Flashcards in Acids & Bases Deck (24)
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1
Henderson-Hasselbalch Equation
ph = pka + log [A-]/[HA]
pka = unique to each buffer system/acid
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Intracellular buffers
-organic phosphates
-proteins
-hemoglovin
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Extracellular buffers
-proteins
-albumin
-phosphate
-bicarbonate <==
4
Bicarbonate Buffering System
H2CO3 H+ + HCO3-
H2CO3 H20 + CO2 (via carbonic anhydrase)
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Bicarb henderson-hassel
pH = 6.1 + log [HCO2-]/[.03*Paco2]
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Normal pH range
7.38 - 7.43 (~7.4)
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Acidemia
more acid in blod than normal (lower pH)
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Alkalemia
more base ==> higher pH
9
Acid-base disturbances
-body try to compensate for pH disturbances: lungs regulate CO2 (minutes) & kidneys regulate bicarb (hours/days)
-compensation will NEVER completely correct to normal pH
10
Respiratory acidosis
-increased CO2 ==> lower pH
-usually ineffective ventilation
-acute (before renal compensation) or chronic
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Compensation rules for respiratory acidsos
-acute: every 10 Torr increase in CO2 ==> pH decrease by 0.08
-chronic: every 1 torr increase ==> bicarb increase by 0.4
12
Acute causes of Respiratory acidosis
-CNS depressants (opiates, alcohol)
-respiratory muscle fatigue (increased work of breathing)
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Chronic causes of Respiratory acidsosis
-central hypoventilation (e.g. obesity hypoventilation syndrome)
-neuromuscular disease (e.g. ALS)
-chronic lung disease (emphysema, bronchiectasis)
-hypothyroidism
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Respiratory Alkalosis
-too little CO2 ==> increased pH
-due to increased ventilation
-can
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Compensation rules for respiratory alkalosis
-acute: every 10 Torr decrease in CO2 ==> pH increase by 0.08
-chronic: every 1 torr decrease ==> bicarb decrease by 0.4
16
Acute causes of Resp Alk
-pain
-anxiety/panic
-fever
-mechanical ventilation
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Chronic causes of Resp Alk
-living at altitude
-brain injury
-chronic salicylate toxicity
-pregnancy
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Metabolic acidosis
-increased acid ==> decreased HCO3- ==> lower pH
-respiratory compensation ==> increased ventilation resulting in decreased pCO2
-compensation rules:
-expected pCO2 = 1.5[HCO3-] + 8 +/-2 ==> "winter's formula"
19
Major categories of metabolic acidosis
-anion gap = [Na+] - ([Cl-] + [HCO3-]) ==> elevated anion gap indicates additional acid that is being buffered by bicarb ==> increased amount of unmeasured anions
-non-anion gap = loss of bicarbonate (e.g. via GI losses or renal losses)
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Causes of metabolic acidosis (anion gap)
-pneumonic: MUD PILES
-Methanol
-Uremia
-DKA
-propylene Glycol
-INH
-Lactate
-Ethylene Glycol
-Salicylates
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Causes of metabolic acidosis (non-anion gap)
-GI losses (i.e. diarrhea)
-Renal losses (RTA)
-Too much IV saline (increase Cl- w/loss of bicarb)
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Metabolic Alkalosis
-excess HCO3- results in higher pH
-rapid respiratory compensation w/decreased ventilation ==> increased pCO2
-will not hypoventilate to point of hypoxemia; thus not completely
-compensation rule: increased [HCO3-} of 1mEq/L increases PaCO2 by 0.7 Torr
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Causes of metabolic alkalosis
-vomiting or NG tube suction (via loss of gastric acid)
-ingestion of NaHCO3
-ingestion of other alkali
-hypovolemia
-diuretics
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