Likewise, clinical signs and symptoms, such as with the examination of mucous membranes of patients, lack the objectivity required for accurate clinical decision making. Commonly used methods, such as orthostatic tilt testing, are often unable to differentiate conditions of mild dehydration and may be unnecessary or impractical in patients with severe fluid losses. Traditional ED methods for determining the hydration status of patients have been shown to have significant limitations in specificity and sensitivity. The NASA Johnson Space Center Committee for the Protection of Human Subjects (institutional review board) approved the experimental protocol and all subjects gave their written informed consent. The results were compared used a standard t test analysis. Echocardiographic measurements of orthostatic changes in stroke volume were obtained before and after the protocol period using a standard tilt testing methodology. The same point on the external surface of the skin was used in both the measurements (before and after dehydration). The superficial dermis surface and the bone–tissue interface were used as the measurement boundary landmarks (see Fig. During both the measurements the subjects were in the supine position for which they had been equilibrated. Using an ultrasound technique previously described in the literature (17.5 MHz linear array transducer), the skin tissue and interstitial thickness superficial to the calcaneous and immediately below the lateral malleolus were measured both before and after the study period. This study involved healthy volunteer subjects who were participating in an extended period of 6° head down tilt bed rest protocol in which a mild dehydration is an established common consequence (average loss of plasma volume of ~10%). In this study, we examine the potential use of ultrasound measurements of interstitial fluid and dermal soft tissue thickness for the detection of conditions of mild to moderate dehydration. What is needed are simple objective measures that can be obtained with tools readily available in an ED environment and require very little patient manipulation. Invasive measurements of central fluid volume status are impractical for most patient scenarios and might not always detect mild fluid losses. Even an optimized tilt test has shown limited utility in detecting mild to moderate intravascular fluid loss (<10%). Likewise, commonly used techniques that observe changes in heart rate and blood pressure during emergency department (ED) orthostatic testing have been found to be highly variable and lack the sensitivity and specificity to be clinically dependable. Traditional hallmark findings on clinical examination such as the capillary refill are not always predictive of the patient’s state of hydration. The determination of the fluid status is a critically important aspect in the assessment of the emergent patient. Since the technique obtains measurements in the supine position, it also obviates creating orthostatic symptoms in restrictive clinical environments. The method was able to detect significant changes in tissue interstitial fluid under conditions of mild dehydration. This study looks at the possibility of using ultrasound as a method for the objective measurement of tissue dehydration. Traditional tilt testing has been a less than satisfactory technique for determining the hydration status of patients. In the eight healthy subjects studied, there was an average of a 13% diminution in both the ankle and pretibial soft tissue and interstitial thickness after tilt bed rest ( p = 0.05) that coincided with mildly decreased orthostatic induced changes in stroke volume. Also the echocardiographic measurements of orthostatic induced changes in stroke volume were obtained. The soft tissue and interstitial thickness superficial to the calcaneous and immediately below the lateral malleolus were measured in the supine position using high frequency ultrasound both before and after the treatment. This study involved healthy subjects in which a mild dehydration was a consequence of tilt bed rest (average loss of plasma volume of ~10%). In this study, we examine the potential use of ultrasound measurements of soft tissue and interstitial fluid thickness for the detection of conditions of mild to moderate dehydration. Several studies have suggested that clinical indicators of a patient’s fluid status that are frequently used in practice are highly variable and not useful in the differentiation of these patients.
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