Anatomy of Anaesthesia in Labour Flashcards
Pain from which structures of the female reproductive system is transmitted via sensory nerve fibres?
- adnexae (ovaries + fallopian tubes)
- uterus
- vagina
- perineum
What motor functions does the female reproduction system have?
- Uterine “cramping” (e.g. menstruation)
- Uterine contraction (e.g. during labour)
- Pelvic floor muscle contraction (e.g. during sneezing)
How do we know what nerve fibres carry out which function in the reproductive tract?
If structure supplied is ABOVE levator ani muscle
=> PELVIS
=> sympathetic, parasympathetic and visceral afferent
If structure supplied is BELOW levator ani muscle
=> PERINEUM
=> somatic motor and somatic sensory
What type of nerves carry out the uterine “cramping” and “contraction”?
hormonally driven
=> sympathetic/parasympathetic
What type of nerves carry out pelvic floor muscle contraction?
somatic motor
What sensory nerve fibres are responsible for pain in the adnexae, uterus and upper part of the vagina?
visceral afferents
What sensory nerve fibres are responsible for pain from the lower part of the vagina and the perineum?
somatic sensory
How do sensory nerve fibres get to the SUPERIOR aspect of pelvic organs / those touching the peritoneum, and where do these fibres enter/exit the spinal cord?
- Visceral afferents
- Run alongside sympathetic fibres
- Enter spinal cord between levels T11-L2
- Pain is perceived by patient as suprapubic
How do sensory nerve fibres get to the INFERIOR aspect of pelvic organs / those NOT touching the peritoneum, and where do these fibres enter/exit the spinal cord?
- Visceral afferents
- Run alongside parasympathetic fibres
- Enter spinal cord at levels S2, S3, S4
- Pain perceived in S2, S3, S4 dermatome (perineum)
What sensory nerve fibres are responsible for pain sensation in structures which cross between the pelvis and the perineum? (e.g. urethra, vagina)
ABOVE levator ani – in the pelvis
- visceral afferents (parasympathetic - craniosacral)
- S2, S3 and S4
BELOW levator ani – in the perineum
- somatic sensory (pudendal nerve)
- S2, S3 and S4
What sympathetic autonomic nerves are found in the pelvis?
- Sacral sympathetic trunks
- T11-L2
- Superior hypogastric plexus
What parasympathetic autonomic nerves are found in the pelvis?
- Sacral outflow (S2, 3, 4)
- Pelvic splanchnic nerves
- Mix with sympathetics in INFERIOR hypogastric plexus
Pain in the female reproductive system localises to what 2 regions in the spinal cord?
- T11-L2
- S2-S4
If a structure in the female reproductive tract is described as being in the body cavity, how can the type of its sensory nerve fibre be identified?
- If in body cavity => pelvis => autonomic nerves
- if touching peritoneum = more Superior = follows Sympathetics back (T11-L2)
- if NOT touching peritoneum = more Inferior = follows parasympathetics back (S2-4)
What are the 3 main types of anaesthesia used in labour?
Spinal anaesthetic (into subarachnoid space)
Epidural anaesthetic (into epidural space)
Pudendal nerve block
How is spinal anaesthesia given and what structures are affected by the numbing agent?
- Given via lumbar puncture
- Numb from waist down
- Intraperitoneal, subperitoneal and somatic structures are numbed
What structures are numbed by an epidural block?
Subperitoneal and somatic structures
What structures are numbed by a pudendal nerve block?
Somatic structures innervated by pudendal nerve
At what level does the spinal cord become the cauda equina?
L2
At what spinal level is anaesthetic given in a spinal or epidural procedure?
Anaesthetic injected into L3-L4 (L5) region
What layers does the needle pass through during an epidural anaesthetic?
Needle passes through:
- supraspinous ligament
- interspinous ligament
- ligamentum flavum
- epidural space (fat and veins)
What layers must the needle pass trough during a spinal anaethetic?
- supraspinous ligament
- interspinous ligament
- ligamentum flavum
- epidural space (fat and veins)
+ dura mater
+ arachnoid mater
+ subarachnoid space (contains CSF)
If the sympathetic nerves exit the spinal cord between levels T1-L2, how do sympathetics reach the organs below the level of L2?
Below L2 level
- Nerve signals travel down sympathetic chain to ganglia lower down than L2
- These gangla distribute nerve signals via connections with lumbar, sacral and coccygeal spinal nerves
How can we tell if anaethesia is working?
- All spinal nerves + named nerves contain sympathetics
- Sympathetics supply all arterioles (sympathetic tone)
=> Blockade of sympathetic tone to all arterioles in lower limb = VASODILATION
=> skin looks flushed, warm lower limbs, reduced sweating, hypotension
Describe the course of the pudendal nerve?
- Exits pelvis via GREATER sciatic foramen
- Passes posterior to sacrospinous ligament
- Re-enters pelvis/perineum via LESSER sciatic foramen
- Travels in pudendal canal through obturator fascia
(with internal pudendal artery and vein)
What bony prominence can be used as a landmark to administer pudendal nerve block during labour?
ischial spine (this is where the sacrospinous ligament attaches, which the pudendal nerve crosses over)
What circumstances in labour may indicate the need for a pudendal nerve block?
- Forceps delivery
- Painful vaginal delivery
- episiotomy incision
How is a pudendal nerve block partially used during perineal suturing?
- local anaesthetic is injected along site of tear/episiotomy
=> anaesthetise branches of pudendal (not FULL block)
What can occur if branches of the pudendal nerve are stretched or torn during labour?
If fibres within the levator ani or external anal sphincter are torn
=> muscle weakened (1st, 2nd, 3rd degree)
=> can cause incontinence/ prolapse
What direction is an incision made during an episiotomy and why is this the case?
– Posterolateral direction
=> into the relatively “safe” fat filled ischioanal fossa
=> avoids the incision extending into the rectum
