration in maternal uterine blood

Question 8

Fick Equation: Cf

Answer 8

Concentration of substance in fetal blood

Question 9

Fick Equation: D

Answer 9

Thickness of the placental membrane

Question 10

How does pregnancy affect anesthetic requirement (MAC)?

Answer 10

• Assoc with 25-40% decrease in anesthetic requirement

- Thought to be related to circulating levels of progesterone

Question 11

Newborns and MAC

Answer 11

• 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

Question 12

Physiologic changes altering response to anesthetics occur during pregnancy: HR

Answer 12

Increased

Question 13

Physiologic changes altering response to anesthetics occur during pregnancy: CO

Answer 13

Increased

Question 14

Physiologic changes altering response to anesthetics occur during pregnancy: blood volume

Answer 14

increased

Question 15

Physiologic changes altering response to anesthetics occur during pregnancy: PCV

Answer 15

Decreased

Question 16

Physiologic changes altering response to anesthetics occur during pregnancy: hgb

Answer 16

Decreased

Question 17

Physiologic changes altering response to anesthetics occur during pregnancy: plasma protein

Answer 17

Decreased

Question 18

Physiologic changes altering response to anesthetics occur during pregnancy: oxygen consumption

Answer 18

Increased

Question 19

Physiologic changes altering response to anesthetics occur during pregnancy: minute ventilation

Answer 19

Increased

Question 20

Physiologic changes altering response to anesthetics occur during pregnancy: FRC

Answer 20

Decreased

Question 21

Physiologic changes altering response to anesthetics occur during pregnancy: gastric emptying time

Answer 21

Increased

Question 22

Physiologic changes altering response to anesthetics occur during pregnancy: gastric pH

Answer 22

Decreased

Question 23

Physiologic changes altering response to anesthetics occur during pregnancy: GFR

Answer 23

Increased

Question 24

Physiologic changes altering response to anesthetics occur during pregnancy: renal blood flow

Answer 24

Increased

Question 25

Which physiologic changes altering the response to anesthetics increase during pregnancy?

Answer 25

``` HR CO Blood volume O2 consumption Minute ventilation Gastric emptying time GFR Renal blood flow ```

Question 26

Which physiologic changes altering the response to anesthetics decreased during pregnancy?

Answer 26

``` PCV Hgb Plasma protein FRC Gastric pH ```

Question 27

Discuss effect of pregnancy on epidural analgesic technique

Answer 27

- 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

Question 28

How much should you decrease your epidural injectate volume in pregnant animals?

Answer 28

About 1/3 of patients at term

Question 29

Important considerations for canine castrations

Answer 29

- 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

Question 30

Important considerations for feline c sections

Answer 30

Oxymorphone, hydromorphone dose in cats = 0.3mgkg | Can also use 0.3mgkg Butorphanol for less likelihood of an excitatory reaction

Question 31

Important considerations for equine c sections

Answer 31

BW used for calculation of doses should be estimated no preg weight

Question 32

precautions for anesthetizing pregnant mares: first and second trimester

Answer 32

Generally uneventful

Question 33

Precautions for anesthetizing pregnant mares: third trimester

Answer 33

- 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

Question 34

What drugs susceptible to “ion trapping” in the fetal circulation?

Answer 34

- 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

Question 35

What are the most commonly used drugs that are weak bases?

Answer 35

- 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

Question 36

What precautions should pregnant women take when working near anesthetized animals?

Answer 36

- 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