Research Article

An Observational Study on The Relationship of Patient’s Body Mass Index and Depth of Spinal Needle Insertion


Background: The distance from the skin to the subarachnoid space varies at different levels of the vertebrae and from patient to patient. Knowing the distance from the skin to the subarachnoid space beforehand may help the procedure go more smoothly and ensure that the spinal needle use is of the right length.
Methods: An observational study was conducted on 100 patients posted for infra umbilical surgeries of various specialties under spinal anaesthesia. Intraoperatively after a successful spinal with midline approach at the L3-L4 level, the length of the needle from the skin to the subarachnoid space was immediately measured and this actual length was compared with the expected length obtained using Bonadio's formula. The relationship between a patient's BMI and depth of spinal needle insertion and the reliability of Bonadio's formula to predict skin-to-subarachnoid space was studied.
Results: From our study, a positive correlation was obtained between patients' weight, BMI, waist circumference and depth of spinal needle insertion and also between the Skin to Subarachnoid space distance (SSD) measured intraoperatively with the predictive value obtained using Bonadio's formula. The correlation between height and arm circumference was not much significant.
Conclusion: Skin-to-subarachnoid space distance correlates with weight more than BMI. Bonadio's formula can be used to calculate the skin to subarachnoid space depth before performing spinal anaesthesia. After seeing the results, weight was the variable which had a significant correlation with Spinal Needle Depth (SND), hence we formulated two equations using weight to predict the depth of spinal needle insertion to reduce the incidence of multiple attempts during the procedure and to enhance patient comfort.
The regression equation using actual values of needle depth:
SND = 2.292 + [0.044 x weight]
And regression equation using Bonadio's values of needle depth is:
Needle depth= 2.681 + [0.037 x weight]

[1] Kim HJ, Kim WH, Lim HW, Kim JA, Kim DK, Shin BS, Sim WS, Hahm TS, Kim CS, Lee SM. Obesity is independently associated with spinal anesthesia outcomes: a prospective observational study. PLoS One. 2015; 10(4):e0124264.
[2] Hazarika R, Choudhury D, Nath S, Parua S. Estimation of Skin to Subarachnoid Space Depth: An Observational Study. J Clin Diagn Res. 2016; 10(10):UC06-UC09.
[3] Razavizadeh MR, Fazel MR, Mosavi M, Sehat M. The relationship between patients' anthropometric characteristics and depth of spinal needle insertion. Anesth Pain Med. 2016; 6(2).
[4] Bonadio WA, Smith DS, Metrou M, Dewitz B. Estimating lumbar-puncture depth in children. N Engl J Med. 1988; 319(14):952-3.
[5] Christopher M. Bernards: Epidural and spinal anaesthesia in; Paul G. Barash Clinical anaesthesia 6th edition bolster Kluwer Lippincott Williams & Wilkins New York; 2010: 927-95.
[6] David L Brown. Spinal, Epidural and Caudal Anaesthesia, chapter 42. Anaesthesia Ronald D. Miller; 5th edition: 1491-98.
[7] Crossman AR, Standring S. Neuroanatomy: Ventricular system and subarachnoid space. Gray's Anatomy, 40th edition. Elsevier; 2008. P. 237 - 46.
[8] Abe KK, Yamamoto LG, Itoman EM, Nakasone TA, Kanayama SK. Lumbar puncture needle length determination. Am J Emerg Med. 2005; 23(6):742-6.
[9] Craig F, Stroobant J, Winrow A, Davies H. Depth of insertion of a lumbar puncture needle. Arch Dis Child. 1997; 77(5):450.
[10] World Health Organization. Obesity: preventing and managing the global epidemic.
[11] Arzola C, Davies S, Rofaeel A, Carvalho JC. Anthropometric variables and lumbar dural sac width using ultrasound. Canadian Journal of Anesthesia. 2006; 53(1):26291
[12] Taman HI, Farid AM, Abdelghaffar WM. Measuring skin to subarachnoid space depth in Egyptian population: A prospective cohort study. Anesth Essays Res. 2016; 10(3):468-72.
IssueVol 9 No 4 (2023): Autumn QRcode
SectionResearch Article(s)
Spinal anaesthesia Body mass index Bonadio's formula Spinal needle depth

Rights and permissions
Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
How to Cite
Paulina S, Ramachandran H, Kalappa R, Sathyamurthy S. An Observational Study on The Relationship of Patient’s Body Mass Index and Depth of Spinal Needle Insertion. Arch Anesth & Crit Care. 2023;9(4):325-328.