6, 7 & 8. Obstetric drugs

Question 1

What does pregnancy mean for neuroaxial LA doses?

Why?

Answer 1

Reduced epidural/spinal space so reduced dose as more spread.
Increased nerve sensitivity.
Reduced PaCO2 so reduced buffering meaning LA’s stay free bases for longer.

Question 2

What happens to MAC in pregnancy and why?

What Mac should we aim for and why?

Answer 2

Reduced by 40% due to the effects of progesterone

Mac over 1 can cause reduced tone.

Question 3

What is the differences in Mac and equilibrium time in pregnant people?

Answer 3

Lower MAC needed but higher equilibrium time as higher pulmonary blood flow

Question 4

What is the mechanism of milk release in breast feeding?

Answer 4

Suckling
Hypothalamic dopamine inhibition
Prolactin release
Milk gland stimulation

Intermittent oxytocin release causes ejection

Question 5

How do drugs cross to breast milk and how long does that last?

How does this change in the first week of breast feeding?

Answer 5

Plasma
Capillaries
Mammary interstitium
Lactocyte walls
Milk

Maternal plasma
Equilibriates with milk
Mum quickly redistributes to other tissues
Drug moves from milk to plasma to re-equilibriate

Initially wide gap junctions allowing more movement, but little milk production at this time (colostrum), so little transfer. Gap junctions start to tighten over next few days.

Question 6

What are the general rules when giving drugs to mum?

Answer 6

Use:
Short acting
Ionised
Lipophobic
Protein bound
Kid safe drugs