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Does body mass index relate to palpability of bony landmarks in the parturient presenting for neuraxial anaesthesia
Abstract Number: T2A-7
Abstract Type: Original Research
Increasing numbers of parturients of high body mass index (BMI) are presenting for obstetric care.1 The incidence of impalpable bony landmarks of the back is poorly defined. The quality of back surface landmarks in pregnant women is an independent predictor of successful first attempt at neuraxial blockade and repeated needle insertions increase complication rates.2 Pre-procedural ultrasound has been shown to reduce the number of needle passes in parturients with impalpable bony landmarks.2 We aimed to discover the relationship of BMI to impalpable bony landmarks and the sonographically determined distance from skin to epidural space (DES) at a standard insertion site in these women.
We recruited fifty consenting non-labouring women with BMI >30 kg/m2. Participants were seated, minimising lumbar lordosis. The scapulae (SC), iliac crests (IC), anterior superior iliac spine (ASIS), posterior superior iliac spine(PSIS), vertebral spinous processes (SP) and sacral cornua (SC) were palpated and graded on a four-point scale: visible = 1; palpable without skin indentation = 2; palpable with skin indentation = 3; impalpable = 4. A low-frequency (GE Venue 40 2-5MHz) probe measured DES at the L3/4 interspace in the parasagittal oblique and transverse planes.
All fifty participants were included in data analysis. Mean BMI was 37.9 kg/m2 and mean DES was 7.1 cm. Subgroup analysis of sixteen patients with BMI >40 kg/m2 showed mean BMI of 44.8 kg/m2 with mean DES of 7.9 cm. Table 1 shows the percentage of women with impalpable landmarks and the respective DES.
Our study shows that parturients with BMI >40 kg/m2 are more likely to have impalpable SP, SC and ASIS, and DES longer than our standard epidural and spinal needles. To minimise repeated needle insertions, pregnant women with BMI >40 kg/m2 and impalpable spinous processes need pre-procedural ultrasound and consideration should be given to use of a needle longer than the standard for the initial attempt, based on the measured DES.
1. McKeating A, Maguire PJ, Daly N, Farren M, McMahon L, Turner MJ. Trends in maternal obesity in a large university hospital 2009-2013. Acta Obstet Gynecol Scand 2015;94(9):969-75.
2. Creaney M, Mullane D, Casby C, Tan T. Ultrasound to identify the lumbar space in women with impalpable bony landmarks presenting for elective caesarean delivery under spinal anaesthesia: a randomised trial. Int J Obstet Anesth. 2016;28:12-16.