What are the medications and dosing regimens for spinal (subarachnoid) anesthesia?

From the Guidelines

Spinal anesthesia typically involves injecting local anesthetics, sometimes combined with opioids, into the subarachnoid space to block sensory and motor function below the injection level, with the most commonly used medications including bupivacaine, lidocaine, and ropivacaine, and dosing regimens such as hyperbaric bupivacaine 0.5% at 10-15mg for procedures below the umbilicus. The choice of medication and dosing regimen for spinal anesthesia depends on various factors, including the type of surgical procedure, patient characteristics, and desired block height.

• Bupivacaine is a commonly used local anesthetic for spinal anesthesia, with a typical dose range of 10-15mg (2-3ml) for procedures below the umbilicus, and 12-20mg (2.4-4ml) for higher blocks 1.
• Lidocaine is another option, providing shorter duration anesthesia lasting 60-90 minutes, with a typical dose of 50-100mg 1.
• Ropivacaine offers intermediate duration with potentially less cardiovascular depression and motor block, with a typical dose range of 15-22.5mg 1.
• Additives like fentanyl (10-25mcg) or morphine (0.1-0.3mg) can enhance analgesia duration, with fentanyl being preferred due to its lower risk of respiratory and cognitive depression 1.
• The onset of spinal anesthesia typically occurs within 5-10 minutes, with duration varying from 1-4 hours depending on the medication chosen, and baricity (hyperbaric, isobaric, or hypobaric) affecting medication spread within the CSF and can be manipulated based on patient positioning 1.
• A test dose of 10mg bupivacaine (or equivalent) is recommended to recognize an intrathecal catheter while minimizing the risk of high- or total-spinal anesthesia, and should produce clinically evident sensory, motor, or autonomic effects 1.

From the FDA Drug Label

The dose of any local anesthetic administered varies with the anesthetic procedure, the area to be anesthetized, the vascularity of the tissues, the number of neuronal segments to be blocked, the depth of anesthesia and degree of muscle relaxation required, the duration of anesthesia desired, individual tolerance, and the physical condition of the patient

Table 1: Dosage Recommendations

• Lumbar Epidural5 (0.5%) 15 to 30 75 to 150 15 to 30 2 to 4
• Administration7.5 (0.75%) 15 to 25 113 to 188 10 to 20 3 to 5
• Surgery 10 (1%) 15 to 20 150 to 200 10 to 20 4 to 6
• Lumbar Epidural5 (0.5%) 20 to 30 100 to 150 15 to 25 2 to 4
• Administration7.5 (0.75%) 15 to 20 113 to 150 10 to 20 3 to 5
• Cesarean Section Thoracic Epidural5 (0.5%) 5 to 15 25 to 75 10 to 20 n/a*
• Administration7.5 (0. 75%) 5 to 15 38 to 113 10 to 20 n/a*
• Surgery Major Nerve Block† (e.g., brachial plexus block) 57.5 (0.5%)(0.75%) 35 to 5010 to 40 175 to 25075 to 300 15 to 3010 to 25 5 to 86 to 10
• Field Block (e.g., minor nerve blocks and infiltration) 5 (0.5%) 1 to 40 5 to 200 1 to 15 2 to 6
• LABOR PAIN MANAGEMENT Lumbar Epidural Administration Initial Dose 2 (0.2%) 10 to 20 20 to 40 10 to 15 0.5 to 1. 5
• Continuous infusion‡2 (0.2%) 6 to 14 mL/h 12 to 28 mg/h n/an/a
• Incremental injections (top-up)‡2 (0.2%) 10 to 15 mL/h 20 to 30 mg/h n/an/a
• POSTOPERATIVE PAIN MANAGEMENT Lumbar Epidural Administration Continuous infusion§2 (0.2%) 6 to 14 mL/h 12 to 28 mg/h n/an/a
• Thoracic Epidural Administration2 (0.2%) 6 to 14 mL/h 12 to 28 mg/h n/an/a
• Continuous infusion§ Infiltration (e.g., minor nerve block) 25 (0.2%)(0.5%) 1 to 1001 to 40 2 to 2005 to 200 1 to 51 to 5 2 to 62 to 6

The medications and dosing regimens for spinal (subarachnoid) anesthesia are not explicitly stated in the provided text. However, the dosing regimens for lumbar epidural and thoracic epidural are provided.

• Lumbar Epidural: 15 to 30 mL of 0.5% solution (75 to 150 mg) or 15 to 25 mL of 0.75% solution (113 to 188 mg) or 15 to 20 mL of 1% solution (150 to 200 mg)
• Thoracic Epidural: 5 to 15 mL of 0.5% solution (25 to 75 mg) or 5 to 15 mL of 0.75% solution (38 to 113 mg) It is essential to consult standard current textbooks for other local anesthetic techniques, including spinal (subarachnoid) anesthesia, as the provided text does not directly address this topic 2.

From the Research

Medications for Spinal Anesthesia

• Local anesthetics: bupivacaine, ropivacaine, levobupivacaine, and lidocaine are commonly used for spinal anesthesia 3, 4, 5, 6
• Opioids: fentanyl and sufentanil are used as adjuvants to local anesthetics to enhance analgesia and reduce side effects 4, 7, 6

Dosing Regimens for Spinal Anesthesia

• Bupivacaine: 5-12.5 mg, often combined with fentanyl (25 micrograms) or sufentanil (2.5 micrograms) 4, 7, 6
• Ropivacaine: low doses (e.g., 5-10 mg) are used for outpatient procedures 3, 5
• Fentanyl: 25 micrograms, often combined with bupivacaine (5-12.5 mg) 4, 7, 6
• Sufentanil: 2.5 micrograms, often combined with bupivacaine (12.5 mg) 4

Special Considerations

• Combined spinal-epidural anesthesia: using low-dose intrathecal bupivacaine/fentanyl and low-dose epidural bupivacaine can reduce adverse effects and shorten motor recovery 7
• Low-dose spinal anesthesia: using small doses of local anesthetics (e.g., bupivacaine 5 mg) with opioids (e.g., fentanyl 25 micrograms) can reduce hypotension and side effects 6