Motivational influences on anaesthetists' use of practice guidelines.

BACKGROUND: With the proliferation of practice guidelines in anaesthesia comes the possibility that anaesthetists may, during the course of their work, commit 'violations' (actions that are not intended to cause harm to patients, but that deviate from guidelines). These may have a long-term impact on patient safety, and so there is a need to understand what makes anaesthetists decide to follow or deviate from guidelines. METHODS: A questionnaire on the use of guidelines was completed by 629 College Fellows. This presented three anaesthetic scenarios, each of which involved a deviation from a guideline, and asked respondents to rate their beliefs about the likely outcome of the violation, the level of social approval they would have for violating, the amount of control they would have over violating, and the practice of their peers with regard to violating. RESULTS: In all three scenarios, beliefs about the outcome of violating and the amount of control over violating predicted respondents' self-reported likelihood that they would commit the violation. In two scenarios, beliefs about the practice of peers predicted violating. Level of social approval predicted violating in one scenario only. CONCLUSIONS: Anaesthetists' decisions to follow or deviate from guidelines are influenced by the beliefs they hold about the consequences of their actions, the direct or indirect influence of others, and the presence of factors that encourage or facilitate particular courses of action.

Human factors in anaesthetic practice: insights from a task analysis.

BACKGROUND: Despite a growing recognition of the role of human error in anaesthesia, it remains unclear what should be done to mitigate its effects. We addressed this issue by using task analysis to create a systematic description of the behaviours that are involved during anaesthesia, which can be used as a framework for promoting good practice and highlight areas of concern. METHODS: The task steps involved in preparing and delivering anaesthesia were identified using hierarchical task analysis (HTA). The systematic human error reduction and prediction approach (SHERPA) was then used to identify potential human errors at each task step and suggest ways of preventing these errors. RESULTS: The number and type of behaviours involved vary according to the 'phase' of anaesthesia, with tasks in the induction room, including induction of anaesthesia itself, being the most demanding. Errors during preoperative planning and perioperative maintenance could be avoided by measures to support information handling and decision-making. Errors during machine checking, induction, and emergence could be reduced by streamlining or automating task steps, or by making changes to the physical design of the work environment. CONCLUSIONS: We have demonstrated the value of task analysis in improving anaesthetic practice. Task analysis facilitates the identification of relevant human factors issues and suggests ways in which these issues can be addressed. The output of the task analysis will be of use in focusing future interventions and research in this area.

Establishing scales of perceived severity for clinical situations during anaesthesia.

BACKGROUND: In many clinical, teaching, and research situations it would be useful to have graded scales of the urgency or other subjective properties for clinical situations that can arise during anaesthesia. Such a scale could serve as a reference point for the appropriate mapping of the urgency in audible alarms or visual warnings, provide a basis for training of graduated difficulty during anaesthesia simulation, provide a benchmark in risk assessment exercises, guide prioritization of decisions in computerized decision support systems for anaesthesia and help in assessing anaesthetist occupational stress. METHODS: A questionnaire-based instrument was developed to assess the perceived severity of a range of anaesthetic clinical situations. Four scales were tested: the severity of the situation for the patient, the urgency of response required by the anaesthetist, attention required by the anaesthetist, and anxiety experienced. Over 300 anaesthetists in three cohorts of 100 were consulted in the selection of the situations to be studied. The final version of the questionnaire, which included 25 situations, was circulated to a further 229 anaesthetists for validation. The pair-wise relationships of the four properties and hence their independence, was examined using Kendall's tau and correlation analysis. RESULTS: The subjective assessments of urgency and attention were closely related, as were severity and anxiety. Comparing the mean rank for the severity scale with the subjective risk scores revealed a statistically significant correlation of tau=0.647 (P<0.01). CONCLUSION: Subjective assessment of severity by anaesthetists was found to be consistent across the clinical situations studied.

Anaesthetists' intentions to violate safety guidelines.

The Theory of Planned Behaviour has been used to investigate the likelihood that anaesthetists will routinely perform three violations of safety guidelines. The three violations were: failing to visit patients before surgery, failure to perform pre-anaesthetic equipment checks and the silencing of alarms during anaesthesia. These suggested violations arose from discussions with the Medical Defence Union. In forming the intention not to perform these violations, anaesthetists are most influenced by their normative beliefs about the violation, i.e. the opinion they believe a group of peers and other significant other people would hold about them performing the violation. The next most influential factor is their personal norms, i.e. beliefs that the individual has about whether the violation is really right or wrong, followed by behavioural beliefs, i.e. beliefs about the consequences of performing the violation, and control beliefs, i.e. beliefs about how much control they have over performing the violation. The results show that the more intense the anaesthetists' belief that the violations were important, the less likely they were to violate, except for the case of alarm silencing. This result suggests that there may be a basic lack of confidence in the reliability of audible alarms that undermines their utility.

Subsecond observations of EIT voltage changes on the human scalp due to brain stimulus.

A pilot study has investigated the feasibility of imaging human brain function using an electrical impedance tomography (EIT) system time-locked to an evoked response (ER) system. A sixteen-electrode planar EIT configuration was used with polar current injection. We report here measurements on two volunteer patients who were fully awake in all tests. Reference data (with no applied stimulus) yield EIT nearest-neighbour voltage differences over the range 5-28 mV. In comparison with forward calculations [C.M. Towers et al. (2000)], these data suggest a value of skull conductivity of the order of 0.05 S/m. Visual and auditory stimuli were applied as single discrete events to evoke neural responses (VER and AER respectively). In each case, EIT data acquisition commenced at a time between 70 and 740 ms later, taking 308 ms to complete. Average values of voltage pair data over many frames are presented here, with the emphasis on the VER data. When comparing data taken under stimulus conditions against the reference data, voltage differences of up to approximately 3 mV are observed in both AER and VER cases. We attribute these voltage changes to synaptic activity. Preliminary reconstructed images of conductivity are discussed.

Human factors error and patient monitoring.

A wide range of studies have shown that human factors errors are the major cause of critical incidents that threaten patient safety in the medical environments where patient monitoring takes place, contributing to approximately 87% of all such incidents. Studies have also shown that good cognitively ergonomic design of monitoring equipment for use in these environments should reduce the human factors errors associated with the information they provide. The purpose of this review is to consider the current state of knowledge concerning human factors engineering in its application to patient monitoring. It considers the prevalence of human factors error, principles of good human factors design, the effect of specific design features and the problem of the measurement of the effectiveness of designs in reducing human factors error. The conclusion of the review is that whilst the focus of human factors studies has, in recent years, moved from instrument design to organizational issues, patient monitor designers still have an important contribution to make to improving the safety of the monitored patient. Further, whilst better psychological understanding of the causes of human factors errors will in future guide better human factors engineering, in this area there are still many practical avenues of research that need exploring from the current base of understanding.

Anaesthetists' attitudes to monitoring instrument design options.

A survey into the attitudes of anaesthetists to features in monitoring instruments, particularly the design of alarms, visual warnings, alarm limits and the general instrument interface is reported. Questions in the survey had short introductions outlining a clinical scenario followed by items that proposed alternative design features that an instrument might have. Participants were asked to grade their responses to these alternatives on a scale of 1 (strongly disagree) to 5 (strongly agree). The results suggest that anaesthetists would welcome the use of more advanced technology in instrument design. They prefer context-specific messages and alarms. They reject overt control systems for delivering anaesthesia, except for use in exceptional circumstances. Generally, the preferences of anaesthetists are consistent with known principles of safe, ergonomic design.

3D simulation of EIT for monitoring impedance variations within the human head.

A preliminary analysis is presented concerning the use of EIT for detecting impedance inhomogeneities within the human brain. The work to date is centred around the monitoring of two distinct impedance variations: those associated with the application of a carotid clamp during surgery and changes caused by the redistribution of blood flow during auditory stimuli. Using the commercially available Ansoft Maxwell package, a 3D finite element model of the human head has been developed to solve the forward problem. The model is hemispherical in shape and comprises regions of brain, cerebrospinal fluid, skull and skin and includes 16 scalp electrodes each of area 1 cm2. Results from simulations using the model suggest that an EIT system, incorporating diametric current excitation, would require a voltage measurement sensitivity of 100-120 dB in order to detect the impedance variations in the above cases.

Automatic artifact identification in anaesthesia patient record keeping: a comparison of techniques.

The anaesthetic chart is an important medico-legal document, which needs to accurately record a wide range of different types of data for reference purposes. A number of computer systems have been developed to record the data directly from the monitoring equipment to produce the chart automatically. Unfortunately, systems to date record artifactual data as normal, limiting the usefulness of such systems. This paper reports a comparison of possible techniques for automatically identifying artifacts. The study used moving mean, moving median and Kalman filters as well as ARIMA time series models. Results on unseen data showed that the Kalman filter (area under the ROC curve 0.86, false positive prediction rate 0.31, positive predictive value 0.05) was the best single method. Better results were obtained by combining a Kalman filter with a seven point moving mid-centred median filter (area under the ROC curve 0.87, false positive prediction rate 0.14, positive predictive value 0.09) or an ARIMA 0-1-2 model with a seven point moving mid-centred median filter (area under the ROC curve 0.87, false positive prediction rate 0.14, positive predictive value 0.10). Only one method that could be used on real-time data outperformed the single Kalman filter which was a Kalman filter combined with a seven point moving median filter predicting the next point in the data stream (area under the ROC curve 0.86, false positive prediction rate 0.23, positive predictive value 0.06).

The performance of a variable-flow indirect calorimeter.

Indirect calorimetry estimates energy expenditure from measurement of respiratory gas exchange volumes. This paper considers the design and evaluation of an indirect calorimeter, the Europa GEM, suitable for use in nutritional research. The calorimeter is of the ventilated hood, flow-through type and is intended for use with spontaneously breathing patients. Our aim was to develop an accurate, flexible instrument with a high level of automation. Performance was assessed in a laboratory simulation using reference gas injections (n = 24) producing a mean error of 0.3 +/- 2% in oxygen consumption (VO2), 1.8 +/- 1% in carbon dioxide production (VCO2) and 1.4 +/- 1.5% in respiratory quotient (RQ). In order to investigate the effect of FeCO2 on error multiplication a further subdivision (n = 8) of tests at FeCO2 = 0.5%, 0.75% and 1% was made by modulating the air flow through the hood. However, the predicted increase in system accuracy with increasing FeCO2 was not apparent in practice.

Efficiency of the Carden "Ventmasta" in A and D modes during controlled ventilation in children.

We have determined the efficiencies of the enclosed Mapleson A and Mapleson D modes of the Carden "Ventmasta" ventilator during controlled ventilation in 19 anaesthetized children. In addition, we determined the suitability for the A mode of the fresh gas formula, VF = 0.6 x weight0.5. Efficiency was assessed in terms of the fraction of fresh gas delivered to the alveoli. When the minute volume to fresh gas flow ratio exceeded 1.5, fractional delivery of fresh gas was 23% greater in the A mode than in the D mode (0.74 vs 0.60) (P < 0.0001). Under the same conditions, mean end-tidal carbon dioxide concentration in 27 children undergoing ventilation in the A mode with VF = 0.6 x weight0.5 was 4.6% (range 3.5-5.4%). We conclude that the Carden system is up to 23% more efficient in the A mode than in the D mode, and that under the conditions of this study, normocapnia or mild hypocapnia was produced accurately using the formula VF = 0.6 x weight0.5.

Determination of the onset of rebreathing in an enclosed afferent reservoir breathing system in anaesthetized, spontaneously breathing adults: a comparison of three methods.

We used three methods to determine the onset of rebreathing in the Ohmeda enclosed afferent reservoir breathing system and compared the results with the previously published rebreathing characteristics of this system. Of the methods studied, expiratory limb capnography proved unsuitable for determining the onset of rebreathing in this system. Inspiratory limb capnography and minimum inspired carbon dioxide at the mouth did enable the onset of rebreathing to be determined. However the fresh gas flow:minute volume ratio at which rebreathing occurred as determined by these criteria was less than that determined by the Kain and Nunn criteria and thus offer no clinical advantage over the latter.

Recovery after oral surgery with halothane, enflurane, isoflurane or propofol anaesthesia.

We have compared the recovery characteristics of four different techniques for maintenance of anaesthesia in 99 day-case patients admitted for oral surgery. All patients received propofol for induction of anaesthesia followed by halothane, enflurane, isoflurane or propofol infusion for maintenance of anaesthesia. Each patient was subjected to a battery of psychometric tests which included Spielberger state, trait, mood stress and mood arousal questionnaires, Maddox-Wing test and five-choice serial reaction time. All tests were performed before operation and at 0.5, 1, 2, 4, 24 and 48 h after operation. Performance in the reaction time test decreased significantly in the immediate postoperative period, returning almost to preoperative values by 4 h. However, only those patients who received enflurane or propofol had returned to their performance level before surgery by 4 h, although all four groups had achieved this target by 24 h. There was a further improvement in performance at 48 h. Anxiety and stress were high before surgery and decreased rapidly in the postoperative period. The Maddox-Wing test demonstrated a significant impairment in performance in the first 1 h after surgery, which returned to normal by discharge at 4 h. There were no significant differences between the four groups in these latter tests.

Measurement of breath-by-breath gas exchange during general anaesthesia.

We describe a single flow transducer breath-by-breath gas exchange measurement system suitable for use during general anaesthesia. The system uses a Fleisch No. 2 pneumotachograph, a mass spectrometer and a microcomputer to give real-time continuous measurements. Correction for apparent gas exchange attributable to changes in gas stored in the lung (functional residual capacity) is available. The correction assumes no gas exchange of either nitrogen or argon for air-breathing subjects or argon only during anaesthesia, while the inspired concentrations are maintained at atmospheric values. The method has been tested against Douglas bag measurement and compared with results from conventional systems used by other authors. The system measurements show broad agreement with Douglas bag measurements, although the limits of agreement are wide for air-breathing volunteers. The system between-breath variation was typical of breath-by-breath methods in other areas of medical research.

Fresh gas requirements of an enclosed afferent reservoir breathing system in anaesthetized, spontaneously breathing adults.

Using two methods of determining the onset of rebreathing, we have determined the minimum fresh gas flow rate (VF) of the Ohmeda enclosed afferent reservoir breathing system (EAR) in anaesthetized, spontaneously breathing adults. Rebreathing as defined by the Kain and Nunn criteria did not occur when the VF/VE ratio was greater than 0.70. A mathematical model was used to calculate the degree of rebreathing at each VF. From this model, rebreathing did not occur when VF was 0.86 VE or more and this value of VF/VE is considered appropriate to eliminate rebreathing in clinical practice.