Identification of the epidural space-loss of resistance to saline: An inexpensive modification

INTRODUCTION

Epidural anaesthesia, based on successful localization of epidural space, is an integral part of the practice of anaesthesia. This technique has undergone major modifications as a result of improvement in the syringe, needle, catheter and technique following the first demonstration by Dogliotti in 1933.[1,2,3] Superiority of saline versus air in detecting the loss of resistance has always been a question of debate[4].

Syringes such as the Episure^® Autodetect and the Epimatic^® syringe are designed for identification of the epidural space using saline or air, using ‘’a both hands on needle technique’’ for superior control. We describe a similar technique herein using the routinely available material for epidural insertion similar to the expensive syringes available in the market. A video presentation of the technique is also provided.

TECHNIQUE

We use a regular epidural set with Touhy's needle and loss of resistance (LOR) syringe and a pair of sterile gloves and sterile scissors. Under all aseptic conditions, the wrist cuff end of the glove is cut about an inch broad and is rolled twice on to the end of the barrel of the syringe. The LOR syringe is filled with 5 ml of normal saline. After cleaning and draping the area, a local anaesthetic is infiltrated at the site of insertion. Epidural needle is inserted, and as the needle is held by the interspinous ligament, the syringe is attached to the epidural needle. One strand of the glove is rolled up to the plunger of the syringe. At this point, the tension of the rubber holds the plunger in place. Slowly, the needle is inserted inside [Figure 1]. As soon as the needle enters the epidural space the plunger moves inwards due to the tension on the band [Video 1].

Figure 1.

Epidural loss of resistance syringes, the Epimatic, the episure and the modified syringe

DISCUSSION

The loss of resistance technique is based on the fact that ligamentum flavum and interspinous ligament are relatively dense tissue, and as the tip of the epidural needle pierces the ligamentum flavum, there is an abrupt decrease in the resistance and the contents of the syringe enter the epidural space smoothly.[1]

Both air and fluid can be used as a medium for this technique and till date the debate is going on as to which medium is superior. One of the reasons cited for reluctance in using saline is historical; until the seventies syringes were made of glass and were non-disposable. A fluid made the syringes sticky hence air replaced it.[1,5]

Demonstrating a loss of resistance technique is quite different with saline than with air. With saline, the finger pushing constantly on the plunger will belong to the hand advancing the epidural needle while the other hand will rest on the patient's back holding the hub of the needle between thumb and index to prevent sudden inward movement. Whereas when using air, the needle will be advanced by one hand while the finger of the other hand will be intermittently pushing the plunger to check the resistance, as the needle is advanced towards the epidural space. Air is a compressible medium, and high pressure cannot be achieved when compared to non-compressible matter-like fluid. With the new syringes available in the market, it is now possible to use ‘both hands on needle technique’ for better needle control.

Inadvertent dural puncture is a complication that is feared. There is a lower reported incidence of dural puncture with saline as compared to air. Studies, where saline has been used, report an incidence of 0.3–0.5%, whereas while using air, the incidence can be as high as 2%, the reason being that as the epidural space is entered the saline which enters with continuous pressure pushes the dura away thereby reducing the incidence of dural puncture.[5]

The pressure exerted by the saline in the pressurised syringe also raises concern. The pressures applied by the syringes were measured using the TruWave Disposable Pressure Transducer (Edwards LifeSciences), the Episure^® Autodetect syringe and the modified syringe exerted a comparable range of pressures at similar volumes of saline [Figure 2].

Figure 2.

Pressure exerted by the episure syringe and the modified syringe measured using a pressure transducer

In a study using the Episure^® Autodetect syringe in 17 paediatric patients of 9 months to 14 years for identification of the epidural space, no inadvertent dural punctures were noted.[6] Many other complications related to the injection of air in the epidural space are reported in literature.[7,8]

Since the use of air demonstrates no advantage over the use of saline, the possibility of the above complications no matter how remote speaks in favour of use of saline and abandonment of air for this valuable technique.

Our modification is a simple, inexpensive technique which compares to the syringes available in the market in all aspects and would help to encourage the use of saline as the mode of loss of resistance in identification of the epidural space using ‘both hands on needle technique’ leading to better needle control and fewer complications.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.