Background: Epidural placement in lumbar spine is used to provide anaesthesia for surgeries below umbilicus. However the success depends on correct identification of epidural space taking into consideration anatomic variations. Studies have found that ultrasound is an useful tool to help in identification of the epidural space. Hence we used ultrasound to study the variability of skin to epidural space depth at various lumbar spinal levels. 

Study Method: We conducted a prospective observational study of 100 patients in age group of 40 to 60 years to compare the skin to epidural space depth (SED) at L1-L2,L2-L3 and L3-L4 space. We also compared the variation at these levels with respectto sex and BMI. 

Results and Conclusion: We found that the SED was highest at L3-L4 space with a mean distance of 4.15 +/-0.21cm from skin followed by L2-L3 (4.12 +/-0.22 cm) and least distance in L1-L2 space (4.1 +/-0.22cm). Age and sex had no correlation to the SED. However the SED had a significant correlation with the BMI (kg/m2) from which we could compute a formula. Mean (cm)=0.074(BMI)+2.534 where 0.074 is regression coefficient and 2.534 is a constant.