Acid-Base Balance; Abg Analysis

Front 1

What is an acid?

Back 1

substance dissolved in water;
yields H+ ions
lowers pH

Front 2

What is a proton donor?

Back 2

hydrogen
(ie: HCl --> H+ + Cl-

Front 3

what is one of the most tightly regulated ions in the body?

Back 3

H+
35-45nM/L

Front 4

what is a base?

Back 4

substance dissolved in water
yields hydroxide ion (OH-)
remove H+ ions from a sol'n

Front 5

what has a strong affinity for H+ ions?

Back 5

hydroxide ions
NaOH --> Na+ + OH-

Front 6

what is a proton acceptor?

Back 6

bases
remove H+ from a sol'n

Front 7

what is another way of expressing H+ ions concent

Back 7

pH

Front 8

what does pH represent?

Back 8

arterial concentration of H+ ions

Front 9

what happens w/inc H+ ion concentration

Back 9

acidity
lowers pH

Front 10

what is pH of ECF

Back 10

7.35 - 7.45

Front 11

pH is controlled how?

Back 11

homeostatic process

Front 12

what happens w/abnormal fluctuations in pH?

Back 12

break chemical bonds
change shape of proteins
alter cellular fxn

Front 13

pH of <7

Back 13

acidic sol'n
H+ ions prevail

Front 14

pH of >7

Back 14

alkaline (basic) sol'n
OH- ions prevail (hydroxide)

Front 15

What is the Henderson-Hasselbach equation?

Back 15

quantitative measurement describing the relationship b/w plasma pH and the ratio of plasma pCO2 and HCO3

Front 16

what is the primary determinant of pH

Back 16

ratio of pCO2 to HCO3
not the individual values

Front 17

when does pH decrease?

Back 17

increase CO2 or
decrease HCO3

Front 18

what keeps pH from marked changes

Back 18

the buffering system

dec HCO3 --> dec CO2

Front 19

what is the ratio of HCO3 to CO2 at a constant pH

Back 19

20:1

Front 20

ratio of HCO3 to CO2 @ 20:1 is = to a pH of?

Back 20

7.4

Front 21

is the ratio b/w HCO3 and CO2 directly inversely proportional?

Back 21

directly

Front 22

what is the mathematical equation of the Henderson-Hasselbach equation?

Back 22

pH = 6.1 + log(HCO3/0.03 x pCO2)

Front 23

what are the buffering systems?

Back 23

bicarbonate buffers
hemoglobin buffers
other protein buffers
phosphate buffers

Front 24

what are the 3 systems that keep pH in tight control?

Back 24

buffering systems
ventilatory response
renal response

Front 25

what is the response time of the renal system?

Back 25

12 - 24 hours

Front 26

what is the most powerful acid-base regulator system?

Back 26

kidneys

Front 27

what are the 2 most important buffering systems?

Back 27

bicarbonate is #1
Hgb is #2

Front 28

does the phosphate buffering system include the kidneys?

Back 28

no

Front 29

What is the carbonic acid-bicarbonate buffer system?

Back 29

most important in ECF

Front 30

what is the phosphate buffer system?

Back 30

buffers ICF and urn

Front 31

what is the protein buffer system?

Back 31

regulate pH in ECF & ICF
extensive interaction w/other buffer systems

Front 32

What is carbonic acid?

Back 32

H2CO3

Front 33

what is the chemical equation of the bicarbonate buffer system?

Back 33

CO2 + H2O<-->H2CO3<-->H + HCO3

Front 34

what does the bicarbonate buffer system depend on?

Back 34

hydration of CO2 to carbonic acid in plasma and erythrocytes

Front 35

what is the primary role of the bicarbonate buffer system?

Back 35

prevent pH changes d/t acids in ECF

Front 36

what does the bicarbonate system consist of?

Back 36

carbonic acid (weak acid)
and bicarbonate (weak base)

Front 37

what happens to the CO2 produced throughout the day?

Back 37

converted to carbonic acid; this then dissociates into H+ ion and bicarb ion

Front 38

what is the only ICF buffering system?

Back 38

Hgb
has an immediate effect on pH of ECF

Front 39

what is the Hgb buffering system responsible for?

Back 39

prevents drastic alteration in pH w/inc or dec in pCO2

Front 40

what is contained in the cytoplasm of Hgb?

Back 40

large amounts of carbonic andhydrase (enzyme)

Front 41

what does Hgb buffering system do?

Back 41

absorbs CO2 from plasma; converts it to H2CO3;

Front 42

why is CO2 absorbed into ICF?

Back 42

can diffuse easily across RBC membranes

Front 43

what happens when H2CO3 dissociates in the Hgb buffer system?

Back 43

moves into plasma via Cl- shift

Front 44

What is the purpose of Cl- in the Hgb buffer system?

Back 44

helps maintain electrical neutrality

Front 45

How are H+ ions formed?

Back 45

digestive tract
metabolic activities w/in cells

Front 46

to preserve homeostasis, what must happen to H+ ions?

Back 46

rendered harmless
must be eliminated to preserve homeostasis

Front 47

Do buffer systems provide total restoration of homeostasis?

Back 47

no, only a temporary sol'n

Front 48

What are the 2 mechanisms the body uses to eliminate H+ ions?

Back 48

pulmonary
renal

Front 49

how does the body maintain heomeostasis?

Back 49

combo of buffering systems
pulmonary
renal

Front 50

What is pulmonary compensation?

Back 50

control of H+ ion concen through the exhalation of CO2

Front 51

how is alveolar ventilation mediated?

Back 51

chemoreceptors in the medulla;
they respond to changes in CSF pH

Front 52

how is pulmonary compensation stimulated?

Back 52

CO2 can easily cross BBB; reacts w/H2O to produce H+ ions to increase respiration

Front 53

what is the increase in MV for every inc 1mmHg in PaCO2?

Back 53

1-4L/min

Front 54

what does the renal response to pH consist of?

Back 54

increased reabsorption of filtered HCO3
increased excretion of H+
increased production of ammonia (NH3)

Front 55

What is the goal of the renal system?

Back 55

to reabsorb HCO3

Front 56

how much HCO3 is reabsorbed?
where?

Back 56

90%
proximal tubule
10% reabsorbed in distal parts of tubule

Front 57

Is HCO3 normally excreted?

Back 57

No

Front 58

What is the fundamental event in renal regulation of acid-base balance?

Back 58

Na+ - H+ exchange

Front 59

What happens in the Na+ and H+ exchange?

Back 59

permists bicarboniate ions to be reabsorbed and acids to be excreted

Front 60

What is the process by which Na+ and H+ exchange takes place?

Back 60

H+ is actively secreted into the proximal tubule in exchange for Na+
Na+ enters the cell passively

Front 61

What is the goal of the phosphate buffering system?

Back 61

excrete H+ ions

Front 62

What happens in the phosphate buffering system?

Back 62

HCO3 is reabsorbed
H+ is secreted into tubular lumen
H+ then combines with phosphorous (HPO4) to create phosphate (H2PO4)

Front 63

Can H2PO4(phosphate) be reabsorbed?

Back 63

No
r/t charge

Front 64

What happens to H2PO4?

Back 64

it is excreted from tubual

Front 65

What happens when urn pH is 4.4?

Back 65

phosphate saturated;
phosphorous ions no longer available for eliminating H+ ions

Front 66

What is the buffer system after the phosphate buffer system?

Back 66

Ammonia buffer system.
goal is to form NH3 (ammonia)

Front 67

Why is this an important buffering system?

Back 67

when phosphate sytem is completely saturated, this the most imporant urinary buffer

Front 68

what is the biological process of the ammonia buffer system?

Back 68

deamination of glutamate in the proximal tubule mitochondria

Front 69

where is the principal source of NH3 (ammonia) formation

Back 69

proximal tubular cells

Front 70

what happens w/acidemia

Back 70

a marked increase in renal NH3 production

Front 71

what diffuses easily across the membranes in the ammonia buffer system

Back 71

NH3
enters passively

Front 72

what is diffusion trapping?

Back 72

NH4 (ammonium) is unable to cross into tubular cells;
trapped in tubules

Front 73

what does the excretion of NH4 do?

Back 73

effectively eliminates H+

Front 74

what does acidosis lead to?

Back 74

release of catecholamines
this offset myocardial depression

Front 75

what happens w/a pH of 7.2 or less

Back 75

myocardium unable to respond to release of catecholamines
dec SVR/contractility --> dec BP

Front 76

what is another neg effect of pH 7.2<

Back 76

dec in threshold for vf

Front 77

what happens w/pts who have ischemic heart dz or those w/beta blockers/ga

Back 77

detrimental effects of acidemia may be more pronounced

Front 78

what happens w/severe acidosis

Back 78

tissue hypoxia even with
shift to right of oxyhgb curve

Front 79

what happens in lethal hyperkalemia

Back 79

H+ K+ shift across cell membranes

Front 80

what happens to plasma k+ concentrations w/change in pH

Back 80

increase 0.6meq/L for each 0.10 decrease in pH

Front 81

do H+ ions pass the BBB

Back 81

no
CO2 diffuses more easily

Front 82

what produces an adverse effect response to acidosis?

Back 82

respiratory (acute)
chronic metabolic is slower process; kidneys are able to keep up w/changes

Front 83

what is CO2 narcosis?

Back 83

CNS depression
r/t respiratory > metabolic acidosis
greatly dec neuronal activity --> coma

Front 84

what are the vasodilatory effects of acidosis?

Back 84

inc CBF --> inc ICP--> dec CPP--> cerebral ischemia

Front 85

what is another CNS effect of acidosis

Back 85

increases szr threshold

Front 86

what is acidosis caused by?

Back 86

hypoventilation and CO2 retention

Front 87

what are some causes?

Back 87

drug/dz process that decreases alveolar ventilation --> inc CO2 concent in plasma

Front 88

what happens when CO2 crosses BBB

Back 88

dec CSF pH

Front 89

what happens w/inc CO2 in CSF

Back 89

dec CSF pH --> stim of medulla --> inc ventilation

Front 90

what happens w/inc ventilation

Back 90

dec CO2 content --> restoration of CSF pH

Front 91

what happens w/peripheral chemoreceptors?

Back 91

carotid bodies/aortic arch respond to changes in CO2 and O2 concent

Front 92

what happens to the peripheral chemoreceptors w/GA

Back 92

dec carotid body response to acidemia

Front 93

what is the time frame for compensation of acute resp acidosis?

Back 93

varies b/w 6-12 hrs
limited

Front 94

how is comp of acute resp acidosis accomplished?

Back 94

Hgb buffer
ECF H+ exchanged for Na+/K+ from bone/ICF

Front 95

what happens w/the renal response to acute resp acidosis?

Back 95

bicarb retention limited

Front 96

what happens to the HCO3 plasma concentrations?

Back 96

inc 1meq/L for each 10mmHg inc in PaCO2 >40mmHg

Front 97

what does tx consist of ?

Back 97

mechanical ventilation unless a quick tx for a simple etiologic factor can be done

Front 98

how long does complete comp for chronic resp acidosis take?

Back 98

12-24 hrs
peak 3-5 days

Front 99

what happens w/chronic resp acidosis?

Back 99

inc renal secretion of H+ ions --> inc HCO3 plasma concen

Front 100

what is the tx for chronic resp acidosis?

Back 100

rarely mech vent
improve pulm fxn --> elim CO2

Front 101

what happens when PaCO2 is decreased too quickly in pt w/chronic resp acidosis?

Back 101

metabolic alkalosis
CNS irritability

Front 102

what is the goal for mech vent pts who have chronic resp acidosis?

Back 102

return PaCO2 to their normal
titrate O2 so resp drive not depressed
severe hypovent with overcorrection

Front 103

what happens w/ metabolic acidosis?

Back 103

inc blood H+ concent d/t loss of bases or inc acids

Front 104

what causes the occurrence of met acidosis?

Back 104

accum of acids besides CO2
*inc met prod of H+ ions
*dec tubule elim of H+ ions
*GI/renal loss of HCO3
*rapid dilution of ECF w/HCO3 free fluid

Front 105

what happens to met acidosis w/vol anest

Back 105

blunts the carotid body mediated response to acidosis

Front 106

what are the pulm response to met acidosis?

Back 106

inc alveolar vent d/t carotid body stim from H+ ions
*max w/in hrs
*not able to completely normalize even w/inc vent

Front 107

what do buffers in bone do?

Back 107

neutralize non-volatile acids in circulation
seen as bone loss in pts w/CRF

Front 108

What is the formula for the anion gap?

Back 108

(Na + K) - (Cl + HCO3)

Front 109

what is the normal range of the anion gap?

Back 109

9-15 meq/L

Front 110

what are the major cations?

Back 110

Na
K

Front 111

what are the major anions?

Back 111

Cl
HCO3

Front 112

why do we use the anion gap?

Back 112

determines diff dx of met acid

Front 113

what is high anion gap acidosis?

Back 113

> 13 meq/L
SID > 40meq/L

Front 114

what is high anion gap acidosis d/t?

Back 114

*insufficient renal excretion (CRF or uremia)
*alkali tx r/t ABG
*inc pH >7.25 to overcome SE of acidemia
*HD in refractory/profound acidemia
*correct the cause (DKA, salicylates, other substances)

Front 115

what is the tx of resp acidosis?

Back 115

*NaHCO3 if pH <7.10 & HCO3 <21
could transiently inc PaCO2

Front 116

what should be avoided in cardiac arrest/low flow states?

Back 116

bicarb
no improvement of CV response to catecholamines
ICF pH does not improve
MAP/ECF pH may improve

Front 117

what does NaHCO3 reduce in cardiac arrest or low flow states?

Back 117

Ca++

Front 118

What is THAM?

Back 118

tromethamine
lacks Na
effective ICF buffer

Front 119

what is the chemical response of NaHCO3?

Back 119

CO2 + H2O<-->H2CO2<-->H + HCO3

Front 120

Use of bicarb in pt's w/adequate vent?

Back 120

eliminate inc load of CO2

Front 121

when should bicarb be used?

Back 121

best reserved for pts w/adequate vent and pH <7.2

Front 122

what is the cause of lactic acidosis?

Back 122

tissue hypoperfusion
volume rescucitation/oxygenation should be first step

Front 123

what can acidemia potentiate w/GA?

Back 123

depressant effects of most sed and anesth of CNS/CV systems

Front 124

what happens to opioids w/acidosis?

Back 124

they are weak bases
*inc fraction of drug in nonionized form
*penetrate into brain

Front 125

why is aspiration a risk w/an acidotic pt and GA?

Back 125

*inc sedation
*dec airway reflexes

Front 126

what is the CV effects of acidosis and GA?

Back 126

*exaggeration of agents d/t cv dec
*inc response to CV dec w/anesth
*dec sympathetic tone

Front 127

what happens to halothane in acidosis?

Back 127

inc arrhythmogenesis

Front 128

what GA agent should be avoided in acidosis?

Back 128

succs

Front 129

what augments NMB?

Back 129

resp acidosis
*may prevent antagonism w/reversal agents

Front 130

what happens to K in alkalosis?

Back 130

K dec as H+ is exchanged for K

Front 131

what happens to K w/alkalosis?

Back 131

K dec 0.6meq/L w/each 0.10 inc in pH

Front 132

what happens to the oxyhgb dissociation curve in alkalosis?

Back 132

shifts left

Front 133

what happens to Ca binding sites in alkalosis?

Back 133

increases
*NB irritability
*circulatory depression

Front 134

what are adverse effects of alkalosis?

Back 134

*hypokalemia
*CV dysrhythmia
*dig toxicity inc
*inc SVR; poss coronary vasospasm
*resp alkalosis: inc bronchial tone, dec vent effort
*atelectasis

Front 135

what happens to CBF in resp alkalosis?

Back 135

dec CBF
*normal CBF 50ml/100g/min w/a
PaCO2 40mmHg

Front 136

what are vent effects of alkalosis?

Back 136

compensatory hypoventilation
(can dec PaO2)

Front 137

what are the lab values in resp alkalosis?

Back 137

pH >7.45
PaCO2 always <35

Front 138

what happens in respiratory alkalosis?

Back 138

*inc MV > metabolic prod CO2

Front 139

what does resp alkalosis signify?

Back 139

*mech vent
*anxiety
*CNS injury
*hyperthermia
*pain
*hypoxemia
*CNS dz
*sepsis
NEEDS TO BE EVALUATED IMMED

Front 140

How can you tell if it is resp acid/alk?

Back 140

can be completely compensated

Front 141

can met acidosis/alk be compensated

Back 141

Not completely

Front 142

What are the lab values in met alkalosis?

Back 142

pH >7.45
hypercarbonatemia >26meq/L

Front 143

does met alk have a resp component?

Back 143

no

Front 144

what is the result of met alk?

Back 144

dec plasma H+ conc d/t loss of acids or inc body fluid bases

Front 145

What are some causes of met alkalosis?

Back 145

*N/V
*NG suction
*diuretic use (hypokalemia)
*renal hypoperfusion d/t cont stimulus
*Cl- & K+ depletion inc H secretion

Front 146

what is one way to tx met alkalosis a/w resp acid?

Back 146

IVF of KCl instead of mech hyperventilation

Front 147

ABG determination of met alk?

Back 147

serum CO2 1meq > than ABG HCO3
(look for serum CO2 >29)

Front 148

What is WNL of ABG HCO3 and serum CO2?

Back 148

24meq
25meq
(ABG HCO3 >28)

Front 149

what happens if these measurements >4meq/L above normal?

Back 149

primary met alkalosis

conserved HCO3 r/t chronic hypercarbia

Front 150

What can hyperbicarbonatemia indicate?

Back 150

hypovolemia
hypokalemia

Front 151

what is the tx for met alk?

Back 151

*IVF bolus --> inc renal perf
*KCL bolus
*use NS instead of LR (increases Cl/dec HCO3)

Front 152

what should be considered tx w/severe met alkalosis?

Back 152

*IV hydrochloric acid (CVL)
*arginine chloride
*ammonium chloride
*HD
*acetazolamide (Diamox)

Front 153

when should H2 blockers be considered in met alkalosis?

Back 153

w/inc GI losses

Front 154

During postop period: resp acidosis?

Back 154

d/t residual GA and NMB which blunt response to rising CO2

Front 155

during postop period met acidosis?

Back 155

*surgical blood loss
*3rd spacing
*inadequate fluid rescucitation

Front 156

what is cause of resp alk in postop period?

Back 156

pain and anxiety

Front 157

how do you determine resp/met acid-base balance by ABG?

Back 157

*resp if PaCO2 ~ w/change in pH
*met if HCO3 ~ w/change in pH

Front 158

what is an alternative to ABG draws?

Back 158

vein in back of hand

Front 159

VBG can be helpful in determining what?

Back 159

PCO2 and pH during GA
(0.05u < ABG pH)

Front 160

what is the relationship b/w PaCO2 and VBG CO2?

Back 160

PaCO2 4-6mmHg >

Front 161

HCO3 ABG vs VBG?

Back 161

2meq < VBG

Front 162

what can cause false decreases in pH when taking ABG?

Back 162

heparin
PCO2 is directly proportional