Spinal Anesthesia Side Effects and Management
Hypotension is the most common side effect of spinal anesthesia, occurring frequently due to sympathetic blockade-induced vasodilation, and should be managed with vasopressor therapy combined with intravenous fluids rather than relying on preloading alone. 1, 2
Cardiovascular Complications
Hypotension
Incidence and mechanism: Hypotension occurs frequently after spinal anesthesia, caused by arterial and venous vasodilation from sympathetic blockade combined with paradoxical activation of cardioinhibitory receptors (Bezold-Jarisch reflex). 2
Treatment approach: Vasopressor therapy combined with intravenous fluid administration is the recommended treatment for spinal anesthesia-induced hypotension. 1
Vasopressor selection:
- Phenylephrine (α1-adrenergic agonist) is increasingly used and its prophylactic administration immediately after intrathecal injection decreases hypotension incidence. 2
- Ephedrine remains appropriate, especially when hypotension is associated with bradycardia. 2
- Norepinephrine shows promise as an alternative to phenylephrine. 2
Fluid management controversy:
- Crystalloid preloading (before spinal anesthesia) is not effective at preventing hypotension. 2, 3, 4
- Co-loading (fluid given during/after spinal placement) with crystalloid or colloid administered as a rapid bolus over 5-10 minutes is as effective as colloid preloading. 2
- Colloid preloading with hydroxyethyl starch reduces hypotension incidence more effectively than crystalloid, but routine fixed-volume preloading is not recommended by the American Society of Anesthesiologists. 5, 2
Bradycardia
Clinical significance: Bradycardia after spinal anesthesia must always be treated as a warning sign of important hemodynamic compromise. 2
Management: Ephedrine is particularly useful when bradycardia accompanies hypotension. 2
High and Total Spinal Block
Incidence and Risk Factors
Frequency: High or total spinal block requiring cardiovascular and/or respiratory support occurs in approximately 1 in 4,367 spinal anesthesia cases. 6, 1, 7
Higher risk scenarios: More common when spinal anesthesia is attempted following a failed epidural top-up. 6
Catheter-related risks: Inadvertent administration of epidural-dose volumes through an intrathecal catheter can cause high or total spinal blocks, even with relatively small volumes (e.g., 3 mL of 3% chloroprocaine or 1.6 mL of 0.75% hyperbaric bupivacaine with fentanyl). 6, 7
Monitoring and Detection
Block height assessment: The sensory block height should be assessed at least every 5 minutes until no further extension is observed. 6, 1, 7
Warning signs requiring immediate intervention: Increasing agitation, significant hypotension, bradycardia, upper limb weakness, dyspnea, or difficulty speaking. 6, 1, 7
Maximum block development: Typically occurs within 10-15 minutes after intrathecal injection. 7
Management of High/Total Spinal
Circulatory support: Support circulation with vasopressors and intravenous fluids. 6
Respiratory support: Provide supplemental oxygen; tracheal intubation and mechanical ventilation may be required. 6
Preparation: Alternative anesthesia methods should be planned in case block extension fails or complications occur. 6
Catheter-Related Complications
Safety Concerns with Intrathecal Catheters
Dosing errors: Clear labeling of intrathecal catheters and structured communication/handover between healthcare professionals is essential to prevent accidental administration of epidural doses. 6, 1, 7
Aspiration unreliability: Failure to aspirate cerebrospinal fluid does not confirm or exclude correct intrathecal catheter placement; CSF aspiration alone is unreliable. 7
Confirmation method: Motor block assessment at 5 minutes provides better specificity than sensory testing alone for confirming intrathecal catheter position. 7
Documented incidents: Cases of high/total spinal blocks, respiratory arrest, and cardiac arrest have occurred when epidural doses were accidentally administered through mislabeled intrathecal catheters. 6, 7
Catheter Failure Rates
Intrathecal catheter failure: Comparable to epidural failure rates (3.5-32% in literature), with adequate analgesia achieved in most cases. 6
Operative delivery failure: Overall failure rate of 3.5%, rising to 7.1% when catheters previously used for labor analgesia are extended for operative delivery. 6
Post-Dural Puncture Headache (PDPH)
Prevention
Needle selection: The American Society of Anesthesiologists recommends pencil-point spinal needles (≥25-gauge Whitacre or Sprotte) rather than cutting-bevel needles to reduce PDPH risk to less than 1%. 1, 5
Avoid cutting needles: Cutting-bevel designs significantly increase PDPH risk compared to pencil-point needles. 1, 5
Intrathecal Catheter Impact
PDPH incidence: Current evidence does not suggest a difference in PDPH rate between intrathecal catheters and re-sited epidural catheters after inadvertent dural puncture. 6
Epidural blood patch requirement: Evidence is conflicting—one large retrospective study found fewer women with intrathecal catheters required epidural blood patch (adjusted OR 0.82), though the 2023 International Consensus stated insufficient evidence to confirm this benefit. 6
Neurological Complications
Cauda Equina Syndrome
Historical context: Cluster of cases reported in 1990 with micro-catheters (<24-gauge) using repeated high doses of concentrated local anesthetic (particularly hyperbaric lidocaine 5%), leading to FDA removal of micro-catheters from U.S. practice in 1992. 6
Mechanism: Poor flow through micro-catheters causes pooling of concentrated local anesthetic around cauda equina, increasing neurotoxicity risk with repeated dosing. 6
Modern safety: Large retrospective reviews in obstetric patients with intrathecal catheters after inadvertent dural puncture have identified no cases of cauda equina syndrome, spinal/epidural hematoma, or other permanent neurological injury. 6
Other Neurological Risks
Transient radicular symptoms: Isolated case reports of lumbar and cervical radicular symptoms after intrathecal catheter injection, all resolving in early postnatal period. 6
Serious sequelae: PDPH development following inadvertent dural puncture has been associated with subdural hematoma and cerebral venous sinus thrombosis, including one death from each complication in the 2009-2012 MBRRACE-UK report. 6
Conus medullaris damage: No reports from intrathecal catheters, though direct trauma from spinal needles has been documented. 6
Anesthetic Complications in Differential Diagnosis
Local Anesthetic Toxicity
High spinal presentation: Can cause apnea but unlikely to produce dramatic cardiac output drop or hemorrhagic manifestations. 6
Intravascular injection: Inadvertent intravascular injection of local anesthetics may cause seizures and cardiovascular collapse. 6
Treatment: Consider intravenous lipid emulsion (20% Intralipid) in addition to supportive measures if local anesthetic toxicity is suspected. 6
Timing clue: Interval between injection and symptom onset helps confirm or exclude this diagnosis. 6
Position-Related Effects
Lateral Decubitus Positioning
Hemodynamic advantage: Lateral positioning delays onset of hypotension and requires smaller total vasopressor doses compared to immediate supine positioning. 8
Blood pressure changes: Supine positioning causes greater maximum systolic blood pressure decrease (36±13%) and mean arterial pressure decrease (27±13%) compared to lateral decubitus (30±8% and 23±11% respectively). 8
Vasopressor requirement: Supine group required 30 mg ephedrine versus 15 mg in lateral group. 8
Common Pitfalls to Avoid
Do not rely on crystalloid preloading alone: Multiple studies confirm it does not prevent hypotension effectively. 2, 3, 4
Never assume CSF aspiration confirms catheter position: Absence of CSF return does not rule out intrathecal placement. 7
Always label catheters clearly: Dosing errors from mislabeled intrathecal catheters have caused deaths. 6, 1, 7
Monitor vigilantly for 15-30 minutes: High blocks can develop from seemingly appropriate doses, requiring frequent reassessment. 6, 1, 7
Treat bradycardia seriously: It signals significant hemodynamic compromise, not just isolated vagal response. 2