A pressure comparison between midline and paramedian approaches to the cervical epidural space.

BACKGROUND In the cervical spine, the ligamentum flavum (LF) is often incompletely fused at the midline. Therefore, accessing the epidural space (ES) using the loss of resistance (LOR) technique via the midline approach could be less reliable than the paramedian approach. Since the tactile sensation of LOR is due to abrupt loss of pressure upon entering the ES, we have compared pressure changes between the 2 different cervical epidural techniques. OBJECTIVES The aim of this study was to compare pressure changes during the pathway to the cervical ES between the 2 approaches. STUDY DESIGN A prospective, open-labeled, randomized, comparative study. SETTING An interventional pain management practice in a hospital, Republic of Korea. METHODS The 74 patients were randomly assigned to either a midline or paramedian group. The pressure changes were monitored and classified into 4 grades according to the following criteria: Grade I. The pressure waveform sequence consisted of 3 components in chronological order: 1) a high positive pressure just prior to entering the ES; 2) an abrupt pressure decrease at the moment of entering the ES; and 3) a negative peak pressure before cervical epidural pressure equilibration. Grade II. A high positive pressure followed by a precipitous pressure drop, without negative peak pressure upon entering the ES. Grade III. High positive pressure before entering the ES, followed by continuous pressure decrease without negative pressure. Grade IV. No pressure changes before or after entering the cervical ES. RESULTS An abrupt pressure decrease at the moment of exiting the LF or entering the ES was more frequently observed when using the paramedian approach (P < 0.05) with the odds ratio of 4.96 (95% CI, 1.63 - 15.12) as compared with the midline approach. LIMITATIONS A correlation between the abrupt pressure decrease and LOR tactile sensation has been assumed. CONCLUSION Under the assumption that the LOR sensation is due to an abrupt decrease in pressure the moment the needle enters the ES or exits the LF, this study claims that the accuracy of accessing the cervical ES can be improved significantly using the paramedian approach. CLINICAL TRIAL NCT01009385. Institutional Review Board (IRB): H-1208-107-422.