Title predictors of difficult subarachnoid block

S. K. Gvalani, Madhavi Keskar


Background: The aim of this prospective randomised study was to evaluate the association of four patient variables with difficulty in subarachnoid block. These variables are age, BMI, quality of bony landmarks and anatomical abnormality of spine. An attempt was made to prepare a difficulty score to predict this difficulty and assess it’s predictive value.

Methods: 498 patients scheduled for surgical procedures under subarachnoid block were included. Each patient was assigned a difficulty score according to gradation of four variables. The difficulty was assessed in terms of number of levels, number of  attempts, and completeness of  anaesthesia. Since all these variables operated simultaneously and randomly in each patient, multivariate analysis was used with SPSS version 11.5. ROC curves were used to evaluate the sensitivity and specificity of the score. ROC curves were plotted at scores of 2, 3, 4 and 5 and AUC was compared.

Results: This study was successful in preparing a score to predict difficulty in subarachnoid block. A score of 4 or more is indicative of difficulty as far as number of attempts and levels is concerned. However, completeness of anaesthesia could not be predicted with this score.

Conclusions: This difficulty score can enable the anaesthetist to predict a difficult spinal puncture. This is a distinct advantage as multiple attempts are not without hazards.


Difficult subarachnoid block, Difficulty score, Predictive value

Full Text:



Renck H. Neurological complications of central nerve blockade. Acta Anesthesiology Scand. 1995;39:859-68.

Harrison DA. A survey of failure rate, postdural puncture headache and patient satisfaction. Anaesthesia. 1994;49:88-9.

Adams. Obesity and anaesthesia. British J Anaesthesia. 2000;85:91-108.

Hogan QH. Tuffier’s line. The normal distribution of anatomical parameters. Anaesthesia Analg. 1994;78;194-5.

Logic in safe practice of spinal anaesthesia. Anaesthesia. 2000;55:1045-6.

Schlew BL. Ankylosing spondylitis and neuraxial block- a 10 year review. Canadian J Anaesth. 1996;43(1):65-8.

Armitage P, Berry G. Statistical methods in medical research. Blackwell Scientific Publications. 1987:326-9.

De Long, Long DM, Clarke P. Comparing the areas under two or more correlated receiver operating characteristic curves. Biometrics. 1988;44:837-45.

M M Atallah. Development of difficulty score for spinal anaesthesia. British J Anaesthesia. 2004;92:354-60.