Air or nitrous oxide for loss-of-resistance epidural technique?

Purpose: To compare the spinal-epidural spread of gas following loss of res istance (LOR) technique for detection of the,epidural space using air or ni trous oxide (N2O). Methods: Comparison of the spread of air and N2O in the epidural space foll owing LOR technique was performed by using Magnetic Resonance Imaging (MRI) . Ten adult patients ASA grade I sewed as their own control in this prospec tive study. A control MRI (MRI Contr-1) of the dorsolumbar spine was perfor med. Then, an 18 gauge epidural needle was introduced at the L3-4 intervert ebral space using 0.14 ml.kg(-1) N2O for LOR and the MRI (MRI-N2O) was repe ated, Forty eight hours later, an MRI scan (Contr-2 MRI) was performed and, subsequently, an 18 gauge epidural needle was introduced, using 0.14 ml.kg (-1) air for LOR followed by an MRI (MRI-Air) scan. The volumetric measurem ents of gas pockets were done using a formula. Results: Gas bubbles after N2O were few and small compared with larger gas pockets occupying up to three vertebral segments after the use of air for L OR. The volume of air in the epidural space was 2.96 +/- 0.93 ml compared w ith 0.35 +/- 0.32 ml N2O. Conclusion: The use of N2O for LOR technique of detecting the epidural spac e produced very small bubbles detected by MRI compared with the use of air under similar conditions.