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162 Cards in this Set

  • Front
  • Back
What is an acid?
substance dissolved in water;
yields H+ ions
lowers pH
What is a proton donor?
hydrogen
(ie: HCl --> H+ + Cl-
what is one of the most tightly regulated ions in the body?
H+
35-45nM/L
what is a base?
substance dissolved in water
yields hydroxide ion (OH-)
remove H+ ions from a sol'n
what has a strong affinity for H+ ions?
hydroxide ions
NaOH --> Na+ + OH-
what is a proton acceptor?
bases
remove H+ from a sol'n
what is another way of expressing H+ ions concent
pH
what does pH represent?
arterial concentration of H+ ions
what happens w/inc H+ ion concentration
acidity
lowers pH
what is pH of ECF
7.35 - 7.45
pH is controlled how?
homeostatic process
what happens w/abnormal fluctuations in pH?
break chemical bonds
change shape of proteins
alter cellular fxn
pH of <7
acidic sol'n
H+ ions prevail
pH of >7
alkaline (basic) sol'n
OH- ions prevail (hydroxide)
What is the Henderson-Hasselbach equation?
quantitative measurement describing the relationship b/w plasma pH and the ratio of plasma pCO2 and HCO3
what is the primary determinant of pH
ratio of pCO2 to HCO3
not the individual values
when does pH decrease?
increase CO2 or
decrease HCO3
what keeps pH from marked changes
the buffering system

dec HCO3 --> dec CO2
what is the ratio of HCO3 to CO2 at a constant pH
20:1
ratio of HCO3 to CO2 @ 20:1 is = to a pH of?
7.4
is the ratio b/w HCO3 and CO2 directly inversely proportional?
directly
what is the mathematical equation of the Henderson-Hasselbach equation?
pH = 6.1 + log(HCO3/0.03 x pCO2)
what are the buffering systems?
bicarbonate buffers
hemoglobin buffers
other protein buffers
phosphate buffers
what are the 3 systems that keep pH in tight control?
buffering systems
ventilatory response
renal response
what is the response time of the renal system?
12 - 24 hours
what is the most powerful acid-base regulator system?
kidneys
what are the 2 most important buffering systems?
bicarbonate is #1
Hgb is #2
does the phosphate buffering system include the kidneys?
no
What is the carbonic acid-bicarbonate buffer system?
most important in ECF
what is the phosphate buffer system?
buffers ICF and urn
what is the protein buffer system?
regulate pH in ECF & ICF
extensive interaction w/other buffer systems
What is carbonic acid?
H2CO3
what is the chemical equation of the bicarbonate buffer system?
CO2 + H2O<-->H2CO3<-->H + HCO3
what does the bicarbonate buffer system depend on?
hydration of CO2 to carbonic acid in plasma and erythrocytes
what is the primary role of the bicarbonate buffer system?
prevent pH changes d/t acids in ECF
what does the bicarbonate system consist of?
carbonic acid (weak acid)
and bicarbonate (weak base)
what happens to the CO2 produced throughout the day?
converted to carbonic acid; this then dissociates into H+ ion and bicarb ion
what is the only ICF buffering system?
Hgb
has an immediate effect on pH of ECF
what is the Hgb buffering system responsible for?
prevents drastic alteration in pH w/inc or dec in pCO2
what is contained in the cytoplasm of Hgb?
large amounts of carbonic andhydrase (enzyme)
what does Hgb buffering system do?
absorbs CO2 from plasma; converts it to H2CO3;
why is CO2 absorbed into ICF?
can diffuse easily across RBC membranes
what happens when H2CO3 dissociates in the Hgb buffer system?
moves into plasma via Cl- shift
What is the purpose of Cl- in the Hgb buffer system?
helps maintain electrical neutrality
How are H+ ions formed?
digestive tract
metabolic activities w/in cells
to preserve homeostasis, what must happen to H+ ions?
rendered harmless
must be eliminated to preserve homeostasis
Do buffer systems provide total restoration of homeostasis?
no, only a temporary sol'n
What are the 2 mechanisms the body uses to eliminate H+ ions?
pulmonary
renal
how does the body maintain heomeostasis?
combo of buffering systems
pulmonary
renal
What is pulmonary compensation?
control of H+ ion concen through the exhalation of CO2
how is alveolar ventilation mediated?
chemoreceptors in the medulla;
they respond to changes in CSF pH
how is pulmonary compensation stimulated?
CO2 can easily cross BBB; reacts w/H2O to produce H+ ions to increase respiration
what is the increase in MV for every inc 1mmHg in PaCO2?
1-4L/min
what does the renal response to pH consist of?
increased reabsorption of filtered HCO3
increased excretion of H+
increased production of ammonia (NH3)
What is the goal of the renal system?
to reabsorb HCO3
how much HCO3 is reabsorbed?
where?
90%
proximal tubule
10% reabsorbed in distal parts of tubule
Is HCO3 normally excreted?
No
What is the fundamental event in renal regulation of acid-base balance?
Na+ - H+ exchange
What happens in the Na+ and H+ exchange?
permists bicarboniate ions to be reabsorbed and acids to be excreted
What is the process by which Na+ and H+ exchange takes place?
H+ is actively secreted into the proximal tubule in exchange for Na+
Na+ enters the cell passively
What is the goal of the phosphate buffering system?
excrete H+ ions
What happens in the phosphate buffering system?
HCO3 is reabsorbed
H+ is secreted into tubular lumen
H+ then combines with phosphorous (HPO4) to create phosphate (H2PO4)
Can H2PO4(phosphate) be reabsorbed?
No
r/t charge
What happens to H2PO4?
it is excreted from tubual
What happens when urn pH is 4.4?
phosphate saturated;
phosphorous ions no longer available for eliminating H+ ions
What is the buffer system after the phosphate buffer system?
Ammonia buffer system.
goal is to form NH3 (ammonia)
Why is this an important buffering system?
when phosphate sytem is completely saturated, this the most imporant urinary buffer
what is the biological process of the ammonia buffer system?
deamination of glutamate in the proximal tubule mitochondria
where is the principal source of NH3 (ammonia) formation
proximal tubular cells
what happens w/acidemia
a marked increase in renal NH3 production
what diffuses easily across the membranes in the ammonia buffer system
NH3
enters passively
what is diffusion trapping?
NH4 (ammonium) is unable to cross into tubular cells;
trapped in tubules
what does the excretion of NH4 do?
effectively eliminates H+
what does acidosis lead to?
release of catecholamines
this offset myocardial depression
what happens w/a pH of 7.2 or less
myocardium unable to respond to release of catecholamines
dec SVR/contractility --> dec BP
what is another neg effect of pH 7.2<
dec in threshold for vf
what happens w/pts who have ischemic heart dz or those w/beta blockers/ga
detrimental effects of acidemia may be more pronounced
what happens w/severe acidosis
tissue hypoxia even with
shift to right of oxyhgb curve
what happens in lethal hyperkalemia
H+ K+ shift across cell membranes
what happens to plasma k+ concentrations w/change in pH
increase 0.6meq/L for each 0.10 decrease in pH
do H+ ions pass the BBB
no
CO2 diffuses more easily
what produces an adverse effect response to acidosis?
respiratory (acute)
chronic metabolic is slower process; kidneys are able to keep up w/changes
what is CO2 narcosis?
CNS depression
r/t respiratory > metabolic acidosis
greatly dec neuronal activity --> coma
what are the vasodilatory effects of acidosis?
inc CBF --> inc ICP--> dec CPP--> cerebral ischemia
what is another CNS effect of acidosis
increases szr threshold
what is acidosis caused by?
hypoventilation and CO2 retention
what are some causes?
drug/dz process that decreases alveolar ventilation --> inc CO2 concent in plasma
what happens when CO2 crosses BBB
dec CSF pH
what happens w/inc CO2 in CSF
dec CSF pH --> stim of medulla --> inc ventilation
what happens w/inc ventilation
dec CO2 content --> restoration of CSF pH
what happens w/peripheral chemoreceptors?
carotid bodies/aortic arch respond to changes in CO2 and O2 concent
what happens to the peripheral chemoreceptors w/GA
dec carotid body response to acidemia
what is the time frame for compensation of acute resp acidosis?
varies b/w 6-12 hrs
limited
how is comp of acute resp acidosis accomplished?
Hgb buffer
ECF H+ exchanged for Na+/K+ from bone/ICF
what happens w/the renal response to acute resp acidosis?
bicarb retention limited
what happens to the HCO3 plasma concentrations?
inc 1meq/L for each 10mmHg inc in PaCO2 >40mmHg
what does tx consist of ?
mechanical ventilation unless a quick tx for a simple etiologic factor can be done
how long does complete comp for chronic resp acidosis take?
12-24 hrs
peak 3-5 days
what happens w/chronic resp acidosis?
inc renal secretion of H+ ions --> inc HCO3 plasma concen
what is the tx for chronic resp acidosis?
rarely mech vent
improve pulm fxn --> elim CO2
what happens when PaCO2 is decreased too quickly in pt w/chronic resp acidosis?
metabolic alkalosis
CNS irritability
what is the goal for mech vent pts who have chronic resp acidosis?
return PaCO2 to their normal
titrate O2 so resp drive not depressed
severe hypovent with overcorrection
what happens w/ metabolic acidosis?
inc blood H+ concent d/t loss of bases or inc acids
what causes the occurrence of met acidosis?
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
what happens to met acidosis w/vol anest
blunts the carotid body mediated response to acidosis
what are the pulm response to met acidosis?
inc alveolar vent d/t carotid body stim from H+ ions
*max w/in hrs
*not able to completely normalize even w/inc vent
what do buffers in bone do?
neutralize non-volatile acids in circulation
seen as bone loss in pts w/CRF
What is the formula for the anion gap?
(Na + K) - (Cl + HCO3)
what is the normal range of the anion gap?
9-15 meq/L
what are the major cations?
Na
K
what are the major anions?
Cl
HCO3
why do we use the anion gap?
determines diff dx of met acid
what is high anion gap acidosis?
> 13 meq/L
SID > 40meq/L
what is high anion gap acidosis d/t?
*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)
what is the tx of resp acidosis?
*NaHCO3 if pH <7.10 & HCO3 <21
could transiently inc PaCO2
what should be avoided in cardiac arrest/low flow states?
bicarb
no improvement of CV response to catecholamines
ICF pH does not improve
MAP/ECF pH may improve
what does NaHCO3 reduce in cardiac arrest or low flow states?
Ca++
What is THAM?
tromethamine
lacks Na
effective ICF buffer
what is the chemical response of NaHCO3?
CO2 + H2O<-->H2CO2<-->H + HCO3
Use of bicarb in pt's w/adequate vent?
eliminate inc load of CO2
when should bicarb be used?
best reserved for pts w/adequate vent and pH <7.2
what is the cause of lactic acidosis?
tissue hypoperfusion
volume rescucitation/oxygenation should be first step
what can acidemia potentiate w/GA?
depressant effects of most sed and anesth of CNS/CV systems
what happens to opioids w/acidosis?
they are weak bases
*inc fraction of drug in nonionized form
*penetrate into brain
why is aspiration a risk w/an acidotic pt and GA?
*inc sedation
*dec airway reflexes
what is the CV effects of acidosis and GA?
*exaggeration of agents d/t cv dec
*inc response to CV dec w/anesth
*dec sympathetic tone
what happens to halothane in acidosis?
inc arrhythmogenesis
what GA agent should be avoided in acidosis?
succs
what augments NMB?
resp acidosis
*may prevent antagonism w/reversal agents
what happens to K in alkalosis?
K dec as H+ is exchanged for K
what happens to K w/alkalosis?
K dec 0.6meq/L w/each 0.10 inc in pH
what happens to the oxyhgb dissociation curve in alkalosis?
shifts left
what happens to Ca binding sites in alkalosis?
increases
*NB irritability
*circulatory depression
what are adverse effects of alkalosis?
*hypokalemia
*CV dysrhythmia
*dig toxicity inc
*inc SVR; poss coronary vasospasm
*resp alkalosis: inc bronchial tone, dec vent effort
*atelectasis
what happens to CBF in resp alkalosis?
dec CBF
*normal CBF 50ml/100g/min w/a
PaCO2 40mmHg
what are vent effects of alkalosis?
compensatory hypoventilation
(can dec PaO2)
what are the lab values in resp alkalosis?
pH >7.45
PaCO2 always <35
what happens in respiratory alkalosis?
*inc MV > metabolic prod CO2
what does resp alkalosis signify?
*mech vent
*anxiety
*CNS injury
*hyperthermia
*pain
*hypoxemia
*CNS dz
*sepsis
NEEDS TO BE EVALUATED IMMED
How can you tell if it is resp acid/alk?
can be completely compensated
can met acidosis/alk be compensated
Not completely
What are the lab values in met alkalosis?
pH >7.45
hypercarbonatemia >26meq/L
does met alk have a resp component?
no
what is the result of met alk?
dec plasma H+ conc d/t loss of acids or inc body fluid bases
What are some causes of met alkalosis?
*N/V
*NG suction
*diuretic use (hypokalemia)
*renal hypoperfusion d/t cont stimulus
*Cl- & K+ depletion inc H secretion
what is one way to tx met alkalosis a/w resp acid?
IVF of KCl instead of mech hyperventilation
ABG determination of met alk?
serum CO2 1meq > than ABG HCO3
(look for serum CO2 >29)
What is WNL of ABG HCO3 and serum CO2?
24meq
25meq
(ABG HCO3 >28)
what happens if these measurements >4meq/L above normal?
primary met alkalosis

conserved HCO3 r/t chronic hypercarbia
What can hyperbicarbonatemia indicate?
hypovolemia
hypokalemia
what is the tx for met alk?
*IVF bolus --> inc renal perf
*KCL bolus
*use NS instead of LR (increases Cl/dec HCO3)
what should be considered tx w/severe met alkalosis?
*IV hydrochloric acid (CVL)
*arginine chloride
*ammonium chloride
*HD
*acetazolamide (Diamox)
when should H2 blockers be considered in met alkalosis?
w/inc GI losses
During postop period: resp acidosis?
d/t residual GA and NMB which blunt response to rising CO2
during postop period met acidosis?
*surgical blood loss
*3rd spacing
*inadequate fluid rescucitation
what is cause of resp alk in postop period?
pain and anxiety
how do you determine resp/met acid-base balance by ABG?
*resp if PaCO2 ~ w/change in pH
*met if HCO3 ~ w/change in pH
what is an alternative to ABG draws?
vein in back of hand
VBG can be helpful in determining what?
PCO2 and pH during GA
(0.05u < ABG pH)
what is the relationship b/w PaCO2 and VBG CO2?
PaCO2 4-6mmHg >
HCO3 ABG vs VBG?
2meq < VBG
what can cause false decreases in pH when taking ABG?
heparin
PCO2 is directly proportional