Short Review regarding Metabolic Acidosis The Causes, anion gap,urine osmolal gap, Renal Tubular Acidosis, approach to Metabolic Acidosis in Final Slide

1. Metabolic Acidosis
Dr.Samir Jha

2. • Acidosis : is a process that increases [H+]
• Acidemia: When blood pH <7.35
• Metabolic acidosis: When an acid other than
carbonic acid accumnulates in the body
resulting in fall in HCO3- .

3. • Mechanism:
• gain of H+
• loss of HCO3-
• Results in:
• ↓pH (7.35)
• ↓HCO3- (<22mEq/L)
• pCO2 depends on compensation

4. Anion gap
• ([Na+] + [K++) − (*Cl−] + [HCO3
−])
• Anion gap (AG) = [Na++ − (*Cl-] + [HCO3
−])
unmeasured anions subtracted by
unmeasured cations (in ECF)
• Omission of potassium has become widely
accepted, as potassium concentrations, being
very low, usually have little effect on the
calculated gap.
• Normal value: 3–11 mEq/L

5. • ↑AG = ↑ unmeasured anions such as organic
acids, phosphates, sulfates
• ↓AG = ↓ alb or ↑ unmeasured cations (Ca,
Mg, K, Li, bromine, immunoglobulin)

6. Low anion gap
• A low anion gap is frequently caused
by hypoalbuminemia. Albumin is a negatively charged protein and
its loss from the serum results in the retention of other negatively
charged ions such as chloride and bicarbonate. As bicarbonate and
chloride anions are used to calculate the anion gap, there is a
subsequent decrease in the gap.
• In hypoalbuminaemia the anion gap is decreased from between 2.5
to 3 mmol/L per 1 g/dL decrease in serum albumin. Common
conditions that reduce serum albumin in the clinical setting
are hemorrhage, nephrotic syndrome, intestinal obstruction and
liver cirrhosis.
• The anion gap is sometimes reduced in multiple myeloma, where
there is an increase in plasma IgG (paraproteinaemia).

7. • expected AG is [albumin] X2.5
(ie, 10 if albumin is 4 g/dL)

8. Causes
• Renal Tubular Acidosis
• Gastrointestinal Base Loss(loss of HC03-)
• Inorganic acid poisoning(addn of anions)
• Ureteral diversion
• Ketoacidosis: Diabetic, Starvation
• Lactic Acidosis
• Renal Failure
• Poisoning: Ethanol Glycol, Methanol, Aspirin,
Acetaminophen

9. Renal Failure
• Accumulation of organic anions such as
phosphates, sulphates, urate, etc

10. Lactic Acidosis
• Type A: impairment in tissue oxygenation, eg,
circulatory or
• acidosis respiratory failure, sepsis, ischemic
bowel, carbon monoxide, cyanide
• Type B: no impairment in tissue oxygenation,
eg, malignancy, alcoholism, meds (metformin,
NRTIs, salicylates, propylene glycol)

11. • Methanol (windshield fluid, antifreeze, solvents,
fuel): metab to formic acid
• Ethylene glycol (antifreeze): metab to glycolic
and oxalic acids
• Propylene glycol (pharmaceutical solvent, eg, IV
diazepam & lorazepam antifreeze): lactic acidosis
• Salicylates: metabolic acidosis (from lactate,
ketones) respiratory alkalosis due to stimulation
of CNS respiratory center
• Acetaminophen: glutathione depletion -> inc
endogenous organic acid 5-oxoproline in
susceptible host (malnourished, female, renal
failure)

12. Consequence of Acidemia on various
Organ System
Organ System Effect
Cardiovascular System Dec contractility, Arterial vasodilatation,
Dec MAP, Dec CO, Dec response to
Catecholamine, Inc risk of arrhythmias
Respiratory System Hyperventilation(compensatory), Dec
Respiratory Muscle Strength
Metabolic Inc Potassium(Due to H+/K+ pump
exchanging excess H+ with Intracellular K+)
Neurological Altered Mental Status

13. Investigation
• Evaluate history for causes(diarrhea, ingestion
of mineral acids/drugs, kidney diseases,
diabetes, any diversional surgery, starvation)
• For suspected ketonuria (dipstick
acetoacetate) or plasma hydroxybutyrate [as
urine aceto-acetate often not present in early
ketoacidosis due to shunting to ᵝOH butyrate,
aceto-acetate may later turn +ve]

14. If Ketones negative
• renal function, lactate(inc by about 10 fold in
lactic acidosis), toxin screen, and osmolal gap
• Osmolal gap (OG)=measured osmoles -
calculated Osmoles
• calculated osmoles
(2 XNa)+(glucose/18)+(BUN/2.8)
• OG>10 suggests ingestion

15. • In case of hyperchloraemic (normal anion gap)
acidosis with no evidence of gastrointestinal
disturbance and Urine pH is inappropriately
high>5.5 in +nce of systemic acidosis points
toward Renal Tubular Acidosis.

16. Proximal RTA (Type 2)
↓ proximal re-absorption of HCO3
E.g: Fanconi Syndrome, Multiple Myeloma,
Amyloidosis, Myeloma, Carbonic Anhydrase
inhibitor
Urinary pH <5.3, moderate acidosis, serum K+
normal or low

17. Classical Distal RTA (Type 1)
defective distal H+ secretion
E.g.: Congenital, Autoimmune(RA, Sjogren’s),
SLE, Drugs (Lithium, Amphotericin)
pH of a fresh sample of urine is > 5.5. Serum
potassium level is normal or low. Urine anion
gap is positive because of inadequate
hydrogen ion secretion

18. Hyperkalaemic distal RTA (type 4)
Hypoaldosteronism
Obstructive Nephropathy
Drugs: Amiloride, Spironolactone, ACEI, ARB,
NSAIDs
Diseases: Sickle cell, SLE, Amyloidosis
urine pH is < 5.5. Serum potassium level is
elevated. Urine anion gap is positive because
of defective NH3 generation.

19. Compensation
• Early compensation by repsiratory sytem by
hyperventilation wish washes out Co2 to
restore the pH level
• Late compensation is by kidneys which causes
excretion of H+ and retention of HCO3-

21. • Initially resuscitation with IV fluids is often
needed.
• DKA: insulin & IVF; dextrose, IVF, replete K,
Mg, PO4 as needed
• Lactic acidosis: treat underlying condition,
avoid vasoconstrictors
• Renal failure: hemodialysis
• Methanol & ethylene glycol: early fomepizole,
vit. B6 (ethylene glycol), folate(methanol),
hemodialysis (especially if late presentation)
• Alkali therapy: NaHCO3

22. • Use of IV bicarbonate is controversial
• Rapid correction causes hypokalemia or
reduced plasma ionised calcium
• To be used in critical acidosis (pH <7.00)
• In RTA type 1 & 2 supplements of Na & K
bicarbonate are necessary
• In RTA type 4 diuretics of loop or thiazide class
may be effective in increasing acid secretion.

24. Thank you