13.2 Epidural & Combined Spinal-Epidural (CSE) Techniques & PDPH
Key Takeaways
- The epidural space is bounded anteriorly by the posterior longitudinal ligament, posteriorly by the ligamentum flavum and laminae, and laterally by the pedicles and intervertebral foramina; it contains adipose tissue, lymphatics, and the valveless Batson's internal vertebral venous plexus.
- Batson's venous plexus engorges during pregnancy, morbid obesity, and increased intra-abdominal pressure, compressing the epidural space volume and dramatically increasing the risk of accidental intravascular catheter cannulation.
- The standard epidural test dose (3 mL of 1.5% lidocaine with 1:200,000 epinephrine [15 mcg epi]) detects intravascular entry via a heart rate increase ≥20-30 bpm or SBP rise ≥15 mmHg within 30-60 seconds, and detects intrathecal entry via rapid (2-3 min) sensory/motor blockade.
- Post-Dural Puncture Headache (PDPH) results from persistent transdural CSF leakage exceeding production (~0.35-0.5 mL/min), causing caudal brain sag, traction on pain-sensitive meninges/cranial nerves (especially CN VI abducens palsy), and compensatory Monro-Kellie cerebral vasodilation.
- Epidural Blood Patch (EBP) using 15-20 mL of autologous blood placed at or one space below the dural puncture level is the gold standard definitive therapy for PDPH, achieving an 85-90% initial success rate.
Last updated: August 2026
13.2 Epidural & Combined Spinal-Epidural (CSE) Techniques & PDPH
Epidural anesthesia involves administering local anesthetics and adjuvants into the potential space surrounding the spinal dural sac. Combined spinal-epidural (CSE) techniques blend the rapid, reliable onset of subarachnoid anesthesia with the flexibility and prolonged duration of an indwelling epidural catheter. However, breeching the dural architecture introduces the risk of Post-Dural Puncture Headache (PDPH). Masterful understanding of epidural space boundaries, Batson's plexus dynamics, test dose pharmacology, and blood patching protocols is critical for NBCRNA NCE certification.
1. Epidural Space Anatomy & Structural Boundaries
The epidural space is a circumferential, potential anatomical space surrounding the dural sac, extending from the foramen magnum superiorly to the sacrococcygeal ligament (sacral hiatus) inferiorly.
+-------------------------------------------------------------------------+
| EPIDURAL SPACE BOUNDARIES & CONTENTS |
+--------------------+----------------------------------------------------+
| Anatomical Boundary| Anatomical Structure |
+--------------------+----------------------------------------------------+
| **Anterior** | Posterior Longitudinal Ligament & Vertebral Bodies |
| **Posterior** | Ligamentum Flavum and Anterior Laminae |
| **Lateral** | Pedicles and Intervertebral Foramina |
| **Superior** | Foramen Magnum (Dura fuses to periosteum of cranium|
| | preventing cranial spread of epidural local anesth)|
| **Inferior** | Sacrococcygeal Ligament (Sacral Hiatus) |
| **Contents** | Fat, lymphatics, segmental nerve roots, and the |
| | **valveless Batson's internal vertebral venous px**|
+--------------------+----------------------------------------------------+
[EPIDURAL SPACE CROSS-SECTIONAL ARCHITECTURE]
Anterior
[Posterior Long. Ligament]
|
v
[Epidural Space Fat]
|
v
[Dura & Arachnoid Mater]
|
v
[Spinal Cord / CSF Space]
|
v
[Dura & Arachnoid Mater]
|
v
[Epidural Space Fat]
(Batson's Internal Venous Plexus)
|
v
[LIGAMENTUM FLAVUM]
|
Posterior
Batson's Internal Vertebral Venous Plexus
- Structure: A network of thin-walled, valveless veins lying primarily in the anterolateral epidural space that communicates directly with the pelvic veins, azygos system, and intracranial venous sinuses.
- Pathophysiology of Engorgement: Any clinical state that increases intra-abdominal pressure or compresses the inferior vena cava (e.g., pregnancy, morbid obesity, intra-abdominal tumors, ascites, coughing/Valsalva) forces blood into Batson's plexus.
- Clinical Consequences:
- Engorged veins compress and diminish the volume of the epidural space, requiring a $20 - 30%$ reduction in local anesthetic volume in term parturients to prevent excessively high block levels.
- Greatly increases the risk of accidental epidural vein cannulation during catheter placement.
Skin-to-Epidural Space Distance
- In $\approx 80%$ of the adult population, the distance from the skin surface to the ligamentum flavum / epidural space is $4 - 6 \text{ cm}$ (average $\approx 5 \text{ cm}$).
- In thin patients, this distance may be $<3 \text{ cm}$; in morbidly obese patients, it may exceed $8 - 10 \text{ cm}$.
2. Loss-of-Resistance (LOR) Technique & Needle Selection
+-------------------------------------------------------------------------+
| EPIDURAL NEEDLE DESIGNS |
+--------------------+----------------------------------------------------+
| Needle Type | Distinguishing Characteristics |
+--------------------+----------------------------------------------------+
| **Tuohy Needle** | Curved Huber tip with 15° - 30° bevel deflection. |
| (Most Common) | Pushes the dura away upon entry and directs the |
| | catheter along the long axis of the epidural canal.|
| **Hustead Needle** | Modified tip with intermediate (15°) bevel curve. |
| **Crawford Needle**| Straight bevel needle without curve; higher risk of|
| | dural puncture; preferred for steep thoracic angle.|
+--------------------+----------------------------------------------------+
Loss-of-Resistance: Air vs. Saline
+-------------------------------------------------------------------------+
| LOR TO AIR vs. LOR TO SALINE COMPARISON |
+--------------------+------------------------+---------------------------+
| Characteristic | LOR with Air | LOR with Saline |
+--------------------+------------------------+---------------------------+
| **Feel / Spring** | Compressible "spongy" | Non-compressible; smooth |
| | bounce until breach | continuous tactile glide |
| **Pneumocephalus | High risk if dura is | ZERO risk of |
| Risk** | punctured (severe | pneumocephalus |
| | acute headache) | |
| **Block Quality** | Air bubbles can cause | Uniform distribution; |
| | patchy, unblocked | lower incidence of |
| | dermatomes | patchy blocks |
| **Embolism Risk** | Venous air embolism | No air embolism risk |
| | if vein is entered | |
| **CSF Distinction**| Easy to differentiate | Must distinguish CSF from |
| | gas from CSF fluid | injected warm saline |
+--------------------+------------------------+---------------------------+
Differentiating Cerebrospinal Fluid (CSF) from Saline
If fluid returns through the epidural needle or catheter:
- Temperature: CSF is body temperature ($37^\circ\text{C}$ / warm); saline injectate is room temperature (cool).
- Glucose Test Strip: CSF contains glucose ($45 - 80 \text{ mg/dL}$); saline contains $0 \text{ mg/dL}$.
- Protein Strip: CSF tests positive for protein; saline tests negative.
- pH: CSF is slightly acidic/neutral (pH $\approx 7.32$).
Catheter Insertion Depth Rule
- The epidural catheter should be threaded $3 - 5 \text{ cm}$ into the epidural space.
- Depth Formula: $\text{Total Depth at Skin} = \text{Distance from Skin to LOR} + (3 \text{ to } 5 \text{ cm})$.
- Traps: Inserting $<3 \text{ cm}$ increases the risk of premature dislodgement. Inserting $>5 \text{ cm}$ increases the risk of catheter curling, unilateral transforaminal exit, knotting, or venous cannulation.
3. The Epidural Test Dose: Rationale, Pharmacology & Hemodynamics
Every epidural catheter must be formally tested prior to initiating a therapeutic infusion to rule out intravascular or subarachnoid (intrathecal) misplacement.
+-------------------------------------------------------------------------+
| STANDARD EPIDURAL TEST DOSE COMPOSITION |
+-------------------------------------------------------------------------+
| • **Volume:** 3.0 mL |
| • **Local Anesthetic:** 1.5% Lidocaine = 45 mg Lidocaine |
| • **Vasoconstrictor:** 1:200,000 Epinephrine = 5 mcg/mL = 15 mcg Epi |
+-------------------------------------------------------------------------+
+-------------------------------------------------------------------------+
| TEST DOSE INTERPRETATION PROTOCOL |
+-----------------------+-------------------------------------------------+
| Malposition Tested | Positive Test Response Criteria |
+-----------------------+-------------------------------------------------+
| **Intravascular | • **Heart Rate increase ≥ 20 - 30 bpm** or |
| Placement** | **Systolic Blood Pressure rise ≥ 15 mmHg** |
| (Catheter in vein) | within **30 to 60 seconds** of injection |
| | • Subjective symptoms: Metallic taste, auditory |
| | tinnitus, circumoral numbness, palpitations |
| **Subarachnoid | • Rapid development of **warmth, sensory loss, |
| Placement** | and motor block in lower extremities** within |
| (Catheter in CSF) | **2 to 3 minutes** (45 mg lidocaine spinal) |
| **Correct Epidural | • Stable baseline vital signs without rapid T-wave|
| Placement** | changes or profound spinal motor block |
+-----------------------+-------------------------------------------------+
Clinical Nuances in Special Patient Populations
- Laboring Parturients: Uterine contractions can naturally increase heart rate by $15 - 20 \text{ bpm}$. The test dose must be administered immediately between contractions. In obstetrics, a pulse pressure elevation $>15%$ or ECG T-wave amplitude increase $>25%$ provides sensitive confirmation of intravascular injection.
- Beta-Blocked / Elderly Patients: Chronotropic response to epinephrine may be blunted. Look for an acute systolic blood pressure elevation $\ge 15 - 20 \text{ mmHg}$ or pulse pressure widening rather than tachycardia.
- NCE Golden Rule: A negative test dose does never grant absolute immunity against subsequent catheter migration. All subsequent therapeutic boluses must be fractionated ($3 - 5 \text{ mL}$ aliquots every $3 - 5 \text{ minutes}$).
4. Combined Spinal-Epidural (CSE) Technique
Combined Spinal-Epidural (CSE) anesthesia unites the rapid, dense, predictable sensory block of spinal anesthesia with the flexibility and indwelling continuous analgesia of an epidural catheter.
[NEEDLE-THROUGH-NEEDLE CSE TECHNIQUE]
1. Epidural Needle Identifies Space 2. Long Spinal Needle Passed to CSF
[Tuohy 17G/18G] [Tuohy 17G/18G]
|| || [Spinal Needle 25-27G]
|| || ||
v v ||
=== [Ligamentum Flavum] === === [Ligamentum Flavum] ===
[Epidural Space] [Epidural Space]
--- [Dura-Arachnoid] --- --- [Dura-Arachnoid] --- v (Dural puncture)
[Subarachnoid Space] [Subarachnoid Space] ===> (CSF flow)
Inject Spinal Dose
Withdraw Spinal Needle
Thread Epidural Catheter
Clinical Advantages & Potential Pitfalls of CSE
- Advantages: Immediate surgical analgesia (within $2 - 5 \text{ minutes}$); significantly lower total local anesthetic and opioid dose required compared to epidural alone; provides a reliable indwelling route for postoperative analgesia.
- Pitfalls: Failure to obtain CSF through the long spinal needle; inability to verify epidural catheter functionality until the spinal block begins to regress; risk of epidural local anesthetic diffusing through the dural puncture hole (increasing spinal block height).
5. Post-Dural Puncture Headache (PDPH): Pathophysiology & Risk Profile
Post-Dural Puncture Headache (PDPH) is a classic iatrogenic complication resulting from a persistent breach in the dural-arachnoid membrane.
[PDPH PATHOPHYSIOLOGIC CASCADE]
Breach in Dura-Arachnoid Sheath (Accidental Wet Tap / Lumbar Puncture)
|
v
Continuous Transdural CSF Leakage Exceeding Production (>0.35 mL/min)
|
v
Intracranial Hypotension & Loss of CSF Cushion
|
+--------------------------+--------------------------+
| |
v v
[Caudal "Brain Sag" in Upright Position] [Monro-Kellie Doctrine Compensation]
• Gravitational downward displacement • Loss of CSF volume triggers reflex
• Mechanical traction on meninges, anchoring cerebral venous and arterial
dural veins, and tentorium cerebelli vasodilation
• **Traction on Cranial Nerves:** • Vascular component of throbbing
- **CN VI (Abducens):** Diplopia / Strabismus headache
- **CN VII & VIII:** Tinnitus, hearing loss, vertigo
| |
+--------------------------+--------------------------+
|
v
Bifrontal / Occipital Postural Headache (Worse Upright, Relieved Supine)
+-------------------------------------------------------------------------+
| CLINICAL RISK FACTORS FOR PDPH |
+--------------------+----------------------------------------------------+
| Risk Factor | High-Risk vs. Low-Risk Category |
+--------------------+----------------------------------------------------+
| **Patient Age** | Highest in **18 - 40 years** (pliable dura, active);|
| | Lowest in prepubertal children and elderly (>65 yr)|
| **Patient Sex** | **Females > Males (2:1)**; highest in pregnancy |
| | (estrogen-mediated dural elasticity, pushing) |
| **Needle Design** | **Cutting (Quincke) >> Non-cutting Pencil-Point** |
| | (Whitacre / Sprotte reduce risk by >75-80%) |
| **Needle Gauge** | Large (17-18G Tuohy: 70-80% risk after wet tap) >> |
| | Small (25-27G pencil-point: <1% risk) |
| **Bevel Direction**| Perpendicular transects fibers; **parallel to |
| | longitudinal fibers** separates them (lower risk) |
+--------------------+----------------------------------------------------+
Clinical Presentation
- Hallmark Feature: Severe, throbbing postural headache (frontal, occipital, or band-like radiating to the neck and shoulders) that worsens dramatically within 15-30 seconds of sitting or standing and is substantially or completely relieved by lying flat (supine).
- Onset: Typically develops within $12 - 48 \text{ hours}$ post-procedure (rarely immediate, rarely $>5 \text{ days}$).
6. PDPH Management: Conservative Protocols vs. Epidural Blood Patch (EBP)
+-------------------------------------------------------------------------+
| CONSERVATIVE vs. DEFINITIVE PDPH THERAPY |
+--------------------+------------------------+---------------------------+
| Modality | Therapeutic Regimen | Mechanism of Action |
+--------------------+------------------------+---------------------------+
| **Conservative | • Horizontal bed rest | • Minimizes gravitational |
| Measures** | • Aggressive IV / oral | downward brain traction |
| | hydration | • Restores baseline CSF |
| | • Oral / IV Caffeine | • Caffeine (adenosine rec.|
| | (300-500 mg IV) | antagonist) causes |
| | • NSAIDs & Acetaminophen| cerebral vasoconstriction|
| | • Cosyntropin (ACTH) | • ACTH stimulates adrenal |
| | (1 mg IV/IM) | mineralocorticoid & CSF |
| **Sphenopalatine | Transnasal 2-4% | Blocks parasympathetic- |
| Ganglion Block** | Lidocaine swabs | mediated cerebral vasodila|
| **Epidural Blood | **15 - 20 mL sterile | • Gelatinous clot seals |
| Patch (EBP)** | autologous blood** | dural hole immediately |
| (Definitive) | injected at/below level| • Transmits pressure wave |
| | of original puncture | to restore CSF dynamics |
+--------------------+------------------------+---------------------------+
[EPIDURAL BLOOD PATCH (EBP) EXECUTION PROTOCOL]
Step 1: Sterile Setup Step 2: Dual Operator Access
+-----------------------+ +----------------------------------------+
| • Informed consent | | • Operator 1: Aseptic LOR into epidural|
| • Verify absence of | | space at or one space BELOW wet tap |
| contraindications | | • Operator 2: Sterile venipuncture of |
| (coagulopathy, | | 20 mL autologous blood |
| sepsis, local skin | +----------------------------------------+
| infection) | |
+-----------------------+ v
Step 3: Slow Blood Injection
+----------------------------------------+
| • Inject 15 - 20 mL blood slowly |
| • Halt immediately if severe back pain |
| or lower extremity radiculopathy |
+----------------------------------------+
|
v
Step 4: Post-Procedure Care
+----------------------------------------+
| • Maintain supine position for 1-2 hrs |
| • 85-90% immediate relief; repeat patch|
| in 24-48 hrs if symptoms recur (95%) |
+----------------------------------------+
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Test Your Knowledge
A CRNA administers an epidural test dose containing 3 mL of 1.5% lidocaine with 1:200,000 epinephrine (15 mcg) to a 28-year-old laboring parturient. Within 45 seconds, the patient's heart rate increases from 78 bpm to 110 bpm and she reports a metallic taste in her mouth. How should the CRNA interpret these findings and what is the immediate action?
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C
D
Test Your Knowledge
Which of the following anatomical and physiological characteristics accurately describes the epidural space and its vascular contents during late pregnancy?
A
B
C
D
Test Your Knowledge
A 26-year-old postpartum patient reports a severe, incapacitating frontal and occipital headache 36 hours after an accidental dural puncture with a 17-gauge Tuohy needle. She also notes double vision (diplopia). What is the specific cranial nerve mechanism responsible for her visual symptoms, and what is the underlying pathophysiology?
A
B
C
D
Test Your Knowledge
A patient with a confirmed, debilitating Post-Dural Puncture Headache unresponsive to 48 hours of aggressive hydration, oral caffeine, and analgesics is scheduled for an Epidural Blood Patch (EBP). Which procedural guideline accurately reflects the gold standard execution and mechanics of this intervention?
A
B
C
D