In order to determine whether the needle tip has reached the epidural space, the following aspects can be used for identification.

(1> Disappearance of resistance: The principle is that the ligamentum flavum tissue is dense and thick, the needle tip has the greatest resistance to passing through, and has a sense of toughness. After passing through the ligamentum flavum, it is the epidural space of the cavity, and the resistance can increase to disappear suddenly.

(2) Negative pressure phenomenon: When the needle tip penetrates the ligamentum flavum and enters the epidural space, a negative pressure phenomenon will occur. The measurement methods include the hanging drop method and the glass tube method. The hanging drop method is to hang a drop of liquid on the needle pedicle, and when the needle is slowly inserted into the epidural space, the hanging drop can be seen sucking. This method sometimes prevents smooth needle insertion. If a puncture needle is used to connect a glass tube filled with liquid, the liquid in the tube can be sucked when the needle tip enters the epidural space. This method is beneficial to operation, and it is more convenient to observe negative pressure, which is the glass tube method (Figure 3-10). The negative pressure phenomenon of this method is more obvious, and there are also a few cases that are not obvious, which has considerable clinical value.

(3) Water column pulsation: Not only the negative pressure phenomenon can be seen in the glass symbol method, but also the liquid water column pulsation can be seen with the change of negative pressure.

This phenomenon is partly obvious, but also of considerable value.

(4> Aspiration test: After the puncture needle is inserted into the epidural space, the reverse collar is used for aspiration, and no cerebrospinal fluid and blood should be aspirated.

(5> Gas injection test: if the puncture needle is in the epidural space.

There should be no resistance during gas injection (Figure 3-11>, (6) Water injection test: same as gas injection. There should be no resistance.

(7) Bubble escape test: After injecting water, immediately remove the syringe, and there should be multiple bubble escape phenomena. EB3-11 gas injection test resistance method (8) Cannulation test (Figure 10-12): If the puncture needle does enter the epidural space, there is generally no difficulty in placing the catheter.

If there is a force in the mouth, it proves that the needle tip is not necessarily in the epidural space.

(9> Trial drug: After the above test is completed, 35ml of local anesthetic can be injected. If an anesthesia plane can appear, it indicates that it has entered the epidural space.

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