ارگونومی در سرویس نجات -ارزیابی ارگونومیک تختخواب تاشو آمبولانس

In a comparative ergonomic study, three combinations of stretchers with incorporated transporters from brand-name manufacturers—so-called “ambulance cots” or “roll-in systems”—were tested with respect to their ergonomic quality. In addition to work analyses during the use of ambulance cots, the strain on the circulatory system of 12 professionals was measured in four standardized carrying tests: carrying of the stretcher on a staircase at normal speed and at increased speed, lifting of the stretcher onto the gurney, and loading the ambulance cot into, as well as unloading it from, an ambulance. Static and dynamic components of the muscle strain of six muscle groups were determined electromyographically. The tests consisted of “normal” carrying, as well as explicitly rapid carrying, of a dummy (78 kg) up and down a flight of stairs using the commercially available ambulance cots, which weighed between 48.5 and 50 kg including a mattress for the patient. Model-specific influences of the cots aside, the rapid carrying led to substantially increased strain on the circulatory system (work-related increases of approximately 10 beats per minute (bpm)). The “lifting of the stretcher onto the gurney” and the “loading/unloading of the roll-in system” cause significantly less strain, but still lead to substantial “physiological costs” of approximately 50 bpm. Increased speed significantly increases muscle strain. The static components of the standardized electromyographic activity, sEA (%), with values of 50% and more, show that even carrying times of only approximately 30 s cause fatigue. Additionally, the test subjects (Ss) subjectively assessed the design elements of the stretchers as well as the gurneys via a questionnaire with approximately 50 items which had been developed specifically for that purpose. The detailed subjective assessment offers a differentiated view of the work situation. The evaluation suggests several concrete changes in order to improve the design with respect to the ambulance cots’ weight, their shape and positioning of handles, and the mechanism of the height adjustment of the gurney. Changes in the design were also recommended in order to reduce the extraordinarily high strain on the paramedics which was measured via peripheral-physiological methods. It became clear that one system which is widely used in several countries has marked weaknesses.

Even though physical stress in the workplace is of somewhat lesser importance today than it used to be, prevention of work-related back and joint problems remains an important task which can only be solved by occupational medicine and ergonomics together (cp. Hartmann, 2000). Although the lifting of heavy loads at work is limited and regulated, for example by the Lastenhandhabungsverordnung in Germany (1996)—a special “Ordinance on Safety and Occupational Health during Manual Material Handling—” it is not always possible to impose weight restrictions in the transportation of sick and injured people and for emergency medical services. Such heavy lifting can lead to long-term damage (see, e.g., Ayoub and Mital, 1989), which is currently recognized as an occupational disease. In the course of transporting sick and injured people, paramedics experience the “heavy loads” which are mentioned in “Occupational Disease no. 2108” in our country. This also applies to both male and female paramedics in the civilian as well as the military sectors in other countries (cp. Furber et al., 1997; Knapik et al., 1998 and Knapik et al., 2000; Restorff, 2000; Rice et al., 1996a and Rice et al., 1996b). The latter often operate under extreme time pressure combined with alarmingly bad overall conditions. The weight to be carried (the sum of the weight of stretcher and patient) frequently exceeds 100 kg. Thus, it appears necessary to make use of all possibilities to reduce strain. In order to increase risk prevention, ergonomically optimized stretchers and gurneys should be utilized. Design features of three common commercial ambulance cots (roll-in systems—as combination of stretcher and gurney) as well as their resulting stress and strain were determined in a comparative ergonomic study by objective measurements and subjective assessments in order to document the existing state and derive suggestions for improvements.

The physical stress from the tests causes static strain which, for most of the muscles, largely exceeds the endurance level of 15% for an 8-h workday. This isolated fact, however, would not be particularly relevant, since continuous patient transport for 8 h is not a realistic situation. Nonetheless, static strain of close to 45% of the descendent part of the trapezius involved in shoulder stabilizing and total strain of approximately 50% combined with prolonged carrying duration—e.g., in a narrow staircase or over several floors—will likely lead to distinct myogelosis in the neck–shoulder area. It should be mentioned in this context that 50% of maximum force can only be kept up for 1 min. If a muscle contraction of 50% of maximum force is required for only 30 s, the subsequently required restitution time, according to Rohmert and Laurig (1993), amounts already to approximately 400% of the holding time, i.e., approximately 2 min. A similar issue exists for the erector spinae, which is responsible for the upright posture of the upper part of the body. In this case, the static strain of approximately 30% also will lead to fatigue after only a few minutes. Along with the apparently high physical strain, one of the most popular roll-in systems in the world causes additional discomfort by its design—independent of the gender of the paramedics and their hand sizes. The results for the Ferno roll-in system, for example, exhibit very high strain for the flexor muscles acting on the wrist and fingers while loading the roll-in system into an ambulance and unloading it from the ambulance. On the one hand, such a high level correlates well with the high force required to release the height locking mechanism of the Ferno gurney. On the other hand, the increased effort during the loading of the Ferno roll-in system into the ambulance can be explained by the fact that the roll-in system must be lifted during pushing since, by design, the front leg and the foot end leg are released simultaneously. This can also be seen in the results for the erector spinae. Additionally, smaller (female) paramedics are disadvantaged. The other models allow the separate release of the front leg. The roll-in system—still supported by the foot end leg—is then placed in the ambulance. Only once the foot end leg reaches the ambulance does this leg become released, and the gurney needs to be lifted. Thus, the phase during which the system must be lifted is substantially shorter in the Stollenwerk and Stryker models, which corresponds with substantially lower strain. It was shown that weight differences of 1.5 kg—with weights of 22.5–24 kg—do not have any relevant effect on the overall strain, objectified via physiological measurements. The weight differences would have to be substantially larger for objective measurement results to be obtained. This does not mean, however, that a further reduction of the stretchers’ weight is not desirable, especially since model-specific differences were quite noticeable subjectively. The handle design should be based compatibly with the anatomy of the hand (cp. Strasser, 1995). If handles have a circular cross section instead of a rounded or hexagon, they should at least possess a bulbous longitudinal section for better distribution of the pressure. The Ferno model also seems to cause high pressure in the palm, which results in the negative rating of the cross-sectional shape as well as the risk of producing pressure points and blisters. However, the Stryker model also reveals a tendency to cause pressure points. This rating probably results from the height of the naps on the textured surface of the handles. While they ensure “fairly good” grip, they also increase the tendency to cause tender spots and blisters. While the handles on the Ferno stretcher provide sufficient grip under dry conditions, this is no longer the case when substantial perspiration occurs in the palm. Palm perspiration mainly occurs while carrying the stretcher on the staircase and it is due to the high associated strain, resulting in substantially reduced grip of the Ferno model's handles, which is clearly shown in the “bad” rating. The Stollenwerk stretcher does not particularly lead to pressure points, and the grip provided by its handles is considered neither good nor bad. Among the results for the Stollenwerk model, the better rating of the grip of the handles at the gurney versus the grip on the stretcher is noticeable. A comparison of the handles shows that those on the stretcher have a smooth surface, whereas the handles on the gurney are slightly gummy and have minor naps on the textured surface. The gurneys’ height adjustment through the release of the legs’ locking mechanism exhibits further differences in the systems’ handling. The Stryker and Stollenwerk models use handlebars and release levers underneath to lift and lower the gurney (see upper and lower part of Fig. 2). The palms face the user, and the release levers are operated with the index fingers. The Ferno model requires maximum supination (outward rotation of the arms) to operate the handlebars, i.e., the palms face away from the user. In order to release the height adjustment, the right hand has to reach for and pull the “pull lever” (see middle part of Fig. 2). In order to improve the paramedics’ freedom of motion while handling the gurney, the foldout handles on the Stryker and Stollenwerk gurneys (see upper and lower part of Fig. 2) are a useful aid. Here, the arms do not have to be positioned in front of the body during lifting, but can be on the sides of the body. Furthermore, folding out these handles increases the distance between the carrier and the system, which allows a straight posture of the torso during lifting. This is the main reason why the paramedics use these handles. Thus, future designs should incorporate additional handles at the foot of the gurney despite the lower loads that can be expected at that end. These and other details (not mentioned here) of the extensive subjective ratings offer a sufficient amount of suggestions for several concrete improvements, especially in the design of the different systems. The goal must be to reduce the paramedics’ extraordinarily high physical strain, which was measured through peripheral-physiological methods. More attention should be paid to compatibility (cp. Strasser, 1995) between the human organism's characteristics and the controllable technical components of the systems. Anatomical and physiological characteristics—for example, those of the hand—are a guiding principle that must not be neglected in the design of working tools according to the principle “fitting the hand equals fitting the person”. The quality of a handle depends on whether ergonomic demands dominate over the ideas of designers or perhaps also over historical forms. Ergonomic variations of the design should be based not only on theoretical considerations, but they must also be quantified through their actual effects at work (see, e.g., Strasser, 1991). It must be mentioned that the results from the subjective ratings, which are often not free of bias and uncontrollable transfer effects (see, e.g., Kendall et al., 1994), must be evaluated in relation to objective measurements, e.g., electromyographic registrations. This fact, however, is not new but has already been observed and demonstrated in different studies (cp. Böhlemann et al., 1994; Strasser, 2000). Nevertheless, objective measurements should also never be considered independently. Only a multidimensional approach (cp. Strasser, 2002/2003) can ensure reliable results in the evaluation of a working tool.