Hypertonic fluids

Hypernatremia can result from water loss (e.g., diabetes insipidus [DI]) hypotonic fluid loss or, less commonly, hypertonic fluid administration or sodium ingestion. 

Figure 10-14 Ion and fluid movement in the nonpigmented ciliary epithelium. Na+ enters the nonpigmented ciliary epithelium from the stromal side either by diffusion or by NaVH+ exchange. Na+, the main cation involved in aqueous formation, is transported extraceUularly into the lateral intercellular channel by a Na+-K+-adenosine triphosphatase-dependent transport system. HC03 forms from the hydration of CO2, a reaction catalyzed by carbonic anhydrase. HC03", the major anion involved in aqueous formation, balances a portion of the Na+ being transported into the lateral intercellular channel. Cl" enters the intercellular space by a mechanism that is not understood. This movement of ions into the lateral intercellular space creates a hypertonic fluid, and water enters by osmosis. Because of the restriction on the stromal side of the channel, the newly formed fluid moves toward the posterior chamber. A rapid diffusional exchange of CO2 allows for its movement into the posterior chamber. (Adapted from Cole DF. Secretion of aqueous humor. Exp Eye Res 1977 25(suppl) l6l-176.)...

Gastric acid secretion can be inhibited by several mechanisms including acid in the stomach (pH 3 inhibits gastrin release), acid in the duodenum, the presence of fat in the pancreas, and hypertonic fluids or hyperglycemia. Somatostatin, a hormone produced by antral mucosal endocrine cells (D cells), inhibits the release of gastrin by directly inhibiting the parietal cells. Somatostatin is also present in other GI tissue and the pancreas. C cells, endocrine cells in the proximal small intestine, secrete secretin in response to mucosal acidification, which also decreases gastric secretion. 

Depletional hyponatremia (excess loss of Na ) is almost always accompanied by a loss of ECF water, but to a lesser extent tlian the Na loss. Hypovolemia is apparent in the physical examination (orthostatic hypotension, tachycardia, decreased skin turgor). Loss of isosmotic or hypertonic fluid is the cause and this can occur through renal or extrarenal losses. If urine Na is low (generally <10 mmol/L), the loss is extrarenal (see Figure 46-2) because the kidneys are properly retaining filtered Na in response to increased aldosterone (stimulated by the hypovolemia and hyponatremia). Causes of extrarenal loss of Na" in excess of H2O include losses from the gastrointestinal tract or skin (see Figure 46-2). 

Potential adverse effects associated with hypertonic fluid administration for circulatory insufficiency include cellular crenation and damage caused by the dramatic fluid shifts, as well as peripheral vein destruction from their high osmolality. Also, in the case of hypertonic sodium chloride solutions, there are the possibilities of neurologic damage from hypernatremia and hyperchloremic metabolic acidosis from hyperchloremia. In the limited number of studies conducted in humans to date, such adverse effects have been uncommon and apparently of little clinical importance. ... 

Patieuts who have iugested large amouuts of sodium [>4 tablespoons (1,400 ruEq Na+) of sodium chloride] or who have received greater thau 5 L of hypertonic fluids are volume expanded, although this may not always be cUuically evident as edema. This results in an osmotic diuresis, polyuria, and a urine osmolality greater than 300 mOsm/kg. The excess sodium wiU be excreted in the urine in patients with normal renal function. 

Hypertonic fluids have a higher concentration of solutes (hyperosmolality) than is found inside the cells, which causes fluid to flow out of the cells and into the extracellular spaces. This causes cells to shrink. 

A loss of fluid from the body without loss of sodium can lead to hypovolemia and concentration of sodium and hypernatremia. Fluid then is hypertonic and can cause cellular shrinkage owing to fluids moving out of cells in an attempt to balance the hypertonic fluid. The symptoms of fluid imbalance can be accompanied by symptoms of electrolyte imbalance and shifts in other electrolytes that occur in an attempt to balance electrolytes. 

Administration of oxytocin may result in fetal bradycardia, uterine rupture, uterine hypertonicity, nausea, vomiting, cardiac arrhythmias, and anaphylactic reactions. Serious water intoxication (fluid overload, fluid volume excess) may occur, particularly when the drug is administered by continuous infusion and the patient is receiving fluids by mouth. When used as a nasal spray, adverse reactions are rare. 

A substrate is a substance that is the basic component of an organism. Protein substrates are amino acids, which are essential to life Protein substrates are amino acid preparations that act to promote the production of proteins (anabolism). Amino acids are necessary to promote synthesis of structural components, reduce the rate of protein breakdown (catabolism), promote wound healing, and act as buffers in the extracellular and intracellular fluids. Crystalline amino acid preparations are hypertonic solutions of balanced essential and nonessential amino acid concentrations that provide substrates for protein synthesis or act to conserve existing body protein. 

Example, sodium-rich medications, sodium bicarbonate, hypertonic IV fluids, nutrition, enemas, dialysis, plasma products (sodium citrate content)... 

Therapeutic fluids include crystalloid and colloid solutions. The most commonly used crystalloids include normal saline, hypertonic saline, and lactated Ringer s solution. Examples of colloids include albumin, the dextrans, hetastarch, and fresh frozen plasma. 

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. 

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. 

Regulation of the osmolarity of extracellular fluid, including that of the plasma, is necessary in order to avoid osmotically induced changes in intracellular fluid volume. If the extracellular fluid were to become hypertonic (too concentrated), water would be pulled out of the cells if it were to become hypotonic (too dilute), water would enter the cells. The osmolarity of extracellular fluid is maintained at 290 mOsm/1 by way of the physiological regulation of water excretion. As with sodium, water balance in the body is achieved when water intake is equal to water output. Sources of water input include ... 

Adding an isotonic solution to the extracellular fluid (ECF) does not change intracellular volume. Adding a hypertonic solution to the ECF decreases cell volume, whereas adding a hypotonic solution increases it (Table 78-1). 

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. 

Osmotic effects are very important from a physiological standpoint. This is because biological membranes including the membrane of red blood cells behave like semipermeable membranes. Consequently, when red blood cells are immersed in a hypertonic solution (e.g., D5 A NS or D5NS), they shrink as water leaves the blood cells in an attempt to dilute and establish a concentration equilibrium across the blood cell membrane. Thus, when hypertonic solutions are administered into the blood stream, the fluid moves from interstitial and cellular space into the intravascular space. Conversely, when cells are placed in hypotonic environment (e.g., V2 NS), they swell because of the entry of fluid from the intravascular compartment, and may eventually undergo lysis. 

Thin ascending limb Fluid entering is hypertonic. The limb is impermeable to water but ion transport does occur, which causes the urine osmolarity to fall. 

Rabinovici R, Rudolph A8, Vernick J, et al. A new salutary resuscitative fluid liposome encapsulated hemoglobin/hypertonic saline solution. J Trauma 1993 35 121. 

Neonates and children (younger than 2 years of age) - Rapid injection (10 mL/min) of hypertonic sodium bicarbonate solutions may produce hypernatremia, a decrease in cerebrospinal fluid pressure and possible intracranial hemorrhage. Do not administer more than 8 mEq/kg/day. A 4.2% solution is preferred for such slow administration. 

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