No abstract

SummaryAnalysis of heart rate variability has been used to study the effects of midazolam, morphine and clonidine on the autonomic nervous system, when administered to patients for premedication. Ninety-five patients were studied 60 min before and 60 min after premedication. Normal saline (n ¼ 25), midazolam 0.08 mg.kg ¹1 (n ¼ 24), morphine 0.15 mg.kg ¹1 (n ¼ 23), or clonidine 2 mg.kg ¹1 (n ¼ 23) were administered intramuscularly by random allocation. A Holter device was connected to the patient during the study period. Using power spectral analysis the low-frequency and high-frequency components were calculated from the Holter recordings. These are markers for sympathetic and parasympathetic activity respectively; the low-to high-frequency ratio was also calculated, a ratio of >1 signifying sympathetic dominance. A significant reduction was noticed in both low-frequency and high-frequency power in the three premedicated groups, whereas no changes were observed in the normal saline group. In the case of midazolam, both the low and high frequencies were decreased but the low-to high-frequency ratio did not change significantly. Morphine and clonidine depressed the low-frequency component more than the high-frequency component and the low-to high-frequency ratio was decreased, suggesting parasympathetic dominance. We conclude that heart rate variability may be a useful tool for investigating the effect of drugs on the autonomic nervous system. Power spectral analysis of heart rate variability has been proposed as a quantitative non-invasive method of assessing the influence of the autonomic nervous system on the heart [1-3]. Assessment of heart rate variability provides useful information in many clinical disciplines [4][5][6][7] including anaesthesia [8]. It may also be related to changes in depth of anaesthesia and central autonomic outflow [9][10][11][12][13][14][15]. Drugs given during the pre-operative period may influence autonomic balance. The purpose of the present study was to examine the effects of certain drugs administered for premedication on autonomic function, by assessing changes in heart rate variability. Patients and methodsWe studied ninety-five ASA I patients, aged 23-35 years, scheduled for elective surgery under general anaesthesia. The study was approved by the hospital's ethics committee and informed consent was obtained from all participants. Patients with a history of cardiovascular, pulmonary or neurological disease were not studied. No patient was taking concurrent medication. The patients were randomly allocated into one of four groups to receive for premedication a 2 ml solution that contained one of the following: normal saline (n ¼ 25), midazolam 0.08 mg.kg ¹1 (n ¼ 24), morphine 0.15 mg. kg ¹1 (n ¼ 23), clonidine 2 mg.kg ¹1 (n ¼ 23). All solutions were given intramuscularly into the deltoid muscle. A Holter continuous ECG recorder was connected to each patient and recordings were obtained for 60 min before administration of the study drug and for 60 min after. During the study perio...

Although single-frequency bioimpedance does give an indication of total body water and change in total body water, it is neither precise nor accurate enough to be the sole guide to fluid therapy. The proportion of total impedance contributed by the knee-ankle segment, which contains relatively little water, was significantly greater in the patients than in the controls, probably reflecting better drainage of fluid from the lower limb in the supine position.