Spinal Anesthesia: Indications, Contraindications, and Technique
Primary Recommendation
Spinal anesthesia is indicated for lower abdominal, pelvic, perineal, and lower extremity surgery in adults, with specific local anesthetic selection and dosing based on surgical duration and site: use lidocaine 40-60 mg for procedures <1 hour, bupivacaine 7.5-12 mg for procedures 2-5 hours, and ensure coagulation parameters meet safety thresholds before needle insertion.
Indications
Spinal anesthesia is appropriate for:
- Lower extremity surgery (orthopedic procedures, vascular surgery)
- Perineal surgery (anorectal, urologic procedures)
- Lower abdominal surgery (gynecologic, urologic, general surgery below umbilicus)
- Pelvic surgery (cesarean delivery, hysterectomy, bladder procedures)
The technique offers rapid onset, predictable offset, minimal systemic effects, and cost-effectiveness compared to general anesthesia 1.
Absolute Contraindications
Coagulation Disorders and Thrombocytopenia
The most critical contraindication is inadequate hemostasis, as spinal hematoma can cause irreversible neurologic injury. Recent consensus guidelines provide specific laboratory thresholds 2:
Platelet Disorders:
- Immune thrombocytopenia (ITP): Platelet count ≥70 × 10⁹/L required for spinal anesthesia
- Gestational thrombocytopenia: Platelet count ≥70 × 10⁹/L acceptable
- HELLP syndrome/preeclampsia: Platelet count ≥70 × 10⁹/L required
Coagulation Factor Deficiencies:
- Von Willebrand disease: VWF activity ≥50 IU/dL AND FVIII ≥50 IU/dL (can be achieved with desmopressin or factor concentrates)
- Hemophilia A/B: Factor VIII or IX ≥50 IU/dL for mild bleeding history; ≥80 IU/dL for severe bleeding history
- Factor XI deficiency: FXI ≥50 IU/dL for mild bleeding history
- Factor XIII deficiency: FXIII ≥50 IU/dL for mild bleeding history; ≥80 IU/dL for severe bleeding history
- Fibrinogen deficiency: Fibrinogen ≥1.5 g/L (Clauss method) for spinal anesthesia
Inherited Platelet Function Disorders:
- Mild disorders: Acceptable if desmopressin-responsive
- Severe disorders: Case-by-case evaluation with multidisciplinary team
Other Absolute Contraindications:
- Patient refusal
- Infection at injection site
- Increased intracranial pressure (risk of herniation)
- Severe hypovolemia/shock (uncontrolled)
Relative Contraindications
- Sepsis (bacteremia risk of seeding CNS)
- Severe aortic/mitral stenosis (inability to compensate for sympathectomy)
- Pre-existing neurologic disease (medicolegal concerns, difficult assessment)
- Severe spinal deformity (technical difficulty)
Recommended Technique
Patient Preparation
Preoperative fasting:
- Clear liquids: 2 hours minimum
- Light meal: 6 hours minimum
- Consider preoperative carbohydrate drink (evidence supports improved recovery) 3
Positioning: Sitting or lateral decubitus, based on patient comfort and surgical site
Needle Selection
Use pencil-point needles (Whitacre, Sprotte) 25-27 gauge to minimize post-dural puncture headache risk (0-2% incidence). 1
Local Anesthetic Selection and Dosing
For Perineal Surgery:
Lidocaine 1% (hyperbaric):
- Dose: 40 mg (4 mL) provides adequate sensory block to T12 and complete motor block for perineal procedures 4
- Duration: 60-90 minutes
- Onset: 3-5 minutes
Prilocaine 2% (hyperbaric):
- Dose: 10-20 mg for outpatient perianal surgery 5
- 10 mg provides sufficient analgesia with minimal motor block and faster discharge (199 ± 39 minutes)
- Duration: ~3 hours
For Lower Extremity Surgery:
Lidocaine 1% (hyperbaric):
- Dose: 60 mg (6 mL) consistently provides sensory block above L1 and complete motor block 4
- Achieves T8 level reliably
- Duration: 60-90 minutes
Bupivacaine 0.75% (hyperbaric in 8.25% dextrose):
- Dose: 7.5 mg (1 mL) for procedures <2 hours 6
- Provides 2-3 hours of anesthesia
- Lower hypotension incidence compared to tetracaine
- Better for tourniquet tolerance than tetracaine 7
For Lower Abdominal/Gynecologic Surgery:
Bupivacaine 0.75% (hyperbaric):
- Dose: 12 mg (1.6 mL) for intra-abdominal procedures 6
- Duration: 3-5 hours
- Provides adequate sensory level to T4-T6
Tetracaine 1% (hyperbaric):
- Dose: 12 mg for abdominal surgery 7
- Longer duration than bupivacaine (4-6 hours)
- More profound motor block
- Higher hypotension risk
Adjuvants
Epinephrine (0.2 mg):
- Prolongs duration of all local anesthetics 7
- Greatest effect with tetracaine
- Moderate effect with lidocaine and bupivacaine
Fentanyl (10-25 mcg):
- Reduces local anesthetic dose requirements
- Decreases transient neurologic symptoms with lidocaine 1
- Improves quality of block
Critical Pitfalls to Avoid
Inadequate coagulation assessment: Always verify platelet count and coagulation parameters before proceeding in patients with bleeding disorders 2
Excessive lidocaine dosing: 80 mg (8 mL) causes unnecessarily high block (T4) with increased hypotension risk (18% incidence) 4
Insufficient dosing for lower extremity surgery: 40 mg lidocaine fails to provide adequate block in 33% of patients 4
Ignoring surgical duration: Match local anesthetic duration to expected procedure length to avoid inadequate anesthesia or excessive recovery time
Large-bore needle use: Increases post-dural puncture headache risk significantly; always use ≤25-gauge pencil-point needles 1
Monitoring and Management
- Continuous blood pressure monitoring for first 30 minutes
- Treat hypotension (>20% decrease from baseline) with:
- Fluid bolus (250-500 mL crystalloid)
- Vasopressors (phenylephrine 50-100 mcg IV or ephedrine 5-10 mg IV)
- Assess block height before surgical incision
- Monitor for high spinal (respiratory compromise, bradycardia)