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162 Cards in this Set
- Front
- Back
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What is an acid? |
substance dissolved in water;
yields H+ ions lowers pH |
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What is a proton donor?
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hydrogen
(ie: HCl --> H+ + Cl- |
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what is one of the most tightly regulated ions in the body?
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H+
35-45nM/L |
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what is a base?
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substance dissolved in water
yields hydroxide ion (OH-) remove H+ ions from a sol'n |
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what has a strong affinity for H+ ions?
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hydroxide ions
NaOH --> Na+ + OH- |
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what is a proton acceptor?
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bases
remove H+ from a sol'n |
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what is another way of expressing H+ ions concent
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pH
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what does pH represent?
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arterial concentration of H+ ions
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what happens w/inc H+ ion concentration
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acidity
lowers pH |
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what is pH of ECF
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7.35 - 7.45
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pH is controlled how?
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homeostatic process
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what happens w/abnormal fluctuations in pH?
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break chemical bonds
change shape of proteins alter cellular fxn |
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pH of <7
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acidic sol'n
H+ ions prevail |
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pH of >7
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alkaline (basic) sol'n
OH- ions prevail (hydroxide) |
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What is the Henderson-Hasselbach equation?
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quantitative measurement describing the relationship b/w plasma pH and the ratio of plasma pCO2 and HCO3
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what is the primary determinant of pH
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ratio of pCO2 to HCO3
not the individual values |
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when does pH decrease?
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increase CO2 or
decrease HCO3 |
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what keeps pH from marked changes
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the buffering system
dec HCO3 --> dec CO2 |
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what is the ratio of HCO3 to CO2 at a constant pH
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20:1
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ratio of HCO3 to CO2 @ 20:1 is = to a pH of?
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7.4
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is the ratio b/w HCO3 and CO2 directly inversely proportional?
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directly
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what is the mathematical equation of the Henderson-Hasselbach equation?
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pH = 6.1 + log(HCO3/0.03 x pCO2)
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what are the buffering systems?
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bicarbonate buffers
hemoglobin buffers other protein buffers phosphate buffers |
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what are the 3 systems that keep pH in tight control?
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buffering systems
ventilatory response renal response |
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what is the response time of the renal system?
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12 - 24 hours
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what is the most powerful acid-base regulator system?
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kidneys
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what are the 2 most important buffering systems?
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bicarbonate is #1
Hgb is #2 |
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does the phosphate buffering system include the kidneys?
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no
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What is the carbonic acid-bicarbonate buffer system?
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most important in ECF
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what is the phosphate buffer system?
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buffers ICF and urn
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what is the protein buffer system?
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regulate pH in ECF & ICF
extensive interaction w/other buffer systems |
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What is carbonic acid?
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H2CO3
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what is the chemical equation of the bicarbonate buffer system?
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CO2 + H2O<-->H2CO3<-->H + HCO3
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what does the bicarbonate buffer system depend on?
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hydration of CO2 to carbonic acid in plasma and erythrocytes
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what is the primary role of the bicarbonate buffer system?
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prevent pH changes d/t acids in ECF
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what does the bicarbonate system consist of?
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carbonic acid (weak acid)
and bicarbonate (weak base) |
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what happens to the CO2 produced throughout the day?
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converted to carbonic acid; this then dissociates into H+ ion and bicarb ion
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what is the only ICF buffering system?
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Hgb
has an immediate effect on pH of ECF |
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what is the Hgb buffering system responsible for?
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prevents drastic alteration in pH w/inc or dec in pCO2
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what is contained in the cytoplasm of Hgb?
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large amounts of carbonic andhydrase (enzyme)
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what does Hgb buffering system do?
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absorbs CO2 from plasma; converts it to H2CO3;
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why is CO2 absorbed into ICF?
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can diffuse easily across RBC membranes
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what happens when H2CO3 dissociates in the Hgb buffer system?
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moves into plasma via Cl- shift
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What is the purpose of Cl- in the Hgb buffer system?
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helps maintain electrical neutrality
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How are H+ ions formed?
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digestive tract
metabolic activities w/in cells |
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to preserve homeostasis, what must happen to H+ ions?
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rendered harmless
must be eliminated to preserve homeostasis |
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Do buffer systems provide total restoration of homeostasis?
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no, only a temporary sol'n
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What are the 2 mechanisms the body uses to eliminate H+ ions?
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pulmonary
renal |
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how does the body maintain heomeostasis?
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combo of buffering systems
pulmonary renal |
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What is pulmonary compensation?
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control of H+ ion concen through the exhalation of CO2
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how is alveolar ventilation mediated?
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chemoreceptors in the medulla;
they respond to changes in CSF pH |
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how is pulmonary compensation stimulated?
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CO2 can easily cross BBB; reacts w/H2O to produce H+ ions to increase respiration
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what is the increase in MV for every inc 1mmHg in PaCO2?
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1-4L/min
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what does the renal response to pH consist of?
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increased reabsorption of filtered HCO3
increased excretion of H+ increased production of ammonia (NH3) |
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What is the goal of the renal system?
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to reabsorb HCO3
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how much HCO3 is reabsorbed?
where? |
90%
proximal tubule 10% reabsorbed in distal parts of tubule |
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Is HCO3 normally excreted?
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No
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What is the fundamental event in renal regulation of acid-base balance?
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Na+ - H+ exchange
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What happens in the Na+ and H+ exchange?
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permists bicarboniate ions to be reabsorbed and acids to be excreted
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What is the process by which Na+ and H+ exchange takes place?
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H+ is actively secreted into the proximal tubule in exchange for Na+
Na+ enters the cell passively |
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What is the goal of the phosphate buffering system?
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excrete H+ ions
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What happens in the phosphate buffering system?
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HCO3 is reabsorbed
H+ is secreted into tubular lumen H+ then combines with phosphorous (HPO4) to create phosphate (H2PO4) |
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Can H2PO4(phosphate) be reabsorbed?
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No
r/t charge |
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What happens to H2PO4?
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it is excreted from tubual
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What happens when urn pH is 4.4?
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phosphate saturated;
phosphorous ions no longer available for eliminating H+ ions |
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What is the buffer system after the phosphate buffer system?
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Ammonia buffer system.
goal is to form NH3 (ammonia) |
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Why is this an important buffering system?
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when phosphate sytem is completely saturated, this the most imporant urinary buffer
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what is the biological process of the ammonia buffer system?
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deamination of glutamate in the proximal tubule mitochondria
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where is the principal source of NH3 (ammonia) formation
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proximal tubular cells
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what happens w/acidemia
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a marked increase in renal NH3 production
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what diffuses easily across the membranes in the ammonia buffer system
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NH3
enters passively |
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what is diffusion trapping?
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NH4 (ammonium) is unable to cross into tubular cells;
trapped in tubules |
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what does the excretion of NH4 do?
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effectively eliminates H+
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what does acidosis lead to?
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release of catecholamines
this offset myocardial depression |
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what happens w/a pH of 7.2 or less
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myocardium unable to respond to release of catecholamines
dec SVR/contractility --> dec BP |
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what is another neg effect of pH 7.2<
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dec in threshold for vf
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what happens w/pts who have ischemic heart dz or those w/beta blockers/ga
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detrimental effects of acidemia may be more pronounced
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what happens w/severe acidosis
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tissue hypoxia even with
shift to right of oxyhgb curve |
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what happens in lethal hyperkalemia
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H+ K+ shift across cell membranes
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what happens to plasma k+ concentrations w/change in pH
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increase 0.6meq/L for each 0.10 decrease in pH
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do H+ ions pass the BBB
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no
CO2 diffuses more easily |
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what produces an adverse effect response to acidosis?
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respiratory (acute)
chronic metabolic is slower process; kidneys are able to keep up w/changes |
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what is CO2 narcosis?
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CNS depression
r/t respiratory > metabolic acidosis greatly dec neuronal activity --> coma |
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what are the vasodilatory effects of acidosis?
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inc CBF --> inc ICP--> dec CPP--> cerebral ischemia
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what is another CNS effect of acidosis
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increases szr threshold
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what is acidosis caused by?
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hypoventilation and CO2 retention
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what are some causes?
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drug/dz process that decreases alveolar ventilation --> inc CO2 concent in plasma
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what happens when CO2 crosses BBB
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dec CSF pH
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what happens w/inc CO2 in CSF
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dec CSF pH --> stim of medulla --> inc ventilation
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what happens w/inc ventilation
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dec CO2 content --> restoration of CSF pH
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what happens w/peripheral chemoreceptors?
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carotid bodies/aortic arch respond to changes in CO2 and O2 concent
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what happens to the peripheral chemoreceptors w/GA
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dec carotid body response to acidemia
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what is the time frame for compensation of acute resp acidosis?
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varies b/w 6-12 hrs
limited |
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how is comp of acute resp acidosis accomplished?
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Hgb buffer
ECF H+ exchanged for Na+/K+ from bone/ICF |
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what happens w/the renal response to acute resp acidosis?
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bicarb retention limited
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what happens to the HCO3 plasma concentrations?
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inc 1meq/L for each 10mmHg inc in PaCO2 >40mmHg
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what does tx consist of ?
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mechanical ventilation unless a quick tx for a simple etiologic factor can be done
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how long does complete comp for chronic resp acidosis take?
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12-24 hrs
peak 3-5 days |
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what happens w/chronic resp acidosis?
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inc renal secretion of H+ ions --> inc HCO3 plasma concen
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what is the tx for chronic resp acidosis?
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rarely mech vent
improve pulm fxn --> elim CO2 |
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what happens when PaCO2 is decreased too quickly in pt w/chronic resp acidosis?
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metabolic alkalosis
CNS irritability |
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what is the goal for mech vent pts who have chronic resp acidosis?
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return PaCO2 to their normal
titrate O2 so resp drive not depressed severe hypovent with overcorrection |
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what happens w/ metabolic acidosis?
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inc blood H+ concent d/t loss of bases or inc acids
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what causes the occurrence of met acidosis?
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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 |
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what happens to met acidosis w/vol anest
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blunts the carotid body mediated response to acidosis
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what are the pulm response to met acidosis?
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inc alveolar vent d/t carotid body stim from H+ ions
*max w/in hrs *not able to completely normalize even w/inc vent |
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what do buffers in bone do?
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neutralize non-volatile acids in circulation
seen as bone loss in pts w/CRF |
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What is the formula for the anion gap?
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(Na + K) - (Cl + HCO3)
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what is the normal range of the anion gap?
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9-15 meq/L
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what are the major cations?
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Na
K |
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what are the major anions?
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Cl
HCO3 |
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why do we use the anion gap?
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determines diff dx of met acid
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what is high anion gap acidosis?
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> 13 meq/L
SID > 40meq/L |
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what is high anion gap acidosis d/t?
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*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) |
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what is the tx of resp acidosis?
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*NaHCO3 if pH <7.10 & HCO3 <21
could transiently inc PaCO2 |
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what should be avoided in cardiac arrest/low flow states?
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bicarb
no improvement of CV response to catecholamines ICF pH does not improve MAP/ECF pH may improve |
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what does NaHCO3 reduce in cardiac arrest or low flow states?
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Ca++
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What is THAM?
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tromethamine
lacks Na effective ICF buffer |
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what is the chemical response of NaHCO3?
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CO2 + H2O<-->H2CO2<-->H + HCO3
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Use of bicarb in pt's w/adequate vent?
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eliminate inc load of CO2
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when should bicarb be used?
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best reserved for pts w/adequate vent and pH <7.2
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what is the cause of lactic acidosis?
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tissue hypoperfusion
volume rescucitation/oxygenation should be first step |
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what can acidemia potentiate w/GA?
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depressant effects of most sed and anesth of CNS/CV systems
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what happens to opioids w/acidosis?
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they are weak bases
*inc fraction of drug in nonionized form *penetrate into brain |
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why is aspiration a risk w/an acidotic pt and GA?
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*inc sedation
*dec airway reflexes |
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what is the CV effects of acidosis and GA?
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*exaggeration of agents d/t cv dec
*inc response to CV dec w/anesth *dec sympathetic tone |
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what happens to halothane in acidosis?
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inc arrhythmogenesis
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what GA agent should be avoided in acidosis?
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succs
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what augments NMB?
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resp acidosis
*may prevent antagonism w/reversal agents |
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what happens to K in alkalosis?
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K dec as H+ is exchanged for K
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what happens to K w/alkalosis?
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K dec 0.6meq/L w/each 0.10 inc in pH
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what happens to the oxyhgb dissociation curve in alkalosis?
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shifts left
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what happens to Ca binding sites in alkalosis?
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increases
*NB irritability *circulatory depression |
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what are adverse effects of alkalosis?
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*hypokalemia
*CV dysrhythmia *dig toxicity inc *inc SVR; poss coronary vasospasm *resp alkalosis: inc bronchial tone, dec vent effort *atelectasis |
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what happens to CBF in resp alkalosis?
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dec CBF
*normal CBF 50ml/100g/min w/a PaCO2 40mmHg |
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what are vent effects of alkalosis?
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compensatory hypoventilation
(can dec PaO2) |
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what are the lab values in resp alkalosis?
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pH >7.45
PaCO2 always <35 |
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what happens in respiratory alkalosis?
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*inc MV > metabolic prod CO2
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what does resp alkalosis signify?
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*mech vent
*anxiety *CNS injury *hyperthermia *pain *hypoxemia *CNS dz *sepsis NEEDS TO BE EVALUATED IMMED |
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How can you tell if it is resp acid/alk?
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can be completely compensated
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can met acidosis/alk be compensated
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Not completely
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What are the lab values in met alkalosis?
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pH >7.45
hypercarbonatemia >26meq/L |
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does met alk have a resp component?
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no
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what is the result of met alk?
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dec plasma H+ conc d/t loss of acids or inc body fluid bases
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What are some causes of met alkalosis?
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*N/V
*NG suction *diuretic use (hypokalemia) *renal hypoperfusion d/t cont stimulus *Cl- & K+ depletion inc H secretion |
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what is one way to tx met alkalosis a/w resp acid?
|
IVF of KCl instead of mech hyperventilation
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ABG determination of met alk?
|
serum CO2 1meq > than ABG HCO3
(look for serum CO2 >29) |
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What is WNL of ABG HCO3 and serum CO2?
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24meq
25meq (ABG HCO3 >28) |
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what happens if these measurements >4meq/L above normal?
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primary met alkalosis
conserved HCO3 r/t chronic hypercarbia |
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What can hyperbicarbonatemia indicate?
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hypovolemia
hypokalemia |
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what is the tx for met alk?
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*IVF bolus --> inc renal perf
*KCL bolus *use NS instead of LR (increases Cl/dec HCO3) |
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what should be considered tx w/severe met alkalosis?
|
*IV hydrochloric acid (CVL)
*arginine chloride *ammonium chloride *HD *acetazolamide (Diamox) |
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when should H2 blockers be considered in met alkalosis?
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w/inc GI losses
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During postop period: resp acidosis?
|
d/t residual GA and NMB which blunt response to rising CO2
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during postop period met acidosis?
|
*surgical blood loss
*3rd spacing *inadequate fluid rescucitation |
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what is cause of resp alk in postop period?
|
pain and anxiety
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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 |
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what is an alternative to ABG draws?
|
vein in back of hand
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VBG can be helpful in determining what?
|
PCO2 and pH during GA
(0.05u < ABG pH) |
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what is the relationship b/w PaCO2 and VBG CO2?
|
PaCO2 4-6mmHg >
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HCO3 ABG vs VBG?
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2meq < VBG
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what can cause false decreases in pH when taking ABG?
|
heparin
PCO2 is directly proportional |
