Figure 44-7 Techniques of epidural needle insertion most often used in locating the epidural space. A, In the loss-of-resistance technique, the needle is inserted into the ligamentum flavum, and a syringe containing an air bubble is attached to the hub. After compression of the air bubble is obtained by applying pressure to the syringe plunger, the needle is carefully advanced until its entry into the epidural space is confirmed by the characteristic loss of resistance to syringe plunger pressure, and the fluid enters the space easily. B, In the hanging-drop technique, the needle is inserted into the ligamentum flavum, and a drop of saline (or local anesthetic) is placed in the hub. The needle is then carefully advanced until its entry into the epidural space is detected by the drop of solution being "sucked" into the epidural space.