Anatomy of Anaesthesia of Labour Flashcards
What does the levator ani act as a boundary between?
Pelvis and perineum = anything above levator ani is pelvis and anything below is perineum
What modalities are responsible for the motor functions of the reproductive system?
Uterine cramping and contraction = hormonal via sympathetic/parasympathetics
Pelvic floor muscle contraction = somatic motor
What modalities are responsible for pain in the reproductive system?
Adnexae (ovaries + fallopian tubes) = visceral afferents
Uterus = visceral afferents
Vagina = visceral afferents (pelvic part), somatic sensory (perineal part)
Perineum = somatic sensory
How is pain generated in the superior aspect of the pelvic organs (touching peritoneum)?
Visceral afferents = run alongside sympathetic fibres, enter spinal cord between T11-L2
Pain perceived as suprapubic
How is pain generated in the inferior aspect of pelvic organs?
Visceral afferents = run alongside parasympathetic fibres, enter spinal cord at S2-4
Pain perceived at S2-4 dermatome
How is pain generated in structures crossing from the pelvis to perineum?
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
What are the autonomic nerves of the pelvis?
Sympathetic = sacral sympathetic trunks, T11-L2, superior hypogastric plexus Parasympathetics = sacral outflow (S2-4), pelvic splanchnic nerves, emerge from spinal roots
Where do pelvic parasympathetic nerves mix with sympathetic nerves?
In the inferior hypogastric plexus
What are the two important spinal levels for pain sensation in women?
T11-L2 and S2-4
What pelvic organs send their visceral afferents to T11-L2 level?
Those that touch the peritoneum = uterine tubes, uterus, ovaries
What pelvic organs send their visceral afferents to S2-4?
Those inferior to the peritoneum = cervix and superior vagina
What structures does the pudendal nerve supply?
Those within perineum = inferior vagina, perineal muscles, glands, skins
What procedure is the anatomy of an epidural anaesthetic similar to?
Lumbar puncture = anaesthetic injected into L3-4 region
What spinal level does the subarachnoid end at?
S2
What spinal level does the spinal cord become the cauda equina?
L2 level
What structures does the needle pass through when delivering an epidural anaesthetic?
Supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space
What structures does the needle pass through when giving a spinal anaesthetic?
Supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, arachnoid mater, reaches subarachnoid space
What is the sympathetic outlow?
Thoracolumbar = T1-L2
Where do the sympathetic ganglia receive fibres from below L2 level?
Via the sympathetic chain
What do all spinal nerves and their named nerves contain?
Sympathetic fibres
What supply all arterioles?
Sympathetic fibres
What does blockade of sympathetic tone cause?
Vasodilation = may lead to hypotension
Where does the pudendal nerve supply?
Somatic motor and sensory to structures of perineum = nerve block will anaesthetise most of perineum
What is the pudendal nerve a branch of?
Sacral plexus = S2-4
What is the course of the pudendal nerve?
Exits pelvis via greater sciatic foramen
Passes posterior to sacrospinous ligament
Re-enters pelvis via lesser sciatic foramen
What does the pudendal nerve travel in?
Pudendal canal = passageway within obturator fascia
What is used as a landmark for pudendal nerve block?
Ischial spine
What are the indications for pudendal nerve block?
Forceps delivery, painful vaginal delivery, episiotomy incision, perineal suturing post-delivery
What can happen to branches of the pudendal nerve during labour?
Can be stretched = fibres within levator ani or external anal sphincter may be torn (1st-3rd degree) with resulting muscle weakness
What kind of incision is made in an episiotomy?
Posterolateral incision
Where is the incision made in an episiotomy?
Incision made into relatively safe fat-filled ischioanal fossa = avoids incision extending into rectum
