Ronald S. Newbower

An analysis of major errors and equipment failures in anesthesia management: considerations for prevention and detection

Adaptations of the critical-incident technique were used to gather reports of anesthesia-related human error and equipment failure. A total of 139 anesthesiologists, residents, and nurse-anesthetists from four hospitals participated as subjects in directed or open-ended interviews, and 48 of them fu

Preventable anesthesia mishaps: a study of human factors.

A modified critical-incident analysis technique was used in a retrospective examination of the characteristics of human error and equipment failure in anesthetic practice. The objective was to uncover patterns of frequently occurring incidents that are in need of careful prospective investigation. Forty-seven interviews were conducted with staff and resident anesthesiologists at one urban teaching institution, and descriptions of 359 preventable incidents were obtained. Twenty-three categories of details from these descriptions were subjected to computer-aided analysis for trends and patterns. Most of the preventable incidents involved human error (82 per cent), with breathing-circuit disconnections, inadvertent changes in gas flow, and drug-syringe errors being frequent problems. Overt equipment failures constituted only 14 per cent of the total number of preventable incidents, but equipment design was indictable in many categories of human error, as were inadequate experience and insufficient familiarity with equipment or with the specific surgical procedure. Other factors frequently associated with incidents were inadequate communication among personnel, haste or lack of precaution, and distraction. Results from multi-hospital studies based on the methodology developed could be used for more objective determination of priorities and planning of specific investments for decreasing the risk associated with anesthesia.

Preventable anesthesia mishaps: a study of human factors*

A modified critical-incident analysis technique was used in a retrospective examination of the characteristics of human error and equipment failure in anesthetic practice. The objective was to uncover patterns of frequently occurring incidents that are in need of careful prospective investigation. Forty seven interviews were conducted with staff and resident anesthesiologists at one urban teaching institution, and descriptions of 359 preventable incidents were obtained. Twenty three categories of details from these descriptions were subjected to computer-aided analysis for trends and patterns. Most of the preventable incidents involved human error (82%), with breathing-circuit disconnections, inadvertent changes in gas flow, and drug syringe errors being frequent problems. Overt equipment failures constituted only 14% of the total number of preventable incidents, but equipment design was indictable in many categories of human error, as were inadequate experience and insufficient familiarity with equipment or with the specific surgical procedure. Other factors frequently associated with incidents were inadequate communication among personnel, haste or lack of precaution, and distraction. Results from multi-hospital studies based on the methodology developed could be used for more objective determination of priorities and planning of specific investments for decreasing the risk associated with anesthesia.

Critical incidents associated with intraoperative exchanges of anesthesia personnel.

It is a common practice for anesthetists to substitute for one another, especially for short breaks during long surgical procedures. The assets and liabilities of this practice of relief have not been examined previously. In the course of gathering 1,089 reports of preventable errors and failures associated with anesthesia management, we identified 96 which involved a relief anesthetist. This subset was examined in search of common characteristics and patterns of cause and discovery of errors.In 28 incidents, the relief anesthetist discovered an error or the cause of an error. In 10 incidents, the process of relief was identified as having contributed to the commission of an error. Although 70 of the 1,089 incidents were associated with substantive negative outcomes, e.g., death, cardiac arrest, or extended ICU stay, none of those incidents was caused by a relieving anesthetist. There is a strong implication that relief is beneficial more often than not even aside from the presumed beneficial effect on the vigilance of the primary anesthetist (the latter effect was outside the scope of this study). From the descriptions of the causes and discoveries of errors in these relief-related incidents, guidance can be drawn for the safe and effective conduct of the intraoperative exchange of anesthesia personnel.

Continuous Thermal Measurement of Cardiac Output

A thermal-dilution technique for the continuous measurement of cardiac output has been developed. It employs pulmonary-artery sensing of low-level periodic thermal signals generated in the right ventricle of the heart. A resistive element in a modified Swan Ganz®catheter is energized with a periodic electrical waveform. The resulting thermal signal is diluted by blood flow and attenuated by mixing within the heart. Sensed by a thermistor in the pulmonary artery, the thermal signal is processed by a microprocessor-based instrument using a suitable mathematical model. With multiple signal frequencies, separate estimates of the flow-dependent and mixing-dependent attenuation components become possible, allowing continuous monitoring of cardiac output. This technique works well in anesthetized, mechanically ventilated animals, even with average power levels as low as 4 W and corresponding temperature increases of a few hundredths of a degree centigrade. Based on measurements of pulmonary artery thermal noise spectra in humans, we infer that similar performance levels should be attainable with mechanically ventilated human subjects. However, noise spectra from spontaneously breathing critically ill patients suggest that signal-to-noise ratios would be less than satisfactory in that group unless increased signal power is allowed or improved algorithms are developed.

A new anesthesia delivery system.

A prototype anesthesia delivery system has been developed to test the appropriateness of new technological design approaches. The objectives were to eliminate human-factors problems associated with present anesthesia apparatus and to lay a suitable technical foundation for the development of new techniques in anesthesia management. This prototype performs all the functions of a conventional anesthesia machine, as well as many monitoring and surveillance tasks. Eventual incorporation of new teaching functions, and additional monitoring and record-keeping activities, are intended. The system is fundamentally electronic with few moving parts. Reliability, safety, and clarity of operation were the primary criteria in selection and application of the specific technologies employed. The result is a promising first step in the development of a system oriented toward supporting rather than preoccupying the anesthetist.

Piezoelectric Sorption Anesthetic Sensor

The piezoelectric sorption detection method is evaluated for use in construction of an inexpensive, rugged, compact, and fast sensor for measuring the concentration of inhalation anesthetics. 10 MHz quartz crystals were coated with various substances and their frequency shifts measured upon exposure to varying concentrations of halothane, enflurane, and nitrous oxide. For a silicone rubber coating, the response was found to be linear with concentration, with sufficient signal to allow resolution to approximately 0.05 volume percent for either halothane or enflurane, or to 4 percent for nitrous oxide. The devices were sensitive to halothane and enflurane in proportion to their anesthetic potencies, but were slightly less sensitive to equally potent concentrations of nitrous oxide. They were insensitive to CO2 in the physiologic range, but had a significant response to water vapor. The response time of the detector was primarily a function of washout of the sensing chamber. At a 200 ml/min sample flow rate, the time constant was approximately 100 ins. It is concluded that this detection method is suitable for a variety of applications in anesthesia, although, with the coatings presented here, control of or correction for sample humidity is required.

The Development of Indicator-Dilution Techniques

After 87 years, Stewarts fundamental conceptual contribution, the indicator-dilution method for measuring blood flow, is still the basis for a variety of common, practical, and minimally invasive clinical techniques. Given the spectrum of available indicators and their corresponding sensing techniques, we review the relevant transport theory and required assumptions. Various previous developments in the theory of flow and volume measurement are brought together in a formal restatement, based on the general case of dilution of volume indicators, rather than just the special case of mass indicators. The importance of each of the required assumptions is evaluated. Examples discussed include the use of conductivity modifiers and thermal indicators, with and without pulsatile flow. The formalism developed is intended to be helpful in assessing the opportunities and limitations associated with any proposed new indicator-dilution application.

Magnetic fluids in the blood

Recently, several medical applications have been proposed for magnetic fluids. These applications, which are reviewed here, involve introduction of magnetic fluids into the blood with subsequent magnetic guidance or magnetic detection by external devices. The issues associated with achieving magnetic guidance and minimizing toxicity are considered. The technical difficulties involved in any of the proposed applications are substantial, and would appear to outweigh the potential advantages at the present time. However, the research and development efforts in this area have been very limited and, therefore, the opportunities for innovation and further progress are significant.

Sensor for Catheter-Based Measurements of Electncal Conductivity

Measurements of the electrical conductivity of blood have found useful application for almost 100 years. Yet the technology of making those measurements has progressed relatively slowly. To facilitate intravascular conductivity measurements we have developed, refined, and validated a microminiature four-terminal conductivity cell which mounts flush with the surface of a catheter and permits continuous calibrated measurement of conductivity. This, together with our previously published model of blood conductivity, permits continuous measurements of indicator concentration as well as monitoring of blood composition. Discussed here is the rationale for this particular sensor design, including issues which are common to any sensor mounted on the surface of a catheter. The sources and forms of noise, drift, and clotting are discussed, as well as the considerations for optimizing performance.