Intrathecal drug spread.

Correspondence Intrathecal drug spread Editor—I read with interest the review by Hocking and Wildsmith 1 on intrathecal drug spread. I feel they omitted to mention an important aspect of drug spread that could have a bearing for all blocks. They quite rightly stated that vasoconstrictors added to intrathe-cal local anaesthetic could prolong the duration of a block, although not affect the height of block. They failed to mention the effect of i.v. vasopressors on spinal block height. An article by Cooper and Mowbray 2 in 2003 first mentioned the affect of choice of i.v. vasopressor on the rostral spread of spinal anaesthetic. He conducted a formal study that was published in 2004, 3 which showed that when using phenylephrine as the hypotensive rescue drug, the block height, when assessed to cold and light touch sensation, was on average two dermatomes lower compared with ephedrine. Given the increasing use of phenylephrine; particularly in obste-tric anaesthesia, to treat sympathetic blockade related hypotension, it should certainly have been mentioned. Editor—In their review of intrathecal drug spread, Hocking and Wildsmith state that pulse and blood pressure are related to block height. 1 This relationship however is not precise, as there are other more significant influences. 4 Although later, the authors stress the importance of venous return for the maintenance of blood pressure, they omitted the clinically highly significant relationship between a dropping venous return to the right heart and bradycardia. 4 I accept that the cardiovascular responses to spinal blockade formed only a small incidental part of this review. Unfortunately, however, this short sentence relating pulse and blood pressure solely to cephalad spread of spinal anaesthesia could encourage the anaesthetist erroneously to attribute a slowing heart exclusively to the height of the spinal block, so inducing a false sense of security. In 1988, Caplan and colleagues 5 demonstrated the serious consequences of failing adequately to appreciate the significance of bradycardia during spinal anaesthesia. This warning sign must alert the anaesthetist to the possibility and hence the consequences of a dropping venous return, and cannot be passed off as a side-effect of cephalad spread of spinal anaesthesia. Editor—We thank Drs Akerman and Hutter for their interest in our review, and are grateful for the opportunity to respond. Dr Akerman raises an interesting point, but should recognize the various dynamics involved. These are both relevant and important. First, the definitive paper by Cooper and colleagues 3 …