Water retention is when the body accumulates too much water in the interstitial spaces of the tissues and is unable to get rid of it, such as through urination. Excess water can cause swelling in a part of the body. Water and sodium retention is a disorder of water and fluid metabolism due to an imbalance in fluid exchange between the body and the outside, mainly due to a lesion in the glomerular filtration rate. Under normal circumstances, the intake and discharge of sodium and water are in dynamic balance, so the body’s fluid volume can be maintained relatively constant. The kidneys play an important role in regulating the dynamic balance of sodium and water, so the basic cause of sodium and water retention is the disorder of this regulatory function of the kidneys, resulting in a decrease in the discharge of sodium and water from the kidneys and leading to generalized edema. Patients with water retention may develop edema in many parts of the body, usually below the level of the heart, such as the buttocks, back, and even forearms. Edema in the legs will often cause you pain and will be especially noticeable when trying to walk. Severe edema may make it very difficult to put on shoes or socks. If the edema is very severe, the trapped water will begin to leak out through the skin, making the surface of the skin soggy. When the body begins to retain excess water, blood pressure usually increases, and this leads to many complications. The most common of these are Congestive Heart Failure (CHF) and Pulmonary Edema (PE). Once pulmonary edema is present, there is a lack of access to adequate oxygen, resulting in shortness of breath, which can progress further to produce symptoms such as coughing. The clinical examination of water retention is as follows: 1. Blood examination The degree of elevated blood potassium, CPK, SGOT and LDH reflects the degree and extent of skeletal muscle necrosis; the increase of blood myoglobin indicates the possibility of renal failure; the decrease of blood pH, especially after hematologic reconstruction, and the further decrease of pH indicates poor prognosis. 2.Urine examination The presence of myoglobin in the urine should alert the occurrence of renal failure. 3.Oxyl radical detection Because of its chemical instability and short half-life, it is difficult to detect the presence of oxygen radicals can be indirectly determined by measuring malondialdehyde acid that increases proportionally with lipid hydrogen peroxide.