Q: Recently my brother-in-law met with an accident. He broke his left hand and left foot for which he was operated. He is a diabetic and was given 6 bottles of natural saline. What is the purpose of giving natural saline as he did not suffer any loss of blood? Please throw some light on glucose (dextrose) and saline variants, when are they administered and what are they used for?

A:Intravenous (IV) therapy is the administration of fluids directly into a vein. Compared to other routes of administration, this is the fastest way to deliver fluids and medications throughout the body. The indications for it include: a) Establish or maintain fluid or electrolyte balance b) Administer continuous or intermittent medication c) Maintain or correct a patients nutritional state d) Administer diagnostic reagents e) Administer blood or blood components f) Administer fluid to keep vein open g) Monitor hemodynamic functions Patients suffering from blood or fluid loss due to trauma, diarrhoea, vomiting etc. require IV fluids to maintain normal blood pressure, replace ongoing loss and to provide glucose as a fuel for the brain. There are three main types of fluids: 1. Isotonic fluids contain an approximately equal number of molecules as blood (same osmolarity) so the fluid stays within the blood vessels thus expanding the blood volume. This is bacuse the fluid flows from lower concentration area to higher concentration of molecules by osmosis to achieve equilibrium or fluid balance. They are given in states when there is low blood pressure (hypotension) or blood/fluid loss (hypovolemia). Examples - Ringer’s lactate and normal saline. 2. Hypotonic fluids contain a lower number of molecules than blood (have less osmolarity than blood i.e. less sodium ion concentration than blood) so the fluid shifts from the blood vessels to the interstitial space. It dilutes the blood by decreasing its osmolarity. The water is pulled from the blood vessels into the interstitial fluid compartment. Then its osmolarity decreases which draws water into the adjacent cells. This decreases the interstitial space osmolarity (because of the increase of fluid and constant number of molecules within it) which causes fluid to move into the cells. This is helpful when cells are dehydrated as occurs in dialysis patients on diuretic therapy or diabetic patients with very high blood sugar. Examples - 0.45% NaCl or 2.5% dextrose. 3. Hypertonic fluids contain higher number of molecules than blood (higher osmolarity than blood). The fluid shifts from the interstitial space to blood vessels. This increases the interstitial space osmolarity (because of the loss of fluid and constant number of molecules within it) which causes fluid to leak out of the cells thus helping stabilise blood pressure, increase urine output and reduce oedema (swelling due to fluid accumulation). Examples - 5% dextrose and albumin. Intravenous fluids are of 2 types: Crystalloid (normal saline, Ringer’s lactate) are aqueous solutions of mineral salts or other water-soluble molecules. They are isotonic and are therefore effective volume expanders for a short period of time. However, both the water and the electrolytes in the solution can freely cross the semi-permeable membranes of the vessel walls (but not the cell membranes) into the interstitial space, and achieve equilibrium in two to three hours. Examples - sodium chloride solution at 0.9% concentration, which is close to the concentration in blood (isotonic); Ringer’s lactate; Dextrose 5% in water is used if the patient is having low blood sugar or high sodium. The choice of fluids depends on the chemical properties of the medications administered. Colloids (albumin) contain larger insoluble molecules (usually proteins) that are too large to pass out of the capillary membranes and remain within the blood vessels. The large protein molecules give colloid solutions a very high osmolarity due to which they draw fluid from the interstitial and intracellular compartments into the vascular compartment. They are used to reduce oedema (pulmonary or cerebral oedema) while expanding the vascular compartment. Physiologic crystalloids are cheap and widely available because they equilibrate freely across the intravascular and extra-vascular compartments, large volumes may be required to improve perfusion with the risk of fluid overload. However, large volumes of normal saline may cause hyperchloremic acidosis and with no glucose or potassium, its use in some cases of shock, acidosis or electrolyte imbalance could make matters worse. Ringers lactate is a physiologic solution and large volumes do not cause metabolic acidosis. The use of hypotonic solutions advocated by the WHO concerning about sodium overload in treatment of shock in patients with severe malnutrition may be appropriate when the primary problem is depletion of intracellular volume due to dehydration. Hypotonic solutions generally are not advocated for the correction of shock until the circulating volume has been restored with isotonic solutions or colloids. Colloids exert plasma oncotic pressure and offer improved perfusion with less risk of fluid overload. They are expensive, not widely available and are associated with safety concerns like coagulation and allergic reactions.