Ultrasound-guided spinal anesthesia

With the growing incidence of obesity in the western world, ultrasound-guided anesthesia is becoming more common. 

Spinal anesthesia is traditionally administered by identifying relevant surface anatomy and imaging is rarely used for pre-procedural identification of structures. Ultrasound-guided anesthesia in the context of spinal anesthesia allows for real-time visualization of anatomical structures, enhancing the accuracy and safety of the procedure, especially in patients with challenging anatomy ^ref. This technology is particularly valuable for improving the success rate of spinal anesthesia in patients where traditional surface anatomy identification may be more challenging due to increased soft tissue thickness ^ref.

Indications

• lower abdominal and/or pelvic surgery

• pain relief during labor

Contraindications

• overlying skin infection

• concurrent anticoagulant use

• profound hypotension

• history of uncontrolled seizures

Procedure

Positioning

Sitting upright on the bed is the ideal position to administer spinal anesthesia. The feet are placed on a stool, the head and neck are flexed forward with the arms hugging a pillow. Patients are required to flex their backs to increase intervertebral space. 

Patients that cannot sit are placed in the lateral decubitus position with their back parallel to the bed. The neck and thighs are flexed manually ².

Technique

• prepare equipment (usually pre-packaged) and use sterile technique

• position patient appropriately

• using the ultrasound probe, five different views of the spinal canal can be obtained

• for the parasagittal transverse view, place the transducer 3-4 cm lateral to the spinal processes with the transducer cephalad to the sacrum; the transverse processes and the psoas muscle are best visualized using this view

• for the parasagittal articular view, move the transducer back to the midline which allows visualization of the articular processes

• move the transducer laterally (maintaining a parasagittal view) with the transducer turned obliquely directed medially (different from the parasagittal transverse view as the transducer is not parallel to the spinous processes, rather directed towards them) - this visualizes the vertebral laminae and the appropriate intervertebral space can be identified (this is the parasagittal oblique view)

• once the intervertebral space is identified, turn the transducer by 90^o to visualize the intervertebral space

• identify and mark the needle insertion sites, also, measure needle depth required by measuring the distance from the skin to the posterior ligamentous complex

• while inserting the needle, maintain the same cephalad or caudal angle maintained by the probe ³

Complications

• post-dural puncture headache (common)

• hypotension

• total spinal blockade

• seizure

• bladder dysfunction ¹

Outcomes

Several studies have established the feasibility and safety of using the ultrasound-guided technique ^4,5. Some studies have even identified that the use of ultrasound-guided anesthesia is faster and hence more efficient ⁶. Operators had a high success rate with the ultrasound-guided technique and fewer skin punctures ^ref.