Acids & Bases Flashcards
Henderson-Hasselbalch Equation
ph = pka + log [A-]/[HA] pka = unique to each buffer system/acid
Intracellular buffers
- organic phosphates
- proteins
- hemoglovin
Extracellular buffers
- proteins
- albumin
- phosphate
- bicarbonate <==
Bicarbonate Buffering System
H2CO3 H+ + HCO3-
H2CO3 H20 + CO2 (via carbonic anhydrase)
Bicarb henderson-hassel
pH = 6.1 + log [HCO2-]/[.03*Paco2]
Normal pH range
7.38 - 7.43 (~7.4)
Acidemia
more acid in blod than normal (lower pH)
Alkalemia
more base ==> higher pH
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
Respiratory acidosis
- increased CO2 ==> lower pH
- usually ineffective ventilation
- acute (before renal compensation) or chronic
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
Acute causes of Respiratory acidosis
- CNS depressants (opiates, alcohol)
- respiratory muscle fatigue (increased work of breathing)
Chronic causes of Respiratory acidsosis
- central hypoventilation (e.g. obesity hypoventilation syndrome)
- neuromuscular disease (e.g. ALS)
- chronic lung disease (emphysema, bronchiectasis)
- hypothyroidism
Respiratory Alkalosis
- too little CO2 ==> increased pH
- due to increased ventilation
- can
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
Acute causes of Resp Alk
- pain
- anxiety/panic
- fever
- mechanical ventilation
Chronic causes of Resp Alk
- living at altitude
- brain injury
- chronic salicylate toxicity
- pregnancy
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”
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)
Causes of metabolic acidosis (anion gap)
- pneumonic: MUD PILES
- Methanol
- Uremia
- DKA
- propylene Glycol
- INH
- Lactate
- Ethylene Glycol
- Salicylates
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)
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
Causes of metabolic alkalosis
- vomiting or NG tube suction (via loss of gastric acid)
- ingestion of NaHCO3
- ingestion of other alkali
- hypovolemia
- diuretics
Summary of Acid-Base Disturbances
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