Acid base disorders

1. ACID BASE DISTURBANCES

2. BASIC DEFINITIONS
• ACID: A compound which releases H+
• BASE: A compound which accepts H+
• pH: A measure of H+ activity. This number tells us how acidic or
alkaline (or neutral) is the solution.

3. Continua…………..
• Acids are produced daily in the human body (lactic, acetoacetic,
hydroxybutyric) about 80meq/L of H+ per day by both ingestion and
metabolic sources.
• CO2 also produces acid (CO2 + H20 = H2CO3)
• Alkali is also present in the body (HCO3, HPO4)
• But blood is neither acidic nor alkalotic

4. Continua…………
• Normal pH of blood = 7.35-7.45
• In the blood acid and alkali are balanced so pH is stable
• A normal blood pH is important for normal cell functions.

5. Continua…………..
• Extra acid or alkali in the blood is immediately buffered by certain
substances in the blood and then excreted. (e.g HCO3, HPO4, NH3,
proteins and organic acids)
• eg: H + HCO3→ H2CO3 + CO2

6. Continua……………
• If excess acid remains in the blood → ACIDOSIS
• If excess alkali remains in the blood → ALKALOSIS
pH changes
ACIDOSIS causes low pH (Lower than 7.35)
ALKALOSIS causes high pH (higher than 7.45)

7. Important equation
• H + HCO3 H2CO3 CO2 + H2O
• HCO3 Handled by the kidney
• CO2 handled by the lungs

8. COMPENSATION
• Whenever the pH changes in a disease, the body tries to bring it back
towards normal. This is called compensation.
• Compensation is not 100% complete, so pH does not return to
complete normal, if the disease continues.

9. Continua………….
• 3 THINGS WHICH TRY TO COMPESATE
• BUFFERS IN THE BLOOD: act within seconds (HCO3, organic acids)
• LUNGS: within seconds to minutes (by keeping or removing CO2)
• KIDNEYS: within hrs to days ( by handling HCO3 and H+)

10. Continua……………
• IN DISEASE STATES, ACID-BASE BALANCE GETS
DISTURBED, SO ACIDOSIS OR ALKALOSIS (OR MIXED
DISTURBANCES) CAN OCCUR.

11. Things we need to understand acid-base
balance
• ABG (arterial blood gases)
• Serum electrolytes ( Na, K, Cl, HCO3)
• ABG report is written as follows:
• ABG: pH2/pCO2/pO2/HCO3
eg 7.40/45mmHg/78mmHg/25meq
For our discussion, forget about O2

12. Some normal values
• Blood pH: 7.35-7.45
• Blood pCO2: 35mmHg-45mmHg
• Blood HCO3: 22-28meq/L (slightly different in various labs)

13. ACIDOSIS
• RESPIRATORY DUE TO:
• High CO2
• METABOLIC DUE TO:
• Excess acid production
• Decreased acid excretion from
the kidneys
• Loss of HCO3

14. RESPIRATORY ACIDOSIS
• Its due to hypoventilation
• Due to hypovent., CO2 cannot be excreted, so pCO2 rises (think of CO2 as an acid)
• ETIOLOGIES:
• RESP. center depression (morphine, alcohol, sedatives, trauma)
• Obstruction of passage ways (upper air way: foreign body, tonsillar hypertrophy,
vocal cord paralysis, croup, epiglottitis. Lower airway: asthma, cystic fibrosis)
• Neuromuscular pathologies: (kyphosis, resp. muscle paralysis)
• Lung disease (COPD, pneumonia)

15. Respiratory acidosis
• pH is low < 7.35
• Problem is in RESP. SYS. Or LUNGS hence CO2 is retained
• High CO2→ acidosis
• Eg: pH/pCO2/HCO3
• 7.30/50mmHg/30 (Norm pCO2 35-45, HCO3 22-28)

16. Compensation in RESP. acidosis
• Kidneys retain more HCO3
• So there is compensatory rise in HCO3
• End result:
• pH is low
• pCO2 high
• HCO3 high due to compensation

17. S/S of RESP. ACIDOSIS
• Usually occur if it is acute
• Headache, restlessness, dysnea
• Progresses to hyper-reflexia, coma
• Respiratory acidosis maybe seen in late stages of asthma
exacerbation, when the patient gets tired, seen in COPD pts even at
baseline status (chronic acidosis)

18. TXT OF RESP. ACIDOSIS
• Treat the cause
• Don’t give HCO3
• It will combine with H+ in the body and produce more CO2 which cannot be
eliminated. Hence condition is worsened
• May need mechanical ventilation (ventilation takes out CO2 from the
lungs)

19. RESPIRATORY ALKALOSIS
• pH is high
• Problem is with respiratory rate
• Hyperventilation→excess CO2 is eliminated, low CO2 → alkalosis
• Eg: pH/PCO2/HCO3
• 7.50/28/18

20. Compensation
• Kidneys lose more HCO3
• So there is a compensatory fall in serum HCO3
• End result:
• pH: low
• pCO2: low
• HCO3: low due to compensation

21. Causes of respiratory alkalosis
• Anxiety
• Respiratory center stimulation, a psychoneurosis
• Hypoxia (living at high altitudes)
• Patients on ventilators
• Aspirin poisoning
• Kabale is a high altitude town, living there can cause resp. alkalosis

22. RESP. ALKALOSIS S/S
• Acute resp. alkalosis causes low Ca, & K
• S/S Includes:
• Light headedness
• Confunsion
• Seizures
• Hyperventilation
• Tetany due to low Ca

23. TXT OF RESP. ALKALOSIS
• Treat the main cause
• Change ventilator settings
• Can try rebreathing exhaled air in a paper bag.

24. METABOLIC ACIDOSIS
• pH is low <7.35
• Main problem not in respiration
• PROBLEM: Too much metabolic acid is produced in the body, or it can
not be excreted, or too much alkali (HCO3) is lost from the body
• Eg: pH/pCO2/HCO3
• 7.20/30/18

25. compensation
• Lungs excrete more CO2
• So there is compensatory fall in pCO2
• End result:
• pH: low
• HCO3: low (main prob)
• pCO2: low due to compensation

26. • Types of metabolic acidosis
HIGH ANION GAP NORMAL ANION GAP

27. WHAT IS ANION GAP
• Cations: Na+, K+ / anions: HCO3-, Cl-
• Normally the sum of cations should equal to sum of anions
• But Na + K is > HCO3 + Cl
• This diff is called the anion gap
• It is actually the unmeasured anions in the blood (albumin,
phosphates etc)
• Normal A.G = 8-16meq

28. TYPES OF METABOLIC ACIDOSIS
HIGH ANION GAP
• M-methanol
• U-uremia
• D-diab. Ketoacidosis
• P-paraldehyde
• I-infection/sepsis
• L-lactic acidosis
• E-ethanol
• S-salicylate poisoning (aspirin)
NORMAL ANION GAP
• Diarrhea
• Ileostomy
• Renal tubular acidosis(type
1,2&4)
• Acetazolamide (a diuretic)

29. S/S METABOLIC ACIDOSIS
• Headache, mental status changes, restlessness
• Coma may occur

30. TXT OF METABOLIC ACIDOSIS
• Treat the cause
• Drug toxicity (aspirin, methanol)
• Ketoacidosis
• Infection/sepsis
• Diarrhea
• Lactic acidosis: iv fluids, txt the cause
• Uremia: NaHCO3 tab/dialysis (remember renal failure)
Iv HCO3 can be given if needed

31. RENAL TUBULAR ACIDOSIS
• A group of renal disorders (prob in tubules)
• 4 types
• Overall rare, type 4 is most common
• Metabolic acidosis with normal A.G
• Type 4 RTA seen in DM

32. Metabolic alkalosis
• pH is high >7.45
• No primary problem in resp
• Accumulation of excess alkali in the body or loss of acid
• Eg: pH/pCO2/HCO3
7.50/48/35

33. Continua………..
• Classified according to urinary chloride
• Chloride responsive: when Cl is high in urine. Usually, the cause is
vomiting in this group. Urine Cl > 20 mEq/L
• Chloride resistant. Urine Cl- < 20 mEq/L.

34. Compensation
• Lungs excrete less pCO2, so compensatory rise in pCO2
• End result:
• pH: high
• HCO3: high-main prob
• pCO2: high-compensatory

35. CAUSES OF METABOLIC ALKALOSIS
• Vomiting, NG tube suction (loss of acid)
• Excess intake of NaHCO3
• Excess aldosterone
• Excess exogenous steroids,
• Diuretics (thiazide, loop diuretics)
• ALL DIURETICS CAUSE METABOLIC ALKALOSIS EXCEPT ACETAZOLAMIDE WHICH CAUSES
ACIDOSIS

36. S/S
• Cerebral dysfunction
• Restlessness
• Confusion, lethargy
• arrhythmias

37. TXT
• If vomiting or sunction- give iv NS
• If diuretics give iv NS
• If high intake of HCO3, stop it
• If pH >7.7, give isotonic HCL through cental vein