Faced with continuous hypothermia, an addi tional large shift of body water will occur. Whether the cold-induced diuresis is explained on the basis of volume overload or ionic imbalances, it is a ma jor concern. For example, cold water immersion has been shown to increase urinary output by 3.5-fold and this decrease in body water may be a factor contributing to the "rewarming shock" that occurs following active vasodilation induced by rewarm ing treatments ss Potassium ion regulation may be impaired in hypothermia. Hyperkalemia, one of the leading causes of cardiac dysrhythmia 80 is usually an ominous sign of tissue hypoxia From the practical standpoint in the field, one of the only ways to assess hydration is to examine the color of the urine. Most military units insist on vi sually inspecting the degree of darkness of each individual's urine. The more hydrated the indi- vidual, the less dark the urine (see Figure 5-5 in Chapter 5, Pathophysiology of Heatstroke)