A reply

Authors


We would like to thank Dr Lin and colleagues for their interest in our work [1] and for their comments. The literature suggests a strongest effect of epidural volume extension (EVE), in a volume-dependant fashion, in the non-obstetrical population receiving plain bupivacaine [2, 3]. In term parturients, factors such as hormone-induced hypersensitivity to neuraxial-administered local anaesthetics, epidural venous plexus engorgement, the baricity of the injected local anaesthetic and the position of the patient may significantly affect the height of the spinal block. It is possible that EVE has a negligible effect on spinal block height and other characteristics compared with these factors. This is indirectly supported by the fact that few studies suggest an EVE effect (even with close to 10 ml EVE) on the height and duration of block in parturients undergoing spinal anaesthesia [4–6]. Moreover, even when EVE with saline significantly raised the sensory level in one study, it did not reduce the need for intra-operative supplementation nor increase the success rate of spinal anaesthesia [7]. We believe that those results are in agreement with our conclusion, that is, in order to provide an adequate surgical block, EVE is inconsistent at best, and that higher doses of intrathecal bupivacaine, around 10 mg, are needed.

When designing our study protocol, we deemed it unethical to provide spinal anaesthesia to term parturient undergoing caesarean delivery without an intrathecal opioid, as there is strong evidence that spinal opioids improve the quality of block. Moreover, addition of fentanyl to hyperbaric bupivacaine is a better approximation of clinical practice in many institutions worldwide. We agree with Lin et al. that this may have masked a slight difference between the groups that might have appeared had we not included fentanyl. However, if such a difference existed, we feel that it would be a clinically negligible effect. This might be investigated in further trials.

With regards with the slight delay in helping the patients into the wedged supine position, we doubt that such a short delay may have significantly influenced the spread of local anaesthetic within the intrathecal space. This is supported by the absence of statistically significant differences between the groups.

In conclusion, we agree with Lin and colleagues that several factors influence the quality of sensory block in the obstetric setting. We believe, however, that EVE has a negligible effect on spinal block characteristics and is not clinically useful.

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