Background: The 'MEMBRANE IN SYRINGE' technique is, in principle, a modification of the loss of resistance technique for identifying the epidural space in epidural anaesthesia. A plastic membrane is placed halfway inside a syringe dividing the syringe into two compartments. The saline compartment encompasses the nozzle of the syringe (the distal compartment). The plunger is installed in the opposite half of the hallow cylinder. Air is trapped in the space between the membrane and the rubber plunger (air compartment).
Methods: There were altogether 20 epidural procedures to put to the test for this technique. The time spent in the undertaking of the procedure, the amount of normal saline injected, whether there was a feel of loss of resistance with wrinkling of the membrane in the syringe, inadvertent puncture of the dura, the level of epidural block and the insertion depth of epidural needle were recorded.
Results: The procedure took less than 4 minutes to complete in most of the cases. There was no inadvertent dural puncture. The average amount of normal saline injected was less than 1 ml. In 3 cases, despite the absence of the feel of loss of resistance the epidural space was still successfully identified by visible wrinkling of the membrane in the syringe. All catheters were inserted smoothly through the epidural needle and appropriate level of anesthesia was achieved in all the cases.
Conclusions: The advantage of this technique is twofold. Firstly when the syringe is filled with both normal saline and air, it can prevent injection of the air into the epidural space during identification while at the same time it does not molest the feel of compressibility. Secondly, with the membrane separating the normal saline and air, correct placement of the needle tip can also be ascertained with loss of resistance while, as will be seen, the plastic membrane will wrinkle when saline is released into the epidural space.