• Jiseob Kim, Sungwon Jung, Eunyoung Cho, and JiHee Hong.
• Department of Anesthesiology and Pain Medicine, Keimyung University School of Medicine, Republic of Korea.
• Pain Physician. 2020 Mar 1; 23 (2): E203-E210.

BackgroundDuring lumbar epidural injection (LEI) using a midline approach, we might encounter failure of identifying the epidural space owing to an equivocal or absent loss of resistance (LOR) sensation. The reason for such absence of LOR sensation has been suggested as paucity of midline ligamentum flavum, paravertebral muscle, and cyst in the interspinous ligament of the lumbar spine. Despite its low specificity, LOR is the most commonly used method to identify the epidural space.ObjectivesThe purpose of this study was to analyze lumbar epidural pressure decrease patterns and identify factors contributing to this pressure decrease.Study DesignProspective randomized trial.SettingAn interventional pain management practice in South Korea.MethodsThis prospective study included 104 patients receiving LEI due to lumbar radiculopathy. A midline or paramedian approach of LEI was determined with randomization. Among various factors, gender, age, body mass index (BMI), and diagnosis were analyzed using a subgroup that included 60 cases of only a paramedian approach.ResultsGrades I, II (abrupt decrease), and III (gradual decrease) were found as patterns of epidural pressure decrease. Abrupt pressure decrease was more frequently observed in the paramedian group (P < 0.001). Age, gender, BMI, and diagnosis did not show any significant difference in frequencies between abrupt and gradual pressure decrease.LimitationsWe could not match LOR sensation with epidural pressure decrease shown in the monitor.ConclusionsThis study demonstrates that abrupt pressure decrease occurs more frequently with the paramedian approach. However, age, gender, BMI, or diagnosis did not affect the incidence of epidural pressure decrease.Key WordsEpidural, paramedian, midline, pressure decrease.

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