In this observational simulation study, we have obtained a model with the capability to predict which health care worker will develop metabolic fatigue wearing a PPE against biological risks, after 30 minutes of intervention. The model consists of 5 easy-to-obtain non-invasive parameters such as sex, height, muscle mass, bone mass, and IPAQ stratification.
Previous studies have analyzed the use of PPE and how these protective devices affect fine motor skills [18, 19], or how the use of PPE influences the performance of a quality resuscitation [20]. Other types of studies addressed the issues of thermal perception and the perceived effort when working under these conditions [21, 22], or the increase in the HR above the recommended maximum levels [23]. However, we were unable to found equivalent studies to the one presented here..
In this work, CL and HR have been proposed as fatigue parameters. The lactate is a highly sensitive biomarker that provides accurate information about anaerobic metabolism [24, 25], easy to obtain, highly validated at the level of sports physiology [26], and others clinical contexts [27]. A subject with a CL level above 4 mmol/L -lacticaemia- after 20 minutes of rest implies that she/he continues with a high metabolic demand [28]. The other parameter considered critical to determine fatigue was a HR difference (between baseline values and 20 minutes after the end of the simulation) above the 3rd quartile (more than 31 bpm). During the progress of the simulation it is expected that the HR rises but returning to normal values when back in the rest situation. In subjects presenting fatigue however, a long-lasting HR recovery time has being observed [29, 30].
In our study, being female was as a protective factor against metabolic fatigue. In fact, males presented 8.4% more cases of fatigue than females. This difference can be explained by the higher percentage of muscle mass in males [31]. The lower muscle mass in females limits their thermogenic response capacity although this lower adaptation to thermal change does not generate a limitation, but rather makes females more thermally competent when using this type of PPE [32]. Likewise, those subjects with higher heights tolerate the proposed simulation scenario worse. Subjects with the highest height and greater muscle and bone masses not always are better adapted for certain type of physical works [33, 34]. The last variable included in the model is the IPAQ. Subjects with a moderate or high level of activity have a better physiological capacity to work with this type of PPE [35]. Physical activity improves aerobic capacity and improves resistance to metabolic stress [36, 37].
The results point out towards the existence of a pattern of subjects presenting better tolerance to fatigue while wearing the PPE: females of short stature with low muscle and bone mass and physically active. Variables that in principle could be of importance, such as experience (students or workers), training in biological risk, or the level of anxiety [38] did not influence the model.
The model can be useful to differentiate, based solely on baseline demographic and physiological parameters, which health care worker is best suited to work with PPE or, conversely, which subjects will require higher levels of training and care to work satisfactorily while wearing a PPE.
Health care workers must handle biohazard patients but must do so in the most appropriate safer conditions in each context. The use of PPE protects the professional, but also it generates an increase in temperature, tachycardia, higher levels of lactate, increased anxiety, difficulties in either vision or hearing (due to hood and panoramic glasses), etc. All these physiological responses must be taken into account at the time to adapt both the duration of its use and the workload with the objective to facilitate planning and execution of healthcare maneuvers in these complicated situations.
The strength of our study is in the diversity encompassed in the sample, which includes students and professionals, male and females, and nurses and physicians, representing a robust and illustrative sample of the healthcare system.
Our study has several limitations. The first one is the potential bias in the volunteer’s selection which was based solely on the opportunity criteria. All the subjects were recruited in the Public Health System or in the Faculty of Health Sciences of the University of Valladolid, in line with similar studies [39, 40]. Second, although the sample size allows for preliminary results and for an internal validation, it is small enough for carrying out an external validation of the model, which would require a multicenter study to determine the physiological impact on workers wearing PPE under biological risks. Lastly, lactate has been selected as a biomarker because it is easy to obtain, has been previously validated, and with a low price of the test. However, other biomarkers such as cortisol, C-reactive protein, etc., cannot be ruled out and will be considered in future studies. With the above caveats in mind, this model should be interpreted with caution, since it is a preliminary study. In any case, professionals must continue following the operating procedures in force for each health service.
In conclusion, given that a high percentage of subjects suffer from fatigue using PPE in a simulated incident against biological risks, any model aimed to improve the correct selection of health personnel to work under critical and complex situation while wearing a PPE must be considered. Our proposed model is able to differentiate between subjects with good or bad tolerance to perform a simulation during 30 minutes with a PPE, III category, 4B / 5B / 6B type, shedding light on which baseline variables could potentially anticipate work fatigue.