What is the typical dosing for spinal anesthesia in cesarean sections?

Typical Dosing for Spinal Anesthesia for Cesarean Section

For cesarean delivery, the standard single-shot spinal dose is 10-15 mg of hyperbaric bupivacaine 0.5% combined with intrathecal opioids (fentanyl 15-25 μg plus morphine 100-150 μg) to achieve a T4 sensory level. 1, 2

Standard Single-Shot Spinal Technique

Local Anesthetic Dosing

• Hyperbaric bupivacaine 0.5%: 10-15 mg (2-3 mL) is the most widely used formulation in the UK and US, providing predictable dermatomal spread due to its gravity-dependent properties 1, 2
• The FDA-approved dose range is 7.5-10.5 mg for cesarean section, though clinical practice commonly uses up to 15 mg 2
• 12 mg is adequate for most lower abdominal procedures including cesarean delivery 2

Opioid Adjuvants

• Fentanyl 15-25 μg provides intraoperative analgesia and allows for lower local anesthetic doses 1, 3, 4
• Morphine 100-150 μg (0.1-0.15 mg) provides superior postoperative analgesia for up to 24 hours 1
• Do not exceed 100 μg intrathecal morphine as higher doses increase respiratory depression risk without improving analgesia 1
• Alternative: Diamorphine 300 μg can substitute for morphine if unavailable 1

Low-Dose Spinal Technique (Reduced Hypotension)

For patients at high risk of hypotension, use 9-12 mg hyperbaric bupivacaine combined with fentanyl 20-25 μg to achieve adequate surgical anesthesia while minimizing cardiovascular instability 5, 6, 7

Evidence for Dose Reduction

• Bupivacaine 12 mg + fentanyl 15 μg produces equivalent anesthesia to bupivacaine 15 mg alone, but with less hypotension and nausea 7
• Bupivacaine 9 mg + fentanyl 20 μg reduces hypotension incidence from 75% to 15% compared to standard 13.5 mg bupivacaine alone 5
• Bupivacaine 5 mg + fentanyl 25 μg reduces hypotension from 94% to 31% and ephedrine requirements from 23.8 mg to 2.8 mg, though this represents a very low dose 6

Clinical Considerations

The low-dose technique trades slightly lower peak sensory levels (T4-5 vs T2-3) for significantly improved hemodynamic stability, making it particularly valuable for patients with cardiac disease or those at high risk for hypotension 5, 6

Intrathecal Catheter Technique (After Accidental Dural Puncture)

When converting labor analgesia to cesarean anesthesia via intrathecal catheter, administer fentanyl 15-20 μg plus morphine 0.25-0.3 mg initially, followed by incremental hyperbaric bupivacaine 0.5% in 1.25-2.5 mg boluses every 3 minutes until T4 sensory level is achieved 8, 1

Incremental Dosing Protocol

• Initial bolus: 5-7.5 mg bupivacaine after opioid administration 8
• Subsequent increments: 1.25-2.5 mg every 3 minutes until adequate surgical level 8, 1
• Mean total dose: 8.8-15 mg (range 7.5-25 mg) depending on patient response and existing block 8, 1
• Target sensory level: T4 to pinprick for adequate peritoneal manipulation 8, 9

Critical Safety Measures

• Perform all top-ups in a facility equipped to manage high or total spinal block with full monitoring 8
• Hyperbaric bupivacaine 0.5% is preferred over isobaric solutions for more predictable spread and fewer high blocks 8
• Failure rate is 3.5-7.1% for catheter conversion, most commonly due to inadequate block height 8, 9

Monitoring Requirements

Intraoperative

• Standard ASA monitoring continuously: non-invasive blood pressure, ECG, pulse oximetry 1
• Assess sensory level every 5 minutes until no further extension observed 1, 9
• Have vasopressors immediately available (phenylephrine or ephedrine) as hypotension occurs in 25-75% of cases depending on dose 1, 3, 9

Postoperative (When Morphine Used)

• Respiratory rate and sedation assessment hourly for 12 hours, then every 2 hours for next 12 hours 8
• Pulse oximetry monitoring for patients at risk of respiratory depression 8

Common Pitfalls and Caveats

• Do not inject during uterine contractions as cerebrospinal fluid current may carry the drug cephalad, resulting in unintended high motor block 2
• Do not omit multimodal analgesia (paracetamol and NSAIDs intraoperatively after delivery) unless contraindicated 1
• Aspirate for blood and CSF before injection to avoid unintended intravascular injection and systemic toxicity 2
• Dose reduction is mandatory in elderly patients and those with significant comorbidities 1
• Isobaric bupivacaine (12.5-20 mg) can be used but produces less predictable spread than hyperbaric formulations 10