Fall in total body water

Symptoms of increasing lack in body water include thirst, confusion and altered level of conciousness. Signs of lack in body water include dry mucus membranes, decreased elasticity of the skin, decreased intraocular pressure and signs of cardiovascular decompensation such as pallor, sweating, tachycardia and hypotension. As a rule of thumb increasing loss of body water correlates with thirst, dry mucus membranes, decreased skin elasticity, decreased intra-ocular pressure and finally cardiovascular decompensation, see table 3.

Table 3: Decreased body water; symptoms, signs and approximate deficit

Symptom or sign	Deficit	Volume (70Kg man)
Thirst	3%	1.5
Dry Mucosae	5%	2
Decreased skin elasticity	8%	3.5
Fall in intraocular pressure	10%	4.5
Tachycardia Hypotension	$>$ 15 %	6.5

With respect to the main fluid compartments, changes in the ICF are hardest to detect because it is hidden by the ECF . In the ECF changes in the plasma are easier to detect than changes in the interstitial space.