Anaesthesia through the sacral cleft

2021-05-15 11:25 AM

It is important to determine the sacral cleft, the patient lying on the side, back flexion and leg flexion is often used because the patient is comfortable and easy to perform the technique.

Recall anatomy

The sacrum is formed by connecting 5 vertebrae together to form a triangular bone, the base is the line connecting the two posterior superior iliac spines, bounded by the sacroiliac joints and the apex is the fissure forming an equilateral triangle. The sclera in adults ends at the second sacral segment and the maximum distance from the sacral sac to the skin of the Sacro coccyx is about 48mm, in children, it is only about 18mm, this is the distance to remember so that the needle is not inserted. to the spinal cord.

Important anatomical landmarks:

Two posterior iliac spines.

The truncated slit with a diameter of about 5mm is located just above the midline, these three landmarks will form an equilateral triangle.

The venous plexus in the epidural space in the sacral region is very developed, so it is easy to insert the needle into the vein, so remember to always carefully aspirate the syringe before injecting anaesthetic, avoid injecting the drug directly into the vein, avoid in addition, the absorption of the drug into the systemic circulation is also faster and more extensive than with conventional epidural anaesthesia.



Needle number 21-23G, shorter than 50mm, avoid using small and long needles to avoid injecting drugs into the bone because the bone is more porous here.

A local anaesthetic has the same strength as an epidural.

Patient Pose

It is important to identify the sacroiliac cleft. The patient lying on the side, arching the back and flexing the legs is often used because the patient is comfortable and easy to perform the technique.

Carefully disinfect before anaesthesia because this area near the anus is very susceptible to infection. Spread sterile towels. Local anaesthesia is required when a large needle is used.

Insert the needle into the sacral slit perpendicular to the skin surface, then fall 300, insert the needle to a depth of about 45mm. After gently aspiration without blood and cerebrospinal fluid, put one hand on the sacrum, pump a few millilitres of air, if the needle is just under the skin, air bubbles will be seen under the skin, if the needle is on the front of the patient's tailbone it will be very painful; Only when the air is pumped in is gentle and the patient feels a strange sensation in the legs, then it is true that he has entered the sacrum. At that time, a test dose of lidocaine mixed with adrenaline 1:200,000 injected 3ml can be used, if the needle is in the blood vessel, the adrenaline rapid pulse will be immediately seen, and if it is in the subarachnoid space, the lower extremities will be seen. If that doesn't work, the rest of the medication can be pumped.

Dosage: The volume of the drug depends on the area to be analgesia, usually twice as much as the lumbar epidural if the effect is to be high. The usual dose is 20-30ml of lidocaine anaesthetic in adults weighing 70kg (5mg/kg and bupivacaine (2mg/kg).



Figure. Landmark and direction of needle insertion through the sacral fissure.


Insertion into the rectum in the wrong place.

Intravenous injection, embolism due to gas.

Inject the drug into the bone.

Inject the drug under the skin.

Inject the drug into the spinal cord.

Extensive epidural anaesthesia due to overuse of local anaesthetic.

Hypotension is usually milder than with conventional epidurals.

Infection, broken needle...


Surgery in the pelvic area, perineum area, pain relief in the lower extremities...


Local infection.

Acute nerve damage.



Lack of circulating volume is not enough to compensate.