Disorders of fluid and electrolyte balance in the U.S. military result in at least 125 hospitalizations, two lost duty days per event, and 9,300 ambulatory hospital visits per year (60% hyponatremia, 40% dehydration) (Carter et al., 2005; DoD, 2008). Diarrhea is a major infectious disease threat which requires aggressive i.v. fluid replacement in 30% of U.S. troops deployed to Iraq or Afghanistan (Brown et al., 2009). It is also important to recognize that the management and outcome of the 662 severe or penetrating traumatic brain injuries (TBI) reported for the military in 2009 (DoD, 2010) may be hindered by dehydration (Clifton et al., 2002). Fluid and electrolyte imbalances also contribute to heat illness (Carter et al., 2005) and can substantially impair combat fighting effectiveness (Dupont, 2003).
The importance of developing a valid assessment measure of human hydration status for clinical and field use is recognized by the military community as a high priority medical technology gap (MOM ICD v1.3, 2008). In far forward locations (levels I-II), orthostatic testing or gross symptoms are most commonly used to estimate hydration status (Manning et al., 2007). However, level I-II methods share symptoms with numerous other maladies and are insensitive until dehydration is severe or becomes debilitating (Levitt et al., 1992; McGee, 1999). Definitive hydration assessment in rear roles of medical care (levels III-V) requires invasive serial blood and/or urine measurements (Feig, 1977; Mange, 1997). Thus, a field-expedient technology that provides an accurate, non-invasive assessment of hydration status would improve medical triage by allowing better fluid-electrolyte management by medics in theatre (point of care), and by medical personnel in the rear levels of care (treatment and return to duty).