A Comprehensive Approach for the Ergonomic Evaluation of 13 Emergency and Transport Ventilators

Emergency and Transport Ventilator Category Comparison

ICU-like ventilators are too bulky and heavy to be routinely used for emergency transportation. However, these devices are commercially available in Europe for specific use in emergency departments and are sometimes used for transportation of the most critically ill patients. This is the reason why they were considered for evaluation in a specific category. The results that are presented herein are to be considered by taking into account each category with respect to the other, depending on the clinical use of the device.

Significant differences were observed in terms of the task failure rate and objective chronometric tests for simple compared with sophisticated and ICU-like emergency and transport ventilators. Most test failures with the sophisticated emergency and transport ventilators were observed during the ventilatory mode changes, compared with other categories. This difference could be explained by the fact that only a few settings and modes are available on simple devices, whereas many more possibilities and confirmation steps are necessary for the other 2 categories.⁵ Sophisticated and ICU-like emergency and transport ventilators also need 2 or 3 steps to power off, whereas simple devices only need a single button switch. In 2 previous studies,^8,9 the median time periods necessary to perform similar steps were found to be higher, whereas the same trends were observed in home-care ventilators in terms of user-friendliness.¹⁰ Emergency and transport ventilator human/machine interfaces have only marginally evolved over time, and most current devices are somewhat similar from one brand to the other, which may explain such results among a population of well-trained emergency physicians.

Concerning sophisticated emergency and transport ventilators, there was also frequent confusion between spontaneous noninvasive ventilation and invasive ventilation modes, when such an option had to be selected. Another frequent cause of failure was confusion between volume-control continuous mandatory ventilation (VC-CMV) and volume-control intermittent mandatory ventilation (VC-IMV) modes. Indeed, VAC (for “volume assisté contrôlé”), the French acronym that is routinely used (corresponding to VC-CMV) is quite similar to VACI (for “volume assisté contrôlé intermittent,” corresponding to VC-IMV). Another example, the HT70 ventilatory modes, only display English acronyms, and as a result, VC-IMV was frequently mistaken for noninvasive ventilation modes. This type of failure has already been observed by Templier et al.¹ Thus, it clearly seems necessary to standardize the terminology and to simplify mode recognition in order to avoid such failures^1,8–10,16 but also to ensure that the device's human/machine interface is fully adapted to the users' experience and country. With regard to simple emergency and transport ventilators, the failures mainly concerned setting and alarm readings and were considered to be linked to poor monitoring precision.

Mental Work Load Assessment

Mental work load assessment is a modern cognitive psychology tool that provides a new dimension in evaluating the ergonomics of biomedical devices.¹⁴ As already proved in other fields of interest, it can depict significant differences between devices that would not have been noticed using standard tests.¹⁵

As observed in our study, a combination of buttons is frequently required to start or stop a function, the labeling of the buttons may not always be clear, and screens are often absent or somewhat difficult to read. Such problems, which are difficult to explore using standard ergonomic tests, may be evaluated when detailing the different mental work load dimensions, such as performance, effort, or mental demand. Mental work load assessment also enables us to understand why, besides optimal screen monitoring capabilities and/or technical properties, several devices may induce significant mental overload and/or failures due to an increase in the number of steps required to complete a single task.

Human/Machine Interface Differences and the Potential Impact on Task Failure Rate Reduction

It is common in clinical routine that a clinician may operate a specific ventilator without sufficient training, apart from some basic knowledge in mechanical ventilation. Medical errors have been demonstrated to be major determinants in patient safety since the “to err is human” report published in 1999,¹⁷ and errors related to mechanical ventilation occur with the greatest frequency.² Confusing human/machine interface aspects, designed without sufficient input from the end users, may lead to inadequate solutions in the clinical setting.

Although our results may not be totally conclusive, the screen interface and the availability of curve monitoring were associated with a better perceived user-friendliness and willingness to use, which may thus indirectly affect the task failure rate despite the fact that simple devices also led to fewer task failures. Similar results have already been observed by Uzawa et al,⁸ who took into account 4 modern ICU ventilators and observed that different human/machine interface designs resulted in different rates of operational failures.

Technological improvements have led to significant improvements in mechanical ventilator performance over recent decades.⁶ According to the literature, the most recent sophisticated emergency and transport ventilators do actually have technical capacities closer to those of standard ICU devices.^7,18 The technological evolution of more complex devices should also be accompanied by the emergence of evolved human/machine interfaces, in order to decrease mental work load and reduce task failures.¹⁹ Biomedical systems and ergonomic improvements are necessary to generate the appropriate design requirements, in response to health-care constraints,²⁰ and such ergonomic studies with sufficient input from clinicians should be a priority for manufacturers.

Limitations of the Study

Our study suffers from several limitations. First, as also proposed by several investigators,^1,8–10 the subjects were not supposed to have any operational experience in using most of the models in the study, since for all basic operational tasks, the clinicians should not have referred to the operating instructions for the sake of task failure reduction, especially in the case of emergency. One may consider that this study also demonstrates that proper training for practitioners is mandatory. However, although some devices (Oxylog 3000 and Vela) were already known to some of the users and may therefore have been considered as references, a huge failure rate was witnessed using the Oxylog 3000, which demonstrated that ergonomic improvements are also mandatory. Second, the NASA-TLX results should be considered with caution because ergonomic assessment and mental work load are new notions in emergency practice, and NASA-TLX is a difficult test to interpret.¹³ Before each test and for each participant, we explained the progress analyses and the fact that it was emergency and transport ventilator ergonomics that was being evaluated and not the physicians' own capabilities. Finally, we used a computerized NASA-TLX version, which has been associated with a higher mental work load value than the paper-and-pencil version.²¹