High-resolution, high-throughput imaging with a multibeam scanning electron microscope.

Electron-electron interactions and detector bandwidth limit the maximal imaging speed of single-beam scanning electron microscopes. We use multiple electron beams in a single column and detect secondary electrons in parallel to increase the imaging speed by close to two orders of magnitude and demonstrate imaging for a variety of samples ranging from biological brain tissue to semiconductor wafers.

Gaseous dynamics of the rabbit maxillary sinus.

To better understand the mechanisms underlying maxillary sinus function, the gas composition of the sinus antrum in spontaneously breathing and tracheotomized rabbits (n = 17) was compared. The gas composition of samples (n = 117) obtained from rabbit maxillary sinuses was determined by gas chromatography. Results demonstrated significant differences (P < .005) in sinus gas composition between nasal breathing and tracheotomized animals for oxygen (02) and carbon dioxide (CO2). In tracheotomized animals O2 levels decreased while CO2 levels increased markedly to suprasystemic levels. This unexpected finding may be due to reduced sinus blood flow and the effects of nasal versus tracheal respiration. We conclude that the gaseous dynamics and perhaps the function of the maxillary sinus vary under different respiratory conditions. A better understanding of these processes may lead to earlier diagnosis and the development of improved treatments for sinus disease.

The effects of intravenous cimetidine and metoclopramide on gastric pH and volume in outpatients.

STUDY OBJECTIVE: To evaluate and compare the preinduction effects of intravenously (IV) administered cimetidine alone and combined with metoclopramide on gastric contents and postoperative nausea and vomiting in outpatients undergoing elective surgery. DESIGN: Patients were allocated randomly to 4 groups with 20 patients in each group. SETTING: Ambulatory surgery at a university-affiliated city hospital. PATIENTS: Eighty patients undergoing elective gynecologic or orthopedic procedures were studied. INTERVENTIONS: Outpatients in Group 1 and inpatients in Group 2 served as controls. Outpatients in Group 3 received 300 mg of cimetidine, and outpatients in Group 4 received 300 mg of cimetidine and 10 mg of metoclopramide. All drugs were administered IV as an infusion over a 15-minute period, 30 to 45 minutes prior to induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: After induction of general anesthesia and endotracheal intubation, stomach contents were retrieved and volume and pH measured. Group 1 outpatients had a large residual gastric volume of 29.2 +/- 15.9 ml, with a very low pH of 2.32 +/- 1.23 and 15% frequency of postoperative vomiting. These patients are at high risk of developing significant pneumonitis in the event of the aspiration of gastric contents. The combination of cimetidine and metoclopramide in Group 4 provided the optimal, or safest, condition--i.e., high gastric pH [6.15 +/- 0.71 (p less than 0.005)] and low gastric volume [11.6 +/- 7.37 ml (p less than 0.001)], with no postoperative vomiting. CONCLUSIONS: The combination of cimetidine and metoclopramide given to ambulatory patients during the preinductive phase may prevent severe pulmonary consequences should aspiration occur and is more effective in this regard than cimetidine alone.

Comparative hemodynamic effects of propofol and thiamylal sodium during anesthetic induction for myocardial revascularization.

The safety and efficacy of propofol, a new intravenous anesthetic agent, have been demonstrated in healthy patients. Twenty-one patients, ASA III-IV, undergoing elective myocardial revascularization, were randomly chosen to receive either propofol, 2.5 mg/kg, or thiamylal, 4 mg/kg. for the induction of anesthesia. Hemodynamics were recorded at one and three minutes after drug administration during spontaneous respiration. After the addition of halothane and pancuronium with controlled ventilation, measurements were made immediately prior to and one minute after intubation. Five patients were dropped from the study, four due to airway problems and one due to severe hypotension following an induction dose of propofol. Statistics were done using data from the remaining 16 patients, eight in each group. Administration of propofol resulted in significant decreases in mean arterial pressure (MAP), systemic vascular resistance (SVR), and left ventricular stroke work index (LVSWI); as well as an increase in heart rate (HR). These changes were further accentuated by the addition of halothane and pancuronium prior to intubation. Patients in the thiamylal group experienced no significant hemodynamic changes until halothane and pancuronium were added and controlled ventilation was instituted. With these additions, the thiamylal group showed significant decreases in MAP and LVSWI immediately prior to intubation. Both groups experienced significant increases in HR following intubation, but no evidence of myocardial ischemia was seen in either group. All other parameters returned toward control values. Propofol appeared to be safe and effective for the induction of anesthesia in this group of patients, although its hemodynamic effects were greater than those of thiamylal.

The safety and efficacy of esmolol during myocardial revascularization.

The safety and efficacy of esmolol during high-dose fentanyl anesthesia were studied in 37 patients undergoing coronary artery bypass grafting (CABG). The anesthetic management consisted of fentanyl 75 micrograms/kg, pancuronium 0.15 mg/kg, and O2. To assess the safety of esmolol, it was administered in a double-blind manner to 17 anesthetized patients prior to surgical incision. Infusion of the drug was increased in stepwise fashion to obtain administration rates between 100 and 300 micrograms X kg-1 X min-1. Esmolol produced small but significant increases in pulmonary capillary wedge pressure (PCWP) (8.3 +/- 1.7 to 13.2 +/- 2.0 mmHg) when compared with placebo (10.9 +/- 1.0 to 12.1 +/- 0.6 mmHg) (P less than 0.05). For the other studied parameters (heart rate, mean arterial pressure, central venous pressure, cardiac index, stroke index, left ventricular stroke work index, systemic vascular resistance, and peripheral vascular resistance), no significant differences were observed between esmolol and placebo. To evaluate the efficacy of esmolol, 20 patients were randomly assigned to an esmolol group (n = 11) or a placebo group (n = 9). The study medication was infused from 5 min before induction through initiation of cardiopulmonary bypass. Infusion of esmolol at 200 micrograms X kg-1 X min-1 prevented tachycardia in response to intubation. In the esmolol group the heart rate increased from 63.4 +/- 2.7 to 67.6 +/- 2.9 beats/min after intubation, while in the placebo group it increased from 61.4 +/- 4.3 to 72.4 +/- 3.4 beats/min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)