OB regional anesthesia: spinal, epidural, caudal

What are the stages of labor?
-1st stage (cervical stage)
-2nd stage (pelvic stage)
-3rd stage (placental stage)

What does the 1st stage (cervical stage) of labor begin and end with?
Begins with contractions and ends with complete cervical dilation

What does the 2nd stage (pelvic stage) of labor begin and end with?
Begins with complete cervical dilation and ends with birth of infant

What does the 3rd stage (placental stage) of labor begin and end with?
Begins with birth of infant and ends with placental delivery

Unlike somatic pain, visceral pain may feel?
Dull and vague and may be harder to pinpoint

How is somatic pain generally described?
As musculoskeletal pain

Why is somatic pain usually easier to locate than visceral pain?
Because many nerves supply the muscles, bones and other soft tissues
-somatic pain also tends to be more intense

What is 1st stage labor pain from?
-uterine contractions and distention
-cervical dilation and distention

How is 1st stage labor pain transmitted?
-visceral afferent (sympathetic) nerve fibers
-somatic nerve fibers

In 1st stage labor pain, Visceral nerve fibers accompany:
-sympathetic nerves
-para-cervical nerves
-lumbar sympathetic chain
-enter the dorsal horns of the spinal cord at the T10-L1 level

Somatic nerve fibers include?
-pelvic floor
-vaginal surface of the cervix
-upper vaginal pain
-perineum
-enter the spinal cord at the S2-S4 sc

With visceral pain, early labor pain is located where?
T11 and T12 dermatomes

The intensification of contractions with visceral pain is located where?
T10 and L1

1st stage labor pain can be alleviated with?
-para-cervical block
-lumbar sympathetic block
-para-vertebral block
-epidural block

This is a late stage 1 and stage 2 event
Somatic pain

Somatic pain results from distention of the?
-pelvic floor
-vagina
-perineum

Somatic pain is transmitted primarily through?
-sacral and pudendal plexus
-lumbar plexus

Where in the pelvis are the sacral and pudendal plexus located?
S2-S4 (pudendal nerve)

Where in the pelvis is the lumbar plexus located?
-L1 (Ilioinguinal nerves)
-L1-L2 (genito-femoral nerves)
-L2-L3 (lateral femoral cutaneous nerves)

Para-cervical block entails the particular risks of:
-intravenous injection
-intra-arterial injection
-intra-fetal injection
*note particularly the proximity of the presenting part

Name the types of regional nerve blocks effective for analgesia during labor and delivery
-uterine and cervical (visceral pain)
-perineal and vaginal (somatic pain)
-all pain of parturition

What are types of uterine and cervical (visceral pain) regional nerve blocks effective for analgesia during labor and delivery?
-bilateral para-cervical blocks (obstetrician placed)
-bilateral lumbar sympathetic blocks at L2
-bilateral para-vertebral somatic blocks at T10-L1
-segmental lumbar epidural block T10-L1

What are types of perineal and vaginal (somatic pain) regional nerve blocks effective for analgesia during labor and delivery?
-bilateral pudendal nerve blocks (obstetrician placed)
-bilateral sacral root blocks S2-S4
-“true saddle block” (subarachnoid block) S1-S5
-low caudal epidural block S2-S4

What are types of all pain of parturition regional nerve blocks effective for analgesia during labor and delivery?
-any combo from visceral and somatic categories
*”modified saddle block” with upper level T10 or higher
*lumbar epidural from T10-S4
-caudal epidural from T10-S4

Labor effects what in Maternal physiology?
-respiratory system
-cardiovascular system
-endorphins
-Adrenergic response
-acid-base balance

With labor, minute ventilation increases up to?
300%

When in labor, increased minute ventilation does what?
-results in marked hypocarbia
-leads to hypoventilation between contractions
-maternal and fetal hypoxemia
-utero-placental and feto-placental vasoconstriction

What effects of labor on maternal physiology happens in the respiratory system?
-Intermittent increases and decreases of minute ventilation
-left shifted oxyhemoglobin dissociation curve
-O2 consumption increases up to 75%

What effects of labor on maternal physiology happens in the cardiovascular system?
-labor leads to an increase in maternal cardiac output (CO) by 10-25%
-primarily increased stroke volume (SV)
-BP increase 5-20%
-delivery leads to auto-transfusion to mother
-analgesia may decrease uterine vascular resistance

What effects of labor on maternal physiology happens with endorphins?
-maternal concentrations of beta-endorphins increase in pregnancy with further increases with labor
-epidural analgesia attenuates this further increase
-may contribute to the pregnant patients decreased anesthetic needs

What effect do catecholamines (Adrenergic response) have?
-increase cardiac stress
-decrease UBF

What increases catecholamine levels?
Pain, stress and anxiety
*epidural analgesia attenuates these rises

How do catecholamines facilitate early extrauterine life?
-surfactant production
-blood flow to vital organs
-thermo-regulation

What effects of labor on maternal physiology happens with acid-base balance?
-pain, anxiety and muscle activity lead to metabolic acidosis
-increased levels of lactic acid in 2nd stage labor
-effective analgesia attenuates lactic acidosis

Name the anatomic changes of pregnancy affecting regional techniques
-engorgement of epidural veins leads to more unintentional venous cannulation and unintentional injection of local anesthetics
-specific gravity of CSF in pregnant patients decreases

It is more difficult for pregnant patient’s to achieve ____ ____
Lumbar flexion

Progressive accentuation of the ____ ____ alters “surface-to-vertebral-anatomy
Lumbar lordosis

Spinal cord terminates as the?
“Conus medullaris” at L1

This attaches the conus medullaris to the coccyx?
Filum terminale

This is made of the nerves of the lower lumbar and sacral roots
“Cauda equina”

This is the nonvascular membrane closely attached to the dura
Arachnoid mater

This is a “potential space” that exists between the dura and the arachnoid mater
Subdural space

(Unintentional) sub dural injection may explain:
-some failed spinal anesthetics
-some slow to develop high spinal blocks with epidurals

The dura mater extends from?
The foramen magnum to S2

This extends from the foramen magnum to the sacral hiatus
Epidural space

This forms the posterior boundary of the epidural space
Ligamentum flavum

Contents of the epidural space include:
-nerve roots
-fat
-lymphatics
-blood vessels

Contraindications to SPA/EPI
-patient refusal
-communication barrier
-increased intracranial pressure (2*mass lesion)
-skin or soft tissue infection at insertion site
-uncorrected maternal hypovolemia
-coagulopathy

Contraindications to SPA/EPI due to coagulopathy?
-platelets <100,000 -low molecular weight heparin (Lovenox) is a clinical risk factor for neuraxial anesthesia -anticoagulants

Postural factors effect anesthetic spread with?
Spinal anesthesia

Position less influential on ___ ___ ___ than with SPA
Epidural anesthesia spread

This is type of anesthesia is infrequently used but may be useful in selected patients when epidural contraindicated
Caudal anesthesia

In spinal anesthesia, what technique is most often used?
“Single shot”

What type of needle has lower incidence of post-dural puncture headache (PDPH)?
Non-cutting needles

Needle off midline will result in?
No CSF
-and possibly pain to the right or left

With SPA: para-median approach, insertion is?
-1 cm lateral
-1 cm caudal
-10-15 degrees off midline to the cephalad spinous process

What is most commonly used regional technique in OBA?
Epidural analgesia/anesthesia

What technique is utilized most often for labor pain control?
Continuous midline technique

Steps (1-9) of epidural technique
-position patient first
-place monitors: FHM, maternal SO2 + NIBP
-mask and hat/hair cover
-open kit, then properly glove sterilely
-prep x 3 in sterile fashion
-allow betadine to dry
-drape sterilely
-set up your tray
-wet seal glass syringe

Steps (10-18) of epidural technique
-infiltrate the area with 1% Lido
-place 17G Tuohy cannula into interspinous ligament
-loss of resistance
-inject 3-5 ml NS
-place catheter
-remove cannula
-connect adapter
-inject “test dose” (2.5-3 ml lido 1.5% with epi)
-tape securely

How should you infiltrate the area with 1% Lido when using epidural technique?
-use smallest cannula (25, 27G)
-inject slowly
-do not “fan” or repeat “in and out”
-inject SQ Interspinous ligaments

What do engorged spinal veins do to CSF space?
-decrease the space and displace CSF into the thoracic region

Is fat increased or decreased in the epidural space?
Neither. It is unchanged.

What do hormonal changes do to the ligamentum flavum?
-Softens it
-increased risk of wet tap

Where does the dura mater terminate?
S2

What meningeal layer is CSF found in?
SUB arachnoid space

What is the key factor in obtaining the level of block desired?
VOLUME
-guideline is 1-2 mL per segment
-adjust (<5 ft 2 in) or (>6 ft 2 in)

Test dose for lidocaine + epinephrine
(2.5-) 3 cc 1.5% Lidocaine + Epinephrine

Caudal anesthesia
-requires correct identification of the sacral hiatus
-angle of insertion 45 degrees, contact bone, redirect to 15 degrees, insert approx. 1-2 cm
-use test dose

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