What is the correct sequence and clinical practice for combined spinal epidural (CSE) anesthesia using a Tuohy (18-gauge) and Spinocan (25-gauge) needle?

Combined Spinal-Epidural Anesthesia: Correct Sequence and Clinical Practice

The needle-through-needle technique using an 18-gauge Tuohy needle with a 25-gauge pencil-point spinal needle (such as Spinocan) is the recommended approach for combined spinal-epidural (CSE) anesthesia, providing rapid onset with the flexibility of epidural extension. 1

Equipment Setup and Preparation

• Use pencil-point (atraumatic) spinal needles instead of cutting-bevel needles to minimize the risk of post-dural puncture headache 1
• The spinal needle should protrude at least 13-15 mm beyond the tip of the Tuohy needle for adequate dural puncture 2, 3
• Ensure equipment, facilities, and support personnel are immediately available to treat potential complications including hypotension, respiratory depression, and local anesthetic systemic toxicity 1

Step-by-Step Technique Sequence

1. Epidural Space Identification

• Insert the 18-gauge Tuohy needle using loss-of-resistance technique to identify the epidural space 2, 3
• The needle-through-needle approach provides better tactile feedback for confirming correct midline placement 1

2. Spinal Component

• Once epidural space is confirmed, advance the 25-gauge Spinocan needle through the Tuohy needle until dural puncture is achieved 2, 3
• Confirm free flow of cerebrospinal fluid - this indicates both successful spinal placement AND correct midline epidural needle position 1
• Inject spinal medications (typically low-dose local anesthetic with opioid) 1
• Remove the spinal needle completely

3. Epidural Catheter Placement

• Thread the epidural catheter through the Tuohy needle 3-5 cm into the epidural space 2, 3
• Remove the Tuohy needle while securing the catheter
• The catheter entering the dural puncture site is theoretically possible but clinically unfounded with proper technique 4

Drug Selection and Dosing

• Combine low-dose local anesthetic with opioid for both spinal and epidural components to minimize motor block while providing effective analgesia 1
• The spinal component provides rapid onset (typically ready for surgery in 22-23 minutes with needle-through-needle technique) 3
• Use dilute concentrations of local anesthetics (e.g., bupivacaine 0.1-0.125%) with opioids for epidural maintenance 1

Clinical Advantages Over Single Techniques

• CSE provides faster onset than epidural alone (approximately 7 minutes faster) with equivalent or superior analgesia 1, 3
• The technique allows for reduced total drug dosage compared to epidural-only techniques 5, 4
• Needle-through-needle CSE is more reliable than epidural alone because successful spinal flow confirms correct epidural space identification 1
• Patient acceptance is significantly better with needle-through-needle technique (85%) compared to double-segment approaches (66.6%) 3

Common Pitfalls and How to Avoid Them

• Inadequate spinal needle length: Ensure the spinal needle extends at least 13-15 mm beyond the Tuohy tip; 10 mm protrusion has shown inadequacy in 15% of patients 2, 3
• Failure to confirm CSF flow: Always verify free CSF flow before injecting spinal medications - this confirms both spinal and epidural placement 1
• Testing the epidural catheter too late: The epidural catheter cannot be tested until after spinal injection, so proper initial Tuohy placement is critical 1
• Motor block concerns: Use low-concentration local anesthetics with opioids to achieve selective sensory blockade while preserving motor function 1

Monitoring and Complications

• Vigilantly monitor during and after any epidural injection to detect potential subarachnoid migration of medications 4
• Pruritus frequency is increased with CSE compared to epidural alone, but fetal and neonatal side effects are not increased 1
• The incidence of post-dural puncture headache with 25-gauge pencil-point needles is comparable to epidural-only techniques 5, 3
• Hypotension and bradycardia can occur; have vasopressors and atropine immediately available 1, 5

When CSE is Particularly Indicated

• Labor analgesia when rapid onset is desired but duration may exceed single-shot spinal effects 1
• Anticipated difficult airway or high-risk obstetric patients where avoiding general anesthesia is critical 1
• Major orthopedic surgery requiring dense initial block with extended postoperative analgesia 2, 4