Hypovolaemia is associated with a stress reponse, causing the release of catecholamines and stress hormones. Clinically the tongue will be dry, patient will feel thirsty. Blood pressure will be lower and pulse will be higher with a low central pressure. Skin eleasticity reduction is a late sign and signifies chronic dehydration rather than hypovolaemia. haematocrit is the amount of red cells that make up the plasma usually about 42-48 %. In hypovolaemia, the water content of blood is reduced and therefore solute and cellular component rises in proportion.this raises the haematocrit. The kidneys try to conserve water therefore urine is rich in solute and poor in water content therefore this raises the specific gravity i.e more solid components in the urine.
