SESSION 2 BLOOD GAS ANALYSIS AND OSMOMETRY Lab Report

SESSION 2 BLOOD GAS ANALYSIS AND OSMOMETRY - Lab Report Example rescent molecule, it has to travel through an optical isolator( black coating) to prevent interference by unspecific light with the light detection system. Osmolality measures the total number of osmotically active particles in a solution and is equal to the sum of the molalities of all the solutes present in that solution. The four colligative properties are changed by the dissolving of the solute in solvent. Osmolarity refers to osmoles per litre, whilst osmolality refers to osmoles per kg water( There is a slight difference between plasma molality and molarity because of the non-acqueous components present such as proteins and lipids that make up about 60% of the total volume. Thus serum is only 94% water and the molality of a substance in serum is about 6% higher than its molarity. Molality is preferred because it is independent of temperature). The osmolality of physiological fluids is mainly determined by small molecules that are present in high concentrations. For example in serum, sodium, potassium, chloride, bicarbonate, urea and glucose are the only components present in high enough concentrations to individually affect the osmolality. Together these make up over 95% of total osmolality of serum. Larger serum molecules contribute little to the overall osmolality. A useful estimate of the osmolality is calculated from: The difference between the measured and the calculated osmolality is known as the osmolar gap. If there are unmeasured osmotically active species present then these will increase the gap. The normal osmolar gap is up to 10mmol/L and values in excess of this usually indicate the presence of an exogenous agent. The most common is ethanol, but methanol, the ethylene glycol, acetone and isopropyl alcohol will also contribute if present. Different causes of hyponatraemia can be distinguished by serum osmolality measurement. It is increased in hyperosmolar hyronatraemia(eg: hyperglycaemia), normal in psuedohyponatraemia and decreased in