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Biomedical subjects

J S Gravenstein

Publications and source records attributed to J S Gravenstein.

At least 19 recordsLinked to original sources
PubMed1991

Comparative effects of cuff size and tightness of fit on accuracy of blood pressure measurements.

To determine the effect of snugness of cuff wrap on the accuracy of blood pressure (BP) measurements, we performed two studies on 6 healthy volunteers. In both studies, control values were obtained from the right upper arm with cuffs of appropriate size and snug fit. Study 1 had two phases. In the first, cuffs of appropriate size were wrapped snugly around the upper left arm of seated subjects. The effects of two other degrees of cuff snugness on the measurement of BP were evaluated by placing a filled 250-mL intravenous fluid bag between the cuff and arm over the triceps, measuring BP, then draining the same bag of half its contents and then all of its contents without rewrapping the cuff ("loose," "very loose" fit), each time measuring BP. The second phase of study 1 was identical in procedure, except that the cuffs used on the left arm were one size too small. In study 2, the experimental cuffs were placed just above the right ankle. To alter the signal-to-noise ratio, BP was raised or lowered: the standing position elevated mean BP by an average of 90 mm Hg, and elevation of the legs decreased mean BP by an average of 43 mm Hg. In study 1, we found that appropriately sized cuffs, whether wrapped tightly or loosely, gave correct BP readings. Cuffs snugly wrapped, but too small for the subject, gave high BP readings, on the average by approximately 10 mm Hg. Loose wrapping of small cuffs gave variable results in individual subjects that exaggerated systolic BP from 2 to 80 mm Hg. In study 2, elevating the legs or standing decreased or increased BP consistently. Loose wrapping of appropriately sized cuffs around the ankles of the subjects had no additional significant effect on BP.

Ankle↗
PubMed1991

The automated anesthesia record.

The handwritten anesthesia record requires the attention of the anesthesiologist. During critical moments, however, the anesthesiologist may be too busy to record data by hand; handwritten records, therefore, can be inaccurate. The volume of data that must be monitored during anesthesia today makes it impossible to record data by hand often enough to enable a meaningful review of the anesthetic procedure. Automated systems, therefore, are required for the correct capture of intraoperative data; such systems are now becoming available.

Anesthesia↗
PubMed1990

Monitoring for disconnection: ventilators with bellows rising on expiration can deliver tidal volumes after disconnection.

Anesthesia ventilators with bellows that rise on expiration (standing bellows) are favored over ventilators with bellows that descend during expiration (hanging bellows). Standing bellows will not rise if there is a disconnection, and thus they facilitate detection of disconnections. Yet, during a disconnection of ventilators with standing bellows, mechanical inspiration compresses the empty bellows beyond its resting position; with expiration the elastic bellows recoils and aspirates up to 140 ml, depending upon the fresh gas flow. Tidal volumes recorded after disconnection ranged from 50 to 140 ml (mean, 112.2 +/- 9.22 [SD]) at adult settings and from 55 to 90 ml (mean, 69.8 +/- 4.28 [SD]) at pediatric settings. Thus, spirometers that measure tidal volume (VT) in the expiratory limb of the breathing system may falsely indicate an expiratory VT after a disconnection of the breathing system at the Y-piece or the endotracheal tube. Existing low-pressure alarms and capnography alarms provide redundant warning of disconnection, however, should the ventilator continue to deliver small VTs after a disconnection.

Air Pressure↗
PubMed1990

Work and rest cycles in anesthesia practice.

A questionnaire inquiring about existing and desirable work and rest patterns appeared in a newsletter mailed to about 22,000 anesthesiologists and anesthesiology residents and 24,000 nurse anesthetists (CRNA). Almost 3,000 anonymous replies were received and analyzed. Respondents reported mean work weeks of 47.5 h (CRNA) to 69.8 h (residents), longest continuous period of administering anesthesia without a break of 6.6 h (CRNA) to 7.7 h (residents), and longest period of administering anesthesia with or without breaks of 14.1 h (CRNA) to 20 h (resident). However, the respondents considered it safe to administer anesthesia without a break for 4.2 (CRNA) to 5.2 h (anesthesiologists) and with break for 12.8 h (CRNA) to 15 h (residents). A substantial number of respondents believed that they work at least occasionally beyond their perceived self-limitations. The majority of respondents recalled having made errors in the administration of anesthesia that they attributed to fatigue. These results may not be representative of work patterns or attitudes among American anesthesia providers because of the small sample size and the resultant potential for bias. Yet, the subject deserves attention and further study because fatigue can affect professional performance, ability to learn, and family life.

Anesthesiology↗
PubMed1989

The uses of the anesthesia record.

The typical, handwritten anesthesia record of the 1980s does not satisfy its many users. The document is used for clinical care by the anesthetist, nurses, physicians, and technicians in postanesthesia, intensive, and postoperative surgical care units; for historical information by the billing officer, the statistician, and the anesthetist in preparation for a future anesthetic; and for the review of the quality of care by clinical peers and lawyers. For all of these users the typical record contains some to much unnecessary information and lacks some to much needed information. Electronic capture, storage, retrieval, and formatting of data can generate electronic displays or paper records tailored to answer the needs of specific users. The anesthetist in particular will benefit from a well-designed system that takes the place of the traditional handwritten anesthesia record.

Anesthesiology↗
PubMed1989

Sampling intervals for clinical monitoring of variables during anesthesia.

Although five minutes is the sampling interval mentioned by the American Society of Anesthesiologists for monitoring blood pressure and heart rate during anesthesia, most patients are monitored more closely by continuous auscultation and with the help of automated instruments. Yet this difference between the interval recommended and that actually used indicates that sampling intervals are not defined clearly enough. Therefore, we present three methods with which to determine sampling intervals during monitoring. To explore the feasibility of these methods we examined data gathered every 7.5 seconds during three typical, noncatastrophic physiologic perturbations induced in an anesthetized dog. We chose hypercapnia secondary to rebreathing, hypotension secondary to deep anesthesia, and hypoxemia secondary to a low concentration of inspired oxygen as realistic examples of what can occur during operation and anesthesia. We studied three variables: respired carbon dioxide, femoral arterial blood pressure, and oxygen saturation of hemoglobin (pulse oximeter). The data obtained during monitoring were subjected to three methods of analysis: (1) recording of sets of data, with various starting times, at five-minute intervals only (moving grid); (2) Fourier analysis; and (3) analysis of slopes. For the data of the experiment, the Fourier analysis yielded, on average, longer sampling intervals than did the analysis of slopes.

Anesthesia, General↗
PubMed1989

Modern trends in monitoring in anaesthesia: its benefits and costs.

Many monitoring devices, including peripheral arterial catheters, multichannel electrocardiographs, pulmonary artery catheters, capnographs, and pulse oximeters, have vied for acceptance in modern operating rooms. Considerable costs are associated with the use of these monitors. These costs are not limited to the purchase price of the equipment, but extend to the cost of any complications. The use of new equipment is fostered by the belief that new monitors improve the care of patients. However, for some invasive monitoring modalities, it is difficult to demonstrate clinical benefit.

Anesthesia↗
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↗