Anatomy of Anaesthesia of Labour

Question 1

What does the levator ani act as a boundary between?

Answer 1

Pelvis and perineum = anything above levator ani is pelvis and anything below is perineum

Question 2

What modalities are responsible for the motor functions of the reproductive system?

Answer 2

Uterine cramping and contraction = hormonal via sympathetic/parasympathetics
Pelvic floor muscle contraction = somatic motor

Question 3

What modalities are responsible for pain in the reproductive system?

Answer 3

Adnexae (ovaries + fallopian tubes) = visceral afferents
Uterus = visceral afferents
Vagina = visceral afferents (pelvic part), somatic sensory (perineal part)
Perineum = somatic sensory

Question 4

How is pain generated in the superior aspect of the pelvic organs (touching peritoneum)?

Answer 4

Visceral afferents = run alongside sympathetic fibres, enter spinal cord between T11-L2
Pain perceived as suprapubic

Question 5

How is pain generated in the inferior aspect of pelvic organs?

Answer 5

Visceral afferents = run alongside parasympathetic fibres, enter spinal cord at S2-4
Pain perceived at S2-4 dermatome

Question 6

How is pain generated in structures crossing from the pelvis to perineum?

Answer 6

Above levator ani = visceral afferents, parasympathetics, spinal cord levels S2-4
Below levator ani = somatic sensory, pudendal nerve, spinal cord levels S2-4, localised pain within perineum

Question 7

What are the autonomic nerves of the pelvis?

Answer 7

Sympathetic = sacral sympathetic trunks, T11-L2, superior hypogastric plexus 
Parasympathetics = sacral outflow (S2-4), pelvic splanchnic nerves, emerge from spinal roots

Question 8

Where do pelvic parasympathetic nerves mix with sympathetic nerves?

Answer 8

In the inferior hypogastric plexus

Question 9

What are the two important spinal levels for pain sensation in women?

Answer 9

T11-L2 and S2-4

Question 10

What pelvic organs send their visceral afferents to T11-L2 level?

Answer 10

Those that touch the peritoneum = uterine tubes, uterus, ovaries

Question 11

What pelvic organs send their visceral afferents to S2-4?

Answer 11

Those inferior to the peritoneum = cervix and superior vagina

Question 12

What structures does the pudendal nerve supply?

Answer 12

Those within perineum = inferior vagina, perineal muscles, glands, skins

Question 13

What procedure is the anatomy of an epidural anaesthetic similar to?

Answer 13

Lumbar puncture = anaesthetic injected into L3-4 region

Question 14

What spinal level does the subarachnoid end at?

Answer 14

S2

Question 15

What spinal level does the spinal cord become the cauda equina?

Answer 15

L2 level

Question 16

What structures does the needle pass through when delivering an epidural anaesthetic?

Answer 16

Supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space

Question 17

What structures does the needle pass through when giving a spinal anaesthetic?

Answer 17

Supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, arachnoid mater, reaches subarachnoid space

Question 18

What is the sympathetic outlow?

Answer 18

Thoracolumbar = T1-L2

Question 19

Where do the sympathetic ganglia receive fibres from below L2 level?

Answer 19

Via the sympathetic chain

Question 20

What do all spinal nerves and their named nerves contain?

Answer 20

Sympathetic fibres

Question 21

What supply all arterioles?

Answer 21

Sympathetic fibres

Question 22

What does blockade of sympathetic tone cause?

Answer 22

Vasodilation = may lead to hypotension

Question 23

Where does the pudendal nerve supply?

Answer 23

Somatic motor and sensory to structures of perineum = nerve block will anaesthetise most of perineum

Question 24

What is the pudendal nerve a branch of?

Answer 24

Sacral plexus = S2-4

Question 25

What is the course of the pudendal nerve?

Answer 25

Exits pelvis via greater sciatic foramen
Passes posterior to sacrospinous ligament
Re-enters pelvis via lesser sciatic foramen

Question 26

What does the pudendal nerve travel in?

Answer 26

Pudendal canal = passageway within obturator fascia

Question 27

What is used as a landmark for pudendal nerve block?

Answer 27

Ischial spine

Question 28

What are the indications for pudendal nerve block?

Answer 28

Forceps delivery, painful vaginal delivery, episiotomy incision, perineal suturing post-delivery

Question 29

What can happen to branches of the pudendal nerve during labour?

Answer 29

Can be stretched = fibres within levator ani or external anal sphincter may be torn (1st-3rd degree) with resulting muscle weakness

Question 30

What kind of incision is made in an episiotomy?

Answer 30

Posterolateral incision

Question 31

Where is the incision made in an episiotomy?

Answer 31

Incision made into relatively safe fat-filled ischioanal fossa = avoids incision extending into rectum