Bicarbonate acid-base balance

This electrolyte plays a vital role in the acid-base balance of the body. Bicarbonate may be given IV as sodium bicarbonate (NaHC03) in the treatment of metabolic acidosis, a state of imbalance that may be seen in diseases or situations such as severe shock, diabetic acidosis, severe diarrhea, extracorporeal circulation of blood, severe renal disease, and cardiac arrest. Oral sodium bicarbonate is used as a gastric and urinary alkalinizer. It may be used as a single drug or may be found as one of the ingredients in some antacid preparations. It is also useful in treating severe diarrhea accompanied by bicarbonate loss. 

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Concentration limits for chloride and acetate in PN typically are linked to limitations for sodium and potassium. The usual ratio of chloride acetate in PN is about 1 1 to 1.5 1. Chloride and acetate primarily play a role in acid-base balance. Acetate is converted to bicarbonate at a 1 1 molar ratio. This conversion appears to occur mostly outside the liver. Bicarbonate never should be added to or coinfused with PN solutions. This can lead to the release of carbon dioxide and potentially result in the formation of calcium or magnesium carbonate (very insoluble salts). 

Along with the respiratory system, the renal system maintains acid-base balance by altering the excretion of hydrogen and bicarbonate ions in the urine. When the extracellular fluid becomes acidic and pH decreases, the... 

The C02-bicarbonate buffer is a little different from buffers using the usual kind of acids and bases, but it is extremely important in maintaining the acid-base balance of the blood. The acid form of the bicarbonate buffer is actually a gas dissolved in water. Dissolved C02 is turned into an acid by hydration to give H2C03. Hydrated C02 is then much like a carboxylic acid. It gives up a proton to a base and makes bicarbonate, HCO 3. 

The kidney regulates the acid-base balance of the body by control over resorption of sodium ions, which may exchange for hydrogen ions in the kidney tubule. Since most dietaries are of acid-ash, the urine is usually more acid than the original plasma filtrate and much of the phosphate excreted is thus changed to the acid monosodium salt, Within the range of normal variability, with an alkaline ash diet, the urine may become alkaline, and in extreme instances, some sodium bicarbonate may be excreted. 

It is not yet clear which estimates of the ratio between the levels of protein and of carbohydrate metabolism during hypoxia should be regarded as reliable. It seems likely that the increase in respiratory quotient in freshwater fish to values of 2.5-2.8, as found by Mohamed and Kutty (1983a, 1986), indicates a predominance of protein expenditure over that of carbohydrate. A hypoxic environment shifts the acid-base balance of the fish towards acidosis (Kotsar, 1976), thereby inducing the redistribution of electrolytes, alteration of ion exchange and the activity of Na+-K+-Mg2+-ATPases and alkaline phosphatases. It also leads to an increased level of C02 in the blood, which enhances the bicarbonate buffer system (Kotsar, 1976). In section 2.1, we... 

The kidneys not only secrete hydrogen ions but they also regenerate bicarbonate ions. The renal handling of electrolytes also influences acid-base balance. 

Bicarbonate Helps maintain acid—base balance Re-absorbed (80-90%) Re-absorbed, ascending loop Re-absorbed... 

If ingested, the formic acid should be diluted with milk or water in alert patients. Careful gastric aspiration with a nasogastric tube may be attempted to limit systemic absorption. The goal of the clinical management is to correct the acidosis. Acidosis may be treated with sodium bicarbonate or by hemodialysis. Immediate hemodialysis may remove formic acid from systemic circulation. Acid-base balance, electrolytes, and kidney function should be monitored closely. 

Sodium is an electrolyte (cation) in extracellular fluid (tissue spaces and vessels) and regenerates and transmits nerve impulses. Sodium affects water distribution inside and outside cells. Sodium also combines readily in the body with chloride (CL) or bicarbonate (HC03) to promote acid-base balance (Ph). 

Carbonic anhydrase inhibitors increase excretion of sodium, potassium, and bicarbonate by blocking carbonic anhydrase, which is an enzyme that maintains acid-base balance. Carbonic anhydrase inhibitors are contraindicated in the first trimester of pregnancy. 

Acid-base balance. The Henderson-Hasselbalch equation is also used to calculate theoretical bicarbonate and total CO2 concentrations when pH and PCO2 are measured. Theoretical and measured results generally agree within 2.0 mmol/L. 

A description of acid-base balance involves an accounting of the carbonic (H2C03, HCOh COa", and CO2) and noncar-bonic acids and conjugate bases in terms of input (intake plus metabolic production) and output (excretion plus metabolic conversion) over a given time interval. The acid-base status of the body fluids is typically assessed by measurements of total CO2 plasma pH and PCO2, because the bicarbonate/carbonic acid system is the most important buffering system of the plasma. Occasionally, measurement of total titratable acid or base, or other acid and base analytes (e.g., lactate and ammonia [NH3]) is necessary to determine the etiology of an acid-base disorder. 

Because bicarbonate is a small ion, it is freely filtered at the glomerulus. The bicarbonate load delivered to the nephron is approximately 4,500 mEq/day. To maintain acid-base balance, this entire filtered load must be reabsorbed. Bicarbonate reabsorption occurs primarily in the proximal tubule (Fig. 51-1). In the mbular lumen, filtered bicarbonate combines with hydrogen ion secreted by the apical Na+-H+-exchanger to form carbonic acid. The carbonic acid is rapidly broken down to CO2 and water by carbonic anhydrase located on the luminal surface of the brush border membrane. The CO2 then diffuses into the proximal tubular cell, where it reforms carbonic acid in the presence of intracellular carbonic anhydrase. The carbonic acid dissociates to form hydrogen ion, that can again be secreted into the tubular lumen, and bicarbonate that exits the cell across the basolateral membrane and enters the peritubular capillary. 

The question arises whether or not the changes in elimination due to the variations in the acid-base balance affect citric acid specifically. Melius and Lipton (M18) thus found that, in experimental alkalosis produced in rats after injection of bicarbonate, only about 50 % of the increase of urinary organic acids is due to citrate. Evans et al. (E8), who did not find the same result in man after bicarbonate administration, state also that citrate represents less than 50 % of the inerease of organic acids in urine produced in man by hyperventilation. 

The cationic charge in blood is neutralized by two major anions, Cl and HC03. The chloride ion plays a role in acid-base balance, maintenance of osmotic pressure within an acceptable range, and oxygen transport by hemoglobin. The bicarbonate anion is the form in which most waste CO2 is carried in the blood. 

If any two of the variables are known, the third can always be calculated. Indeed, blood gas analyzers (Fig. I) are programmed to provide this information which is printed out on the report I orni and usually includes the measured POi us well. There are a multitude of other calculated values oit some blood gas analyzer print outs, such as base excess and standard bicarbonate. These nitty be mostly disregarded in the routine assessment of a patient s acid-base balance. 

The bicarbonate ion (HCO3A is the second-largest anionic contributor to maintaining acid-base balance, and its secretion from the pancreas helps to neutralize the contents of the small intestine. Respiration controlling the carbon dioxide concentration of the blood (PaCOj) and renal excretion of bicarbonate are the two main homeostatic influences on plasma bicarbonate. Within the renal tubular lumen, carbonic anhydrase converts carbonic acid into carbon dioxide, which diffuses into the epithelial cells and forms carbonic acid, which later dissociates to bicarbonate. 

Therapeutic doses of salicylate produce definite changes in the acid—base balance and electrolyte pattern. Compensation for the initial event, respiratory alkalosis, is achieved by increased renal excretion of bicarbonate, which is accompanied by increased Na and excretion plasma bicar-... 

The carbonic anhydrase inhibitors block the action of the enzyme carbonic anhy-drase which is needed to maintain the acid-base balance (hydrogen and bicarbonate ion balance). Inhibition of this enzyme causes increased sodium, potassium, and bicarbonate excretion. Prolonged use can result in metabolic acidosis. 

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