Spinal (Subarachnoid) anaesthesia

TABLE P-4 Indications and precautions for spinal anaesthesia 

• Review general care principles and start an IV infusion.

• Infuse 500-1 000 mL of IV fluids (normal saline or Ringer’s lactate) to pre-load the woman and avoid hypotension. This should be done 30 minutes before anaesthesia.

• Prepare 1.5 mL of the local anaesthetic: 5% lignocaine in 5% dextrose. Add 0.25 mL of adrenaline (1:1 000) if the anaesthetic needs to be effective for longer than 45 minutes.

• Ask the woman to lie on her side (or sit up), ensuring that the lumbar spine is well flexed. Ask the woman to flex her head onto her chest and round her back as much as possible.

• Identify and, if required, mark the proposed site of injection. A vertical line from the iliac crest upward will cross the woman’s vertebral column between the spines of the fourth and fifth lumbar vertebrae. Choose this space or the space just above it. 

Sterility is critical. Do not touch the point or shaft of the spinal needle with your hand. Hold the needle only by its hub. 

• Inject 1% lignocaine solution using a fine needle to anaesthetize the woman’s skin.

• Introduce the finest spinal needle available (22- or 23-gauge) in the midline through the wheal, at a right angle to the skin in the vertical plane.

Note: Fine needles tend to bend.

• If the needle hits bone, it may not be in the midline. Withdraw the needle and reinsert it, directing it slightly upwards while aiming for the woman’s umbilicus.

• Advance the spinal needle towards the subarachnoid space. A distinct loss of resistance will be felt as the needle pierces the ligamentum flavum.

• Once the needle is through the ligamentum flavum, push the needle slowly through the dura. You will feel another slight loss of resistance as the dura is pierced. 

• Remove the stylet. Cerebrospinal fluid should flow out the needle. 

• If cerebrospinal fluid does not come out, reinsert the stylet and rotate the needle gently. Remove the stylet to see if the fluid is flowing out. If you fail two times, try another space.

• Inject 1-1.25 mL of the local anaesthetic solution. For pregnant women who have not delivered, a smaller dose of the drug is needed since the available subarachnoid space is reduced due to engorged epidural veins.

• Help the woman to lie on her back. Have the operating table tilted to the left or place a pillow or folded linen under her right lower back to decrease supine hypotension syndrome.

• Recheck the woman’s blood pressure. A fall in blood pressure is likely. If there is significant hypotension, give the woman more IV fluids (500 mL quickly):

- If this does not raise her blood pressure, give ephedrine 0.2 mg/kg body weight IV in 3 mg increments;

- If blood pressure continues to fall after giving IV ephedrine boluses four times, give ephedrine 30 mg IM.

• Give oxygen at 6-8 L per minute by mask or nasal cannulae.

• After injecting the local anaesthetic solution, wait 2 minutes and then pinch the incision site with forceps. If the woman can feel the pinch, wait 2 minutes and then retest.

Anaesthetize early to provide sufficient time for effect. 

• After surgery, keep the woman flat for at least 6 hours with only a single pillow beneath her head to prevent post-spinal headache. She must not sit up or strain during this period

• After surgery, keep the woman flat for at least 6 hours with only a single pillow beneath her head to prevent post-spinal headache. She must not sit up or strain during this period

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