We are grateful to Dr. Marret et al. for their constructive comments. We agree with their comment that “although the distribution of radiographic spread is well correlated with the spread of analgesic block, this does not mean that [epidurography] is a reliable technique and that the two methods agree.” We also do agree that the Bland and Altman method is proper to confirm whether the two different methods agree.
However, we have not shown the agreement of the two methods; we have rather shown the correlation. In our article, we confirmed that the distribution of radiographic spread correlates well with the spread of analgesic spread. Dr. Marret et al. have noted this correlation in their figure 1 (Y = 0.80 X + 0.48; r = 0.93, P < 0.0001). This is what we intended to mention in our manuscript. We have not mentioned that the distribution of radiographic spread agrees with the spread of analgesia completely. Dr. Marret et al. point out that the radiographic spread overestimated the analgesic spread in all cases. However, we have neither overestimated nor underestimated those values. We have investigated the correlation between those values, and we got the relation expression; the analgesic spread = 0.8 × the radiographic spread. This means that, for example, if the radiographic spread is 10 segments, the analgesic spread would be approximately eight dermatomes in many cases.
We understand the comments regarding the bias and limits of agreement. However, we believe that this method is very useful to predict the dermatomal distribution of analgesic block because it is impossible to predict the cephalad and caudal spread of anesthetic, whether it will spread unilaterally and the general pattern of spread without epidurography. Thus, we concluded that epidurography could help to predict the dermatomal distribution of analgesic block.
* Okayama University Medical School, Okayama, Japan. firstname.lastname@example.org