Increased Postoperative Arterial Blood Pressure Stability with Continuous Epidural Infusion of Clonidine in Children

Abstract

To the Editor: We want to add additional information to our previous study published in Anesthesia & Analgesia(1). This information concerns the variability of postoperative hemodynamic variables associated with continuous postoperative epidural infusion of clonidine and ropivacaine in children. Following Ethical Committee approval and written parental informed consent, 60 boys (ASA physical status 1–2) aged 1–4 yr undergoing hypospadias repair were randomized to receive one of the following four postoperative epidural infusions after the induction of a standardized isoflurane based anesthetic: Group R: plain ropivacaine 0.1%, 0.2 mg kg−1h−1; Group RC1: ropivacaine 0.08% 0.16 mg kg−1 h−1 + clonidine 0.04 μg −1 h−1; Group RC2: ropivacaine 0.08% 0.16 mg kg−1 h−1 + clonidine 0.08 mg kg−1 h−1; or Group RC3: ropivacaine 0.08% 0.16 mg kg−1 h−1, + clonidine 0.12 μg kg−1 h−1. Further details are given in the original article (1). No difference in overall heart rate or arterial blood pressure levels could be detected between the four study groups during the 48-h observation period. However, the systolic blood pressure variability, measured as the coefficient of variation (CV%) as described by Ghignone et al. (2) was significantly lower than in groups RC2 and RC3 compared with the other two groups (P < 0.001) (Table 1) (Fig. 1). No such difference was observed regarding heart rate variability (Table 1).Table 1: Intrapatient Variability of Hemodynamic VariablesFigure 1: Individual systolic blood pressure recordings in patients receiving a postoperative epidural infusion of either plain ropivacaine 0.1% (group R) or a co-infusion of ropivacaine 0.08% + clonidine 0.12 μg kg−1 h−1 (group RC3). Please note the difference in individual variability and the lack of difference regarding overall blood pressure levels between the two groups.The improved arterial blood pressure stability we observed associated with epidural clonidine administration is most likely explained by two interacting mechanisms. First, systemic uptake of clonidine from the epidural space into the systemic circulation will cause secondary interactions with centers in the brain stem (e.g., locus coeruleus and the vasomotor center) that affect central sympathetic discharge. Second, epidural clonidine in the dose range of 0.08–0.12 μg −1 h−1 is associated with improved postoperative pain relief (1). A reduced nociceptive input is likely to result in reduced blood pressure variability due to a reduction of the pain-generated stress response. However, if improved pain relief would be the main mechanism behind the observed reduction of blood pressure variability, then it is difficult to explain why heart rate variability did not show a similar pattern. Although strict cardiovascular control might not be essential after urogenital surgery in children, improved hemodynamic stability could be of potential benefit in other clinical situations (e.g., after major thoracic or abdominal surgery). We have previously shown that the bioavailability of clonidine is not restricted by epidural administration (3). Thus, one could postulate a similar hemodynamic effect if clonidine instead was administered as an intravenous infusion. Intravenous administration of clonidine would obviously make this property of clonidine useful in situations where epidural administration of clonidine is not an option (i.e., neurosurgery). H. T. G. Bergendahl P. A. Lonnqvist P. De Negri G. Ivani S. Eksborg