|
|
Inputs
|
Height:
Weight:
|
|
Select Volume of distribution (VD) factor:
|
Select Dosing Weight:
|
Select current HCO3- Level:
|
|
Select desired or target HCO3- Level:
|
|
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:
https://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
|
