Effects of elevating the head of bed on interface pressure in volunteers.

OBJECTIVE: Intensive care unit patients are at particular risk for pressure ulcers and ventilator-associated pneumonia. Current guidelines recommend that mechanically ventilated patients be kept in a semirecumbent position with the head of bed elevated 30 degrees -45 degrees to prevent aspiration and ventilator-associated pneumonia. We tested the effects of elevating the head of bed on the interface pressure between the skin of the sacral area and the bed with healthy volunteers. INTERVENTIONS: Interface pressure profiles of the sacral area were obtained for the 0 degrees , 10 degrees , 20 degrees , 30 degrees , 45 degrees , 60 degrees , and 75 degrees head of bed elevated positions from 15 subjects (14 men, one woman). MEASUREMENTS AND MAIN RESULTS: Peak sacral interface pressures increased with large increases in head of bed elevation. The 30 degrees , 45 degrees , 60 degrees , and 75 degrees head of bed positions all had peak interface pressures that were significantly (p < 0.02) greater than the supine measurement and also were different from all other head of bed positions. Affected areas, defined as areas over which an interface pressure >or=32 mm Hg was obtained, increased with large elevation of the head of bed. The affected areas of the 45 degrees , 60 degrees , and 75 degrees head of bed positions were significantly greater than the supine position and were also significantly different from all other head of bed positions. CONCLUSIONS: Raising the head of bed to 30 degrees or higher on a intensive care unit bed increases the peak interface pressure between the skin at the sacral area and support surface in healthy volunteers. At 45 degrees head of bed elevation or higher, the affected area attributed to a skin-intensive care unit bed interface pressure >or=32 mm Hg increased as well. Further study is needed to determine whether the increased peak interface pressures and affected areas that result from raising the head of bed actually increase the incidence of pressure ulcer formation.

Bellows-less lung system for the human patient simulator.

A new bellows-less lung simulator utilising a fixed-volume pressure controller to simulate spontaneous breathing is presented as an alternative to the traditional bellows-driven mechanical lung system in the human patient simulator (HPS). The HPS is a fully interactive, life-like simulator used to train medical students and anaesthesia residents. The lung simulator simulates carinal pressure, which allows for simulation of actively breathing or ventilated patients. In the current HPS implementation, breathing is physically simulated with a pair of bellows and a computer-controlled piston, but, owing to physical and dynamic constraints, the model suffers from a lot of dead space. Furthermore, the set-up incorporates several mechanical components that require time-consuming calibrations, which drives up manufacturing costs. A bellows-less lung simulator has been designed and built which successfully simulates airflow in and out of the mouth by controlling the carina pressure. The new system is able to simulate tidal volumes between 400 and 500 ml, with flow rates of 4.3-5.71 min(-1) at a respiratory rate of 12 breaths per minute. The new design not only matches the ventilation performance of the HPS, but also simulates at 60 breaths per minute, which the HPS cannot maintain.

Waste gas monitor reduces wasted volatile anesthetic.

OBJECTIVE: The increasing focus on health care costs requires that all physicians evaluate practice behaviors. The primary emphasis in anesthesia has been limiting the use of expensive medications and interventions. Reducing waste is another approach, and volatile anesthetics are an appropriate target in that simple reduction of fresh gas-flow (FGF) rates is effective. A monitor that measures and displays the cost of wasted volatile anesthetic was developed and used to determine if real-time display of the cost would result in decreased FGF rates, which, in turn, would decrease wasted anesthetic. METHODS: The waste gas monitor (WGM) measures flow rate at the anesthesia machine's scavenger port, integrates this with agent concentration, and displays the calculated cost, real-time, on a portable computer screen. The WGM equipment was attached to the anesthesia machine in the gynecologic surgery operating room (OR) and those cases performed under general endotracheal anesthesia and lasting longer than one hour were eligible for inclusion. First year anesthesiology residents assigned to the study OR as part of a non-specialty rotation, were the subjects of the study. For each resident, after data were collected from at least two eligible baseline cases (Baseline Phase, WGM not visible and resident unaware of its presence), the monitor was introduced and data collection continued for at least three more eligible cases (Visible Phase). RESULTS: Nine residents were initially enrolled, but due to scheduling difficulties only five residents completed the protocol. Data from cases using the WGM demonstrated a 50% decrease (3.58 +/- 1.34 l/min vs. 1.78 +/- 0.51 l/min (p = 0.009)) in the scavenger flow rates, which resulted in a 48% ($5.28 +/- 0.68 vs. $2.72 +/- 0.80 (p = 0.002)) decrease in hourly cost of wasted volatile anesthetic. There was no difference between the Baseline and Visible phases with regard to use of nitrous oxide or intravenous anesthetic agents. CONCLUSIONS. The WGM decreased wasted volatile anesthetic by encouraging decreased FGF rates.

Modeling in anesthesia.

A model can be defined as an abstraction of reality which accounts for those properties ofa phenomenon that are pertinent to the purpose of the model. Models are used in anesthesia to understand the various physiologic, pharmacological and physical processes that occur during anesthesia. Indeed, many different types of models that comply with our definition can be distinguished. Early models consisted of electrical models of the arterial blood dynamics and cardiovascular system. Physical models of drug uptake and distribution have been developed to explain the kinetics of volatile anesthetics in the body. The goal of this paper is to introduce the reader to some of the types of models that been used to facilitate education and research in anesthesia. These examples will elucidate the steps involved in developing a model and the various types of models that have proven useful.

A comparison of traditional textbook and interactive computer learning of neuromuscular block.

We designed an educational software package, RELAX, for teaching first-year anesthesiology residents about the pharmacology and clinical management of neuromuscular blockade. The software uses an interactive, problem-based approach and moves the user through cases in an operating room environment. It can be run on personal computers with Microsoft Windows (Microsoft Corp., Redmond, WA) and combines video, graphics, and text with mouse-driven user input. We utilized test scores 1) to determine whether our software was beneficial to be the educational progress of anesthesiology residents and 2) to compare computer-based learning with textbook learning. Twenty-three residents were divided into two groups matched for age and sex, and a pretest was administered to all 23 residents. There was no significant difference (P > 0.05) in the pretest scores of the two groups. Three weeks later, both groups were subjected to an educational intervention; one with our computer software and the other with selected textbooks. Both groups took a posttest immediately after the intervention. The test scores of the computer group improved significantly more (P < 0.05) than those of the textbook group. Although prior to the study the two groups showed no statistical difference in their familiarity with computers, the computer group reported much higher satisfaction with their learning experience than did the textbook group (P < 0.0001).

Acceptable ranges for vital signs during general anesthesia.

OBJECTIVE: Define the ranges for normal vital signs during general anesthesia. METHODS: We studied 50 patients undergoing general anesthesia. We asked residents to state desirable ranges for each patient's systolic and diastolic blood pressure (BP), heart rate (HR), SpO2, and PETCO2 during induction, intubation, maintenance, and emergence from anesthesia. We called these ranges the clinical operating range (COR) and observed the frequency, duration, and magnitude of transgressions of these CORs. We also recorded whether the transgressions were treated or tolerated, or whether the COR values were changed. RESULTS: Upper COR values in the maintenance phase for systolic BP were 38% +/- 20% above the preoperative values and 30% +/- 20% above the values recorded just before induction of anesthesia. Lower COR values in the maintenance phase for systolic BP were 27% +/- 9% below preoperative, and 31% +/- 11% below preinduction values. For HR, upper and lower COR values in the maintenance phase were 53% +/- 44% above and 38% +/- 17% below preinduction values, respectively. Transgressions of COR values for BP and HR were common, treatment frequent, and redefinition of COR values rare. CONCLUSION: Clinicians recognize ranges for vital signs during uneventful anesthesia. These CORs may differ from one stage of anesthesia to the next. Transgressions of these ranges are common. Not all transgressions are treated.