A clinical prediction of skin to subarachnoid space depth in parturients undergoing caesarean delivery in a Nigerian population

Few studies on the prediction of skin to subarachnoid space depth (SSD) in African parturients undergoing caesarean delivery are available. We undertook a prospective observational study of 402 parturients scheduled for elective caesarean delivery to determine simple and clinically applicable formulae for predicting skin to SSD. Additionally, the impact of patient characteristics and variables such as age, height, weight, body mass index (BMI), and body surface area on SSD was studied. We employed a Stepwise Multiple Linear Regression Model to predict SSD in normal weight, overweight, and obese parturients using previously described formulae and compared our derived SSDs to these previous formulae for concordance. (Craig, Abe, Stocker, Chong's modified, Prakash, Ma, Hazarika, Taman and Celik). Mean SSD was 6.62 +/- 1.07 cm in the overall population. SSD in normal weight patients was (6.19 +/- 0.92 cm), overweight (6.44 +/- 0.92 cm) and obese (6.97 +/- 1.17 cm). There was a correlation between SSD and BMI (p = 0.001). Formulae for predicting SSD in the overall population, normal weight, overweight and obese parturients were 4.34 + weight x 0.03, 4.43 + weight x 0.03, 4.54 + weight x 0.03 and 3.56 + weight x 0.03, respectively. We also found the Prakash formula to correlate best with our observed SSD. We concluded that SSD correlated well with weight in the overall parturient population and that Prakash's formula was the most accurate of the other previously described formulae in predicting SSD in this subset of African parturients. Impact StatementWhat is already known on this subject? Various formulae exist for predicting skin to subarachnoid space depth in adult patients and parturients.What the results of this study add? New formulae for predicting skin to subarachnoid space in a subset of African parturients are described and only one of the previously described formulae was found to reliably predict depth of the subarachnoid space in this cohort.What the implications are of these findings for clinical practice and/or further research? Formulae for the determination of skin to subarachnoid space depth using weight alone can be predictive for normal, overweight and obese parturients. Knowledge of the predicted depth can help guide appropriate needle selection and minimise wastage, especially in resource poor countries.