Midazolam and fentanyl continuous infusion anesthesia for cardiac surgery: a comparison of computer-assisted versus manual infusion systems.

Continuous infusion of intravenous anesthetics can be achieved either by a manually controlled infusion (MCI) pump, or by a computer-assisted continuous infusion (CACI) pharmacokinetic model-driven infusion system. Randomized double-blind comparisons of the two infusion systems for general anesthesia were performed in 24 patients undergoing coronary artery bypass grafting. Patients were allocated to receive continuous infusions of midazolam and fentanyl by either a MCI device or CACI. Midazolam and fentanyl infusions were independently titrated to maintain hemodynamic stability, defined as mean arterial pressure (MAP) and heart rate (HR) within 20% of baseline values. As directed by the study design, comparable hemodynamic control was achieved in both groups. Mean plasma fentanyl concentrations measured at specific timepoints were similar between groups. The plasma midazolam level for induction was 196 +/- 139 ng/mL in the CACI group and 300 +/- 128 ng/mL in the MCI group, and the fentanyl level was similar in both groups, 6.7 +/- 1.9 ng/mL in CACI and 6.3 +/- 4.6 ng/mL in the MCI group. The drug levels were lower (P < or = .05) for midazolam during maintenance of anesthesia and similar for fentanyl during the maintenance of anesthesia. In the MCI group, the average duration of anesthesia was 246.5 +/- 35.0 minutes, with a mean total fentanyl dose of 30.27 +/- 11.14 micrograms/kg. In the CACI group, the average duration of anesthesia was 230.8 +/- 44.1 minutes, with a mean total fentanyl dose of 34.61 +/- 5.40 micrograms/kg (P > 0.05 for comparisons between groups for duration of anesthesia and total fentanyl dose).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of clenbuterol hydrochloride on pulmonary gas exchange and hemodynamics in anesthetized horses.

We evaluated the effects of clenbuterol HCl (0.8 micrograms/kg, of body weight, IV), a beta 2 agonist, on ventilation-perfusion matching and hemodynamic variables in anesthetized (by IV route), laterally recumbent horses. The multiple inert gas elimination technique was used to assess pulmonary gas exchange. Clenbuterol HCl induced a decrease in arterial oxygen tension (from 57.0 +/- 1.8 to 49.3 +/- 1.2 mm of Hg; mean +/- SEM) as a result of increased shunt fraction (from 6.6 +/- 2.1 to 14.4 +/- 3.1%) and ventilation to regions with high ventilation-perfusion ratios. In contrast, no changes in these variables were found in horses given sterile water. In horses given clenbuterol HCl, O2 consumption increased from 2.23 +/- 0.18 to 2.70 +/- 0.14 ml.min-1.kg-1, and respiratory exchange ratio decreased from 0.80 +/- 0.02 to 0.72 +/- 0.01. Respiratory exchange ratio and O2 consumption were not significantly modified in sterile water-treated (control) horses. Clenbuterol HCl administration was associated with increased cardiac index (from 57.4 +/- 4.0 to 84.2 +/- 6.3 ml.min-1.kg-1), decreased total peripheral vascular resistance (from 108.3 +/- 9.3 to 47.6 +/- 2.8 mm of Hg.s.kg.ml-1), and decreased pulmonary vascular resistance (from 31.3 +/- 3.8 to 13.6 +/- 0.7 mm of Hg.s.kg.ml-1). Our findings indicated that clenbuterol HCl may potentiate hypoxemia as a result of increased shunt fraction in horses anesthetized by the IV route, and caused changes in hemodynamic variables that were consistent with its ability to stimulate beta 2-adrenergic receptors.