I would like to congratulate the authors on a well-conducted trial, regarding a relevant clinical implication of epidural volume extension (EVE) . It is concluded by the authors that EVE does not augment the sensory level of subarachnoid block induced with hyperbaric or plain bupivacaine. This is correctly enough inferred from their observation of statistically similar sensory levels at pre-defined time points between Groups A and B, and between Groups C and D. However, it might be more accurate to draw this conclusion after also comparing the maximum sensory level achieved and the time required to do so, between Groups A and B, and C and D. This is because the maximum sensory level may be achieved earlier with EVE, even though the eventual sensory levels with and without EVE could be the same.
My second observation is regarding the similarities that the authors draw between their findings and those of Yamazaki and colleagues . I would like to point out that in the trial by Yamazaki and colleagues, the block was performed with patients in the lateral position and the epidural volume was injected 20 min after the intrathecal injection. The intrathecal spread and hence the sensory level after a subarachnoid block would be different for a patient in sitting position vs. one in lateral position. Consequently, the effect of EVE can also be expected to be different between varying patient position. More importantly, EVE has been shown to be a time-dependent phenomenon. When performed 20 min after intrathecal injection , it fails to augment the spinal block and even decreases the duration of spinal anaesthesia when performed after two segment regression of spinal block . Hence the cause of failure of EVE in block augmentation with the trial of Yamazaki and colleagues cannot be compared to the present study.
Lastly, no observation is made on the method of confirming correct placement of the epidural catheter. Whether using clinical or radiological method, the confirmation of correct placement of epidural catheter for EVE-based trials is essential. With a non-functioning catheter the ‘apparent' application of EVE would in fact be absent. This would definitely result in erroneous interpretation of the observations.
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2. Yamazaki Y, Mimura M, Hazama K, Namiki A. Reinforcement of spinal anesthesia by epidural injection of saline: a comparison of hyperbaric and isobaric tetracaine. J Anesth
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