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Sodium Bicarbonate Deficit Calculator
The authors make no claims of the accuracy of the information contained herein; and these suggested doses and/or guidelines are not a substitute for clinical judgment. Neither GlobalRPh Inc. nor any other party involved in the preparation of this document shall be liable for any special, consequential, or exemplary damages resulting in whole or part from any user's use of or reliance upon this material.    PLEASE READ THE DISCLAIMER CAREFULLY BEFORE ACCESSING OR USING THIS SITE. BY ACCESSING OR USING THIS SITE, YOU AGREE TO BE BOUND BY THE TERMS AND CONDITIONS SET FORTH IN THE DISCLAIMER.

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Background:

In all cases, the primary goal in treating metabolic acidosis is to focus on reversal of the underlying process causing the acidosis.  Examples:  (1) Renal failure: dialysis if needed.
(2) Alcoholic ketoacidosis: fluids, electrolytes, thiamine, folic acid.  (3) Sepsis/shock: volume resuscitation, vasopressors, etc.  (4) Salicylate intoxication:  IV fluids, alkalinization of the urine, ....   

If there is a severe deficit (HCO3- < 10-12 mEq/L and pH<7.2) correct with sodium bicarbonate.    Sodium bicarb is also useful if the acidosis is due to inorganic acids (especially if renal disease is present).  However, when the acidosis results from organic acids (lactic acid, acetoacetic acid, etc) the role of bicarbonate is controversial.  In most cases of DKA or severe lactic acidosis the administration of sodium bicarbonate does not decrease mortality even when the acidosis is severe.  In sum, sodium bicarbonate should be reserved for severe cases of acidosis only (pH <7.2 and serum bicarbonate levels <10-12 meq/L).  This can be accomplished by adding 1 to 3 ampoules of sodium bicarb to D5W or 1/2NS.   IV-push administration should be reserved for cardiac life support and not metabolic acidosis.


Sodium bicarbonate administration: It is recommended that 50% of total deficit be given over 3 to 4 hours, and the remainder replaced over 8-24 hours. The usual initial target ((desired HCO3- concentration): 10 - 12 mEq/L, which should bring the blood pH to ~7.20. The subsequent goal is to increase the bicarbonate level to 15 meq/L over the next 24 hours.


Koda-Kimble et al:
Replace 50% over 3 to 4 hours and the reminder over 24 hours.  Once the pH is 7.2 - 7.25, the serum [HCO3-] should not be increased by more than 4 to 8 mEq/L over 6 to 12 hours to
avoid the risks of over-alkalinization (paradoxical CNS acidosis; decreased affinity of hemoglobin for oxygen leading to tissue hypoxia and lactic acid production; sodium overload; and hypokalemia).




Format:  [Reference;  Recommendation.]

Reference:

Kurtz I. Acid-Base Case Studies. 2nd Ed. Trafford Publishing (2004); 68:150.

Recommendation:
"Following the acute administration of bicarbonate as a bolus, its effect on the systemic pH will be maximal. Over the subsequent hours, the bicarbonate which was originally administered will be taken up into cells. In addition, the elevation of systemic pH decreases the compensatory ventilatory response. These two effects will decrease the systemic pH from the maximum value that was obtained immediately following the administration of bicarbonate."  Effective volume of distribution of bicarbonate varies with the HCO3- concentration:
Bicarb Vd = (0.4 + 2.6/HCO3-) x Lean body weight.

Bicarbonate deficit = Bicarb Vd x (desired [HCO3-] - measured [HCO3-])


Lean body weight defined as usual IBW equations:
Estimated ideal body weight in (kg):
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.

Important points:
1] Greater degree of metabolic acidosis --> Greater increases in bicarb Vd ---> Larger amounts of bicarb must be administered.

2] Following admin of bicarb (as a bolus), there is a time-dependent decrease in blood HCO3- conc. A portion of the  HCO3- which is initially distributed in the ECF space, subsequently enters the intracellular space.

3] As the blood HCO3- concentration increases, the PCO2 increases as a result of a decrease in alveolar ventilation.

Reference:

Ewald G, McKenzie C (editors). Manual of Medical Therapeutics, 28th edition. Little, Brown and Company. 1995. page 59 and 63.

Since the distribution of bicarbonate is about 50% of lean body weight, ... serum concentration to normal can be estimated as follows: 
HCO3~ deficit (mEq) =  0.5 x lean body wt (kg) x (desired [HCO3-] - measured [HCO3-])

Lean body weight defined as usual IBW equations:
Estimated ideal body weight in (kg):
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.


Reference:

Ghosh A, Habermann TM. Mayo Clinic Internal Medicine Concise Textbook. CRC Press, 2007. p.599:914.

Bicarbonate deficit = 0.2 x weight (kg) x base deficit (mEq/L).

Reference:

Kollef MH, Bedient TJ, Isakow W, Witt CA. The Washington Manual of Critical Care. Lippincott Williams & Wilkins, 2007; p185:583.

"Primary goal in treating metabolic acidosis is reversal of the underlying process. Administration of bicarbonate in controversial, as some clinical parameters may actually worsen... " "However, partial correction should be considered in the setting of life-threatening metabolic acidosis(pH<7.1) or when the serum bicarbonate is low enough (i.e., <10 to
12 mEq/L) that loss of effective respiratory compensation would result in life-threatening acidosis."
Bicarbonate deficit:  The amount of bicarbonate req'd to correct a metabolic acidosis can be estimated from the following formula:

  Volume of distribution (Vd) = Total body weight (kg) x [0.4 + (2.4/[HCO3-])
      (Deficit) mEq of NaHCO3 = Vd x target change in [HCO3-]

Reference:

Koda-Kimble M, Young LY, et al. Handbook of Applied Therapeutics. Lippincott Williams & Wilkins, 2006. P10.3(1104).

It is important to correct the underlying cause and to administer IV bicarbonate to maintain a pH >7.2-7.25.
Bicarbonate dose (mEq): 0.5 (L/kg) x Body weight (kg) x Desired increase in serum HCO3- (mEq/L)

Replace 50% over 3 to 4 hours and the reminder over 24 hours.  Once the pH is 7.2 - 7.25, the serum [HCO3-] should not be increased by more than 4 to 8 mEq/L over 6 to 12 hours to
avoid the risks of over-alkalinization (paradoxical CNS acidosis; decreased affinity of hemoglobin for oxygen leading to tissue hypoxia and lactic acid production; sodium overload; and hypokalemia.

Risk of long-term HCO3- admin:
[1] Excess HCO3- converted to H2CO3-, then to CO2 gas, causing paradoxical metabolic acidosis with rapid penetration of CO2 gas into CNS.
[2] Decreased O2 release from hemoglobin.
[3] Arrhythmogenic.
[4] Increased serum osmolality.


Reference:

http://www.medal.org:
In severe metabolic acidosis, bicarbonate may be given to correct the base deficit in the extracellular fluid within 24 hours. Parenteral bicarbonate therapy may be considered in patients when the pH is below 7.2 and should be discontinued once the pH reaches 7.2

Disclaimer

Listed dosages are for - Adult patients ONLY. PLEASE READ THE DISCLAIMER CAREFULLY BEFORE ACCESSING OR USING THIS SITE. BY ACCESSING OR USING THIS SITE, YOU AGREE TO BE BOUND BY THE TERMS AND CONDITIONS SET FORTH IN THE DISCLAIMER. GlobalRPH does not directly or indirectly practice medicine or provide medical services and therefore assumes no liability whatsoever of any kind for the information and data accessed through the Service or for any diagnosis or treatment made in reliance thereon.

David F. McAuley, Pharm.D., R.Ph.  GlobalRPh Inc.
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