The placenta produces endorphins and enkephalins
* May be analgesic during pregnancy
Endorphin production increases significantly in proportion to the frequency and duration of uterine contractions during labour and delivery
* Role unclear
Progesterone has sedative actions
* Increase 10-20 fold in 3rd trimester
MAC of volatile agents is reduced by 30-40% during pregnancy
* Partly because of endorphins and progesterone
Epidural veins are engorged
Epidural pressure are higher than in non-pregnant women
* Due to increased abdominal pressure
* May increase to 4-10cmH2O in labour, and to 60cmH2O during bearing-down efforts
CSF pressure is not changed at rest
May increase to 70cmH2O during bearing-down efforts