From the FDA Drug Label
The lowest dosage of local anesthetic that results in effective anesthesia should be used to avoid high plasma levels and serious adverse effects The rapid injection of a large volume of local anesthetic solution should be avoided and fractional (incremental) doses should be used when feasible.
The recommended regimen for segmental spinal anaesthesia is not explicitly stated in the provided drug labels. However, it can be inferred that the lowest effective dose of local anesthetic should be used, and fractional (incremental) doses should be administered to avoid high plasma levels and serious adverse effects.
- Key considerations for segmental spinal anaesthesia include:
- Using the lowest effective concentration and lowest effective dose of local anesthetic
- Administering fractional (incremental) doses to avoid rapid injection of a large volume of local anesthetic solution
- Monitoring the patient closely for signs of toxicity or unintended effects 1
- Following the recommended dosages and guidelines for the specific local anesthetic being used, such as lidocaine 2
From the Research
The recommended regimen for segmental spinal anesthesia involves the administration of small doses of hyperbaric local anesthetic through a directional spinal needle while the patient is positioned in a specific way to target selected spinal segments. Typically, 5-7.5 mg of hyperbaric bupivacaine 0.5% is used, sometimes with the addition of 10-25 mcg of fentanyl to enhance analgesia, as seen in a case series where 2 ml of 0.5% (10 mg) hyperbaric Bupivacaine mixed with 0.5ml (25 micrograms) of Fentanyl was used for laparoscopic appendectomy 3. The patient should be positioned with the surgical site dependent (facing downward) for 5-10 minutes after injection to allow the hyperbaric solution to settle at the desired spinal segments. A 25G or 27G pencil-point directional spinal needle is recommended, with the opening oriented toward the target segments. The injection should be performed slowly (over 30-60 seconds) to minimize spread. This technique provides adequate surgical anesthesia while limiting the extent of sympathetic blockade, making it particularly useful for elderly or high-risk patients undergoing lower abdominal, inguinal, or lower extremity procedures. Some key points to consider when performing segmental spinal anesthesia include:
- Minimizing peak block height to reduce the incidence of side effects such as hypotension and bradycardia 4
- Using plain solutions of local anesthetics to reduce the risk of transient neurological symptoms (TNS) 5
- Performing the spinal puncture at or below the L3-L4 interspace to reduce the risk of hypotension and bradycardia 4
- Avoiding the use of procaine in the subarachnoid space due to its association with a higher risk of TNS and other side effects 4. The segmental approach reduces hemodynamic instability by limiting the spread of anesthesia to only the necessary dermatomes, thereby preserving cardiovascular stability better than conventional spinal anesthesia. In terms of local anesthetics, lidocaine remains a popular choice for ambulatory spinal anesthesia due to its reliability and rapid onset, but concerns about TNS have led to interest in alternative agents such as bupivacaine and mepivacaine 6, 5. Intrathecal adjuncts such as fentanyl can be used to enhance analgesia and improve the recovery profile for ambulatory spinal anesthesia 3, 5. Overall, the key to successful segmental spinal anesthesia is careful patient selection, attention to technique, and the use of appropriate local anesthetics and adjuncts to minimize side effects and optimize outcomes.