endocrine and metabolic disorders
Metabolic Acidosis
Treatment of Metabolic Acidosis
Cause treated Sodium bicarbonate(NaHCO3) primarily for severe acidemia—give with caution Treatment is directed at the cause. Hemodialysis is required for renal failure and sometimes for ethylene glycol, methanol, or salicylate poisoning. Treatment of acidemia withsodium bicarbonate(NaHCO3) is clearly indicated only in certain circumstances and is probably deleterious in others. When metabolic acidosis results from loss of HCO3−or accumulation of inorganic acids (ie, normal anion gap acidosis), bicarbonate therapy is generally safe and appropriate. However, when acidosis results from organic acid accumulation (ie, high anion gap acidosis), bicarbonate therapy is controversial; it does not clearly decrease mortality in these conditions, and there are several possible risks. also requires adequate minute ventilation. Patients with compromised respiratory status due to underlying pulmonary disease may not be able meet the increased minute ventilation. Patients requiring Ventilatory Failure will need appropriate ventilator settings to account for increased minute ventilation. Despite these and other controversies, most experts recommend giving bicarbonate IV for severe metabolic acidosis (pH<7.0) primarily because of concerns about worsening cardiovascular instability at lower pH values. Treatment requires 2 calculations (same for both conventional and SI units). The first is the level to which HCO3−must be raised, calculated by the Kassirer-Bleich equation, using a target value for [H+] of 79 nEq/L (79 nmol/L), which corresponds to a pH of 7.10: 79=24×Pco2/HCO3− or Desired HCO3−=0.30×Pco2 The amount ofsodium bicarbonateneeded to achieve that level is NaHCO3required (mEq/mmol)=(desired [HCO3−]−observed [HCO3−])×0.4×body weight (kg) For example, a 70-kg man has severe metabolic acidosis with a pH of 6.92, PCO2of 40 mmHg, and HCO3−of 8 mEq/L (8 mmol/L). The target bicarbonate level needed to achieve a pH of 7.10 is 0.30 × 40 = 12 mEq/L (12 mmol/L). This level is 4 mEq/L (4 mmol/L) more than his current bicarbonate level of 8. To increase bicarbonate by 4, multiply 4 by 0.4 times 70 (the body weight), giving a result of 112 mEq (112 mmol) of HCO3−. This amount ofsodium bicarbonateis given over several hours. Blood pH and HCO3−levels can be checked 30 minutes to 1 hour after administration, which allows for equilibration with extravascular HCO3−. There is no consensus regarding the concentration of bicarbonate solution to use, but it is important to realize that the typical 50-mL ampule of NaHCO3contain 50 mEq ofsodium bicarbonateand can worsen volume overload and also cause hyperosmolality especially if multiple ampules are given over a short period time. Iso-osmotic formulations such as 75 mEq NaHCO3mixed with 1 L of 0.45% saline and 150 mEq NaHCO3mixed with 1 L of sterile water are also used. Alternatives tosodium bicarbonateinclude Lactate, either in the form of lactated Ringer's solution orsodium lactate(metabolized mEq for mEq to bicarbonate when liver function is normal) Sodium acetate(metabolized mEq for mEq to bicarbonate when liver function is normal) Tromethamine, an amino alcohol that buffers both metabolic (H+) and respiratory (carbonic acid [H2CO3]) acid Carbicarb, an equimolar mixture ofsodium bicarbonateand carbonate (the latter consumes CO2and generates HCO3−) Dichloroacetate, which enhances oxidation of lactate These alternatives do not offer a proven benefit oversodium bicarbonatealone and can cause complications of their own. Potassium (K+) depletion, common in metabolic acidosis, should be identified through frequent serum K+monitoring and treated as needed with oral or parenteralpotassium chloride. 