1 New Delhi, India 2 Paris, France
EditorWe read with interest the article by Lena and colleagues1 on the analgesic efficacy of intrathecal morphine and clonidine after coronary artery bypass graft (CABG) and would like to raise some points. First, the consumption of patient-controlled anaesthesia (PCA) morphine in the first 24 h after surgery is higher in the group where morphine 4 µg kg1 was given intrathecally (40.5 mg) than in the control group (37 mg). In contrast, for the patients who received morphine with clonidine 1 µg intrathecally, the PCA requirement was markedly reduced (only 7 mg). This implies that intrathecal morphine has nothing to offer in terms of analgesia in the postoperative period after CABG surgery. Second, patients in the three groups had access to a PCA to deliver i.v. morphine, yet there was wide variation in the degree of pain relief in the three groups. At no point in time did patients in the control group or intrathecal morphine group have a visual analogue scale (VAS) score of zero, unlike the morphine + clonidine group. In the control group, the VAS score was between 20 and 35 mm, which signifies inadequate pain relief. Could this be attributable to a lower dose of morphine? Whether any rescue analgesic was made available to the patients who had higher VAS scores is another matter of concern. The conclusions of the present study cannot be accepted as accurate, as the higher VAS scores in the control, as well as in the morphine group, at almost all the time intervals do not lead to comparable end points of pain relief.
It was also shown that the intraoperative requirement for sufentanil was significantly less in the morphine + clonidine group than the other two groups. It needs to be clarified as to how the dose of sufentanil was determined. Was the anaesthetist administering the drug blinded to the different groups?
An important observation of the study, although not mentioned as a conclusion, is that morphine administered intrathecally in a dose of 4 µg kg1 has no effective analgesic role in the intraoperative or the postoperative period. We feel further study is needed before this drug, which is considered the gold standard for analgesic comparisons, is shown in such a poor light.
B. Singh
D. K. Tempe
M. Gupta
V. Dutt
New Delhi, India
EditorWe thank Dr Singh and colleagues for their comments concerning the PCA morphine consumption in patients who received intrathecal morphine or morphine + clonidine. First of all, there is a misunderstanding about the morphine dose. The mean i.v. morphine dose was not higher in the intrathecal morphine group but was statistically comparable with the one administered to the control group. This does not imply that morphine has nothing to offer in terms of analgesia in CABG patients, but that this dose of intrathecal morphine did not allow a decrease in i.v. morphine consumption in the current study.
VAS scores <30 mm are considered to represent adequate pain relief. Although the median values of VAS scores were lower in the intrathecal clonidine + morphine group, median values of VAS scores ranging between 20 and 35 mm do not signify inadequate pain relief, but only that VAS scores were statistically lower in the morphine + clonidine group compared with the control group.
Intraoperative sufentanil administration was lower in the morphine + clonidine group. As noted in our paper,1 anaesthetists and nurses were blinded to the allocation of patients in the three groups and they adjusted the sufentanil infusion rate to changes in arterial blood pressure and heart rate during CABG surgery. Thus the difference in sufentanil consumption is a valid finding, and is supported by numerous other studies reporting an opioid-sparing effect of clonidine.
P. Lena
F. Bonnet
Paris, France
References
1 Lena P, Balarac N, Arnulf JJ, Teboul J, Bonnet F. Intrathecal morphine and clonidine for coronary artery bypass grafting. Br J Anaesth 2003; 90: 3003