What is the step‑by‑step technique for performing spinal anaesthesia in an adult patient without contraindications undergoing surgeries below the umbilicus, obstetric procedures, or lower‑extremity operations?

Technique of Spinal Anaesthesia

Spinal anaesthesia should be performed using a ≥25-gauge pencil-point needle at the L3-4 or L4-5 interspace, with strict aseptic technique, after confirming the absence of contraindications and limiting pre-procedure intravenous fluids to ≤500 mL to reduce urinary retention risk. 1

Pre-Procedure Assessment and Preparation

Absolute contraindications must be excluded:

• Patient refusal 1
• Active coagulopathy or therapeutic anticoagulation 1
• Infection at the puncture site 1

Laboratory thresholds for safe neuraxial blockade:

• Platelet count ≥75 × 10⁹/L in suspected thrombocytopenia 1
• Fibrinogen ≥1.5 g/L (Clauss method) in hypofibrinogenemic patients 1
• Factor VIII or IX ≥50 IU/dL for mild bleeding history, ≥80 IU/dL for severe bleeding history in haemophilia 1

Fluid management:

• Establish intravenous access before initiating the block 2
• Limit crystalloid administration to ≤500 mL to minimize postoperative urinary retention 1
• Do not administer a fixed bolus volume routinely 2

Aspiration prophylaxis:

• Consider aspiration prophylaxis, particularly in obstetric patients and those at high aspiration risk 2, 3

Equipment Selection

Needle choice is critical for reducing complications:

• Use ≥25-gauge pencil-point needles (Whitacre or Sprotte design) to reduce post-dural puncture headache incidence to <1% 2, 1, 4
• Avoid cutting-bevel needles, which significantly increase PDPH risk 2, 1, 4

Aseptic technique:

• Standard aseptic skin preparation and sterile draping are sufficient 1

Patient Positioning

Position selection should be tailored to the surgical site:

• Sitting position for perianal or perineal surgery minimizes hypotension and motor block 2, 1
• Lateral decubitus with operative side down for unilateral lower extremity procedures (e.g., knee arthroscopy) 2, 1
• Supine position may be used with hyperbaric solutions for bilateral procedures 4

Special technique for difficult anatomy:

• Taylor's approach targeting L5-S1 is useful when midline lumbar approaches are difficult due to calcified ligaments, previous back surgery, or anatomical abnormalities 4

Procedural Steps

Identify the interspace:

• Palpate the iliac crests; a line connecting them crosses the L4 vertebral body or L4-5 interspace 1
• Target L3-4 or L4-5 interspace 1

Needle insertion:

• Insert the ≥25-gauge pencil-point needle via midline or paramedian approach 1
• Advance slowly through skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, and dura mater 1

Confirm cerebrospinal fluid flow:

• Observe free flow of clear CSF before injecting any medication 1
• The absence of CSF on aspiration does not rule out intrathecal placement if using a catheter 4

Drug administration:

• Inject the calculated dose of local anaesthetic slowly to ensure even distribution 1
• For lower extremity surgery, bupivacaine 0.5% hyperbaric 10-12.5 mg (2-2.5 mL) is recommended 4
• Hyperbaric solutions produce more predictable blocks with fewer high blocks compared to isobaric solutions 4
• Consider adding intrathecal morphine 50-100 μg for postoperative analgesia in obstetric cases 3

Intra-Operative Monitoring and Management

Block height assessment:

• Reassess sensory block height at least every 5 minutes after injection until the level stabilizes to detect unintended cephalad spread 4

Cardiovascular monitoring:

• Monitor blood pressure continuously, especially during the first 15-30 minutes 4
• Hypotension occurs in approximately 1 in 4,367 cases requiring cardiovascular support 4
• Treat hypotension promptly with vasopressors (phenylephrine 50-100 μg boluses) combined with intravenous fluids 4, 3

Warning signs of high or total spinal block:

• Agitation, marked hypotension, bradycardia, upper-limb weakness, dyspnea, or speech difficulty require immediate evaluation and intervention 4
• High or total spinal requiring cardiovascular or respiratory support occurs in approximately 1 in 4,400 procedures 4

Post-Operative Care and Discharge Criteria

Mobilization criteria before ambulation:

• Return of perianal sensation (S4-5 dermatomes) 2, 1
• Plantar flexion strength comparable to pre-operative levels 2, 1
• Return of proprioception in the big toe 2, 1
• Test for straight-leg raising at 4 hours from injection; if unable, immediate comprehensive evaluation is required 4

Discharge with residual block:

• Patients may be discharged with residual sensory or motor blockade if the limb is protected and adequate home support is arranged 2, 1
• Provide written and verbal instructions about expected block duration 2, 1

Post-discharge instructions:

• Avoid driving, operating machinery, or consuming alcohol for 24 hours 1
• Provide clear information on PDPH warning signs and emergency contacts 1
• Include information on what to do if post-dural puncture headache occurs 2

Pain management:

• Administer a long-acting NSAID pre-emptively unless contraindicated 1
• Provide an analgesic plan with oral analgesics and written instructions for when the block wears off 2
• Limit routine opioid use to reduce postoperative nausea and vomiting 1

Antiemetic prophylaxis:

• Reserve for high-risk patients (prior PONV, motion sickness, laparoscopic procedures) 1

Critical Pitfalls to Avoid

Technique errors:

• Limit attempts to a maximum of 4; multiple attempts significantly increase complication risk 4
• Never administer epidural-dose volumes through an intrathecal catheter; this can precipitate high or total spinal block 4
• Ensure clear labeling of spinal catheters and structured hand-off communication to prevent dosing errors 4

Positioning errors:

• Avoid changing patient position after hyperbaric bupivacaine injection, as this can cause late cephalad spread even after 65 minutes 5

Fluid management errors:

• Do not force oral intake postoperatively; this may provoke nausea and delay discharge 1