2 types of metabolic alkalosis (ie, chloride-responsive, chloride-resistant) are classified based on the amount of chloride in the urine :
* Chloride-responsive metabolic alkalosis involves urine chloride levels of less than 10 mEq/L and is characterized by decreased ECF volume and low serum chloride levels, such as occurs with vomiting. This type responds to administration of chloride salt.
* Chloride-resistant metabolic alkalosis involves urine chloride levels of more than 20 mEq/L and is characterized by increased ECF volume. This type resists administration of chloride salt. Primary aldosteronism is an example of chloride-resistant metabolic alkalosis.
MEDICAL CARE :
Mild or moderate metabolic alkalosis or alkalemia rarely requires correction. For severe metabolic alkalosis, therapy should address the underlying disease state, in addition to moderating the alkalemia. As with correction of any electrolyte or acid-base imbalance, the goal is to prevent life-threatening complications with the least amount of correction. The initial target pH and bicarbonate level in correcting severe alkalemia is approximately 7.55 and 40 mmol/L, respectively, not values within the reference range.
Consider the severity of hypovolemia or hypokalemia and the degree of alkalosis when managing metabolic alkalosis due to chloride loss from vomiting or other GI losses.
Children with protracted vomiting, whether due to pyloric stenosis or other causes, may develop hypovolemic shock. Intravascular volume expansion with isotonic crystalloid solution is needed, and monitoring of central venous pressure to determine adequacy of volume resuscitation is recommended.
Administer potassium as a chloride salt to patients with hypokalemia to help replenish chloride losses. However, remember that using potassium chloride (KCl) alone to correct hypochloremia is limited because the KCl infusion rate cannot exceed prescribed safe levels.
For persistent severe metabolic alkalosis, administration of HCl or ammonium chloride (NH4Cl) may be considered.
Acetazolamide may help patients with chloride-resistant metabolic alkalosis.
Correction of metabolic alkalosis in patients with renal failure may require hemodialysis or continuous renal replacement therapy with a dialysate that contains high levels of chloride and low levels of HCO3.
Temporary discontinuation of chloruretic diuretics (eg, furosemide, bumetanide, ethacrynic acid) may help patients with metabolic alkalosis due to long-term diuretic use. Potassium-sparing diuretics and carbonic anhydrase inhibitors may be used in patients who require continued diuretic therapy. Patients with accompanying ECF volume contraction occasionally require sodium and potassium administration. If continued diuretic use is indicated, potassium salt supplements may help avoid metabolic alkalosis.
Manage the specific disease that led to metabolic alkalosis.
DRUG TREAYMENT :
1. Chloride solutions -- These solutions are the recommended therapeutic agents for rapid correction of severe metabolic alkalosis, especially metabolic alkalosis due to gastric losses of chloride.
A - Hydrochloric acid (HCl) -- Amount required to correct metabolic alkalosis is determined by estimating the amount of pH deficit, the volume, and the infusion rate of HCl solution.
IV HCl may be indicated in severe metabolic alkalosis (pH >7.55) or when NaCl or KCl cannot be administered because of volume overload or advanced renal failure. May also be indicated if rapid correction of severe metabolic alkalosis is warranted (eg, cardiac arrhythmia, hepatic encephalopathy, digoxin toxicity).
Typical preparation contains 0.1 N solution (ie, 100 mmol H+/L [mEq/L]) in D5W or 0.9% NaCl.
ADULT DOSE : IV via central venous catheter: H+ ion deficit (mEq): 0.3 X weight (kg) X (measured HCO3 - desired HCO3 [mEq/L])
Rate of H+ replacement: 0.1-0.2 mEq/kg/h
For example, 0.1 N solution IV at 100 mL/h provides about 10 mEq/h
Do not use HCl solutions with concentrations >0.2 N (increased venous irritation and potential hemolysis); concentrations >0.1 N have been reported to cause corrosive effects, even when administered through a central venous catheter; injection of HCl into a peripheral vein may cause extravasation and can produce severe tissue necrosis; monitor ABGs and serum electrolyte levels
B - Ammonium chloride (NH4Cl) -- Administer to correct severe metabolic alkalosis related to chloride deficiency. NH4Cl is converted to ammonia and HCl by the liver. By releasing HCl, NH4Cl may help correct metabolic alkalosis.
Available as 500-mg tabs and 26.75% parenteral for IV use. Parenteral contains 5 mEq/mL (267.5 mg/mL).
Adult Dose : 8-12 g/d PO divided q6h
1.5 g IV q6h; dilute solution to concentration <0.4 mEq/mL; not to exceed infusion rate of 1 mEq/kg/h
Pediatric Dose 75 mg/kg/d PO/IV divided q6h; not to exceed 6 g/d and an infusion rate of 1 mEq/kg/h; dilute solution to concentration <0.4 mEq/mL
C - Potassium chloride (Clor-Con, K-Tab, K-Dur) -- Essential for transmission of nerve impulses, contraction of cardiac muscle, and maintenance of intracellular tonicity, skeletal and smooth muscles, and normal renal function.
Adult Dose 20-120 mEq PO qd
Up to 20 mEq/dose IV; dilute in >500 mL IV fluid for peripheral line infusion or >100 mL for central line infusion; not to exceed administration rate of 10 mEq/h unless cardiac monitoring in place
Pediatric Dose 0.5-1 mEq/kg/dose IV; dilute in adequate IV fluid before administering by either peripheral or central IV; not to exceed administration rate of 10 mEq/h unless cardiac monitoring in place
D. - Carbonic anhydrase inhibitors -- These agents may be used to treat chloride-resistant metabolic alkalosis.
- Acetazolamide (Diamox) -- A carbonic anhydrase inhibitor that blocks HCO3 reabsorption in the proximal renal tubules. A recent study demonstrated that acetazolamide causes increased renal excretion of sodium vs chloride, causing a net increase in serum chloride. Acetazolamide is also a diuretic and, therefore, may help decrease ECF volume that frequently accompanies chloride-resistant metabolic alkalosis.
Adult Dose 5-10 mg/kg/d PO/IV divided q6h
Pediatric Dose 5 mg/kg PO qd/qod
8-30 mg/kg/d IV/IM divided q6-8h; not to exceed 1 g/d