Hypertonic and hypotonic

It has been also observed that hypertonic and hypotonic salt solutions tend to irritate sensitive tissue and cause pain when applied to mucous membranes of the eye, ear, and nose, etc., whereas isotonic solution causes no tissue irritation when it comes in contact with the tissue. Obviously, the tonicity of formulations that come in to direct contact with blood, muscle, eye, nose, and delicate tissues is critical. Therefore, the issue of tonicity is important in small- and large-volume injectables, ophthalmic products, and products intended for tissue irrigation. The degree of tissue irritation or hemolysis or crenation observed depends on the degree of deviation from isotonicity, the volume injected, the speed of injection, the concentration of the solutes in the injection, and the nature of the membrane. The parenteral and ophthalmic formulations are therefore adjusted to isotonicity if possible. 

The Effect of Hypertonic and Hypotonic Solutions on Animal Cells. 

The effect of hypertonic and hypotonic solutions on the cell, (a) Crenation occurs when blood cells are surrounded by a hypertonic solution (water leaving > water entering), (b) Cell rupture occurs when cells are surrounded by a hypotonic solution (water entering > water leaving), (c) Cell size remains unchanged when surrounded by an isotonic solution (water entering = water leaving). 

Iso-osmotic is a physico-chemical concept and only depends on the concentration of dissolved molecules and ions. Isotonicity is the concept that takes into account, as well, the properties of the biological membrane in relation to the type of dissolved substances. Thus isotonicity should be interpreted as a physiological concept. Therefore, in this context it is better to speak of selectively permeable instead of semi-permeable. For most applications or routes of administration (bio-membranes), the number of substances for which there is a difference between iso-osmotic and isotonic is limited. For this reason, terms such as hypertonic and hypotonic are commonly used while actually hyper- or hypo-osmotic, respectively, are meant. 

Body fluids, including blood and tears, have the same osmotic pressure as that of a 0.9% w/v sodium chloride solution. Solutions having the same osmotic pressure as that of 0.9% w/v NaCl solution are said to be isotonic with blood. Solutions with a higher osmotic pressure than body fluids are called hypertonic and those with a lower osmotic pressure are called hypotonic. 

A nephron, showing the major sites and percentage (in braces) of sodium absorption along with other features of solute transport. The filtered load = GFR (180 L/day) Xplasma Na+ (140 mEq/L) or 25,200 mEq/day. About 1% of this amount is excreted in voided urine. Sites where tubular fluid is isosmotic, hypertonic, or hypotonic relative to plasma are shown. POT, proximal convoluted tubule LH, loop of Henle DOT, distal convoluted tubule CCD, cortical collecting duct TAL, thick ascending loop. 

Eye drops are often formulated to be isotonic with tear fluid but deviations from tonicity do not cause problems, although hypertonicity may cause stinging of the eye and hypotonicity may increase the permeability of the cornea. 

Crystalloid solutions consist of electrolytes in water. Crystalloid solutions may be isotonic, hypertonic or hypotonic. Isotonic solutions have approximately the same osmolality as plasma and, therefore, may be given rapidly in large volumes into peripheral veins. Hypertonic solutions act to draw water into the extracellular fluid (ECF) from the intracellular fluid and represent a method of rapidly restoring circulating volume at the expense of tissue hydration. Hypotonic solutions are usually only used to correct plasma hypertonicity. Because true hypotonic solutions (e.g. sterile water) cause erythrolysis (Krumbhaar 1914), they can only be given slowly via a central vein (Worthley 1986). For this reason, isotonic solutions containing a metabolizable substrate, such as dextrose, and no electrolytes are usually used. 

Nonionic contrast media in either hypertonic or hypotonic solution, when injected in-tracerebrally or into the subarachnoid space of rats, will cause distinct depression of the central nervous system (CNS) and associated brain functions but no excitation (675). Such depressive action can obscure the excitatory action caused by ionicity or chemotoxicity of myelographic agent. When an isotonic contrast medium is injected and mixed with the normally produced cerebrospinal fluid (CSF) in the subarachnoid space of the rat, the resultant mixture is hypertonic with higher levels of sodium and chloride. This movement of sodium and chloride into CSF without accompaniment of water is unexpected. Mennini et al. (672) noted that contrast enhancement of brain parenchyma is never achieved by direct intracarotid or intravenous injection of nonionic contrast media, unless the BBB is spontaneously or experimentally broken ( 6). 

Like boiling-point elevation and freezing-point depression, osmotic pressure is directly proportional to the concentration of solution. This is what we would expect, because all colligative properties depend only on the number of solute particles in solution. If two solutions are of equal concentration and, hence, have the same osmotic pressure, they are said to be isotonic. If two solutions are of unequal osmotic pressures, the more concentrated solution is said to be hypertonic and the more dilute solution is described as hypotonic (Figure 12.14). 

Aperture impedance measurements of cell volume must take into account the osmolaUty and pH of the medium. A hypotonic medium causes cells to swell a hypertonic medium causes them to shrink. Some manufacturers of aperture impedance counters deHberately provide hypertonic electrolytic media for red blood cell measurements. The shmnken red cells not only become more nearly spherical and thus less affected by orientation, but also less deformable than cells in isotonic media and thus less affected by differences in hemoglobin content. 

Some types of injections must be made iso-osmotic with blood serum. This applies particularly to large-volume intravenous infusions if at all possible hypotonic solutions cause lysis of red blood corpuscles and thus must not be used for this purpose. Conversely, hypertonic solutions can be employed these induce shrinkage, but not lysis, of red cells which recover their shape later. Intraspinal injections must also be isotonic, and to reduce pain at the site of injection so should intramuscular and subcutaneous injections. Adjustment to isotonicity can be determined by the following methods. 

Fluids can be classified further according to their tonicity. Isotonic solutions (i.e., normal saline or 0.9% sodium chloride [NaCl]) have a tonicity equal to that of the ICF (approximately 310 mEq/L or 310 mmol/L) and do not shift the distribution of water between the ECF and the ICF. Because hypertonic solutions (i.e., hypertonic saline or 3% NaCl) have greater tonicity than the ICF (greater than 376 mEq/L or 376 mmol/L), they draw water from the ICF into the ECF. In contrast, hypotonic solutions (i.e., 0.45% NaCl) have less tonicity than the ICF (less than 250 mEq/L or 250 mmol/L) leading to an osmotic pressure gradient that pulls water from the ECF into the ICF. The tonicity, electrolyte content, and glucose content of selected fluids are shown in Table 24—3. 

Hyponatremia is very common in hospitalized patients and is defined as a serum sodium concentration below 136 mEq/L (136 mmol/L). Clinical signs and symptoms appear at concentrations below 120 mEq/L (120 mmol/L) and typically consist of agitation, fatigue, headache, muscle cramps, and nausea. With profound hyponatremia (less than 110 mEq/L [110 mmol/L]), confusion, seizures, and coma maybe seen. Because therapy is also influenced by volume status, hyponatremia is further defined as (1) hypertonic hyponatremia (2) hypotonic hyponatremia with an increased ECF volume (3) hypotonic hyponatremia with a normal ECF volume and (4) hypotonic hyponatremia with a decreased ECF volume.16... 

Commonly administered LVPs include such products as Lactated Ringers Injection USP, Sodium Chloride Injection USP (0.9%), which replenish fluids and electrolytes, and Dextrose Injection USP (5%), which provides fluid plus nutrition (calories), or various combinations of dextrose and saline. In addition, numerous other nutrient and ionic solutions are available for clinical use, the most popular of which are solutions of essential amino acids or lipid emulsions. These solutions are modified to be hypertonic, isotonic, or hypotonic to aid in maintaining both fluid, nutritional, and electrolyte balance in a particular patient according to need. Indwelling needles or catheters are required in LVP administration. Care must be taken to avoid local or systemic infections or thrombophlebitis owing to faulty injection or administration technique. 

It is important that injectable solutions that are to be given intravenously are isotonic, or nearly so. Because of osmotic pressure changes and the resultant exchange of ionic species across red blood cell membranes, nonisotonic solutions, particularly if given in quantities larger than 100 mL, can cause hemolysis or cre-nation of red blood cells (owing to hypotonic or hypertonic solutions, respectively). Dextrose, sodium chloride, or potassium chloride is commonly used to achieve isotonicity in a parenteral formula. 

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