Direct atomic force microscope imaging of EcoRI endonuclease site specifically bound to plasmid DNA molecules.

Direct imaging with the atomic force microscope has been used to identify specific nucleotide sequences in plasmid DNA molecules. This was accomplished using EcoRI (Gln-111), a mutant of the restriction enzyme that has a 1000-fold greater binding affinity than the wild-type enzyme but with cleavage rate constants reduced by a factor of 10(4). ScaI-linearized plasmids with single (pBS+) and double (pGEM-luc and pSV-beta-galactosidase) EcoRI recognition sites were imaged, and the bound enzyme was localized to a 50- to 100-nt resolution. The high affinity for the EcoRI binding site exhibited by this mutant endonuclease, coupled with an observed low level of nonspecific binding, should prove valuable for physically mapping large DNA clones by direct atomic force microscope imaging.

Computer-assisted continuous infusions of fentanyl during cardiac anesthesia: comparison with a manual method.

The design and implementation of a computer-assisted continuous infusion (CACI) system to rapidly attain and maintain a constant plasma fentanyl concentration (PFC), as well as a CACI system that allowed the anesthesiologist to change the plasma level of fentanyl during cardiac anesthesia, were developed. In 30 patients (three groups of 10 patients each) these two automated methods of fentanyl infusion were compared with a manual fentanyl administration method. There was excellent agreement in the measured/predicted PFC ratios with the CACI stable fentanyl level system (ratio = 0.99, n = 91) and in the CACI variable fentanyl level system (ratio = 1.08, n = 79). The stable fentanyl level group of patients received significantly more (P less than 0.05) fentanyl than did the other groups. The CACI variable fentanyl level group of patients had greater hemodynamic stability, required significantly (P less than 0.05) fewer adjuvant drug interventions and experienced significantly (P less than 0.05) fewer hypotensive and hypertensive episodes than the manual, bolus fentanyl (control) group. These data show that a computer-assisted automated infusion of fentanyl is safe and as good as manual methods. CACI has greater potential as a new method of intravenous anesthesia administration.

Closed-circuit and high-flow systems: examining alternatives.

The nonrebreathing system has been with us since Morton demonstrated the administration of diethyl ether in 1846. Its current popularity is evidenced by the extensive use of the Bain system. The greatest advantage, its history of patient safety, is related to the circuit's simplicity and the knowledge that the delivered concentration equals the inhaled concentration. Most disadvantages of the nonrebreathing system are related to the required high delivery rates: operating room and environmental pollution, necessity of scavenging gases, cost of agents, energy loss through no-return operating room ventilation, inhalation of dry gases, and the inability of the anesthesiologist to quantitate patient uptake of oxygen and inhaled anesthetics. Partial rebreathing systems reduce the disadvantages related to high delivery flow rates but, owing to the required rebreathing, do not permit the anesthesiologist to know the inhaled anesthetic concentration. A carbon dioxide absorber is necessary. It is still impossible to quantitate uptake by the patient, and it is difficult to conclude that any real net advantage results from the use of partial rebreathing systems. When modern-day technology provides the practitioner with an appropriate anesthesia machine, it is likely that closed-circuit anesthesia will become the method of choice for anesthesia delivery. Although the economic, ecologic, and physiologic advantages of this system are important, its greatest asset is the ability to monitor important respiratory and cardiovascular variables in patients noninvasively. Important information provided to the anesthesiologist by the patient during closed-circuit anesthesia is lost through the pop-off valve when high-flow systems are used. During closed-circuit anesthesia the gas machine itself becomes a monitor. Practicing anesthesiologists will embrace closed-circuit anesthesia practice when-and if-they are convinced that it provides an opportunity for better and more efficient patient care than other systems.