Anatomy of anaesthesia for labour Flashcards
What is the motor function of the reproductive system in women?
Uterine cramping (menstruation) Uterine contraction (labour) Pelvic floor muscle contraction (sneezing)
What is the sensory function of the female reproductive system?
Pain from adnexae (ovaries and fallopian tubes)
Pain from uterus
Pain from vagina
Pain from perineum
Why is it important to know if the pain is from pelvis or perineum?
Fundamental to deciding which nerve fibre types are carrying out which function
Pelvis: body cavity, sympathetic, parasymp or visceral afference
Perineum; body wall, somatic motor and sensory
What separates the pelvis from perineum?
Levator ani
Which nerve fibres mediate uterine cramping?
Hormonal; sympathetic and parasymp
Which nerve fibres mediate uterine contraction?
Hormonal; symp and parasymp
Which nerve fibres mediate pelvic floor muscle contraction?
Somatic motor
Which nerve fibres mediate pain from adnexae?
Visceral afferents
Which nerve fibres mediate pain from uterus?
Visceral afferents
Which nerve fibres mediate pain from vagina?
Visceral afferents (pelvic) Somatic sensory (perineum)
Which nerve fibres mediate pain from perineum?
Somatic sensory
How is pain sensed from the superior aspect of pelvic organs/ touching peritoneum?
Visceral afferents
Run alongside symp fibres
Enter spinal cord between levels T11-L2
Pain is perceived by patient as suprapubic
How is pain sensed from the inferior aspect of pelvic organs/ not touching peritoneum?
Visceral afferents
Run alongside parasymp fibres
Enter spinal cord at levels S2,3,4
Pain perceived in S2,3,4 dermatome (perineum)
How is pain sensed from the urethra/ vagina in the pelvis (above levator ani)?
Visceral afferents
Parasymp
Spinal cord levels S2,3,4
How is pain sensed from the urethra/ vagina in the perineum below the levator ani?
Somatic sensory
Pudendal nerve
Spinal cord levels S2,3,4
Localised pain within perineum
What spinal cord levels will the symps that supply the pelvis arise from?
Sacral sympathetic trunks
T11-L2
Superior hypogastric plexus
What spinal cord levels will the parasymps that supply the pelvis arise from?
Sacral outflow (S2,3,4)
Pelvic splanchinic nerves
Emerge from spinal roots
Mixes with sympathetic in inferior hypogastric plexus
In the female reproductive system; where will visceral afferents travel to?
Back to T11-L2 from pelvic organs which touch the peritoneum (uterine tubes, uterus, ovaries)
In the female reproductive system; where will the pudendal nerve travel to?
Back to S2,3,4
Organs within the perineum; inferior vagina, perineal muscles, glands, skin
What are the 2 important spinal cord levels in terms of pain from female repro system?
T11-L2
S2-4
Pain sensation from perienum?
Body wall
Somatic sensation
Pudendal nerve
S2,3,4
Pain sensation from pelvis
Body cavity
Autonomics/ visceral afferents
Then distinguish if touching peritoneum or not
Pain sensation from pelvic structures touching peritoneum
Superior
Follows sympathetics
T11-L2
Pain sensation from pelvic structures not touching peritoneum?
More inferior
Follows parasymps
S2,3,4
What are the 3 modes for anaesthesia in labour?
Spinal
Epidural
Pudendal nerve block
Describe a spinal block
Anaesthetizes from waist down; intra and sub peritoneal plus somatic area
Describe an epidural block
Anesthetizes subperitoneal plus somatic innervated by pudendal
Describe a pudendal nerve block
Anaesthetizes areas innervated by pudendal nerve
When does the spinal cord become cauda equina?
L2
Where does the SA space end?
S2
Where is anaesthetic injected in a spinal and epidural?
L3-4 (L5) region
With which pelvic bony landmark is L4 in line with?
Superior point on iliac crests
Through which structures will the needle for an epidural pass through?
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space (fat and veins)
Through which structures will the needle for a spinal pass through?
Supraspinous Interspinous Ligamentum flavum Epidural space Dura mater Arachnoid mater Subarachnoid space
Where do symp nerves exit the spinal cord?
T1-L2
What occurs with sympathetic outflow below L2?
Sympathetic ganglia recieve fibers from L2 via symp chain and then distrubute them via connections with lumbar, sacral and occygeal spinal nerves
Do spinal nerves contain symp?
Yes; with their named nerve (femoral, sciatic, obturator, pudendal)
Which part of the circulation is supplied by sympathetics?
Arterioles
What will blockade of symp tone in arterioles in lower limb result in?
Vasodilation;
skin of lower limbs looks flushed
Warm lower limbs
Reduced sweating
What is a sign that spinal anaesthetic is working?
Vasodilation in lower limbs
Hypotension
What is the nerve of the perineum?
Pudendal nerve; somatic motor and somatic sensory, parasymp (S2,3,4)
Through which structure will the pudendal nerve exit the pelvis and then re-enter the pelvis?
Exit; greater sciatic foramen
Posterior to sacrospinous ligament
Re-enters via lesser sicatic foramen
Through which canal does the pudendal nerve travel in?
Pudendal canal
Passageway within the obturator fascia
With internal pudendal artery and vein (and nerve to obturator internus)
Which aspect of the sacrospinous ligament does the pudendal nerve cross?
Lateral
What can be used as a landmark to administer pudendal nerve block?
Ischial spine (can be felt on internal examination at the 4 and 8 o’clock position)
When is a pudendal nerve block utilised?
Forceps delivery
Painful vaginal delivery
Episiotomy incision
What mechanism for nerve block is utilised for perineal suturing post delivery?
LA is injected along site of tear/ episiotomy to anaesthetise branches of pudendal
How is the pudendal nerve damaged in labour?
Branches can be stretched with resultant stretch of nerve fibres
Fibres within levator ani (puborectalis) or external anal sphincter muscle could be torn and as a result weakened
What are the different types of perineal tears?
1st
2nd
3rd degree
Where is a posterolateral episiotomy incision made?
“Safe” fat filled ischioanal fossa to avoid the incision extending into the rectum
Where is a medial episiotomy incision made?
Not used as much as if further tearing occurs, it will involve the anal sphincter
What is a 1st degree tear?
Fourchette and vaginal mucosa are damaged and underlying muscles are exposed but not torn
What is a 2nd degree tear?
Posterior vaginal walls and perennial muscles but anal sphincter is intact
What is a 3rd degree tear?
Extends to anal sphincter that is torn, but rectal mucosa is intact
What is a 4th degree tear?
Anal canal is opened, and tear may spread to rectum
