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J S Gravenstein

Publications and source records attributed to J S Gravenstein.

At least 55 records · Page 3Linked to original sources
PubMed1987

The effect of fatigue on the performance of a simulated anesthetic monitoring task.

In a simulated monitoring situation, 21 anesthesia residents were tested for their ability to detect significant changes in four critical variables in the presence of a concurrent distraction. Each resident was tested after a night without clinical responsibility (rested) and after 24 hours of in-house call (fatigued). When fatigued, the residents scored significantly worse on the vigilance test than when rested (57.2 +/- 15.4 versus 65.9 +/- 10.9, P less than 0.02). Despite the small population size, the possibility of subject and investigator bias, and the artificial setting, these results support the intuitive proposition that a fatigued person is less likely than a rested person to detect important changes in monitored variables.

Adult↗
PubMed1987

Capnography and the Bain circuit II: Validation of a computer model.

Validation of a computer model is described. The behavior of this model is compared both with mechanical ventilation of a test lung in a laboratory setup that uses a washout method and with manual ventilation. A comparison is also made with results obtained from a volunteer breathing spontaneously through a Bain circuit and with results published in the literature. This computer model is a multisegment representation of the Bain circuit and connecting tubing. For each segment, gas pressure, gas volume flow, and partial pressure of carbon dioxide are calculated for any number of breaths wanted. As a result, the time course of these variables can be generated for any location or, conversely, the carbon dioxide distribution in the system can be calculated for any time instant. A test lung, the human lungs, the ventilator bellows, and the reservoir bag are each represented by a single segment. The shapes of pressure and flow curves and of the capnograms taken at different locations in the Bain tubing are in good agreement. The washout study permits measurement of the time delay between the first expiration and the arrival of carbon dioxide at a particular location. The carbon dioxide level in the test lung decreases during inspiration and is stable during expiration. Quantitative agreement between model and experimental transport delays and carbon dioxide levels is such that the differences can be explained by the inaccuracy of the measurement. This is concluded from a sensitivity analysis. The study of the effect of segment size shows an almost optimal agreement between model behavior and experimental results for a 36-segment model. Execution of a thorough validation is imperative before such models can be used for clinical management and decision making or for teaching.

Airway Resistance↗
PubMed1987

Computer-assisted capnogram analysis.

Characteristic abnormal carbon dioxide waveforms from patients with mechanically ventilated lungs are observed when, for example, valves are incompetent, the airway is obstructed, the breathing circuit becomes disconnected, or a patient overrides mechanical ventilation with spontaneous breaths. Automated observation of the carbon dioxide waveform provides a uniform, concise, and consistent interpretation of the capnogram. This article describes a computer algorithm for analyzing and classifying capnograms as normal or as belonging to one of the categories above. The algorithm also generates a diagnostic message when the capnogram deviates from a learned norm for at least three consecutive waveforms (and thus reduces the influence of artifacts). Clinical experience shows reliable waveform recognition by the algorithm.

Algorithms↗
PubMed1987

The electronic clipboard: a semiautomatic anesthesia record.

An electronic clipboard has been designed, built, and tested, which produces an anesthesia record semiautomatically. Physiologic data are recorded up to once a minute automatically. Two keys number and time 'drug' and 'event' entries. The accurate monitoring of heart rate and blood pressure and the timing of event data are much improved over hand-written entries.

Anesthesiology↗
PubMed1986

Essential monitoring examined through different lenses.

When we ask, what renders essential a particular monitoring approach during routine anesthesia for a healthy patient, perplexing questions, rather than satisfying answers, are raised. I have examined these questions with the help of three lenses that focus on the relationship between the outcome of anesthesia and the detection, and thus correction, of abnormalities during anesthesia. The first lens looks at whether the monitoring modalities accepted by anesthesiologists as "minimal" and "essential" have been scientifically proven to affect outcome from routine anesthesia. A second lens views how well monitors reveal the integrity of the organism and its components. Currently available monitors describe the output of cells or organs but relay little information about the viability of cells. Thus, they describe the symptoms rather than the causes of the pathophysiology related to anesthesia. Today's monitors also measure input, for example, the supply of oxygen, perhaps the most routinely measured of all the variables. The third lens looks at whether there are nonclinical influences on monitoring practice. This lens views the gap between recognizing monitoring possibilities and adopting them clinically; it also views geographic differences in monitoring, as well as social pressures exerted through legal proceedings. Finally, currently recognized essential monitors such as blood pressure measurement, electrocardiography, and oxygen analysis are mentioned, and candidates for inclusion in the list of essential monitors, such as oximeters, capnographs, and the automated record, are discussed.

Anesthesia, General↗
PubMed1986

The automated anesthesia record.

Many phases of modern anesthesia keep the anesthetist too busy to obtain and plot physiologic data or to record anesthetic events. Yet the anesthesia record serves as a log book, a clinical management tool, a trend and pattern plotter, as well as a medical-legal document. If these functions are important, an automated anesthesia recording system is needed for charting the data reliably and accurately. Automating the anesthesia record also lays the ground work for abstracting the data and generating records with specific information sought by the anesthetist, the physicians in the recovery room and intensive care unit, the administrators of the hospital, as well as representatives with interest in medical-legal problems.

Anesthesia↗
PubMed1986

Future use of computers in anesthesia.

Computers are beginning to appear in the operating room and intensive care units. At this time most computers are reserved for complex cases. However, it is now possible to discern what role the computer may play in the future, for routine cases. An outline of a conceivable integrated computerized system in anesthesia is presented.

Anesthesiology↗
PubMed1985

Capnography and the Bain circuit I: A computer model.

The Mapleson D anesthesia breathing system has no valves and allows rebreathing of carbon dioxide. Its coaxial version is known as the Bain system. The interpretation of capnograms obtained during its use requires an understanding of the interrelationships of patient and system variables. Toward that end, a systematic description of mechanical ventilation with the Bain circuit was undertaken based on the physical laws of gas transport. The mathematical formulation of the model contains the relations between pressure, flow, and volume in the tube, alveolar space, and ventilator. The flows, calculated from these relations, are used to determine the CO2 concentrations in the different parts of the model. Two sets of data are used--patient and system. The patient data, used to solve the equations numerically, are lung-thorax compliance, CO2 inflow into alveolar space (CO2 production), functional residual capacity, dead space volume, airway resistance, and respiratory quotient. The ventilation system data comprise the dimensions and volumes of the Bain circuit, ventilator, connectors, and tubes; spill valve pressure; resistances to flow in the individual tube parts; ventilator settings; and fresh-gas flow rates. After incorporation of a volunteer's respiratory variables into the model, capnograms obtained from the model compared well with those obtained from the volunteer. The structure of the model is such that it permits easy introduction or changes of patient and system variables to obtain individual results or model specific circumstances. This flexibility makes it a useful tool for understanding the properties of the Bain circuit under a variety of clinical circumstances. The results may be displayed in a number of different ways.

Anesthesia, General↗
PubMed1985

Tissue hypoxia distal to a Peñaz finger blood pressure cuff.

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (PO2) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (PO2, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.

Acidosis↗
PubMed1985

Helium retards endotracheal tube fires from carbon dioxide lasers.

Polyvinyl chloride (PVC) endotracheal tube segments were exposed to a 5.0-W CO2 laser beam in the presence of different fractions of oxygen and either helium or nitrogen. Time from onset of exposure until ignition was recorded, and mean time to ignition (MTI) was calculated after 10 exposures with the same gas mixture. A second series was done with 40% oxygen in either nitrogen or helium and a laser intensity of 7.5, 10.0, or 12.5 W; a third with 40% oxygen, 60% helium, and 2% halothane and a 10.0-W laser beam; and a fourth with 40% oxygen and 60% helium and a 10.0-W laser beam directed at the radioopaque barium sulfate stripe on the tube. With 5.0-W and 20% oxygen in either nitrogen or helium, segments did not ignite. With concentrations of oxygen greater than 20% in nitrogen, segments ignited sooner than with comparable concentrations in helium: MTIHe = 55.6 s and MTIN2 = 27.6 s in 40% oxygen (P less than 0.05). Sixty per cent helium remained protective at laser intensities up to 10.0 W (MTIHe = 42.6 s vs. MTIN2 = 14.3 s) (P less than 0.05). However, at 12.5 W, MTIHe = 11.5 s and MTIN2 = 11.3 s. Two per cent halothane in 40% oxygen and 60% helium reduced MTIHe to 25.3 s compared with 42.3 s without halothane. With the laser directed at the barium stripe, MTIHe was 7.2 s and MTIN2 1.1 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗