Anatomy of normal labour/anaesthesia during labour

Question 1

How can the position of the fetal head be identified during vaginal examination?

Answer 1

On vaginal examination the posterior fontanelle, sagittal suture, vertex and anterior fontanelle are palpable (where the baby’s head is in the occipito-anterior position i.e. baby is facing the floor)

Question 2

How may a medial episiotomy reduce the risk of faecal incontinence developing after a difficult vaginal delivery?

Answer 2

A vaginal tear can extend towards the rectum, causing damage to the anal sphincters and even extend through the rectal mucosa. This can result in faecal incontinence
An episiotomy is a deliberate incision of the vagina and pelvic floor to avoid the extension of a vaginal tear towards the rectum

Question 3

What is the major structure incised during a median episiotomy and what potential issues are faced if further tearing occurs?

Answer 3

Perineal body - if further tearing occurs it can result in faecal incontinence

Question 4

Describe the course of the pudendal nerve

Answer 4

The pudendal nerve emerges from the pelvis, below the piriformis, in the greater sciatic foramen. It then curves over the ischial spine and sacrospinous ligament. It then enters the pernieum just inferior to the ligament and passes forward in the fascial canal on obturator internus

Question 5

Describe the motor and sensory innervation provided by the pudendal nerve

Answer 5

Main motor innervation to the perineum as well as sensory innervation to most of the skin of the perineum and external genitalia
It provides innervation to the perineal muscles, external anal sphincter and external urethral sphincter

Question 6

If a pudendal nerve block is performed during labour, are the uterine contractions affected?

Answer 6

A pudendal nerve block provides anaesthesia over dermatomes S2-4, which is the majority of the perineum and the inferior quarter of the vagina. It does not block pain from the superior birth canal (superior vagina and uterine cervix) so the mother is able to feel uterine contractions

Question 7

Which maternal or fetal nerve injuries can be caused during delivery?

Answer 7

Fetal skull has no mastoid processes (form at around 4 years) so the fetal facial nerve (CN VII) may be injured as the fetus has no protection for it emerging from the stylomastoid formaen and it may be injured during forceps delivery

Question 8

Which maternal or fetal nerve injuries can be caused during delivery?

Answer 8

Fetal skull has no mastoid processes (form at around 4 years) so the fetal facial nerve (CN VII) may be injured as the fetus has no protection for it emerging from the stylomastoid formaen and it may be injured during forceps delivery

Klumpke’s palsy - lower trunk of brachial plexus injured (C8 and T1) due to pulling on arm during delivery - causes ‘claw hand’ and sensory loss on medial aspect of upper limb

Erb’s palsy - upper trunk of brachial plexus injured (C5, 6) because baby’s shoulder gets stuck during delivery - causes ‘Waiter’s tip’ and sensory loss on lateral aspect of upper limb

Neurapraxia of the common fibular nerve leading to a temporary foot drop in the mother due to being in the lithotomy position for too long