1. Acid and base balance physiology and disturbances
Dr. Ayad Abbas Salman

2. PH
If hydrogen ion of pure H2O at room temperature is equal to 1/ mol/L
→ [H+] = 1/
→ [H+] = 10-7
→ log [H+] = -7
→ -log [H+] = 7
→ pH = 7

3. solutions Neutral solution → [H+] = [OH-] = 10-7 → pH =7
Acidic solution → [H+] > [OH-] → pH < 7
Alkaline solution → [H+] < [OH-] → pH > 7
Range of blood pH which compatible with life is only (7-7.8) 6 times change in hydrogen ion concentration.

4. Acidosis : process that tend to lower pH
Acidosis : process that tend to lower pH. ◊ Alkalosis: process that tend to rise pH ◊ Acidaemia: ↓ in blood pH < 7.35 ◊ Alkalaemia: ↑ in blood pH > 7.45

5. Compensatory Mechanism
Physiological responses to changes in [H+] are characterized by 3 phases:
1.Immediate chemical buffering.
2.Respiatory compensation.
3.Slower but more effective renal response that may nearly normalize arterial pH.

6. Chemical buffering 1.Bicarbonate (H2CO3/HCO3-):
is most important buffering in the extracellular fluid.
H2O + CO2 (ac)↔(al) H2CO (ac) ↔(al) H+ +Hco3
  ↑ PaCO2 Normally eliminated by lung

7. 2.Haemoglobin (HbH/Hb-):
Although restricted inside RBC, but it is an important buffer in the blood.
H+ + KHb (al) ↔(ac) HHb +K+ 

8. 3.Protein other than Hb:
play a major role in buffering of intracellular fluid.
Protein possess both acidic & alkaline groups.
Acidic group called carboxyl group.
Alkaline group called amino group.
NH2 + H (al) ↔ (ac) NH3
COOH + OH- (ac) ↔ (al) COO + H2O

9. 4.Phosphate (H2PO4-/ HPO4-2):
it is important urinary buffer. 
↑ [H+] →HCl + Na2HPO4 →NaH2­PO4 (kidney) + NaCl
di (Na) phosphate mono (Na) phosphate   
↑[OH-] →NaOH + NaH2PO4 → NaHPO4 + H2O excreted by kidney

10. 5-Amonia (NH3/NH4+): it is also important urinary buffer.
NH3 + H → NH4 (excreted by kidney)

11. Respiratory compensation
Change in pH sensed by :
chemoreceptors in brain stem
↑pH → hypoventilation → ↑PaCO2
↓ pH → hyperventilation → ↓PaCO2

12. Renal compensation
1.Ability of kidney to control the amount of HCO3- reabsorption.
2.Ability of kidney to form new HCO3-.
3.Ability of kidney to eliminate H+ in the form of titrable acid and ammonium ion.
EXAMPLES:
► H+ + HPO → H2PO4 (excreted by kidney)
► NH3 + H NH4 (excreted by kidney)

13. Normal values and analysis
PaCO2 = HCO3 =
SBC* = BE** = zero.
* SBC: it is plasma [HCO3] from fully oxygenated (PaO2 = 100) blood which has been equilibrated to PCO2 40 mmHg at 37○C.
** BE: Base Excess: is an amount of strong acid or base required to titrate the pH to 7.4 at PCO2 40 mmHg

14. Clinical disorders PaCO2 Change: Respiratory acidosis
Respiratory alkalosis
Hc03 Change:
Metabolic acidosis
Metabolic alkalosis

15. examples Diag. BE Hco3 Paco2 PH UMac -20 10.8 41 7.05 URal 5 24 21
7.58
CMac
-15
13.4 23
7.27
CMal 20
42.8 55
7.55

16. Physiological effect of acidosis
1.pH < 7.20 → direct myocardiac depression and ↓ peripheral vascular resistance → hypotension.
2.Tissue hypoxia (although O2 dissociation curve shift to the left)
3.Hyperkalaemia
4.CNS depression mainly in respiratory acidosis (CO2 narcosis) → ↑ cerebral blood flow → ↑ intracranial pressure.

17. Respiratory acidosis Causes of respiratory acidosis:
1.Alveolar hyperventilation
● CNS depression e.g: 1.cerebral ischemia 2.cerebral trauma 3.drug induced
● Neuromuscular disorder: myopathy, neuropathy
● Chest wall abnormality e.g kyphoscoliosis
● Pleural abnormality e.g pneumothorax, pleural effusion
● Airway obstruction: foreign body, tumor → upper airway
asthma, COPD → lower airway
● Paranchymal lung disease:1.Pulmonary Oedema 2.Pulmonary Emboli 3.Pneumonia 4.Aspiration 5.Interstitial lung disease

18. 2.↑ CO2 production
● ↑ in enteral or paraentral nutrition of carbohydrate
● Intense shivering
● Prolong seizure activity
● Thyroid storm
● Excessive thermal injur

19. management ● Treatment of the cause
● Treatment of the cause
● May → respiratory depression → mechanical ventilation
● I.V NaHCO3 is rarely necessary (i.e not used)

20. Metabolic acidosis causes
anion Gap: defined as the difference between major measured cations and major measured anions.
Anion gap = [Na+] -([Cl-] + [HCO3-] ) normally (9-15).

21. ● 1.Incresed anion gap
↑ production of non volatile acids e.g renal failure, DKA (diabetic ketoacidosis), lactic acidosis.
Ingestion of toxins e.g salicylatye, methanol, sulfer
Rhabdomyositis

22. 2.Normal anion gap
↑ GIT loss of HCO3: diarrhoea, ingestion of CaCl2/MgCl2, fistula (pancreatic, biliary, small bowel)
↑ renal loss of HCO3: renal tubular acidosis, hypoaldosteronism
Dilutional: large amount of HCO3 free fluid
Total paraenteral nutrition
↑ intake of chloride containing acid e.g ammonium chloride

23. management ph < 7.2 → Na HCO3 (8.4 %) should be given
NaHCO3 = (BE X body weight) /3
giving 1/2 the dose and reassess the values
● Treatment of the cause

24. Alkalosis (physiological effect)
1.Hypokalemia
2.Difficult to give up O2 to tissue → hypoxia.
3.↓ ionized Ca+2 → circulatory depression and neuromuscular irritability.
4.Respiratory alkalosis → ↓ cerebral blood flow, ↑ systemic vascular resistance and may → coronary vasospasm.

25. Resp. Alkalosis
1○ ↓ in PaCO2 by inappropriate ↑ in alveolar ventilation relative to CO2 product.
It is compensated by ↓ [HCO3] in plasma.

26. causes ● Central stimulation:
1.pain 2.anxiety (hystria) 3.stroke 4.ischemia 5.feve
6.infection 7.drug induced e.g salicylate
● Peripheral stimulation:
1.hypoxia 2.high altitude 3.pulmonary disease (CHF, pulmonary oedema, pulmonary emboli, asthma (severe)
● Iatrogenic: ventilator induced

27. management Treatment of the cause is enough
For severe (pH > 7.6) i.v HCl or NH4Cl4 (ammonium chloride) my be indicated

28. II.Metabolic alkalosis 1○ ↑ in HCO3 Causes
1. Chloride sensitive: those causes associated with ↓ NaCl and ECF depletion
● GIT: vomiting, gastric drainage, chloride diarrhoea
● renal: diuretic
● sweat: cystic fibrosis

29. 2.Chloride resistance:
those associated with enhanced mineralocorticoid activity
● hyperaldosteronism, cushing syndrome
3.Miscellanous
● massive blood transfusion
● alkaline treatment with renal insufficiency
● hyper Ca+2 e.g metastasis

30. management Treatment of underlying cause
For chloride sensitive causes i.v normal saline and K+ replacement
When pH > 7.6 i.v :
1.HCl
2.ammonium chloride
3.Vit.C (5-10 g/day)
4.haemodialysis may be considered

31. Thank you