Bicarbonate therapy metabolic alkalosis with

In metabolic alkalosis and respiratory acidosis, pH does not usually deviate significantly from normal, but treatment can be required to maintain Pao2 and PaC02 at acceptable levels. Treatment should be aimed at decreasing plasma bicarbonate with sodium and potassium chloride therapy, allowing renal excretion of retained bicarbonate from diuretic-induced metabolic alkalosis. 

Acidosis and alkalosis are infrequent. Metabolic acidosis is a side effect of acetazolamide therapy and is due to bicarbonate loss in the PCT. All the K+-sparing diuretics can cause metabolic acidosis by H+ retention in the cells of the collecting duct. Metabolic alkalosis is associated with the loop and thiazide drugs. Reflex responses to volume depletion cause reabsorption of HCO-3 in the PCT and H+ secretion in the collecting tubule. 

Metabolic alkalosis may also be generated by the gain of exogenous alkali. This may be seen as a result of bicarbonate administration or from the infusion of organic anions that are metabolized to bicarbonate, such as acetate, lactate, and citrate. The milk-alkali syndrome was historically a common cause of metabolic alkalosis in patients with peptic ulcer disease secondary to the ingestion of large quantities of milk products and antacids. This syndrome has become increasingly uncommon with the advent of alternative effective therapies for dyspeptic syndromes. 

The administration of bicarbonate is to be used with cautioa The indiscriminate use of bicarbonate is particularly dangerous in resuscitation of patients with metabolic acidosis as a concomitant of hypovolaemic shock lactic acid itself is innocuous and is readily removed by the liver as soon as the perfusion of the tissues is re-established. If administration of bicarbonate causes alkalosis and shifts the oxygen dissociation curve to the left, there is interference with oxygen unloading at the cellular level in tissues which are already hypoxic. Treatment of metabolic acidosis by bicarbonate therapy is reserved for situations in which partial correction of the pH is needed to restore cardiac function, which is depressed by acidaemia as described in Chapter 4. 

Diuretic therapy is a common iatrogenic origin of metabolic disturbances of acid-base physiology. Diuretics are administered for their naturetic properties particularly in patients with cardiac, hepatic, pulmonary and renal disease, to rid the body of excess extracellular fluid. When the loss of sodium is matched by losses of other extracellular electrolytes in proportion to their extracellular concentrations, no disturbance of acid-base balance occurs. In cases where there is a disproportionate loss of bicarbonate, the result is metabolic acidosis. Conversely when there is an exaggeration of loss of ammonium or chloride ions by comparison with sodium, this leads to metabolic alkalosis. 

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