Background

Subarachnoid spinal block is a safe option for general anesthesia in lower body surgeries.

This procedure temporarily blocks nerve signals to cause loss of sensation and muscle control.

The spinal cord is surrounded with three protective layers as:

The dura mater

Arachnoid mater

Pia mater

The subarachnoid space lies between the arachnoid and pia mater. It consists of cerebrospinal fluid that gives support to the spinal cord and brain.

Indications

Lower abdominal surgery: Like appendicitis surgery, hernia repair, or caesarean surgery.

Pelvic surgery: As in surgeries such as prostatectomy, hysterectomy or perineal operations.

Lower limb surgery: Including knee and hip replacement surgeries, and the surgeries that are done on the legs.

Urological procedures: For instance, cystoscopy, prostate surgery, or bladder surgery.

Orthopedic procedures: Especially for the abdominal surgery below umbilicus such as hip or knee joint surgery.

Gynecological procedures: This includes dilatation and curettage (D&C) or cesarean section.

Contraindications

Infection at the injection site: Any local infection, for instance skin infections or abscesses at the site of spinal punctures increases the risk spreading the disease to the CNS.

Allergy or hypersensitivity to local anesthetics: If the patient has allergy to the anesthetic agents used (for example lidocaine, bupivacaine) in this case, spinal block is contraindicated.

Increased intracranial pressure: Patients with a history of potential causes of raised ICT like brain tumor, head injury or any pathological conditions can cause worsening of the disease due to vasodilation of the cerebral vessels or changes in cerebrospinal fluid induced by spinal anesthesia.

Severe cardiovascular disease: Those with severe heart disease like uncontrolled arrhythmias, or severe valvular heart disease, are likely to experience adverse effects from the block.

Coagulopathy or anticoagulant therapy: The situations include hemophilia patients and patients on anticoagulant therapy are prone to the development of bleeding into the spinal cord (epidural hematoma) or subarachnoid space.

Spinal deformities: It is not easy to place the needle in the spinal canal because individuals with severe scoliosis or other structural problems in the spine may be at severe risk of getting injured.

Outcomes

Subarachnoid spinal block offers rapid and effective anesthesia in cases of emergency surgeries.

The procedure gives complete loss of sensation in the targeted area thus it is effective for surgeries involving the lower extremity part.

Patients those are at higher risk for complications from general anesthesia should prefer surgery with a spinal block.

The effect of the spinal block may extend up to a postoperative period for several hours after the surgery.

Many patients do not experience long-term neurological effects from spinal block.

Equipment required

• Spinal Needle 
• Syringe 
• Anesthetic Agent 
• Monitoring Equipment 

Patient Preparation

All necessary equipment is available in good condition including local anesthetics, syringes, and needles. 

Intravenous access for fluid administration and emergency medications should be prepared. Preloading with IV fluids is done to reduce the risk of hypotension during spinal block. 

Patients should follow as instructed by the physician. Fast for 6 to 8 hours before the procedure to reduce the risk of aspiration. 

Informed Consent:  

Patients should understand procedure, benefits, risks, and alternatives for consent. 

Patient Positioning

Patient should be seated with arched back or on side for better access to lumbar spine. 

The patient should be sited on the edge of the bed/table with their feet supported on a stool. 

Patient positioned laterally or sitting with assistance for spinal anatomy identification, with preference for sitting due to accuracy. 

                Fig. Subarachnoid spinal block 

Technique

Step 1-Pre-procedure Assessment:

Check patient history including allergy history, chronic disease history, previous operation history.

Check laboratory values include platelet count and coagulation profiles.

Step 2-Preparation:

Wash the skin with an antiseptic solution.

Give the pre-procedural medicine to sedate the patient if required.

Needle Insertion: The most frequent used approach is between the L3-L4 or L4-L5 lumber vertebrae.

The needle should be inserted perpendicular to the skin, moving further through the subcutaneous tissue, ligamentum flavum, till it reaches the subarachnoid space.

Step 3-Confirmation of Needle Placement:

CSF Return: Once the needle reaches the subarachnoid space, CSF will return through the needle.

Step 4-Injection of Local Anesthetic: The anesthesiologist will slowly inject the local anesthetic, observing the patient’s response.

Step 5: Withdrawal of needle:

Withdraw the needle and cover the site with a sterile dressing.

Step 6-Patient Monitoring: Patients should be carefully observed for symptoms of increased risk of side effects such as hypotension, bradycardia, or respiratory depression.

Complications

Hypotension (Low Blood Pressure):
Due to sympathetic blockade, there is vasodilation and decreased return of blood that can lead to an abrupt drop in blood pressure.
The treatment includes fluids and vasopressors if required.
Bradycardia (Slow Heart Rate):
By spinal anesthesia, there can be an influence on the autonomic nervous system that may cause a drop-in heart rate

It can be managed with atropine or other drugs to increase the heart rate.
Respiratory Depression:
Though very rare, it can occur at high levels or with the block placed improperly impacting respiratory muscles; it happens especially when the block ascends too high.
In severe cases, mechanical ventilation is required.
Post-Dural Puncture Headache (PDPH):
This is a frequent complication, related to leakage of CSF through the site of puncture; it may cause headache worsening with sitting or standing.
Management includes hydration, caffeine, and, as needed, an epidural blood patch to seal the leak.
Infection:
Infection at the injection site or more seriously, meningitis or epidural abscess, can occur. Proper sterile techniques reduce this risk.

References

Spinal Anesthesia – StatPearls – NCBI Bookshelf (nih.gov)

Subarachnoid block for surgery of lower half of the body and lower limbs: A clinical study – PMC (nih.gov)

References

Spinal Anesthesia – StatPearls – NCBI Bookshelf (nih.gov)

Subarachnoid block for surgery of lower half of the body and lower limbs: A clinical study – PMC (nih.gov)