A multifactorial analysis of the spread of epidural analgesia.

The controversies about the factors determining the spread of epidural analgesia are partly due to inappropriate methodology or sample size of previous studies. We performed a multivariate regression analysis on 803 ASA class 1-2 non-atherosclerotic adults, undergoing lumbar epidural anaesthesia according to a predefined standardised procedure. The spread of epidural analgesia is more accurately studied by analysing dose/segment (R2 = 0.671) instead of spread (R2 = 0.271) as dependent variable. The impact of local anaesthetic (2\% lidocaine CO2 or 0.5\% bupivacaine) and addition of adrenaline is not significant. Spread significantly increases with increasing age, weight, body-mass index, dose of local anaesthetic, addition of fentanyl, higher site of injection, and decreasing body height. The impact of age and dose is higher under the age of 40 and at doses lower than 20 ml. Increasing the total dose increases the dose needed to block one spinal segment. Unknown idiosyncratic factors still determine a certain proportion of the sample variance. The addition of adrenaline to lidocaine and the use of bupivacaine improve the predictability of spread. In conclusion, we found clinically significant correlations between a group of factors and epidural spread. Alternative anaesthetic solutions lead to different degrees of predictability.