Unit 9 - Acid Base Flashcards
1
Q
details how PaCO2 and HCO3- influence pH
A
Henderson-Hasselbach equation
2
Q
most important buffer system in the blood
A
bicarb
3
Q
2nd most important buffer in the blood
A
Hgb
4
Q
renal compensation of buffers
A
- Reabsorption of filtered bicarb
- Removal of titratable acids (non-volatile acids)
- Formation of ammonia
5
Q
why is acidosis often accompanied by hyperkalemia
A
H+ is transported into cells, K+ is transported out of cells
6
Q
normal anion gap
A
8-12 mEq/L
7
Q
anion gap =
A
Na+ - (Cl + HCO3)
8
Q
causes of increased anion gap metabolic acidosis
A
MUDPILES
Methanol
Uremia
DKA
Paraldehyde
Isoniazid
Lactate
Ethanol, ethylene glycol
Salicylates
9
Q
examples of increased lactate assoc with increased anion gap metabolic acidosis
A
sepsis
decreased O2 delivery
cyanide poisoning
10
Q
causes of normal anion gap metabolic acidosis
A
HARDUP
Hypoaldosteronism
Acetazolamide
Renal tubular acidosis
Diarrhea
Uterosigmoid fistula
Pancreatic fistula
11
Q
time it takes for compensation of respiratory vs metabolic disorders
A
- Compensation for metabolic disorders is rapid (over several minutes) due to changes in minute ventilation
- Compensation for respiratory disorders is slow (over several days) due to change in H+ excretion in urine
12
Q
how does the body compensate for respiratory acidosis
A
increased HCO3-
13
Q
how does the body compensate for respiratory alkalosis
A
decreased HCO3-
14
Q
how does the body compensate for metabolic acidosis
A
decreased PaCo2
15
Q
how does the body compensate for metabolic alkalosis
A
increased PaCO2
16
Q
5 questions to ask when evaluating a blood gas
A
- is the pH normal
- is the PaCO2 normal
- is the HCO3- normal
- has compensation occured
- if there’s metabolic acidosis, is the anion gap normal or increased
17
Q
CV effects of acidosis
A
↑ P50 (right = release)
↑ SNS tone
↑ risk dysrhythmias
↓ contractility
Direct myocardial depression
18
Q
CNS effects of acidosis
A
↑ cerebral blood flow
↑ ICP
19
Q
pulmonary effects of acidosis
A
↑ PVR
20
Q
CV effects of alkalosis
A
↓ P50 (left = love)
↓ coronary blood flow
↑ risk dysrhythmias
21
Q
CNS effects of alkalosis
A
↓ cerebral blood flow
↓ ICP
22
Q
pulm effects of alkalosis
A
↓ PVR
23
Q
electrolyte changes assoc with alkalosis
A
hypokalemia
↓ ionized calcium
24
Q
pH that indicates need for mechanical ventilation
A
< 7.2
25
PaCO2 =
CO2 production / alveolar ventilation
26
3 etiologies of respiratory acidosis
1. increased CO2 production
2. decreased CO2 elimination
3. rebreathing
27
Most common cause of resp acidosis
hypoventilation
28
causes of ↑ CO2 production
* sepsis
* overfeeding
* MH
* intense shivering
* prolonged seizure activity
* thyroid storm
* burns
29
causes of ↓ CO2 elimination
* airway obstruction
* ↑ Vd
* ↑ Vd/Vt
* ARDS
* COPD
* respiratory center depression
* drug overdose
* inadequate NMB reversal
30
in **acute** resp acidosis, every 10 mmHg increase in PaCO2 = pH increase by ____
for every 10 mmHg increase in PaCO2, pH increases by **0.08**
31
in **chronic** resp acidosis, every 10 mmHg increase in PaCO2 = pH increase by ____
for every 10 mmHg increase in PaCO2, pH decreases by **0.03**
32
why is resp acidosis assoc with hypoxemia
Alveolar nitrogen is inert – concentration remains constant
↑ Alveolar CO2 displaces alveolar O2 = arterial hypoxemia
33
why does P50 increase with respiratory acidosis
Curve shifts to the right – releases more O2 to tissues
**Partially compensates for hypoxemia**
34
why is cardiac and smooth muscle depression assoc with respiratory acidosis
Acidosis inside muscle affects contractile protein & enzymatic function
| myocardial depression, vasodilation
35
SNS effects of respiratory acidosis
SNS stimulation - CO2 activates
| unless acidosis is severe, offsets smooth muscle depression
36
effects of SNS stim with resp acidosis
* Tachycardia = ↑ myocardial O2 consumption & ↓ delivery
* Vasoconstriction = ↑ SVR = ↑ myocardial O2 consumption
* Dysrhythmias, prolonged QT
* Oculocardiac reflex is more common following precipitating event
37
why is K+ increased in respiratory acidosis
* Activates H+/K+ pump
* Buffers CO2 acid in exchange for releasing K+ into plasma
38
why is Ca2+ increased in resp acidosis
Ionized Ca2+ competes with H+ for binding sites on plasma proteins
## Footnote
Acidosis: plasma proteins buffer H+ and release Ca2+ = ↑ inotropy
39
ICP with resp acidosis
increased
* CO2 freely diffuses across BBB
* Decreased CSF pH = ↓ cerebrovascular resistance = ↑ CBF & vol.
40
when does CO2 narcosis occur
PaCO2 > 90 mmHg
41
how does hypercarbia affect pulmonary vs peripheral blood vessels
opposite effect on pulmonary blood vessels vs. peripheral blood vessels
* In the lungs, CO2 is a direct-acting vasoconstrictor - can cause pHTN and ↑ RV workload
42
when does respiratory alkalosis occur
when alveolar ventilation exceeds CO2 production
43
etiologies of resp alkalosis
* Iatrogenic: mechanical ventilation - **most common**
* Hypoxia (high altitude, low FiO2, profound anemia)
* Pain/anxiety
* Pregnancy
* Drugs: progesterone, salicylates
* Pulmonary embolism
* Reduced mechanical dead space with same alveolar ventilation (removing HME, changing from mask to ETT)
44
how does the body compensate for respiratory alkalosis
kidneys excrete HCO3- to return pH to normal
| This may take several days
45
how does the body compensate for respiratory alkalosis
kidneys excrete HCO3- to return pH to normal
| This may take several days
46
CV effects of resp alkalosis
* Dysrhythmias
* Decreased coronary blood flow
* Decreased myocardial contractility
* Decreased P50 (left shift)
47
CNS effects of resp alkalosis
* Inhibition of respiratory drive
* Cerebral vasoconstriction (↓ CBF and ↓ ICP)
* Neuronal irritability
* Confusion
48
electrolyte changes with resp alkalosis
Decreased serum K+
Decreased serum Ca2+
49
best treatment for resp alkalosis
reverse underlying cause
## Footnote
* In spontaneously ventilating patient, treat with sedation (concern when pH > 7.6)
* In mechanically ventilated patient, treat by reducing minute ventilation on the ventilator
50
causes of metabolic acidosis
accumulation of nonvolatile acids, loss of bicarbonate, or large volume resusication with sodium chloride solution
51
anion gap =
major cations - major anions
*or*
([Na+] – [Cl-] + [HCO3-])
52
is accumulation of acids assoc with gap or non-gap metabolic acidosis
gap
53
is loss of bicarb/ECF dilution caused by gap or non gap acidosis
non gap
54
how does the body compensate for metabolic acidosis
eliminate CO2 by increasing minute ventilation
55
PaCO2 decreases by ____ mmHg for every HCO3- decrease of ____ mEq/L
PaCO2 decreases by **1-1.5** mmHg for every HCO3- decrease of **1** mEq/L
56
when should bicarb be admin with metabolic acidosis
generally useful in non-gap acidosis (most etiologies produce bicarb loss)
controversial in gap acidosis
## Footnote
Best used for gap as a temporary measure if pH < 7.2 and patient is hemodynamically unstable
57
treatment of uremia or drug-induced gap acidosis
dialysis
58
what causes metabolic alkalosis
increased bicarbonate and/or loss of nonvolatile acids
59
etiologies of metabolic alkalosis assoc with addition of HCO3-
bicarb admin
massive transfusion
| (liver converts transfusion preservatives to HCO3)
60
etiologies of metabolic alkalosis assoc with addition of HCO3-
bicarb admin
massive transfusion
| (liver converts transfusion preservatives to HCO3)
61
etiologies of metabolic alkalosis assoc with loss of nonvolatile acid
* Loss of gastric fluid (**most common**): vomiting, NG suction
* Loss of acid in urine
* Diuretics
* ECF depletion = increased Na+ reabsorption
62
causes of metabolic alkalosis assoc with increased mineralocorticoid activity
Cushing’s syndrome
Hyperaldosteronism
63
how does the body compensate for metabolic alkalosis
body will retain CO2 by reducing minute ventilation
64
PaCO2 increases by ____ for every HCO3- increase of 1 mEq/L
**0.5-1 mmHg**
65
treatment of metabolic alkalosis
fix underlying cause
* Acetazolamide (carbonic anhydrase inhibitor): increases renal excretion of HCO3-
* Spironolactone (mineralocorticoid antagonist)
* Dialysis
66
acid base disturbance assoc with large volume NS resuscitation
hyperchloremic metabolic acidosis
67
why do salicylates cause metabolic acidosis
inhibit krebs cycle
68
when should bicarb be given for anion gap metabolic acidosis
temporary measure if pt's pH is < 7.2 and hemodynamically unstable
## Footnote
bicarb can cause intracellular acidosis in the setting of inadequate ventilation/perfusion
