title: Estimation of Skin to Subarachnoid Space Depth: An Observational Study.
abstract: BACKGROUND
  In a patient, the skin to Subarachnoid Space Depth (SSD) varies considerably at different levels of the spinal cord. It also varies from patient to patient at the same vertebral level as per age, sex and Body Mass Index (BMI). Estimation of the skin to SSD reduces complications related to spinal anaesthesia.
  
  
  OBJECTIVE
  To measure the skin to SSD in the Indian population and to find a formula for predicting this depth.
  
  
  METHODS
  Three hundred adult patients belonging to American Society of Anaesthesiologist class I and II, undergoing surgery using spinal anaesthesia in various surgical specialities of Gauhati Medical College were selected by systemic sampling for this prospective, observational study. Patients were divided into three groups: Group M containing male patients, Group F containing non-pregnant female patients, and Group PF containing pregnant female's patients. SSD was measured after performing lumbar puncture. The relationship between SSD and patient characteristics were studied, correlated and statistical analysis was used to find a formula for predicting the skin to SSD. Statistical analysis was done using Statistical Package for Social Sciences (SPSS 21.0, Chicago, IL, USA). One-way ANOVA with post-hoc(Bonferroni correction factor) analysis was applied to compare the three groups. Multivariate analysis was done for the covariates followed by a multivariate regression analysis to evaluate the covariates influencing SSD for each group separately.
  
  
  RESULTS
  Mean SSD was 4.37±0.31cm in the overall population. SSD in adult males was 4.49±0.19cm which was significantly longer than that observed in female's 4.18±0.39cm which was comparable with SSD in parturient 4.43±0.19 cm. The formula for predicting the skin to SSD in the male population was 1.718+0.077×BMI+0.632×Height, in nonpregnant female population was 1.828+0.077×BMI+0.018×Height+0.007×Age and 0.748+0.209×BMI+4.703×Height-0.054×weight in parturient females, respectively.
  
  
  CONCLUSIONS
  Skin to SSD correlated with the BMI in all the patients in our study.
authors.affiliation: Associate Professor, Department of Anaesthesiology and Critical Care, Gauhati Medical College and Hospital , Guwahati, Assam, India .
authors.forename: Rajib
authors.initials: R
authors.lastname: Hazarika
authors.affiliation: Professor and Head of the Department, Department of Anaesthesiology and Critical Care, Gauhati Medical College and Hospital , Guwahati, Assam, India .
authors.forename: Dipika
authors.initials: D
authors.lastname: Choudhury
authors.affiliation: Post Graduate Trainee, Department of Anaesthesiology and Critical Care, Gauhati Medical College and Hospital , Guwahati, Assam, India .
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Nath
authors.affiliation: Post Graduate Trainee, Department of Anaesthesiology and Critical Care, Gauhati Medical College and Hospital , Guwahati, Assam, India .
authors.forename: Samit
authors.initials: S
authors.lastname: Parua
keywords: Body mass index; Lumbar puncture; Spinal anaesthesia