1. Metabolic acidosis & Metabolic alkalosis
Dr.R.Anitha
Prof.S.Shivakumar unit

2. Metabolic acidosis

3. Primary Change Secondary change Net effect  Hco3  Pco2  pH ( H+)
Pco2 should  by 1.2 mmHg for each mEq  plasma Hco3

4. Causes of metabolic acidosis
Inability to excrete dietary acid load
Renal failure
Renal tubular acidosis type 1 &4
Increased H+ load
Lactic acidosis
Ketoacidosis
Toxin ingestions
Increased HCO3 loss
diarrhoea

5. Normal anion gap or hyper chloremic acidosis
AG = Na+– (Hco3  + Cl )
Normal = 12 ± 4 ( 8  16 )
Measure of unmeasured anion (protiens)
Normal anion gap or hyper chloremic acidosis
High anion gap

6. Metabolic acidosis Lactic acidosis Ketoacidosis Diarrhoea
High anion gap
Normal anion gap
Lactic acidosis
Ketoacidosis
Renal failure
Toxin ingestions
Salicylate
Methanol
Ethylene glycol
Diarrhoea
Renal tubular acidosis

7. Clinical features Kussmals respiration (increased depth than rate)
Neurologic symptoms: lethargy to coma
In severe acidosis (pH< 7.1):
Cardiac arrhythmia
Reduced cardiac contractility
Decreased inotropic response to catecholamines.
Chronic acidosis
Impaired growth in children
Osteomalacia/osteopenia

8. Treatment Treat the underlying cause NaHCO3 therapy:
Severe metabolic acidosis (pH<7.1)
Chronic acidosis (sodium or potassium citrate)
To alkalanise urine in salicylate poisoning

9. NaHCO3 therapy in severe acidosis: pH <7.1
Always treat the pH and not the HCO3
Only one half of bicarbonate deficit to be corrected in initial 12 hrs
NaHCO3 dose= desired HCO3 – observed HCO3 * 50%of body wt
desired HCO3 =12 meq/L in HAG acidosis and meq/L in NAG

10. Example
A 24 yr old type 1 diabetic male, weighing aroud 50 Kg presenting with fever, tachypnoea and abd pain to the EMU
pH HCO pCo
Urine ketones +
BP 100/70 PR 128/min
Start IV saline 0.9%,
insulin bolus &continuous infusion drip,
start NaHCO3 therapy to bring the pH to 7.2

11. Calculation of desired HCO3
H = 24 x Pco2 (Modified Henderson equation) Hco3
pH = HC03 = PCo2 =20.8
When pH is 7.0, H+ = 100 neq
To make the pH 7.2, H+ = 63, the desired HCO3(y)
63 = 24 x 20.8/ y
y = 24 x 20.8/ 63 = 7.9 = desired HCO3
NaHCO3 dose= desired HCO3 – observed HCO3 * 50%of body wt
= 7.9 – 5 * 25 = 73 meq

12. Complications of NaHCO3 therapy
Sodium and volume overload – dangerous in states of shock – slow continuous UF/ CVVH/intermittent dialysis(HD/PD)
Hypernatremia
Hypokalemia
Overshoot alkalosis
On correction of the cause metabolism of organic anions(lactate, ketoacids) will produce HCO3 – potential HCO3

13. CHRONIC ACIDOSIS
Imeq/kg/day of alkali either as Shohl’s solution or NaHCO3 tablets
Shohl’s solution = 140g citric acid + 98g hydrated crystalline salt of sodium citrate in dist water to make 1000ml ( 1ml=1meq)

14. Potassium in metabolic acidosis
Usually hyperkalemia occurs
Potassium depletion common – GI loss/renal loss/treatment of DKA
Initial plasma K relatively normal or high – metabolic acidemia cause K to move out of cells in to ECF.
Careful freq monitoring of potassium during treatment and correct hypokalemia (<3.5) at once.

15. Summary AG Normal Anion Gap High Anion Gap cause
H/O diarrhoea,DM, Toxin ingestion, C/F of shock
Sr Ketone, lactate, urine pH/osm gap/AG, pl osm gap
Treat
The cause
The pH only in severe acidosis pH<7.1

16. Metabolic alkalosis

17. Pco2 should  by 0.6 mmHg for each mEq  plasma Hco3
Primary Change
Secondary change
Net effect
 Hco3
 Pco2
 pH ( H+)
Pco2 should  by 0.6 mmHg for each mEq  plasma Hco3

18. Metabolic alkalosis Generation Maintenance
H+ loss in GIT (vomiting or NG suction) or in urine (diuretics)
Maintenance
Perpetuation of metabolic alkalosis – requires impairment in renal HCO3 excretion

19. Maintenance Decreased effective arterial volume Decreased GFR
Secondary hyperaldosteronism
Na retention/H+ excretion

20. Chloride depletion
Chloride loss
reabsorption
Bicarbonate
Increase

21. Potassium depletion Intracellular acidosis Paradoxical aciduriak k k H k H H H H k k k k H H k k k H H H k H k H
Paradoxical aciduria
Extracellular alkalosis

22. Cause of metabolic alkalosis
Gastrointestinal loss
vomiting or NG suction
Renal loss
Loop or thiazide diuretic
Mineralocorticoid excess
Postchronic hypercapnea
H+ movement into cells
Hypokalemia

23. For a clinically relevant etiologic classification
Urine Cl- conc
<10meq/L
Chloride Depletion Alkalosis
Decreased effective arterial volume
CDA
>20meq/L
Potassium Depletion Alkalosis
Mineralocorticoid excess
KDA

24. CDA KDA Gastric acid loss Chloruretic diuretics Posthypercapnic state
With hypertension
Primary aldosteronism
Secondary aldosteronism
With normotension
Bartter syndrome
Gitelman syndrome

25. Clinical features
Signs of volume depletion in CDA (hypotension, tachycardia..)
Singn of volume expansion in KDA (hypertension)
Signs of hypokalemia
In severe metabolic alkalosis (pH > 7.55)
hepatic encephalopathy,
cardiac arrhythmia,
digitalis cardiotoxicty or
altered mental status

26. General management principles
Correction of fluid defecit
Correction of hypokalemia and hypochloremia
Correction of pH if it is severe alkalosis (pH > 7.55)

27. Chloride Depletion Alkalosis
ECF volume contraction
Volume correction by NaCl
Further repletion KCl
ECF volume overload
NaCl contraindicated
T.Acetazolamide 250mg bd/tds

28. Potassium depletion alkalosis
Potassium replacement
Removal of source of mineralocorticoid excess
Blockade –
Amiloride 5-10mg
Triamtrene 100 mg bd
Spiranalactone mg
Hypomagnesemia to be corrected

29. Severe hypokalemia (<2meq/l)
Make the metabolic alkalosis and hypovolemia resistant to saline therapy
Because severe hypokalemia cause impairment in Cl- reabsorption in distal tubule
Replacement of only one half of potassium defecit will normalise Cl- reabsorption

30. In very severe alkalosis (pH > 7.55)
c/f of hepatic encephalopathy, cardiac arrhythmia, digitalis cardiotoxicty or altered mental status
HCl (0.1N)administration in central venous catheter 25meq/hr
Amount of HCl= 0.5* body wt*(plasma HCO3-24)

31. Summary Urine cl Chloride depletion alkalosis (CDA)
Potassium depletion alkalosis (KDA)
CDA
ECF vol contraction – NaCl, KCl
ECF vol overload – acetazolamide, K supp
KDA
K replacement
Remove or block the source

32. Summary cont…
pH >7.55
Hcl therapy

33. Take home message
Identify the cause with history, C/F, ABG, lab analysis.
Single HCO3 value cannot replace ABG
Treat the cause
Treat the pH only when there is severe acidosis or alkalosis
Always correct the pH not the HCO3

35. Thank you