Use of loss of resistance, to carbon dioxide, in identifying the epidural space.

The use of air, in localizing the epidural space, has been associated with suboptimal or “patchy” anesthesia as well as the rare occurrence of venous and cerebral air emboli. Saline has been documented to be superior and devoid of these side effects.[12] However, saline, being virtually incompressible with respect to air, is significantly more difficult to use for localization of the epidural space.

Carbon dioxide (CO2) would allow for the same ease of localization as air. This occurs as the bulk modulus of CO2 is almost identical to that of the air.[34] It thus has a similar "feel" when used for identification of the epidural space. CO2 is also readily absorbed across cell membranes and is more rapidly eliminated, from tissues, than air.[567] Furthermore, CO2 is actively transported, utilizing carbonic anhydrase, from the cerebral spinal fluid.[8]

A preliminary device has been developed, which allows for CO2 to be uncomplicatedly administered, through a three-way stopcock, into a traditional glass syringe. This device is illustrated in the [Figure 1].

Figure 1

This device allows for a syringe to be filled, with CO2, to assist in epidural space localization

Preliminary testing of this technique, on cadaveric bovine spinal sections, has demonstrated that CO2 may be a reasonable alternative, to both air and saline, for epidural space localization. Further research is necessary to fully assess the potential benefits, and limitations, of this technique.