Michael L. Good

Patient simulation for training basic and advanced clinical skills

Introduction  Patient simulators are increasingly used in the education and training of healthcare professionals. This paper describes the history of human patient simulator development, the features of contemporary simulators, the acquisition of basic and advanced clinical skills using patient simulators, and the benefits, cost, limitations and effectiveness of this innovative learning modality.

Pharmacokinetic-pharmacodynamic model for educational simulations

Pharmacokinetic-pharmacodynamic (PK-PD) models play an important role in educational simulations. The parameters of PK-PD models described in the scientific literature are obtained from studies in which the drug concentrations and the drug-effect data are measured simultaneously. Simultaneous PK-PD studies cannot be expected to incorporate all possible combinations of drugs and patient physiology that are desired for educational simulations. To solve this problem, the authors elaborate on the traditional simultaneous PK-PD model, creating a new model that accepts parameter data from different, more readily available, nonsimultaneous pharmacologic studies. These data are incorporated in the model using a novel estimation procedure for the parameters k/sub e0/ and EC/sub 50/. A sensitivity analysis of the parameter estimation procedure confirms that the time of peak effect following a bolus and the dose-response curve are accurately reflected by the new model. It also demonstrates how inconsistencies among the different parameter sets affect simulation of the recovery phase. The model is extended to incorporate any monotonic parametric or nonparametric dose-response curve. For the neuromuscular relaxant vecuronium, the authors demonstrate that data from different pharmacologic studies are available, and that the described estimation procedure leads to parameter estimates that are within the standard deviations of the parameters determined in a simultaneous PK-PD study.

Influence of Pulse Oximetry and Capnography on Time to Diagnosis of Critical Incidents in Anesthesia: A Pilot Study Using a Full-Scale Patient Simulator

Objective. Many studies (outcome, epidemiological) have tested the hypothesis that pulse oximetry and capnography affect the outcome of anesthetic care. Uncontrollable variables in clinical studies make it difficult to generate statistically conclusive data. In the present study, we eliminated the variability among patients and operative procedures by using a full-scale patient simulator. We tested the hypothesis that pulse oximetry and capnography shorten the time to diagnosis of critical incidents. Methods. A simulator was programmed to represent a patient undergoing medullary nailing of a fractured femur under general anesthesia and suffering either malignant hyperthermia, a pneumothorax, a pulmonary embolism or an anoxic oxygen supply. One hundred thirteen anesthesiologists were randomly assigned to one of two groups of equal size, one with access to pulse oximetry and capnography data and the other without. Each anesthesiologist was further randomized to one of the four critical incidents. Each anesthetic procedure was videotaped. The time to correct diagnosis was measured and analyzed. Results. Based on analysis of 91 of the subjects, time to diagnosis was significantly shorter (median of 432 s vs. >480 s) for the anoxic oxygen supply scenario (p = 0.019) with pulse oximetry and capnography than without. No statistical difference in time to diagnosis was obtained between groups for the other three critical incidents. Conclusions. Simulation may offer new approaches to the study of monitoring technology. However, the limitations of current simulators and the resources required to perform simulator-based research are impediments to wide-spread use of this tool.

Learning about new anesthetics using a model driven, full human simulator.

Objective.New pharmacological agents are introduced into medical practice at an ever-increasing pace. Teaching how to use new medications in the clinical setting presents educational challenges and puts patients at risk. Methods.Patients and clinical settings in which remifentanil might provide clinical advantages over existing anesthetics were identified. A simulator curriculum was developed to demonstrate the use of remifentanil in the sample cases. The simulation was designed to highlight the clinical advantages and potential side effects of remifentanil. A screen displaying the concentrations of remifentanil in plasma and in the hypothetical effector site was developed. A simulator was modified (addition of an infusion pump and a pharmacokinetic screen display) and transported to several cities in the U.S.A. An instructor guided small groups of anesthesiologists and anesthetists through a structured program that enabled participants to observe drug effects in simulated patients. Results.There were 836 participants in the remifentanil program, which was offered in 58 cities in the U.S.A. Surveys were completed by 574 anesthesiologists. There was a significant difference in comfort level for using remifentanil after the session compared to before (Chi-square, p< 0.001.) The statement: “Clinical simulation experience is a means to learn about new agents like remifentanil”was rated as “excellent” by 81% and as “good” by 19% of participants. No participant found the experience to be “not useful.” Conclusions.Patient simulation is a novel method of introducing new drugs to the medical community and is perceived by anesthesia providers as a valuable addition to available teaching methods.

Modeling obstetric cardiovascular physiology on a full-scale patient simulator.

To our knowledge, this is the first attempt at adapting an existing cardiovascular model to simulate the hemodynamics of a particular patient population. Despite attempts to define the physiologic alterations in advance, we discovered there were critical parameters not completely defined in the literature. These were discovered through the iterative process of testing, comparing resulting vital signs with targets, and literature review. A list of the parameters that should be sought for future modeling efforts is provided (Table 3), but this list is by no means exhaustive. As further work is performed in this area, additional independent and essential parameters will be identified (pressure characteristics of valvular anomalies, for example). To define a physiology that is less well described in the literature, empirical alterations and best-guess estimates of parameter changes will be required with significantly more iterations. Finally, we have described only modeling of cardiovascular physiology, modeling the respiratory system will require a similar process.

Comparison of tests for detecting leaks in the low-pressure system of anesthesia gas machines

Small leaks in the low-pressure system (LPS) of the anesthesia gas machine can cause hypoxia or patient awareness. We sought to determine the relative sensitivities of the various tests recommended for detecting LPS leaks before anesthesia. Special adapters were fashioned to create leaks of six different sizes in the LPS that were equivalent to the following: a single 25-, 22-, 20-, or 15-gauge needle, two 15-gauge needles, or a 2.5-mm endotracheal tube connector. With each leak condition, five different leak tests were performed on three each of the following machines: Ohmeda Modulus I [TM], Ohmeda Modulus II [R]-Plus, and North American Drager Narkomed (2A, 3 and 4), for a total of 54 leaks to be detected for each leak test (3 x 3 x 6). The number of leaks detected with each test was compared by Fishers exact test, P < 0.05 being considered significant. Only the negative pressure leak test detected all 54 leaks, a significant difference from the positive pressure test, which detected the least number of leaks, 28 (P < 0.05). Some leak tests are more suitable for specific anesthesia machines. Adoption of the negative pressure test as a universal LPS leak test may prevent the risks associated with using the wrong test for the particular anesthesia machine: hypoxic gas or patient awareness. (Anesth Analg 1997;84:179-84)

Logistics of Conducting a Large Number of Individual Sessions with a Full-Scale Patient Simulator at a Scientific Meeting

Objective. To design and implement the logistics of accommodating a largenumber of participants in individual, hands-on sessions on a full-scalepatient simulator during a major scientific meeting or continuing medicaleducation course. Methods. We used our method during the 11th World Congressof Anaesthesiologists in Sydney, Australia to facilitate studying the impactof pulse oximetry and capnography on the time taken by anesthesiologists tocorrectly identify critical incidents on a full-scale patient simulator.Each study participant spent 15 minutes in 4 sections of the study area: theanesthesia and monitoring equipment briefing room, the simulator briefingroom, the simulation room and the debriefing room. Results. There were 113participants during five days (15 during instructor training and 25, 23, 24and 26 on subsequent exhibit days). We were oversubscribed daily. However,there were 9 no-shows during the 4 days of the study, which generated aparticipant absence rate of 9.2%. The average number of participantsover the 4 days of the study was 24.5 per day compared to our capacity of 27per day. The feedback we obtained from the participants about the simulationexperience and the format of the exercise was positive and enthusiastic.Conclusions. We have developed a practical and viable method that can beadapted for use at scientific meetings and courses, which improvesaccessibility of individual, hands-on sessions on full-scale patientsimulators to a larger audience than previously attainable. Our method isapplicable for continuing medical education courses as well as researchpurposes in the form of prospective studies during scientific meetings andcourses.

Duration of carbon dioxide absorption by soda lime at low rates of fresh gas flow

STUDY OBJECTIVE To determine the impact of a low fresh gas flow rate on the duration of carbon dioxide (CO2) absorption by soda lime. DESIGN Nonclinical, experimental. SETTING Experimental laboratory. METHODS In vitro test with Sodasorb and a semiclosed breathing circle ventilating a test lung with a CO2 inflow of 250 ml per minute. Fresh gas flow rates of 0.25, 0.5, 1, 2, and 4 L/min were studied. MEASUREMENTS AND MAIN RESULTS CO2 was measured at the breathing circuit test lung interface with a mainstream capnometer. Duration of CO2 absorption was determined as the time for the inspired CO2 tension (PICO2) to increase from 0 mm to 7 mm of mercury. The times of this interval were recorded four times for each fresh gas flow rate and compared by analysis of variance; p less than 0.05 was considered significant. Time to soda lime failure was significantly longer at 2 L/min than at 1 L/min fresh gas flow and at 1 L/min than at 0.25 L/min fresh gas flow. CONCLUSION Because soda lime color indicators are unreliable, when a semiclosed breathing circle is used at a low rate of fresh gas flow without CO2 monitoring, the CO2 absorbent must be replaced more frequently.

Low-battery characteristic of the professional instruments ns-2ca nerve stimulator

During the development of a device to simulate thumb twitch response to electrical stimulation of the ulnar nerve in an anesthetized patient, we used a neuromuscular blockade (NMB) monitor from Professional Instruments (Model NS-2CA, Houston, TX). We observed that when the batteries are low in that particular model of N M B monitor, only three (instead of four) current pulses are generated during train-of-four (TOF) stimulation. This characteristic was reproducible with other N MB monitor units of the same model. Our clinical colleagues reported encountering this characteristic behavior in the operating room on multiple occasions. When consulted, the manufacturer confirmed our observation. To the unwary clinician, this characteristic may lead to incorrect interpretation o f the degree of N M B during TOF stimulation. To the informed clinician, the characteristic low-battery behavior of the NS-2CA N M B monitor can be exploited as a warning o f impending battery failure. A three-pulse T O F could be used as a prompt to press the battery check button and verify that the batteries are low and need to be replaced.

Rapid detection of cardiac troponin I using antibody-immobilized gate-pulsed AlGaN/GaN high electron mobility transistor structures

We report a comparison of two different approaches to detecting cardiac troponin I (cTnI) using antibody-functionalized AlGaN/GaN High Electron Mobility Transistors (HEMTs). If the solution containing the biomarker has high ionic strength, there can be difficulty in detection due to charge-screening effects. To overcome this, in the first approach, we used a recently developed method involving pulsed biases applied between a separate functionalized electrode and the gate of the HEMT. The resulting electrical double layer produces charge changes which are correlated with the concentration of the cTnI biomarker. The second approach fabricates the sensing area on a glass slide, and the pulsed gate signal is externally connected to the nitride HEMT. This produces a larger integrated change in charge and can be used over a broader range of concentrations without suffering from charge-screening effects. Both approaches can detect cTnI at levels down to 0.01 ng/ml. The glass slide approach is attractive for inex...