Recent technological progress has improved pneumatic performances of both anaesthesia and intensive care unit (ICU) ventilators [1-5]. Several lung model studies, however, demonstrated that technical differences among ICU [2,6], transport [7,8] and home ventilators [9-12] may markedly affect their performance, especially regarding the trigger function and the pressurization process. We have reported that the most-recent anaesthesia ventilators perform comparably to recent-generation ICU ventilators in terms of pneumatic function and the delivery of pressure support ventilation [1,2].
A study of anaesthesia management characteristics on severe morbidity and mortality demonstrated equipment check with protocol and checklist, and documentation of the equipment check was significantly associated with decreased risk . Recently, Larson and colleagues  reported that anaesthesia machine checkout continues to be a problem despite the publication of multiple checklists. Therefore, the design, user-friendliness and required training for the use of the machine are becoming major criteria for the global assessment and the choice of a ventilator .
Usually, the choice of an anaesthesia ventilator depends upon the specific requirements of the purchaser, which must be noted formally in the specifications for a request for proposal . In 2004, the biomedical department initiated a process to replace the anaesthesia workstations of the three anaesthesia departments of our university teaching hospital of Montpellier. Regarding the recent literature concerning the pneumatic performances of the new anaesthesia ventilators and the results of the bench-test evaluations that we performed [1,2,15], we found that the available models were similar and could not be differentiated with respect to their pneumatic performance . Although manufacturers of anaesthesia ventilators are familiar with technological bench-test assessments, they are unable to easily evaluate the user interfaces of the machines they develop. Unlike ICU  and home mechanical  ventilators, no study has evaluated the user-friendliness of the new anaesthesia workstations.
In this context, the objective of the current study was to evaluate the user-friendliness of four anaesthesia workstations that satisfy the same specifications: Kion (Maquet-Siemens) Avance (GE-Datex-Ohmeda), Felix (Taema) and Primus (Drager).
The four anaesthesia workstations tested were categorized into two groups according to their generation (i.e. date of production): (1) first-generation (was available in 1997): Kion (Maquet-Siemens, Germany); (2) second-generation (available since 2002–2003): Avance workstation (GE-Datex-Ohmeda, USA) equipped with the model 7900 ventilator, Felix (Taema, Antony France) and Primus (Drägerwerk AG, Lübeck, Germany). The main characteristics of the four evaluated workstations are reported in Table 1. The machines were provided by the manufacturers after a full revision had been made just prior to our investigation. All machines were stock, without modifications, and all were tested in operating conditions conforming to the manufacturer's specifications. These four anaesthesia workstations satisfied the specifications in terms of overall cost (purchase and maintenance contract), performance and ventilation options: pressure support ventilation, pressure-controlled ventilation and volume-controlled ventilation.
After IRB approval and informed consent, 20 volunteers who had more than 5 yr of anaesthesia experience participated to the study. The volunteers were 12 users among 85 nurse-anaesthetists who worked in the institution (7 men, 5 women, age: 35–50 yr) and eight physicians among 74 anaesthesiologists who worked in the institution (6 men, 2 women, age: 34–47 yr) with sound experience in mechanical ventilation in the context of anaesthesia in the operating room, from the three anaesthesia departments at the same hospital, differing in location but also by their surgical specialities.
To enable the evaluators to evaluate the user-friendliness, each anaesthesia workstation was loaned by the respective manufacturer to each department for a period of 2 weeks. Each evaluator was trained before the evaluation period of each anaesthesia workstation by a company representative, who remained in the operating room throughout the evaluation period. All the evaluators taking part in the study had to use the anaesthesia workstation in clinical practice, to remove and reassemble the respiratory circuit of each ventilator during the evaluation period and to remove the respiratory circuit of each ventilator at the end of the test period for evaluation of the amount of water condensation. Each evaluator tested each of the four workstations in a random order. However, the first-generation workstation (Kion) had been used for 5 yr in two out of the three anaesthesia departments in comparison to the three other workstations of the second-generation for which the evaluators had no clinical experience.
Criteria of the user-friendliness scale
The user-friendliness scale evaluated 10 criteria (Table 2), including two design and monitoring criteria (design, dimensions, ease of use of the unit and layout, legibility of screen), four maintenance criteria (self-test of the ventilator; removal and installation of the unit's breathing circuit and absorber; filling and fitting the absorber; and condensation and accumulation of water in the unit's breathing circuit) and four ventilation use criteria (alarm settings, ventilation mode settings; manual ventilation with the unit; and switching from manual to volume-controlled ventilation). Each criteria was evaluated from 0 (poor) to 10 (excellent). The overall score for each tested workstation by a user was calculated on a 100 point basis.
Data values are presented as mean ± SD or median (range). Comparative statistics relied on the Kruskall–Wallis one-way analysis of variance on ranks. Post hoc analysis was performed with the Scheffé test if analysis of variance reached significance. Significance was set at P < 0.05. Statistical analyses were performed using SAS©/STAT software version 8.1 (SAS Institute, Cary, NC, USA).
Figure 1 shows the mean results obtained by the evaluators for all the criteria on the four workstations. The mean score obtained for the workstation of the first-generation was significantly lower than those obtained by the three other workstations of the second-generation (P < 0.05). No significant difference in the overall user-friendliness score was observed for the three second-generation workstations.
Design and monitoring criteria
Figure 2a shows that the first-generation workstation obtained a significantly lower score than the three second-generation workstations for the design criteria (P < 0.01). For the screen, the highest score was obtained by Felix, which has the largest screen and associated characters (Fig. 2b).
For the self-test criteria, there was no significant difference between the four workstations (Fig. 3a). For the Circuit change, no significant difference was observed between the first- and the second-generation workstations, however, Primus obtained a significantly higher score (P < 0.05) than the workstation of the first-generation and the two other second-generation workstations (Fig. 3c). For the Absorber change and condensation criteria, Kion and Felix obtained a significantly lower score (P < 0.01) than Avance and Primus (Fig. 3b and d).
Ventilation use criteria
For the Alarms and the Setting criteria, there were no significant differences between the four workstations (Fig. 4a and b), especially between the first- and the second-generation workstations. There was a significant difference (P < 0.05) between Avance and Primus for the Manual criterion (Fig. 4c) and between Primus and the three other workstations for the Switch criteria (Fig. 4d).
The main result of our study is that this novel user-friendliness scale showed that the most-recent generation of workstations (second-generation) is significantly more appreciated by users than the first-generation workstation (Fig. 1). To our knowledge, this is the first study which evaluated the performance of anaesthesia workstations using a user-friendliness scale to identify both positive and negative elements. On the positive side, it was noted that the evaluators found the ventilation use criteria were good to excellent, both for the first- and the second-generation workstations (Fig. 4). Moreover, the use of a user-friendliness scale, developed ‘in-house', helped the anaesthetic staff to ‘consensually' choose the future workstation for their anaesthesia department. On the negative side, two anaesthesia workstations obtained a mediocre score for the condensation evaluation which underlines that some components of the circuit and the absorber require improvement by the manufacturers (Fig. 3).
In fact, significant differences between the four anaesthesia workstations were found for seven of the user-friendliness criteria (Design, Screen, Absorber, Circuit, Condensation, Manual and switch). It is important to note that the user-friendliness in terms of current maintenance was a preponderant consideration when choosing between the four anaesthesia workstations. Moreover, the screen size seems to be important for legibility, as the Felix, which has the largest screen size, stood out from the three other anaesthesia workstations for the screen criteria (Fig. 2).
We cannot compare the results of the current study with others, because no other similar study has compared these four anaesthesia workstations. However, it is interesting to note that despite the apparent complexity of these new machines, which all offer several ventilation modes (pressure support, volume-controlled and pressure-controlled ventilation) and monitoring capacities, the user-friendliness of the adjustment of the several ventilation modes was considered good, and even excellent for all four anaesthesia workstations. The fact that the technical characteristics of the anaesthesia workstation are closely similar (Table 1), including the ventilation options, limited the bias of a preference for a more complete ventilator.
An analysis of the results according to the type of evaluator, nurse-anaesthetist vs. anaesthesiologist, showed that the type of evaluator had no significant influence on the results (data not shown). Moreover, the purchase and operation costs could not influence the evaluators, as the negotiations between the manufacturers and the biomedical department had not ended at the time of our evaluation.
The validation of such a user-friendliness scale will require other evaluations relating to the anaesthesia departments of different cities and countries whose specific constraints may influence the choice of a anaesthesia workstation. To do this, we would have to evaluate the reproducibility of this user-friendliness scale for other sites, other workstations and also over time.
In addition, anaesthesia ventilators are increasingly evolving towards the concept of anaesthesia workstation: ventilation of the patient, monitoring of the haemodynamic and respiratory functions of the patient, administration of halogenated gases and monitoring of the depth of anaesthesia.
Therefore, the workstation contains many other non-ventilator-related elements, which must be considered when evaluating the overall user interface.
Studies have shown that an excess workload and/or changes in the vigilance of anaesthesiologist may be attributed to the equipment and associated with an increase in the number of undesirable incidents [5,13,14,19]. Thus, we can speculate that a better user-friendliness of workstations might contribute to decreasing the workload of users, and thus increasing patient safety.
Our study has some limitations. Firstly, through the profile of the participants was representative of our French institution, we cannot directly apply these results to other categories of users (i.e. other institutions in France and/or in countries other than France). The evaluation was carried out in three departments in order to limit any bias related to a particular type of anaesthesia activity or the influence of one of the industrial manufacturers during the presentation of its product. Unfortunately, we were not able to analyse the possible influence of one of the departments on the user-friendliness of these ventilators because of insufficient power. Secondly, there is no standard methodology for this type of study that requires us to choose our methods and criteria. We followed general recommendations and observing the users. Probably, some other aspects were not addressed with the present user-friendliness scale such as detect and correct a fault when the machine failed the self-test and during an emergency that resulted from a change in the patient (e.g. bronchospasm). Thirdly, we did not evaluate the real time each evaluator used each of the tested workstations during the 2-week trial. Fourtly, the first-generation workstation (Kion) had been used for 5 yr in two out of the three anaesthesia departments, in comparison to the three other workstations of the second-generation for which the evaluators had no clinical experience.
In conclusion, this novel user-friendliness scale showed that the most recent workstations (second-generation) were more appreciated by users than a first-generation workstation. Anaesthesia ventilators have benefited from considerable advances in design and technologies. User-friendliness is probably of major importance for the choice of an anaesthesia workstation. Other studies are needed to validate the reproducibility of the results obtained with this user-friendliness scale. A simple, reproducible test of user-friendliness for anaesthesia workstation might help both anaesthetist staff in the choice of a new anaesthesia workstation and manufacturers for the development of their equipment. Further studies are needed to better evaluate the influence of the user-friendliness of anaesthesia workstation on the patient safety.
The authors would like to thank the nurse-anaesthetists and the anaesthesiologists for the time they devoted to performing the tests. They would also like to thank the manufacturers for providing us with the machines and Patrick McSweeny for assistance with the English manuscript. Support was provided solely from institutional and/or departmental sources (Department of Anesthesia, Hôpital Saint-Eloi, CHU Montpellier, Montpellier, France).
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