learning aid,teaching aid by Dr.M Ravi chandra

1. “If one advances confidently in
the direction of his dreams, he
will meet with a success
unexpected in common hours
--Henry David Thoreau
"Shoot for the moon. Even if you miss
it, you will land among the stars….!"
- Les Brown

2. DR.M.RAVICHANDRA,M.S
ASST. PROFESSOR OF SURGERY
RIMS ,SRIKAKULAM

3. Strong and Weak Acids and Bases
 A strong acid ..rapidly dissociates and releases
large amounts of H+ in solution….HCl
 Weak acids ..less tendency to dissociate their
ions … is H2CO3
 A strong base … reacts rapidly and strongly with
H+ and quickly removes these from a solution…
OH-
 A typical weak base is HCO3-
 Most of the acids and bases in the extracellular
fluid that involved in normal acid-base
regulation are weak acids and bases

4.  Volatile acids:
 Can leave solution and enter the atmosphere.
 H2C03 (carbonic acid).
 Pco2 is most important factor in pH of body tissues.
 Pco2 is a measurement of tension or partial
pressure of carbon dioxide in the blood.
The normal arterial pCO2 is 4.1- 5.6 k Pa (31- 42
mmHg)

5.  Fixed Acids:
 Acids that do not leave solution.
 Sulfuric and phosphoric acids.(H2SO4&H3PO4)
 Catabolism of amino acids, nucleic acids, and
phospholipids.

6.  Organic Acids:
 Byproducts of aerobic metabolism, during anaerobic
metabolism and during starvation, diabetes.
 LACTIC ACID, KETONES ,PYRUVIC ACID

7. Normal Hydrogen Ion Concentration and pH of Body
Fluids
 the blood H+ concentration is normally maintained
within tight limits around a normal value of about
0.00004 mEq/L (40 nEq/L)
Ph= log 1/H= -log [H]
Ph=7.4

8. pH = pK + log HCO3
CO2

10. DEFENCE MECHANISMS
AGAINST pHCHANGES

11. 1.CHEMICAL BUFFER SYSTEMS

13. There are three primary systems that
regulate the H+ concentration
(1) the chemical acid-base buffer systems of
the body fluids
(2) the respiratory center
(3) the kidneys

14.  a buffer system is a combination of two
compounds that minimizes pH changes when
acid or base is added to a solution
 A pair of substance is involved: one substance yield H+ ion
when PH is increased the other binds with H+ ion when pH
is decreased.

15.  Chemical buffer system
 Combination of weak acid and weak base
 Binds to H+ as H+ concentration rises
 Releases H+ as H+ concentration falls
 Can restore normal pH almost immediately
 Three major chemical buffer systems
 Bicarbonate system
 Phosphate system
 Protein system

16.  Accomplished by converting:
 Strong acid  Weak acid
 Strong base  Weak base

17.  bicarbonate/carbonic acid
 major plasma buffer
 phosphate: H2PO4- / HPO42-
 major urine buffer
 ammonium: NH3 / NH4+
 also used to buffer the urine
 proteins: important in ICF
 Hb: is the main buffer against CO2 changes

18. BICARBONATE BUFFER SYSTEM
 Carbonic acid (H2CO3)
 Weak acid
 Bicarbonate ion (HCO3-)
 Weak base
 CO2 + H20  H2CO3  H+ + HCO3-
 Works along with respiratory and urinary system
 These systems remove CO2 or HCO3-
 THE RATIO OF BICARBONATE TO CARBONIC ACID IS
NORMALLY 20:1
 Alterations in the ratio alters Ph irrespective of
absolute concetrations

19. NaOH + H2CO3 H2O + Na HCO3
HCl + Na HCO3 NaCl + H2CO3

20. BICACARBONATE BUFFER

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23.  pK 6.1
 the concentrations of CO2 and HCO3 not great.
 the most powerful extracellular buffer in the body
 the two elements of the buffer system are
regulated by the kidneys and the lungs

24. PHOSPHATE BUFFER SYSTEM
 Dihydrogen phosphate ion (H2PO4-)
 Weak acid
 Monohydrogen phosphate ion (HPO42-)
 Weak base
 H2PO4-  H+ + HPO42-
 More important in buffering kidney filtrate than in
tissue

25. The main elements of the phosphate buffer
system are H2PO4- and HPO4
NaOH + NaH2PO4 H2O+ Na2HPO4
HCl + Na2HPO4 NaCl + NaH2PO4

26.  pK 6.8
 8 % of the concentration of the bicarbonate
buffer
 the total buffering power less than that of the
bicarbonate buffering system.

27.  the phosphate buffer is important in the tubular
fluids of the kidney for two reasons
(1) phosphate concentrated in the tubules
(2) the tubular fluid has lower pH than the
extracellular fluid does
- bringing the operating range of the buffer
closer to the pK (6.8) of the system
 important in buffering intracellular fluid
because the concentration of phosphate in this
fluid is many times that in the extracellular
fluid

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29. PROTEIN BUFFER SYSTEM
 Proteins are more concentrated than bicarbonate
and phosphate buffers
 Accounts for ~75% of all chemical buffering of body
fluids
 Buffering ability due to certain functional groups of
amino acid residues

30.  except for the red blood cells, the slowness
with which H+ and HCO3 move through the cell
membranes often delays the maximum ability of
the intracellular proteins to buffer extracellular
acid-base abnormalities.
 the pKs of many of these protein systems close
to 7.4.

31. The buffer system buffers each other by shifting
hydrogen from buffer to other

32.  Exhalation of carbon dioxide
 Powerful, but only works with volatile acids
 Doesn’t affect fixed acids like lactic acid
 CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
 Body pH can be adjusted by changing rate
and depth of breathing

33.  the overall buffering power of the respiratory
system is one to two times as great as the buffering
power of all other chemical buffers in the ECF
combined

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36.  Alkalosis
→↑urinary HCO3- (base)
 Acidosis
→↓urinary HCO3-
new HCO3- production

37.  pH< 7.35 acidosis
 pH > 7.45 alkalosis

39.  A CONDITION WHERE THE PCO2 IS ABOVE THE
NORMAL RANGE
 MORE THAN 5.6 kilopascals
 (or) more than 42mmof hg

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47. compensatory mechanisms in respiratory acidosis
compensatory mechanisms in respiratory acidosis
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48.  Inadequate ventilation of anaesthetized
patient
 When the effects of muscle relaxants have
not worn off or been fully reversed at the
end of anaesthesia
 Risk increases when the patient has pre
existing pulmonary disease like ch. Bronchitis
or emphysema
 Thoracic & upper abdominal incisions

49.  A CONDITION WHERE THE ARTERIAL PCO2 IS
BELOW THE NORMAL RANGE
 LESS THAN 31 MM OF HG
 (OR) LESS THAN 5.6 KILO PASCALS

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53.  Excessive pulmonary ventilation during
ANAESTHAESIA (Hyperventilation)
 High altitudes
 Hyperpyrexia
 Hypothalamic lesions
 Hysteria

55.  A condition where there is a deficit of base
or excess of acid other than carbonic
acid(H2CO3)

56. Ulcerative colitis
Gastro colic fistula
High intestinal fistula
Prolonged intestinal
aspiration

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60.  This is a calculated estimation of the
undetermined or unmeasured anions in the
blood
 This is some times used to establish the
cause of metabolic acidosis
ANIONGAP= (Na) _ (HCO3+Cl)
NORMAL ANION GAP IS 10-16 mmol / L

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64.  KETOACIDOSIS
 LACTIC ACIDOSIS
 SALICYLATES POISONING
 SPIRITS –ETHANOL & METHANOL
 ALDEHYDES
 RENAL FAILURE

65.  DIARRHOEA
 RENAL TUBULAR ACIDOSIS
 URETEROSIGMOIDOSTOMY
 TOTAL PARENTARAL NUTRITION
 ACETAZOLAMIDE
 INTESTINAL OBSTRUCTION
 INTESTINAL FISTULA

66.  Increased ventilation
 Renal excretion of hydrogen ions if possible
 K+ exchanges with excess H+ in ECF
 ( H+ into cells, K+ out of cells)

67.  A CONDITION WHERE THERE IS BASE EXCESS
OR DEFICIT OF ANY ACID OTHER THAN
CARBONIC ACID

68. Cortisone excess
Cushings syndrome

69. CHEYNE STOKES RESP
TETANY
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72.  RESPIRATORY- RETENTION OF
CARBONDIOXIDE BY THE LUNGS
 RENAL – EXCRETION OF BICARBONATE BY THE
KIDNEYS

73. Changes in Arteial Concentrations
of H + , HCO 3 - & CO 2 in Acid-Base Disorders
Primary HCO 3 Cause of HCO3- Cause of CO2
H + CO 2
Disorder -
Change Change
Respiratory
Acidosis ↑ ↑ ↑
Renal Primary
Compensation Abnormality
Respiratory
Alkalosis ↓ ↓ ↓
Metabolic
Acidosis ↑ ↓ ↓ Reflex
Primary
Ventilatory
Abnormality
Metabolic Compensations
Alkalosis ↓ ↑ ↑

74.  Respiratory Acidosis ; ↑PCO2 & [H+]
 Respiratory Alkalosis ; ↓PCO2 & [H+]
 Metabolic Acidosis
; compensatory reflex hyperventilation ⇒ ↓PCO2
1. Tubular acidosis; ↓HCO3- reabsorption & H+ secretion
2. Diarrhea & Vomiting(intestinal); ↓HCO3-
3. Diabetes Mellitus; ↑acetoacetic acid (ketone body)
4. Ingestion of acids; aspirin, methyl alcohol
5. Chronic renal failure; ↓acid excretion
6. Hypoxia (severe exercise); ↑lactic acid

75.  Metabolic Alkalosis
; compensatory reflex hypoventilation ⇒ ↑PCO2
1. Diuretics; ↑distal tubule flow
⇒↑Na+ reabsorption & H+ secretion
2. Excess Aldosterone; ↑H+ secretion
3. Vomiting; ↓H+ (upper gastric content)
4. Ingestion of alkaline drugs; sodium bicarbonate

76. Summary of Acid-Base Disturbances
Uncompensated Compensated
pH [HCO 3 - ] P CO2 pH [HCO 3 - ] P CO2
24 40
Normal 7.4
mEq/L mmHg
Respiratory
Acidosis ↓ - ↑ ↓ ↑ ↑
Respiratory
Alkalosis ↑ - ↓ ↑ ↓ ↓
Metabolic
Acidosis ↓ ↓↓ - ↓ ↓↓ ↓
Metabolic
Alkalosis ↑ ↑↑ - ↑ ↑↑ ↑

78. HAVE A NICE DAY
HAVE A NICE DAY
*Image by 8771253@N06 via Flickr