Acid base balance Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diabetes Diploma in Software based statistics PhD ( physiology), IDRA , FICA Certifícate in USGRA

A lot of confusion !! What is what ? Sometimes anions are called bases ? Sometimes called acids E. g. bicarbonate , chloride Know the definition !!

An acid is an hydrogen ion donor Acid = H+ + base H2CO3 = H+ + HCO3 – H3PO4 = H + + H2PO4– A base is an hydrogen ion acceptor

What is an alkali ! An alkali produces hydroxyl ions in solution NaOH = Na + + OH- Alkali is strong – more hydroxyl ions in solution while more hydrogen ions means strong acid

Sorenson !! In 1909 , he found out that enzyme activity changes with minute or minimal changes of hydrogen ion concentration 0.0001 mole pr liter of hydrogen ion 10 -4 moles per liter 0.000001 = 10 -6 moles per liter Write like this – take the power and make it positive 4 and 6 Negative logarithm of hydrogen ion concentration in moles per liter

pH change and hydrogen ion change is never linear Example: a solution with a pH of 4 has 10 times the hydrogen ion concentration of a solution with a pH of 5 and 100 times the hydrogen ion concentration of a solution with a pH of 6

What is neutral pH ?? Water dissociates into equal amounts of hydrogen ions and OH ions In chemistry , the equilibrium has been found to be H+ OH- = 10-14 Water contains equal H and OH Hence the neutral pH is 7

pH of blood ! Acids have more H+ ions and less pH than 7 Which is strong – 0.0001 or 0.000001 Alkali more than 7 Blood is faintly alkaline - 7.4 pH of 7 -- Oxygenation of Hb is impaired

Henderson hasselbach pH=pKa + log([k]/[HA]) lactic acid (pKa, = 3.9) is a stronger acid than carbonic acid (pKa, = 6.1) because, at any given pH, lactic acid will be more dissociated and therefore will release more H+ than carbonic acid.

Replenished continuously hence able to have that pH

Our life is acidogenic

Approx 10 neq for 0.1 pH change We need to have a pH between 7.36 – 7.44 approx What happens if it changes It is dangerous then how it is avoided

Buffers !! A buffer is a solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH. Fast pH changes are not allowed

Water is great ! HCl + H2O ↔ H3O+ + Cl− NaOH + H2O ↔ Na+ + H2O + OH− Alterations in this “balance” lead to significant cardiovascular problems caused by dysfunction of transcellular ion pumps

ECF The body's chemical buffer system consists of three individual buffers out of which the carbonic acid bicarbonate buffer is the most important. ( EC water ) Phosphate buffer Protein buffer

HCO3 + H2CO3 Strong alkali NaOH + H2Co3 = NaHCO3 + H2O Strong acid

carbonic acid bicarbonate buffer pH = 6.1 + log HCO3/ H2CO3 6.1 + log 27/1.35 6.1 + log 20 6.1 + 1.3 = 7.4

Phosphate buffer system Na2HPO4 and NaH2PO4 HCl + Na2HPO4 = NaH2PO4 + Nacl NaOH +NaH2PO4 = Na2HPO4 + H2O Kidney tubules and RBCs

Protein buffer system Protein Buffers in Blood Plasma and Cells. Nearly all proteins can function as buffers.  Proteins are made up of amino acids, which contain positively charged amino groups and negatively charged carboxyl groups. The charged regions of these molecules can bind hydrogen and hydroxyl ions, and thus function as buffers.

Intracellular buffer with immediate ECF effect Haemoglobin exists within the red cell as a weak acid (HHb) and its potassium salt (KHb) Hemoglobin is a protein

Can we repeat ?? Or go ahead ?

Respiratory regulation CNS receptors

RS - works how ? Doubling the respiratory rate for less than 1 minute, removing “extra” CO2, would increase the blood pH by 0.2. This situation is common if you are exercising strenuously over a period of time. To keep up the necessary energy production, you would produce excess CO2(and lactic acid if exercising beyond your aerobic threshold). This helps to keep you from developing acidosis.

Physiology ! Medullary CNS receptors CO2 more permeable than HCO3 Ventilation increase Peripheral carotid receptors – more hyoxemic insult

Upto 7 stimulation – hyperventilation But below 7 – may not have the effect Think of kussmaul respiration Think of carbondioxide narcosis

If we give massive doses of bicarbonate For eg 27 meq to 54 meq/litre Depression of respiration PCO2 increase from 40 to 80 Carbonic acid content becomes 2.7 pH remains the same pH = 6.1 + log HCO3/ H2CO3 6.1 + log 27/1.35 6.1 + log 20 6.1 + 1.3 = 7.4

Renal regulation The kidneys control acid-base balance by excreting either acidic or basic urine Excreting acidic urine reduces the amount of acid in extracellular fluid Excreting basic urine removes base from the extracellular fluid

Three mechanisms Reabsorption of bicarbonate Acidification of buffer salts Secretion of ammonia

Normally 4000 meq of HCO3 reabsorbed /day

Acidification of buffer salts

Oxidation of glutamine

Urine pH may vary from 4.5 to 7.8 What is normal ??

Inter-relation of buffers HC03- is a useful marker of metabolic acid changes but not in a linear fashion. We expect the bicarb to decrease this much ? But does this happen ? Changes in HC03- are dependent upon respiratory acid-base variations.

ECF mechanisms are instantaneous Respiratory may take a few hours Kidneys may take hours to days But mechanisms by the kidneys permanent

Thank you all