Acids and Bases and Buffers

1
Acids and Basesand Buffers

• Buffers Resist changes in pH
• When H added, buffer removes
• When H removed, buffer replaces
• Types of buffer systems
• Carbonic acid/bicarbonate
• Protein
• Phosphate

• Acids
• Release H into solution
• Bases
• Remove H from solution
• Acids and bases
• Grouped as strong or weak

2
Buffer Systems
3
ACIDS AND BASES

•  Acid is a substance that can donate H ions and
  a base is a substance that can accept H ions .
  These properties are independent of charge. Thus,
  H2CO3, HCl, NH4, and H2PO4- all can act as
  acids
•     H2CO3    lt-gt    H    HCO3-
•          HCl   lt-gt    H    Cl-
•       NH4    lt-gt    H    NH3
•     H2PO4-   lt-gt   H    HPO42-
•       Acid                Base

4
General Acid-Base Relationships

• Concentration of H ions in body 40 Nano
  mol/lit
• 40 / 1000,000,000
• 4 / 100,000,000
• 4 10-8
• Log 410-8 (Log 4) - 8
• (0,6) 8 -7.4
• PH - Log H concentration
• PH 7.4

5
General Acid-Base Relationships LAW OF MASS
ACTION

• The velocity of a reaction is proportional to the
  product of the concentrations of the reactants
• Co2 H2O ?Co3H2 ? Co3H- H
• H (K) Co3H- / Co3H2
• H (k) 24 / 400.03
• H (k) 24/ 1.2
• H (k) 20
• PH Pk Log 20
• PH 6.1 1.3
• PH 7.4

6
General Acid-Base Relationships

• Henderson-Hasselbach equation
• pH pK log HCO3 _ /pCO2
• H 24 x pCO2/HCO3_
• ???0.1?pH unit ? 10 nm/L H

7
Respiratory Regulation ofAcid-Base Balance

• Respiratory regulation of pH is achieved through
  carbonic acid/bicarbonate buffer system
• As carbon dioxide levels increase, pH decreases
• As carbon dioxide levels decrease, pH increases
• Carbon dioxide levels and pH affect respiratory
  centers
• Hypoventilation increases blood carbon dioxide
  levels
• Hyperventilation decreases blood carbon dioxide
  levels

8
Respiratory Regulation ofAcid-Base Balance
9
Renal Regulation of Acid-Base Balance

• Secretion of H into filtrate and reabsorption of
  HCO3- into ECF cause extracellular pH to increase
• HCO3- in filtrate reabsorbed
• Rate of H secretion increases as body fluid pH
  decreases or as aldosterone levels increase
• Secretion of H inhibited when urine pH falls
  below 4.5

10
Kidney Regulation of Acid-Base Balance
11
Hydrogen Ion Buffering
12
Acidosis and Alkalosis

• Acidosis pH body fluids below 7.35
• Respiratory Caused by inadequate ventilation
• Metabolic Results from all conditions other than
  respiratory that decrease pH
• Alkalosis pH body fluids above 7.45
• Respiratory Caused by hyperventilation
• Metabolic Results from all conditions other than
  respiratory that increase pH
• Compensatory mechanisms

13
Regulation of Acid-Base Balance
14
Regulation of Acid-Base Balance
15
Acidosis and Alkalosis
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
Vacoular H - ATPase (1)
HCO3- Na
3 Na
ATP
2 K
HCO3- Na
Na
K
CA II
H HCO3
H2O CO2
H
Na
H2O CO2
3 HCO3 -
HCO3
Net effect of Na/H , H - ATPase
Reabsorption Of 70 of bicarbonate
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
Approach to Acid-Base Disorders

• 1. Consider the clinical setting!
• 2. Is the patient acidemic or alkalemic?
• 3. Is the primary process metabolic or
  respiratory?
• 4. If metabolic acidosis, gap or non-gap?
• 5. Is compensation appropriate?
• 6. Is more than one disorder present?

31
Simple Acid-Base Disorders

• Primary Compensatory
• Disorder pH H Disorder
  Response
• Metabolic acidosis ? ??? ??HCO3_ ? pCO2
• Metabolic alkalosis ? ???????HCO3_ ?
  pCO2
• Respiratory acidosis ? ???????pCO2 ? HCO3_
• Respiratory alkalosis ? ???????pCO2 ? HCO3_

32
Metabolic Acidosis

• Etiology Inability of the kidney to excrete the
  dietary H load, or increase in the generation of
  H (due to addition of H or loss of HCO3-)

33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Metabolic Acidosis Elevated Anion Gap

• AG Na - (Cl- HCO3-) 12 2
• Note Diagnostic utility is best when AG gt 25
• Causes Ketoacidosis
• Lactic acidosis
• Intoxications
• Renal failure
• Rhabdomyolysis

37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
Renal Tubular Acidosis

• Type 1 (distal) Type 2 (proximal) Type 4
• Defect ??distal acid. ??prox HCO3 reab
  ??aldo
• HCO3 May be lt 10 12-20 gt 17
• Urine pH gt 5.3 Variable lt 5.3
• Plasma K Usually low Usually low High
• Response Good Poor Fair
• to HCO3 Rx

50
Calculation of Bicarbonate Deficit

• Bicarb deficit HCO3- space x HCO3-
  deficit/liter
• HCO3- space 0.4 x lean body wt (kg)
• HCO3- deficit/liter desired HCO3- - measured
  HCO3-

51
Approach to Metabolic Acidosis
Anion Gap
High
Normal
Osmolar Gap
GI Fluid Loss?
No
Yes
Normal
Increased
Diarrhea Ileostomy Enteric fistula
Urine pH
Uremia Lactate Ketoacids Salicylate
Ethylene glycol Methanol
lt 5.5
gt 5.5
Serum K
Distal RTA (Type 1)
High
Low
Type 4 RTA
Proximal RTA (Type 2)
52
Metabolic Alkalosis

• Etiology Requires both generation of metabolic
  alkalosis (loss of H through GI tract or
  kidneys) and maintenance of alkalosis (impairment
  in renal HCO3 excretion)
• Causes of metabolic alkalosis
• Loss of hydrogen
• Retention of bicarbonate
• Contraction alkalosis
• Maintenance factors Decrease in GFR, increase
  in HCO3 reabsorption

53
Use of Spot Urine Cl and K
Very Low (lt 10 mEq/L)
Vomiting, NG suction Postdiuretic,
posthypercapneic Villous adenoma,
congenital chloridorrhea, post- alkali
Urine Chloride
gt 20 mEq/L
Low (lt 20 mEq/L)
Urine Potassium
Laxative abuse Other profound K depletion
gt 30 mEq/L
Diuretic phase of diuretic Rx, Bartters,
Gitelmans, primary aldo, Cushings, Liddles,
secondary aldosteronism
54
Treatment of Metabolic Alkalosis

• 1. Remove offending culprits.
• 2. Chloride (saline) responsive alkalosis
  Replete volume with NaCl.
• 3. Chloride non-responsive (saline resistant)
  alkalosis
• Acetazolamide (CA inhibitor)
• Hydrochloric acid infusion
• Correct hypokalemia if present

55
Calculation of Bicarbonate Excess

• Bicarb excess HCO3- space x HCO3- excess/liter
• HCO3- space 0.5 x lean body wt (kg)
• HCO3- excess/liter measured HCO3- - desired
  HCO3-

56
Respiratory Acidosis

• Causes of Respiratory Acidosis
• Inhibition of medullary respiratory center
• Disorders of respiratory muscles and chest wall
• Upper airway obstruction
• Disorders affecting gas exchange across
  pulmonary capillaries
• Mechanical ventilation

57
Respiratory Alkalosis

• Causes of Respiratory Alkalosis
• Hypoxemia
• Pulmonary disease
• Stimulation of medullary respiratory center
• Mechanical ventilation

58
Mixed Acid-Base Disorders Clues

• -- Degree of compensation for primary
• disorder is inappropriate
• -- Delta AG/delta HCO3_ too high or too low
• -- Clinical history