A reply

Abstract

We thank Checketts and Wildsmith for their letter. In reply, intra-operative heparin was given at the request of the surgeon, after blood began clotting in the graft. The first dose was given more than 2 h after the epidural insertion. Coagulation studies were performed intra-operatively and at the end of surgery. Results following 20 000 units heparin were: APTT 70.3 s (normal 22–31), TCT 14.1 (8–10) and heparin units 0.15 ml−1 (therapeutic range 0.35–0.7). The patient had been receiving heparin by infusion at the referring hospital and some degree of heparin resistance was apparent. In view of the abnormal clotting studies, we planned to wait until the coagulation status had returned to normal before considering removal of the epidural catheter. Removal was further delayed following the surgical decision to start heparin infusion postoperatively. We disagree that there is no good evidence that a postoperative epidural provides benefit to this high-risk patient group. Regional anaesthesia is associated with increased graft blood flow [1] and the results from the PIRAT study [2] showed a significant effect on reoperation rates for graft occlusion between the GA and GA/RA groups (22% vs. 4%). This difference did not appear to be due to either differences in patient population, intra-operative or postoperative care and remained present after controlling for multiple baseline risk factors using logistic regression analysis. Faced with this evidence, the independent study monitoring committee recommended the early termination of the trial after 100 patients (cf. planned recruitment of 120 for a power of 0.80). Other investigators [3] have found a similar difference in incidence of graft failure, (6/20) in GA group vs. (1/25) RA. These findings were present with no evidence of technical problems as assessed by independent observers using arteriograms at the end of surgery. We suggested a time interval of 4 h (2 half-lives) should elapse before an epidural catheter is removed in a patient who has received intravenous heparin by infusion, as this is analogous to the recommendations for LMWH and central neuroaxial block [4]. The recommendation of Wildsmith and McClure that it would be safe to remove a catheter within 1–2 h of stopping heparin infusion after consultation with a surgeon does not infer that coagulation will be normal at this time. Vandermuelen et al. noted three epidural haematomas were associated with catheter removal within 2 h of stopping heparinisation. We feel it unlikely that anyone would attempt a spinal/epidural procedure within 1–2 h of stopping a heparin infusion. We agree with others [5] that the removal of an epidural catheter should be done under the same circumstances as it is inserted.