As mentioned above, the techniques for spinal and epidural anaesthesia differ. However—just like in case of general anaesthesia—there is a preoperative stage where medical history, medications, and allergies are taken into account. The techniques for spinal and epidural anaesthesia (following the preoperative stage) have been provided below.

• Spinal anaesthesia technique:
  • Checking of spinal anatomy: This is done to allow for safe needle placement and drug delivery to ensure reduced risk of complications, such as spinal cord injury, nerve damage, or failed anaesthesia.
  • Drug administration: A small amount of local anaesthetic is directly injected via a needle into the cerebrospinal fluid (CSF) in the subarachnoid space (the space surrounding the spinal cord) in the lower back (lumbar region). This results in the rapid numbing of the target region (1 to 5 minutes for numbing).
  • Monitoring: Vital signs like blood pressure, heart rate, and oxygen saturation are continuously monitored and complications like low blood pressure (hypotension) and slow heartbeat (bradycardia)—which may require treatment with intravenous fluids, ephedrine, or atropine—are looked out for.
  • Onset of anaesthesia: Numbing is checked using a pinprick test or cold swab.
  • Post-procedure care: After the completion of the procedure, patients are positioned flat on their back to allow even distribution of the anaesthetic and continuously monitored for complications like low blood pressure (hypotension), spinal headache (headache caused due to cerebrospinal fluid (CSF) leakage through the dura matter), nerve damage, and in rare cases, respiratory and cardiovascular compromise (a situation where the normal functioning of the lungs and heart is impaired or weakened, potentially leading to life-threatening conditions).
• Epidural anaesthesia technique:
  • Identification of epidural space: The epidural space, i.e., the site of injection is identified to ensure safe needle placement.
  • Needle insertion and catheter placement: A Tuhoy needle is inserted to access the epidural space, which lies just outside the dura mater surrounding the spinal cord. Once the epidural space is located, a catheter is inserted to deliver local anaesthetics and/or pain relief medications.
  • Test dose administration: Before administering the final dose, a small amount of anaesthetic mixed with epinephrine is administered to the patient and the patient is subsequently checked for tachycardia (rapid heartbeat) or metallic taste (indicating accidental vein injection) and rapid numbness or motor block (indicating accidental dural puncture). If both are negative, the anaesthetic is administered.
  • Drug administration: A local anaesthetic (e.g., bupivacaine) is injected into the epidural space (the space outside the dura matter)— either as a single dose (bolus) or continuously—through the catheter to block nerve signals and provide pain relief. This technique results in slow numbing of the target region (10 to 25 minutes for numbing).
  • Monitoring: Vital signs like blood pressure, heart rate, and oxygen saturation are continuously monitored, and signs of low blood pressure (hypotension) looked out for.
  • Onset of anaesthesia: Numbing is checked using a pinprick test or cold swab.
  • Post-procedure care: After the completion of the procedure, the catheter is removed and patients are observed for complications like low blood pressure (hypotension), infection, or bleeding (and in rare cases, dural puncture‒associated headache).

As with general anaesthesia, the risks associated with spinal anaesthesia may be common or rare depending on the root cause or the patient’s medical history or genetics.

• Common risks
  • Hypotension (low blood pressure): This is caused when the anaesthetic blocks the sympathetic nerves (nerves that control the body's "fight-or-flight" response, which prepares the body for situations requiring heightened alertness or quick action), resulting in reduced cardiac output. Symptoms include dizziness, nausea, fainting, or, in severe cases, cardiovascular collapse.
  • Post-dural puncture headache (PDPH): This is caused by the leakage of cerebrospinal fluid (CSF) through the puncture site in the dura mater. Symptoms include severe headache, stiffness in the neck, nausea, and sensitivity to light.
  • Nausea and vomiting: These are the result of low blood pressure (hypotension) or visceral nerve irritation (a condition in which, nerves that carry signals between the internal organs (viscera) and the central nervous system (CNS) get inflamed, injured, or compressed).
    Back pain: This is caused due to local tissue trauma or muscle spasm at the injection site.
  • Difficulty urinating (Urinary retention): This is caused due to the inability of sacral nerves—which control bladder function—to transmit signals.
• Rare but serious risks:
  • High or total spinal block: This is caused by the excessive spread of the anaesthetic into higher spinal levels, potentially affecting respiratory muscles or the brainstem. Symptoms include difficulty in breathing, low blood pressure (hypotension), slow heartbeat (bradycardia), or loss of consciousness.
  • Neurological complications: These are caused as a result of direct nerve injury, spinal cord trauma, or hematoma (leakage of blood from the blood vessels into the surrounding tissue). Symptoms include persistent numbness, weakness, tingling, or in extremely rare cases, paralysis.
  • Infection: Meningitis (infection of the membranes enveloping the brain and spinal cord, i.e., meninges) and brain abscess (infection of the brain) can be caused as a result of contamination during the procedure. Symptoms include severe back pain, fever, and neurological issues, such as memory problems, difficulty in thinking, confusion, changes in sensation, and even seizures.
  • Bleeding (Spinal hematoma): This is caused due to the accidental puncture of the blood vessels during anaesthesia. This is especially common in patients with blood clotting disorders or who are on anticoagulants (agents that do not allow the blood to clot). Symptoms include severe back pain and neurological deficits ranging from ranging from pain and numbness to paralysis and autonomic dysfunction (a condition where the part of nervous system that controls core functions, like heart rate, blood pressure, digestion, and temperature regulation, does not function properly).
  • Allergic reactions: These are caused when the patient is sensitive to the anaesthetic drug or preservatives used. Symptoms include rash, itching, or anaphylaxis (a severe, potentially life-threatening allergic reaction that occurs immediately after exposure to an allergen).

If spinal or epidural anaesthesia fails, i.e., the anaesthetic does not work as expected and does not provide the desired level of pain relief, or if the patient is incompatible with the anaesthetics used in these techniques, the doctors can choose to go with general anaesthesia for the procedure.