The Anatomy of Anaesthesia for labour Flashcards
Above the levator ani muscle = _____
Below the levator ani muscle= _________
Above the levator ani muscle = pelvic
Below the levator ani muscle= perineum
Which nerve fibre types are found in the perineum?
Body wall
Somatic motor and somatic sensory
How do fibres responsible for uterine ‘cramping’ (e.g. menstruation) get from CNS to organs?
Hormonal (sympathetic/parasympathetic)
How do fibres responsible for uterine contraction (e.g. during labour) get from CNS to organs?
Hormonal (sympathetic/parasynpathtic)
How do fibres responsible for pelvic floor muscle contraction (e.g. during sneezing) get from CNS to organs?
Somatic motor
How do fibres carrying pain from adnexae (ovaries and fallopian tubes) get to the CNS?
Visceral afferents
How do fibres carrying pain from uterus get to the CNS?
Visceral afferents
How do fibres carrying pain from vagina get to the CNS?
Visceral afferents (pelvic part)/somatic sensory (perineum)
How do fibres carrying pain from perineum get to the CNS?
Somatic sensory
- Superior aspect of pelvic organs / touching the peritoneum
- Visceral afferents
- Run alongside _________ ______
- Enter spinal cord between levels _____
- Pain is perceived by patient as ________
- Superior aspect of pelvic organs / touching the peritoneum
- Visceral afferents
- Run alongside sympathetic fibres
- Enter spinal cord between levels T11-L2
- Pain is perceived by patient as suprapubic
- Inferior aspect of pelvic organs / not touching peritoneum
- Visceral afferents
- Run alongside ______________ _____
- Enter spinal cord at levels __, __, __
- Pain perceived in __, __, __ ________ (________)
- Inferior aspect of pelvic organs / not touching peritoneum
- Visceral afferents
- Run alongside parasympathetic fibres
- Enter spinal cord at levels S2, S3, S4
- Pain perceived in S2, S3, S4 dermatome (perineum)
How do structures crossing from the pelvis to the perineum e.g. urethra, vagina: above the levator ani sense pain?
Via visceral afferents
Parasympathetic
Spinal cord levels S2, S3, S4
How do structures below the levator ani sense pain?
Somatic sensory
Pudendal nerve
Spinal cord levels S2, S3, S4
Localised pain within perineum
Describe the autonomic sympathetic nerves of the pelvis?
Sacral sympathetic trunks
T11-L2
Superior hypogastric plexus
Describe the autonomic parasympathetic nerves of the pelvis?
Sacral outflow (S2, 3, 4)
Pelvic splanchnic nerves
Emerge from spinal roots
Mixes with sympathetics in inferior hypogastric plexus
Which pelvic organs touch the peritoneum?
Uterine tubes, uterus, ovaries
Which organs are inferior to peritoneum?
Cervix and superior vagina
Which organs are within the perineum
Inferior vagina, perineal muscles, glands, skin
What are the various types of anesthesia used in labour?
Spinal anaesthetic
Epidural anesthetic
Pudendal nerve block
At what level does spinal cord become cauda equina?
L2 vertebra
What level does subarachnoid space end at?
S2
Where is spinal and epidural anaesthetic injected into?
L3-L4 (L5) region
What does the needle pass though in epidural anesthetic?
Supraspinous ligament
Interspinous ligament
ligamentum flavum
Epidural space (Fat and veins)
What does needle pass through in spinal anaesthetic?
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space (Fat and veins)
Dura mater
Arachnoid mater
Finally reaches subarachnoid space (contains CSF)
Sympathetic outflow originates from _______ centres in the _____
Sympathetic nerves exit spinal cord with__-__ _____ nerves
Travel to _________ chains running the length of the ________ ______
Sympathetic outflow originates from autonomic centres in the brain
Sympathetic nerves exit spinal cord with T1-L2 spinal nerves
Travel to sympathetic chains running the length of the vertebral column
After sympathetic chains sympathetic outflow passes into …..
Spinal nerves (anterior and posterior rami/named nerves)
How does sympathetic outflow happen below level L2?
Sympathetic ganglia recieve fibres from L2 level via the sympathetic chain and distrubite tham via connections with lumbar, sacral and coccygeal spinal nerves
All spinal nerves and their named nerves contain ______ ______; including femoral, sciatic, obturator, pudendal
All spinal nerves and their named nerves contain sympathetic fibres; including femoral, sciatic, obturator, pudendal
What does blockade of sympathetic tone cause due to spinal anaesthetic?
Block of sympathetic tone to all arterioles in lower limb;
Vasodilatation
- skin looks flushed
- warm limbs
- reduced sweating
What does the pudendal nerve supply?
Nerve of the perineum
Somatic motor and somatic sensory to structures of the perineum
What does pudendal nerve block cause?
Anaesthesia of majority of perineum
The pudendal nerve;
Exits pelvis via ______ ____ ______
Passes posterior to _________ _______
Re-enters pelvis/perineum via ______ _____ _______
The pudendal nerve;
Exits pelvis via greater sciatic foramen
Passes posterior to sacrospinous ligament
Re-enters pelvis/perineum via lesser sciatic foramen
What does the pudendal nerve travel within and with?
Passageway within obturator fascia
With internal pudendal artery and vein (and nerve to obturator internus)
What can be used as a landmark to administer pudendal nerve block?
Ischial spine
When can pudendal nerve block be used during labour?
- forceps delivery
- painful vaginal delivery
- episiotomy incision
How is pudendal nerve anaesthetised in perineal suturing after delivery?
LA is injected along site of tear/episiotomy to anesthetise branches of pudendal
What can be stretched and torn during labour?
- pudendal nerve
- fibres within the levator ani
- external anal sphincter
How is episiotomy performed?
Posterolateral (mediolateral incision)
- made into the relatively ‘safe’ fat filled ischianal fossa and avoids the incision extending into the rectum
