The efficacy of guanfacine in reducing perioperative hemodynamic changes and volatile anesthetic requirement

Anti-pressor effects of whole body exposure to static magnetic field on pharmacologically induced hypertension in conscious rabbits

Acute effects of whole body exposure to static magnetic field (SMF) on pharmacologically induced hypertension in a conscious rabbit were evaluated. Hypertensive and vasoconstrictive actions were induced by norepinephrine (NE) or a nonselective nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-l-arginine methyl ester (l-NAME). The hemodynamics in a central artery of the ear lobe was measured continuously and analyzed by penetrating microphotoelectric plethysmography (MPPG). Concurrently, blood pressure (BP) changes in a central artery, contralateral to that of the MPPG measured ear lobe, were monitored. Magnetic flux densities were 5.5 mT (Bmax), the magnetic gradient peaked in the throat at the level of approximately 0.09 mT/mm, and the duration of exposure was 30 min. The results demonstrated that under normal physiological conditions without treatment of pharmacological agents, there were no statistically significant differences in the hemodynamics and BP changes between the sham and the SMF exposure alone. Under pharmacologically induced hypertensive conditions, the whole body exposure to nonuniform SMF with peak magnetic gradient in the carotid sinus baroreceptor significantly attenuated the vasoconstriction and suppressed the elevation of BPs. These findings suggest that antipressor effects of the SMF on the hemodynamics under NE or l-NAME induced high vascular tone might be, in part, dependent on modulation of NE mediated response in conjunction with alteration in NOS activity, thereby modulating BPs.

Modulatory effects of static magnetic fields on blood pressure in rabbits

Acute effects of locally applied static magnetic fields (SMF) on pharmacologically altered blood pressure (BP) in a central artery of the ear lobe of a conscious rabbit were evaluated. Hypotensive and vasodilator actions were induced by a Ca(2+) channel blocker, nicardipine (NIC). Hypertensive and vasoconstrictive actions were induced by a nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME). The hemodynamic changes in the artery exposed to SMF were measured continuously and analyzed by penetrating microphotoelectric plethysmography (MPPG). Concurrently, BP changes in a central artery contralateral to that of the exposed ear lobe were monitored. SMF intensity was 1 mT and the duration of exposure was 30 min. A total of 180 experimental trials were carried out in 34 healthy adult male rabbits weighing 2.6-3.8 kg. Six experimental procedures were chosen at random: (1) sham exposure without pharmacological treatment; (2) SMF exposure alone; (3) decreased BP induced by a single intravenous (iv) bolus injection of NIC (100 microM/kg) without SMF exposure; (4) decreased BP induced by injection of NIC with SMF exposure; (5) increased BP induced by a constant iv infusion of L-NAME (10 mM/kg/h) without SMF exposure; (6) increased BP induced by infusion of L-NAME with SMF exposure. The results demonstrated that SMF significantly reduced the vasodilatation with enhanced vasomotion and antagonized the reduction of BP via NIC-blocked Ca(2+) channels in vascular smooth muscle cells. In addition, SMF significantly attenuated the vasoconstriction and suppressed the elevation of BP via NOS inhibition in vascular endothelial cells and/or central nervous system neurons. These results suggest that these modulatory effects of SMF on BP might, in part, involve a feedback control system for alteration in NOS activity in conjunction with modulation of Ca(2+) dynamics.

The efficacy of clonidine for reducing perioperative haemodynamic changes and volatile anaesthetic requirements in children

BACKGROUND

Oral clonidine given as a premedicant in adults has been shown to reduce intraoperative inhalation anaesthetic requirements and provide perioperative haemodynamic stability. We conducted the current study to ascertain whether or not these beneficial effects of clonidine can be reproduced in children.

METHODS

In a prospective, randomized, double-blind, controlled clinical trial, 60 children (ASA I) aged 5-11 yr, received placebo (control), 2 micrograms kg-1 clonidine, or 4 micrograms kg-1 clonidine orally 105 min before induction of anaesthesia. Anaesthesia was induced with halothane, nitrous oxide in oxygen via mask and maintained with halothane and 60% nitrous oxide in oxygen. The halothane concentration was titrated to the concentration required to maintain haemodynamic stability (defined as 20% of blood pressure (BP) and heart rate (HR)) for maintenance of anaesthesia. The end-tidal concentration of halothane was monitored throughout anaesthesia. On completion of surgery, nitrous oxide and halothane were discontinued. Following confirmation of recovery from anaesthesia and muscle relaxation, the endotracheal tube was removed.

RESULTS

Higher inspired concentrations of halothane (%) were required in the control and 2 micrograms kg-1 clonidine-treated groups (mean SD: 1.1 +/- 0.2 and 1.0 +/- 0.2, respectively) than in the 4 micrograms kg-1 clonidine-treated group (0.6 +/- 0.1) for haemodynamic stability (P < 0.05). Clonidine, 4 micrograms kg-1, significantly reduced the intraoperative lability (coefficient of variation) of systolic and diastolic BP and HR compared with the other two regimens.

CONCLUSION

Oral clonidine premedication at a dose of 4 micrograms kg-1 provided intraoperative haemodynamic stability and reduced anaesthetic requirements in children. However, we are unable to extrapolate these observations to younger children and infants.