An epidural is a common method of pain relief involving the precise delivery of medication near the spinal cord. This procedure requires a specialized set of tools designed for accuracy and patient safety within the delicate area of the spine. Understanding these instruments can help demystify the process of receiving this regional anesthesia. The system relies on different components: a primary needle, a smaller guide needle, and a flexible tube that remains in the body.
The Specialized Touhy Needle Design
The main instrument used to access the epidural space is the Touhy needle. It is significantly longer than a standard needle, typically measuring three to five inches in length, with a wider diameter (16 to 18 gauge). The shaft is marked with centimeter graduations, allowing the clinician to precisely track the depth of insertion toward the spine.
The most characteristic feature is the blunt, curved tip, sometimes called a Huber tip. This design pushes aside tissue and ligaments instead of cutting them, reducing the risk of puncturing the dura mater. This shape also facilitates the “loss of resistance” technique, confirming entry into the epidural space. The tip features a side-facing bevel, which allows the catheter to be threaded at an angle.
The Necessity of the Introducer Needle
Because the Touhy needle is large and blunt, it cannot pierce the skin directly. Therefore, a smaller, sharper introducer needle is used first to create a stable pathway. This introducer needle is sharp and straight, resembling a traditional long hypodermic needle.
Its purpose is to puncture the tough outer skin and subcutaneous tissue, which the blunt Touhy needle cannot penetrate smoothly. The introducer creates a small, stable sheath through which the Touhy needle is passed. This step stabilizes the insertion and prevents the larger needle from deflecting. Once the Touhy needle is guided through the introducer, the introducer is immediately removed, having served its temporary function.
The Flexible Epidural Catheter
The Touhy and introducer needles are temporary tools; the device that remains to deliver pain medication is the epidural catheter. This catheter is a thin, flexible tube, typically made from nylon or polyurethane. It has a small diameter, often 19 or 20 gauge.
The catheter is carefully threaded through the hollow core of the Touhy needle after the epidural space is confirmed. It is advanced a short distance, and then the Touhy needle is gently withdrawn over the catheter, leaving the flexible tube in place. The catheter’s flexibility allows it to remain in the epidural space for continuous pain relief without causing trauma. The external end connects to a port for administering medication, completing the ongoing pain management system.