Technique or Treatment
Once the patient has undergone appropriate selection, the optimal patient position for the procedure must be established.
The procedure is usually carried out with the patient in the sitting or lateral decubitus position. The patient’s comfort is tantamount. The goal of positioning is to help establish a straight path for needle insertion between the spinal vertebrae. The most commonly used position is the sitting position. This is because, in the lateral decubitus position, the spinal anatomy is usually not laterally symmetrical as it is in the sitting position.
With the patient positioned in the sitting position and leg hanging from the side of the bed, he/she should be encouraged to maintain a flexed spine position to help open up the interspace. The sitting position is appropriate for spinal anesthesia with a hyperbaric solution.
Either left or right lateral decubitus positions are viable options as well.
After the patient is in the proper position, the access site is identified by palpation. This is usually very difficult to achieve with obese patients because of the amount of subcutaneous fat between the skin and the spinous process. The space between 2 palpable spinous processes is usually the site of entry. The patient should wear a hat or cover for his/her hair to maintain asepsis.
Strict aseptic technique is always necessary, achievable with chlorhexidine antiseptics with alcohol content, adequate hand-washing, mask, and cap. Cleaning always starts from the chosen site of approach in circles and then away from the site. Allow time for the cleaning solution to dry. In the spinal kit, the drape placement is on the patient’s back to isolate the area of access. Local anesthetic (usually about 1 ml 1% lidocaine) is used for skin infiltration, and a wheal is created at the site of access chosen, either midline or paramedian.
In the midline approach, the spinal approach to the intrathecal space is midline with a straight line shot. After infiltration with lidocaine, the spinal needle is introduced into the skin, angled slightly cephalad. The needle traverses the skin, followed by subcutaneous fat. As the needle courses deeper, it will engage the supraspinous ligament and then the interspinous ligament; the practitioner will note this as an increase in tissue resistance. Next later will be the ligamentum flavum, and this would present like a “pop.” On popping through this ligament, is the approach to the epidural space, which is the point of placement for epidurally-administered medications and catheters. This also presents the point where the loss of resistance is felt to the injection of saline or air. For spinal anesthesia, the clinician proceeds with needle insertion until penetration of the dura-subarachnoid membranes, which is signaled by free-flowing CSF. It is at this point that the administration of spinal medication takes place.
For the paramedian approach, the skin wheal from the local anesthetic is placed about 2 cm from the midline, and the spinal needle advances at an angle toward the midline. In this approach, the supraspinous and interspinous ligaments are usually not encountered. Hence, there is little resistance encountered until reaching the ligamentum flavum.