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This observational, exploratory study took part during a period of 5 months. 20 physicians completed queries after each sortie in order to evaluate their subjective workload during their shifts as physicians providing pre-hospital emergency care. Furthermore, a chest-belt (Zephyr BioHarness™ 3, Zephyr Technology Corp., Annapolis, MD, USA) was used to gather electrocardiograms (ECG) during their shifts. All physicians were specialized in emergency medicine; a supplementary qualification that every physician in Germany may obtain after two years of clinical work including at least 6 months in intensive care medicine or 12 months in anesthesia or the emergency department. [20] The local Ethics Committee at Klinikum rechts der Isar, Technische Universität München approved the study (N° 5771/13; May 11th, 2015). Written informed consent was obtained from all participants and all data concerning the participating physicians as well as their patients were raised anonymously. No limitations regarding food intake, activity, sleep or medication were given. During the shift changes no study personnel was present; the emergency physicians filled in the query and put on the chest-belt themselves. Parts of the results, specifically the results regarding the validity of linear and non-linear HRV metrics, have been published earlier. [15] In Germany, a system of pre-hospital physician-based emergency care is established. In cases where a life-threatening injury or severe sickness (according to a catalogue of certain keywords) is likely, the rescue coordination center sends an emergency physician response vehicle to the scene. [21] This vehicle is staffed with an emergency physician and a paramedic. From July to November 2015 the emergency physicians were asked to fill in a query after each sortie. The query contained the NASA-tlx,[3] alarm time and date and the alarm code. Pursuant to the physicians’ emergency protocols, the timestamps for alarm, arrival at the patient and handover of the patient at the admitting emergency ward as well as initial NACA scores for each patient were obtained. The sorties took place in a suburban environment in Southern Germany. After the study period, all participating physicians were asked to complete a survey on their strain related to the alarm codes that they were confronted with during their duties as emergency physicians. A detailed description on the processing of the ECG raw data gathered from the chest-belt and the computation of HRV metrics is provided elsewhere. [15] Use of the NACA scoring-system for patient characteristics: The National Advisory Committee for Aeronautics (NACA, a precursor institution of today’s NASA) score is a scoring system that assesses an emergency patient’s severity of injury or illness by eight levels. [22, 23] After it has been originally introduced as a scoring system for trauma patients 24h after admission to a hospital, the modified NACA score presented by Tryba and colleagues in 1980 can be used for pre-hospital injury severity assessment as well. [23, 24] The grades of the NACA score and their verbal descriptions (used in their German translation for this study) are provided in Table 1. As the category NACA 0 (‘No injury or disease’) is not part of the emergency physician’s protocols, it has not been included. Also, cases with an initial NACA score of VII (death of the patient) were excluded. The NACA score well predicts the mortality and the need for ventilation therapy of patients and has substantial inter-rater reliability. [22–24] Table data removed from full text. Table identifier and caption: 10.1371/journal.pone.0202215.t001 Verbal description of the NACA score’s categories. Verbal descriptions of the NACA sore’s categories. Simplified version adapted from Alessandrini H, Oberladstätter D, Trimmel H, Jahn B, Baubin M. NACA-Scoringsystem. Notfall + Rettungsmedizin 2012; 15: 42–50. Abbreviations: CPR, cardiopulmonary reanimation.
Evaluation of subjective workload via NASA task load index: In line with prior work in the field of anesthesia,[9] a six-dimensional version of the NASA-tlx was used for the evaluation of subjective workload; it included the categories mental demands, physical demands, temporal demands, performance, effort, and frustration. [25] Each rating scale ranges from 0 to 20; the steps do not have an additional description. For the study a German transcription of the simplified paper and pencil version of the NASA-tlx provided on the online appearance of the NASA was used. [26] An English translation of the query as well as the German version used for the study are provided in the supplementary material (S1 Text).
Based on the times gathered from the physician’s protocols, the timespan from the physician’s arrival at the patient to the handover of the patient at the admitting emergency ward was identified. Due to their high potential to differentiate workload in emergency medicine[15] as well as in anesthetists providing general anesthesia,[9] PeEn and mean HR were included in the analysis[9, 27] of these ECG segments.
Evaluation of physician pre-sortie anxiety related to the alarm code: The physicians were asked to complete a survey on their strain when reading a certain alarm code. Therefore, a query presented all alarm codes that occurred during the study period (N = 99) in a randomized order. The physicians were asked to rate each alarm code. The Likert scale ranged from ‘not nervous at all’ (1) to ‘very nervous’ (5).
To evaluate the NASA-tlx, descriptive statistics for the NASA-tlx scores and the physician’s physiological workload correlates according to NACA scores were computed. It was accounted for repeated measurements within subjects. Thus, general linear mixed models (GLMM) were used to explore differences among the subjective and physiological workload correlates. In line with our own prior publications,[9, 15] as well as the results of other researchers in the field,[28, 29] the analysis was not adjusted for experience, sex and age. Statistical analysis was performed using the software package SPSS Statistics 24.0.0.0 (IBM Corp. Armonk, NY, USA) and statistical significance was defined as p < 0.05.
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