Block 4: Acid-Base Physiology Flashcards
(141 cards)
1
Q
What is acid-base balance?
A
Regulation hydrogen ion (H+) concentration in body fluids → for normal cell/organ function and survival
2
Q
How does the H+ influence acid-base balance?
A
Highly reactive where concentration is precisely regulated within a narrow normal range
3
Q
What is the function of H+ concentration?
A
- Alters distribution of electrolytes
- Alters activity of enzymes involved in ATP production
4
Q
How do lungs contribute to acid-base balance?
A
Regulate the elimination of CO2, a source of carbonic acid
5
Q
How do kidneys contribute to acid base balance?
A
Eliminate H+ and HCO3-
6
Q
What is tissue perfusion?
A
Ensures delivery of O2 and nutrients → Maintaining aerobic metabolism
Decreased perfusion → anaerobic metabolism and accumulation of lactic acid
7
Q
What are volatile acids? Example?
A
Can dissociate forming a gas eliminated by the lungs
Carbonic acid (H2CO3)
8
Q
How leads to CO2 production?
A
- Formed during aerobic metabolism
- Combines with water to form carbonic acid
- H2CO3 dissociates into H+ and bicarb
9
Q
What happens if there is an accumulation of CO2?
A
↑ Carbonic acid → ↓ pH
10
Q
What are nonvolatile acids?
A
Not gases → cannot be eliminated from the lungs; eliminated primarily by kidneys
11
Q
How does nonvolatile acid differ from volatile gases?
A
Lower production → takes longer to reach comparable degree of acidity in kidney failure than respiratory failure
12
Q
What causes fluctuations of H+?
A
- Daily ingestion
- Metabolic production
- Utilization of acids and bases
13
Q
What are the types of buffer systems?
A
- Chemical
- Respiratory
- Renal
14
Q
What is the function of chemical buffers?
A
Intracellular and extracellular buffers that neutralize excess acids and bases
15
Q
What is the function of respiratory buffers?
A
eliminates carbonic acid (H2CO3) in the form of CO2 in exhaled air
16
Q
What is the function of renal buffers?
A
regulates the excretion of bicarbonate (HCO3-) and H+ from nonvolatile acids
17
Q
What is important for local acid-base balance?
A
Good tissue perfusion
18
Q
What are components of chemical buffers?
A
- Consist of a weak acid and a weak base.
- Convert strong acids/bases to weak ones.
19
Q
How long does chemical buffer take to buffer?
A
Max efficiency with an hour after imbalance
React almost immediately
20
Q
What are the types of chemical buffers?
A
- Bicarbonate buffer system
- Phosphate buffer system
- Intracellular and extracellular proteins
21
Q
How do you calculate pH of a buffer system?
A
Henderson–Hasselbalch equation
22
Q
Describe the chemical regulation of bicarb buffer system?
A
The ratio of bicarbonate (HCO3-) to carbonic acid (H2CO3) is 20:1
23
Q
What is pKa?
A
Dissociation constant of weak acid
24
Q
What is the ideal buffer system?
A
pKa = pH of solution
25
What is the purpose for bicarbonate buffer system?
pKa=6.1 (and blood pH=7.4) → still an important ECF buffer because:
1. Lungs can regulate the level of carbonic acid
2. Kidneys can regulate the level of bicarb
26
How does the bone contribute to acid and base balance?
1. H+ ions move into bone to be buffered by hydroxyapatite and carbonates → release of Ca and phosphate from bone
2. Prolonged ↑ H+ → activate osteoclasts → bone resorption
3. Electrolyte loss and resorption → bone demineralization and increased risk of fractures
27
How does respiration regulate acid-base balance?
1. CO2 diffuses from pulmonary capillaries into alveoli and is then eliminated in exhaled air
2. If CO2 accumulates, then the concentration of H+ in body fluids increases
28
How control respiratory reg?
Brainstem respiratory center → feedback mechanism between it and the lungs
H+ excess trigger a neural reflex
29
How does ↑ H+ neural reflex?
1. ↑ rate and contraction of respiratory muscles
2. ↑ breathing rate and depth
3. Eliminate CO2 → ↓ carbonic acid → ↑ pH
30
How does the respiratory system compensate for extreme acidosis?
Hyperventilation ceases
Reflex fails
31
How does the respiratory system compensate for extreme alkalosis
Ventilation is depressed, leading to:
1. Accululation of CO2 → ↑ carbonic acid → ↓ pH
32
What is compensatory hypoventilation?
Lungs retain CO2 → more carbonic cid
33
How is hypoventilation not really noticed?
Subsequent hypoxemia and hypercapnia stimulate respiration
34
How long does it take for respiratory reg compensate?
Maximal compensation takes 24-48 hours
Chemoreceptors detect H+ changes
35
What may cause a delay is respiratory reg?
1. Transporting blood
2. Initiating a relex response
36
What are the respiratory compensation limitations?
1. If lungs are source of acidosis or alkalosis.
2. Diminished stimulus to respiratory center
3. Lung disease
4. Neuromuscular disease
37
How does the renal regulate acid-base?
Regulates bicarbonate and nonvolatile acids
38
What is normal pH of urin?
Usually acidic
4-8, average: 6
39
What are the mechanisms of renal reg?
1. Conservation of bicarbonate by tubular reabsorption.
2. Secretion of H+ into urine; synthesis of new bicarbonate.
3. Excretion of H+ buffered by ammonia
40
How does it take longer for the renal system to regulate acid-base?
8-12 hours – begin to have effect
4-6 days – maximum effectiveness
Slowest yet most effective → H+ and HCO3- can be excreted if need → capable of completely retuning pH to normal
41
How causes disruption to renal reg?
1. Kidney impariment
2. They are a source of the imbalance
42
Describe how the renal system conserves bicarb ions?
43
Describe how the renal system secrete H+ in the urine and creates new HCO3-?
44
What is the difference between compensation and correction?
**Compensation:** Chemical buffers, renal or respiratory function return pH within normal range → Underlying disease
**Correction:** Condition responsible for imbalance is controlled or no longer present → pH is within normal range
45
What is intracellular pH?
1. Major impact on cell function
2. Affected by changes in both the H+ concentration and ECF
3. Varies with different cell types
4. Clinical pHi measurement is not feasible
46
What are the mechanism for regulating pHi?
1. buffers
2. HCO3-
3. Transporters
47
What are the simple acid-base imbalances? Distinguish the types?
1. Respiratory acidosis
2. Respiratory alkalosis
3. Metabolic acidosis
4. Metabolic alkalosis
48
What is the difference between respiratory and metabolic imbalances?
R: Due to alteration in CO2 elimination by lungs
M: Due to alterations in the level of nonvolatile acids or bases HCO3
49
How are the clinical manifestation of acid-base imbalances?
1. Effects of acidosis or alkalosis on cell functions.
2. Effects of underlying disease process causing acid-base imbalance.
3. Manifestations of respiratory or renal compensation.
50
What is the normal ratio of bicarb to carbonic acid?
20:1
51
What ions control neuromuscular function?
Hydrogen and calcium ions that bind to negative charged plasma intracellular proteins and
52
How is neuromuscular function affected by acidosis?
Reduced NM excitability by ↑ levels of calcium that blocks sodium channels in nerves and muscles → decreases neuromuscular excitability → muscle weakness, weak reflexes
Excess H+ ions bind to negative charges causing fewer sites available for Ca2+
53
How is neuromuscular function affected by alkalosis?
↑ NM excitability → fewer H+ compete with Ca2+ for PB sites → less Ca2+ blocks sodium channels
54
What are the NM function of alkalosis?
1. Trousseasu
2. Hyperactive reflexes
3. Paresthesias
4. Convulsion
5. Larynospasm
6. Tetany
55
How is the CNS altered by acidosis?
Increased cerebral BF → decreased sodium entry → vasodilation of cerebral blood vessels → HA, increased intracranial pressure
56
How is the CNS altered by alkalosis?
Vasoconstriction of cerebral BV → ↓ cerebral BF and O2 delivery → DZ, AX, SZ, Confusion, coma
57
How does acidosis affect perfusion?
1. Negative ionotropic effect → decrease in cardiac contractility → Decreased perfusion
2. Increased sympathetic tone initially helps compensative
3. Increased arterial BP
4. Decreased responsiveness of adrenergic receptors
5. Vasodilation from impaired Na entry into cell
58
How does alkalosis affect perfusion?
Biphasic effect on cardiac countability
Associated with hypokalemia → increased vascular reactivity → coronary artery vasospasm → MI, angina
59
How does alkalosis affect SVR?
Vasodilation and decreased SVR at pH ≤ 7.65
Vasoconstriction and increased SVR at pH > 7.65
60
How does metabolic acidosis effect electrolyte levels?
Caused by an excess of inorganic acids or sulfuric acids: Excess H+ enter cells in exchange for movement of K+ out of cells → hyperkalemia
Caused by excess organic acids or ketoacid → H+ and anion move into the cell
61
How can metabolic alkalosis affect electrolyte levels?
H+ move out of cells in exchange for K+ movement into cells → Hypokalemia
62
What has respiratory acidosis affect electrolyte levels?
↑ serum P
63
What has respiratory alkalosis affect electrolyte levels?
↓ serum P
64
What is the relationship of Phosphofructokinase and acid-base balance?
Acidosis → PFK depression → imparts glycolysis and ATP production → Decreased ATP → weakness and fatigue
Alkalosis → PFK ↑ → stimulates glycolysis → ↑ use of P
65
How does acidosis affect oxygenation?
Hemoglobin–oxygen dissociation curve shifts to right → decreased affinity of Hb and increased unloading of O2 to cells → Beneficial
66
How does alkalosis affect oxygenation?
Hemoglobin–oxygen dissociation curve shifts to left → Increased affinity of Hb → Decreased unloading → Adverse effects
67
What are the lab tests we could do to assess acid-base status?
1. Arterial blood gases
2. Venous blood gases
3. Base excess
4. Anion gap
68
What is the most useful test for A-B assessment?
ABG
69
What does ABG measure?
1. pH
2. PaCO2
3. PaO2
4. HCO3-
5. Total CO2 (TCO2)
70
What is acidosis?
Pathophysiologic process resulting in excess amount of H+ in the body
71
What is normal pH?
7.35–7.45
72
What is acidemia?
State of excess H+ and base deficit (low pH) in the blood
73
What is alkalosis?
Pathophysiologic process resulting in a deficit of H+ in the body
74
What is alkalemia?
State of H+ deficit and base excess (elevated pH) in the blood
75
How can acidosis and alkalosis be present at the same time?
Two or more processes may drive pH in opposite directions
A patient’s acid-base status could be abnormal even if pH is within a normal range
76
What is PaCO2?
Pressure exerted by CO2 dissolved in arterial blood plasma
77
How affects PaCO2?
Below-normal pH and increased PaCO2 indicate respiratory acidosis.
Above-normal pH and decreased PaCO2 indicate respiratory alkalosis.
78
Describe the effects of PaCO2 with compensation?
If pH is low because of metabolic acidosis, lungs compensate by decreasing PaCO2
A low PaCO2 level is **not** the cause of the low pH
79
How does the kidneys compensate for respiratory acid-base imbalance?
increasing or decreasing HCO3–.
If pH is low because of respiratory acidosis, kidneys compensate by increasing serum HCO3–.
In that case, increased HCO3– level is not the cause of the low pH because HCO3– is a base.
80
What is total CO2? What is it for?
All forms of CO2 in blood
Acid is added to blood sample → CO2 gas liberated and measured
81
What is PaO2?
Pressure exerted by O2 dissolved in arterial blood plasma → points out if acidosis is present
82
Describe how PaCO2 and HCO3- levels react to AB imbalances?
83
What is an anion gap?
Used when the type of imbalance is unclear
Differentiates the cause of metabolic acidosis and identifies acid-base imbalances
84
Anion gap detects _____ amount of anions?
Increased
Sum of concentration of all cations equals the sum of concentration of all anions
85
What is are common causes of high anion gaps?
1. Lactic acidosis
2. Ketoacidosis
3. Renal failure
86
What are the factors that stabilize a normal anion gap?
1. Chloride ↑
2. HCO3 below normal
Reciprocal relationship between Cl- and HCO3-
87
What are the characteristics of respiratory acidosis?
1. Elevated PaCO2 (hypercapnia) and H2CO3-
2. Blood pH <7.35
3. Ratio of bicarbonate to carbonic acid below 20:1
88
What is acute vs chronic respiratory acidosis?
Acute: present before renal compensation
Chronic: present after renal compensation is complete
89
What are the causes of respiratory acidosis?
Impaired elimination of CO2 by lungs:
1. Respiratory diseases or conditions
2. CNS dysfunction
3. Neuromuscular disorders
4. Electrolyte imbalances
5. Metabolic conditions
90
How does respiratory disease cause the acidosis (respiratory)?
1. Impaired alveolar ventilation or diffusion of CO2 from blood into alveoli.
2. Increased production of CO2 without an increase in ventilation
91
How does respiratory acidosis cause CNS dysfunction?
1. Decreased central drive to breathe: neural centers receive input → peripheral chemoreceptors → stimulate breathing
92
What medication can cause respiratory acidosis?
General anesthetics, barbs, opioid analgesis
93
What can ↓ central drive to breathe?
1. Increased intracranial pressure
2. Sleep apnea
3. Cardiopulmonary arrest
94
How can respiratory acidosis causes NM disorders?
1. Restrict lung expansion
2. Obstruct airflow
Interfere with innervation or contractility of the muscles of inspiration
Fluid accumulation in the abdominal cavity
95
How can respiratory acidosis causes electrolyte imbalances?
1. Severe hypokalemia → Decreased contraction of respiratory muscles leads to hypoventilation
2. Severe hypophosphatemia → Decreased availability of phosphate and respiratory muscle contractility → hypoventilation
96
How can respiratory acidosis causes metabolic conditions?
increase CO2 production without increased CO2 elimination → increase body temp and overfeeding with carbs
97
What is permissive hypercapnia?
↑ in PaCO2
Low tidal volume ventilation
98
What are clinical manifestation of uncompensated respiratory acidosis?
Arterial blood pH < 7.35
PaCO2 elevated
HCO3- normal
99
What are clinical manifestation of compensated respiratory acidosis?
1. Increased bicarbonate resorption
2. Increased H+ excretion
3. Serum bicarbonate level increases.
4. pH elevates to normal.
5. Urine becomes more acidic.
100
What are the characteristics of respiratory alkalosis?
CO2 deficit (hypocapnia)
Increases ratio of bicarbonate to carbonic acid above 20:1.
101
What is the difference between the types of respiratory alkalosis?
Acute: Presense of hypocapnia before renal compensation
Chronic: Presence of hypocapnia after renal compensation is complete
102
How does hyperventilation cause respiratory alkalosis?
increased alveolar ventilation → Increse in CO2
103
How does CNS dysfunction cause respiratory alkalosis?
decreased oxygen delivery → activate peripheral chemoreceptors → respiratory centers in brain → excessive CO2 elimination → alkalosis
104
What are causes of respiratory alkalosis?
1. Emotions
2. Lung disease
3. Endogenous substances
4. Brain lesions
5. Medication: Salicylates
6. Hypermetabolic states
7. Mechanical ventilation
105
What are the signs of respiratory alkalosis?
1. Increased neuromuscular excitability.
2. Increased effort to breath due to increased rate or depth of breathing.
106
What is the clinical manifestations of uncompensated respiratory alkalosis?
1. Arterial blood pH > 7.45
2. PaCO2 decreased
3. Serum bicarbonate normal
107
What is the clinical manifestations of renal compensated respiratory alkalosis?
1. Decreased bicarb resorption
2. Decreased H+ excretion
3. Decreased serum bicarb levels
4. pH decreases to normal
Manifestations more severe in acute cases
108
What are the characteristics of metabolic acidosis?
1. Decreased blood pH (due to H+ excess)
2. Decreased HCO3–
3. Normal PaCO2
4. Ratio of bicarbonate to carbonic acid: <20:1
109
What are the causes of metabolic acidosis?
1.Elevated anion gap
2. Normal anion gap
110
Describe elevated anion gap metabolic acidosis?
Increase production of or decrease elimination of fixed acids
111
Describe normal anion gap metabolic acidosis?
Increase base bicarbonate loss or decrease production or renal reabsorption of bicarbonate
112
What are the causes of elevated anion gaps?
1. Lactic acidosis
2. Diabetic and alcoholic ketoacidosis
113
What is the difference between lactic acidosis types?
Type A: Conditions that cause imbalance between oxygen demands and oxygen supply (hypoxia)
Type B: Due to conditions other than hypoxia
114
What is ketoacidosis?
abnormal lipid metabolism → increased ketoacid production
115
What is diabetic ketoacidosis?
Insulin deficiency and resistance
116
What is alcoholic ketoacidosis?
excessive ingestion of alcoholic beverages
117
How can renal failure cause elevated anion gap?
Decreased GFR → impaired daily excretion of fixed acids and deceased renal production of ammonia, decreasing ability to excrete H+ buffered in urine
118
How can pregnancy cause elevated anion gap?
Decreased perfusion → hemorrhage, sepsis, severe HTN, compression of umbilical cord
119
What are the poisons that cause elevated anion gap?
MULEPAK
1. Methanol
2. Uremia (caused by renal failure)
3. Lactic acidosis
4. Ethylene glycol
5. Paraldehyde (and other drugs)
6. Aspirin (and other salicylates)
7. Ketoacidosis
120
How does ethylene glycol cause elevated anion gap?
121
What are the cause of metabolic acidosis that have normal anion gap?
1. Loss of HCO3--rich intestinal fluid
2. Impaired HCO3- resorption in kidneys
122
What causes hyperchloemic metabolic acidosis?
When chloride increases, HCO3- decreases → due to ↑ in renal excretion of HCO3 to maintain electrical neutrality in ECF
123
What is type 1 renal tubular acidosis?
Defect in H+ pump in DCT → impaired H+ ion secretion into urine → failure of H/K ATPase
124
What is type 2 renal tubular acidosis?
Impaired HCO3- resorption in PCT → Involves increased K+ excretion
125
What are clinical manifestation of uncompensated metabolic acidosis?
1. Arterial blood pH < 7.35
2. PaCO2 normal
3. Serum HCO3- below normal
126
What are the signs of metabolic acidosis compensation?
1. Increased rate/depth of breathing
2. Kussmaul respirations (deep/labored breathing)
127
What are the signs of respriratory compensation of metabolic acidosis?
1. CO2 elimination increases.
2. Serum H2CO3 decreases.
3. pH rises to normal
128
What are the characteristics of metabolic alkalosis?
1. State of H+ deficit and increased blood pH
2. Increased HCO3-
3. Normal PaCO2
4. Ratio of bicarbonate to carbonic acid: >20:1
129
What are the mechanisms that cause of metabolic alkalosis?
1. Excessive loss of hydrogen ions.
2. Excessive intake of base.
3. Excessive renal retention of bicarbonate.
130
What is contraction alkalosis?
Loss of ECF volume without comparable HCO3 loss
131
What are the factors that impair renal HCO3 excretion?
1. Circulating fluid volume deficit
2. Potassium or chloride deficiency
3. High aldosterone levels
132
What are the common causes of metabolic alkalosis?
1. Loss of gastric fluid (hypochloremic metabolic alkalosis)
2. Loop and thiazide diuretics
3. Excessive or too rapid correction of acidosis.
4. Large amounts of bases
5. Posthypercapnic metabolic acidosis
6. Milk alkali syndrome
133
What is posthypercapnic metabolic acidosis?
When PaCO2, and thus carbonic acid, is quickly lowered, elevated bicarbonate has less acid to buffer
134
What is milk alkali syndrome?
Hypercalcemia and metabolic alkalosis resulting from ingestion of large amounts of milk and antacids containing calcium carbonate
135
What are the clinical manifestations of metabolic alkalosis?
1. Changes in blood gases.
2. Decreased rate and/or depth of breathing.
3. Impaired cell oxygenation.
4. Increased neuromuscular excitability
136
What are the clinical manifestations of uncompensated metabolic alkalosis?
1. Arterial blood pH > 7.45
2. PaCO2 normal
3. Serum HCO3- above normal
137
What are the signs of respiratory compensation of metabolic alkalosis?
1. CO2 elimination decreases
2. Serum H2CO3 increases
3. pH lowers to normal
138
What is mixed acid-base imbalances?
Two or more types of acid–base imbalances
If a change in bicarbonate or PaCO2 **exceed the normal limits of compensation**, it usually indicates the presence of mixed acid-base imbalance
139
What factors determine the type of acid-base imbalances in a patient?
1. Patient history
2. Clinical manifestations
3. Lab tests
140
What is the stepwise approach of analyzing A-B imbalances?
1. Check blood pH (acidemia or alkalemia)
2. Determine whether the imbalance is of respiratory or metabolic origin on the basis of changes in PCO2 or HCO3-
141
What are the directions that change values of acid-base imbalances?
**R**espiratory
**O**pposite
**RO:** Respiratory origin, pH and CO2 change in opposite directions.
**M**etabolic
**E**qual
**ME:** Metabolic origin, pH and HCO3- change in the same direction.
**M**ixed acid-base imbalances
