Osmolality Health Dictionary

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Osmolality: From 1 Different Sources

n. the concentration of body fluids (e.g. plasma, urine) measured in terms of the amount of dissolved substances per unit mass of water. It is usually given in units of mOsm kg?1 or Osm/l. Symbol: Os or osmol.
Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Parenteral Nutrition

In severely ill patients – especially those who have had major surgery or those with SEPSIS, burns, acute pancreatitis (see PANCREAS, DISORDERS OF) and renal failure – the body’s reserves of protein become exhausted. This results in weight loss; reduction in muscle mass; a fall in the serum albumin (see ALBUMINS) and LYMPHOCYTE count; and an impairment of cellular IMMUNITY. Severely ill patients are unable to take adequate food by mouth to repair the body protein loss so that enteral or parenteral nutrition is required. Enteral feeding is through the gastrointestinal tract with the aid of a nasogastric tube; parenteral nutrition involves the provision of carbohydrate, fat and proteins by intravenous administration.

The preferred route for the infusion of hyperosmolar solutions is via a central venous catheter (see CATHETERS). If parenteral nutrition is required for more than two weeks, it is advisable to use a long-term type of catheter such as the Broviac, Hickman or extra-corporeal type, which is made of silastic material and is inserted via a long subcutaneous tunnel; this not only helps to ?x the catheter but also minimises the risk of ascending infection.

Dextrose is considered the best source of carbohydrate and may be used as a 20 per cent or 50 per cent solution. AMINO ACIDS should be in the laevo form and should contain the correct proportion of essential (indispensable) and non-essential amino acids. Preparations are available with or without electrolytes and with or without fat emulsions.

The main hazards of intravenous feeding are blood-borne infections made possible by continued direct access to the circulation, and biochemical abnormalities related to the composition of the solutions infused. The continuous use of hypertonic solutions of glucose can cause HYPERGLYCAEMIA and glycosuria and the resultant POLYURIA may lead to dehydration. Treatment with INSULIN is needed when hyper-osmolality occurs, and in addition the water and sodium de?cits will require to be corrected.... parenteral nutrition

Hypodipsia

n. pathological failure to drink enough to maintain the body’s normal plasma osmolality. Like its most extreme form, adipsia, it is most commonly due to lesions of the thirst centre in the anterior hypothalamus.... hypodipsia

Osmolar Gap

the difference between the measured serum osmolality and the calculated osmolality using the following formula:

It is an aid to the diagnosis of severe *anion gap acidoses. The normal range for the difference is ± 10 mOsm/kg. A high osmolar gap is normally due to the presence of acetone, mannitol, or an alcohol.... osmolar gap

Peripheral Parenteral Nutrition

(PPN) the delivery of nutrients directly into a peripheral vein (in the arm). Feed solutions must have a low *osmolality (<1200 mOsm/l), and PPN can be given only for a short period (less than four weeks). There is a risk of *phlebitis. See artificial nutrition and hydration; total parenteral nutrition.... peripheral parenteral nutrition

Water-deprivation Test

a test for *diabetes insipidus in which fluid and food intake is withheld completely for up to 24 hours, with regular measurement of plasma and urinary *osmolality and body weight. Normally (and in a person with psychogenic *polydipsia) the output of *vasopressin will be increased in order to concentrate the urine as the plasma osmolality rises; correspondingly, the urine osmolality also rises and its volume diminishes. In a patient with diabetes insipidus, however, the urine osmolality will remain low and of high volume while the patient steadily dehydrates. The test must be abandoned if the patient loses 3% of body weight.... water-deprivation test

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