Subarachnoid Block (SAB) / Spinal Anesthesia.

Описание: Subarachnoid Block (SAB) / Spinal Anesthesia – Overview

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🧠 Definition:

Subarachnoid block (SAB), commonly called spinal anesthesia, is a regional anesthesia technique where a local anesthetic is injected into the subarachnoid space (between the arachnoid mater and pia mater) to block nerve transmission in the spinal cord.


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📍 Site of Injection:

Between L3–L4 or L4–L5 interspaces
(Below the level of the spinal cord termination — usually at L1–L2 in adults)



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⚗️ Drugs Commonly Used:

1. Local Anesthetics:

Bupivacaine (Heavy/Hyperbaric 0.5%) – most common

Lidocaine (5%) – short-acting

Ropivacaine, Tetracaine



2. Additives (optional):

Adrenaline (epinephrine) – prolongs effect

Opioids (e.g., fentanyl, morphine) – for postoperative pain relief





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⚙️ Mechanism of Action:

Local anesthetic blocks nerve transmission by inhibiting sodium channels in the spinal nerves, leading to:

Sensory block (loss of pain, temperature)

Motor block (muscle relaxation)

Sympathetic block (vasodilation → ↓BP)



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🧍‍♂️ Position for Procedure:

Sitting position – spine flexed like “C”

Lateral decubitus position – especially for obstetric or uncooperative patients



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🩺 Procedure Steps:

1. Aseptic preparation and draping


2. Identify intervertebral space (usually L3–L4)


3. Local infiltration with lidocaine


4. Insert spinal needle (e.g., Quincke 25G)


5. Feel “pop” as needle enters subarachnoid space


6. Confirm CSF flow


7. Inject anesthetic slowly


8. Withdraw needle and place patient in desired position




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⏱️ Onset and Duration:

Onset: 2–5 minutes

Duration: 1.5–3 hours (depends on drug and dose)



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⚠️ Complications:

1. Immediate:

Hypotension

Bradycardia

Nausea/vomiting

Respiratory arrest (high spinal)


2. Late:

Post-dural puncture headache

Urinary retention

Backache

Meningitis (rare, due to infection)



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💉 Indications:

Lower abdominal surgery

Lower limb surgery

Cesarean section

Perineal and urologic procedures



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🚫 Contraindications:

Absolute:

Patient refusal

Infection at puncture site

Coagulopathy or anticoagulant therapy

Raised intracranial pressure (ICP)


Relative:

Hypovolemia

Sepsis

Severe spinal deformity



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