The development of evidence-based clinical practice guidelines. Integrating medical science and practice.

Practice guidelines are rapidly becoming preferred decision-making resources in medicine, as advances in technology and pharmaceutics continue to expand. An evidence-based approach to the development of practice guidelines serves to anchor healthcare policy to scientific documentation, and in conjunction with practitioner opinion can provide a powerful and practical clinical tool. Three sources of information are essential to an evidence-based approach: a) an exhaustive literature synthesis; b) meta-analysis; and c) consensus opinion. The systematic merging of evidence from these sources offers healthcare providers a scientifically supportable document that is flexible enough to deal with clinically complex problems. Evidence-based practice guidelines, in conjunction with practice standards and practice advisories, are invaluable resources for clinical decision making. The judicious use of these documents by practitioners will serve to improve the efficiency and safety of health care well.

Photodeactivation of ethyl violet: a potential hazard of Sodasorb.

Breathing circuit cannisters containing functional CO2 absorbent are critical to prevent rebreathing CO2 during general anesthesia using closed or semiclosed breathing systems. Ethyl violet is the indicator dye added to Sodasorb to indicate impending exhaustion of the absorbent. A case of CO2 rebreathing due to failure of ethyl violet indicator in exhausted Sodasorb was encountered. Laboratory investigation demonstrated that dye failure could result from photodeactivation caused by fluorescent lights. Using a fixed intensity fluorescent light source and quantitative spectrophotometric analysis, a highly significant dose-response relationship was demonstrated between duration of light exposure and the decrease in ethyl violet concentration. After 24 h of fluorescent light exposure with a received flux density of 46 nwatts/cm2 at 254 nm, the concentration of functional ethyl violet remaining in pulverized Sodasorb was 16% of the baseline value. Furthermore, using multiple light sources of various intensities, the greater the intensity of light, the more rapid the rate of decline of the ethyl violet concentration. It is recommended to minimize the problem by using ultraviolet filters and incorporating additional ethyl violet in Sodasorb. Finally, ethyl violet undergoes temporal deactivation after a Sodasorb container is opened, even if it is stored in the dark.

Effect of hypocapnia on local cerebral glucose utilization in rats.

The effect of hypocapnia on regional cerebral glucose utilization (L-CMRg) was studied in 14 Sprague Dawley rats. After cannulation of femoral vessels, halothane was discontinued and anesthesia was maintained with 70% N2O in oxygen. The animals' lungs were mechanically ventilated to achieve normocapnia (PaCO2 = 40 +/- 2 mmHg) in group A or hypocapnia (PaCO2 = 25 +/- 2 mmHg) in group B. L-CMRg was measured by the 14C-2-deoxyglucose autoradiographic method. Twenty-six anatomically discrete structures representing cortical, subcortical, limbic, and brainstem areas were studied. In hypocapnic animals, mean values for L-CMRg were higher in 25 out of 26 structures studied. The increase in L-CMRg was heterogenous. The structures that had higher L-CMRg during normocapnia showed the greatest increase in L-CMRg. When the two groups were compared using a profile analysis, in six regions (lateral and ventral thalamus, inferior colliculus, lateral habenulla, medial geniculate body, and auditory cortex), a value of P less than 0.05 was obtained.

A 10-microm infrared camera.

An IR camera has been built at the University of California at Berkeley for astronomical observations. The camera has been used primarily for high angular resolution imaging at mid-IR wavelengths. It has been tested at the University of Arizona 61- and 90-in. telescopes near Tucson and the NASA Infrared Telescope Facility on Mauna Kea, HI. In the observations the system has been used as an imager with interference coated and Fabry-Perot filters. These measurements have demonstrated a sensitivity consistent with photon shot noise, showing that the system is limited by the radiation from the telescope and atmosphere. Measurements of read noise, crosstalk, and hysteresis have been made in our laboratory.

Endotracheal tube cuff residual volume and lateral wall pressure in a model trachea.

The authors constructed a D-shaped tracheal model with an elastic posterior wall, thus simulating normal tracheal anatomy more closely than previous models. The performance of 9-10 tracheal tube cuffs, of 2-3 different tube sizes (7.0-10.0 mm, ID), from six different manufacturers were tested in the model. Cuff residual volumes ranged from 1.78 to 27.35 ml. Cuff pressure and lateral wall pressures exerted by the cuff on the model were measured at the time a seal was achieved which just prevented leakage of water past the cuff. When a seal was achieved with a volume of air in the cuff less than cuff residual volume, wall pressure tended to be low (less than 35 torr) and cuff pressure closely approximated wall pressure. There was no relationship between cuff brands in the wall pressure required to effect a seal in the model. The authors conclude that intratracheal tubes should have cuffs with large residual volumes. This would permit some latitude in tube size selection while ensuring that a seal could be achieved before the cuff is inflated to its residual volume.