Acid-base disorders and ABG Flashcards
most biologic reactions are most efficient at
pH 7.4
-to maintain:
-buffer systems
-excretion of excess acid or alkali via kidneys and lungs (mostly kidney)
-acidemia < 7.36
-alkalemia > 7.44
primary acid base disorders
-dictated henderson-hasselbalch equation
-disturbance in respiratory or metabolic process
-metabolic acidosis- too little HCO3-
-respiratory acidosis- too much CO2
-metabolic alkalosis- too much HCO3-
-respiratory alkalosis- too little CO2
-you can have more than one!
compensation
-metabolic disorder -> compensation with respiratory
-respiratory disorder -> metabolic compensation
-metabolic acidosis- increase ventilation
-metabolic alkalosis- decrease ventilation
-respiratory acidosis- increase renal reabsorption of HCO3- in prox tubule and increase renal excretion of H in distal tubule
-respiratory alkalosis- decrease renal reabsorption of HCO3- in prox tubule and decrease renal excretion of H in distal tubule
CO2
-pH < 7.4 and CO2 < 35 = metabolic acidosis
-pH < 7.4 and CO2 > 45 = respiratory acidosis
-pH > 7.4 and CO2 < 35 = respiratory alkalosis
-pH > 7.4 and CO2 > 45 = metabolic alkalosis
respiratory acidosis
-CO2 > 45
-shift to R: CO2 + H2O <-> H2CO3-
-increased carbonic acid - must compensate
-buffering of carbonic acid- 2 phases:
-1. ACUTE: H2CO3 -> H+HCO3-
-H goes into cell in exchange for K and Na and buffered by protein
-HCO3- reabs via kidney
-2. CHRONIC:
-H ions are excreted as NH4 in urine
-HCO3- reabs via kidney
-ex. hypoventilation, opiates, COPD, asthma, OSA, muscle strength
respiratory alkalosis
-CO2 < 35
-CHRONIC: often asymptomatic due to renal compensation
-decreased renal reabsorption of HCO3-
-decreased renal excretion of H+
-ACUTE: breathe into paper bag increase CO2 inspired
-ex. hyperventilation, pain, anxiety, hypoxemia
metabolic acidosis
-low HCO3- <22
-will compensate by hyperventalating to increase CO2 expired
-many causes: must calculate anion gap
-offending substance is an acid that dissociates into H+ ion (producing acidosis) and accompanying anion (producing widened gap)
-toxic ingestions
-states of acid ingestion
calculate anion gap
-calculate anion gap
-anion gap = Na - (Cl + HCO3-)
-if anion gap is elevated -> metabolic acidosis
-12-14 is normal
-<14 is normal
metabolic acidosis anion gap
-uremia- kidney failure
-DKA
-INH- treats TB
-salicylates- aspirin
-ethylene glycol- automotive antifreeze (toxic ingestion)
-paraldehyde- treats epilepsy
-methanol- wood alcohol (toxic ingestion)
-excessive iron
-lactate- diabetes, alcohol ingestion -> lactic acidosis
normal limits anion gap
-look for disorder of GI tract of renal disorder
-loss of HCO3- by kidney or GI tract
-GI- diarrhea, pancreatic fistula
-renal- renal tubular acidosis
-urine pH > 7 during acidosis suggests -> RTA (renal tubular acidosis)
-lose bicarb in urine causes alkaline urine
-chloride rises as you lose bicarb so anion gap is unchanged
metabolic alkalosis
-lungs cant fully compensate due to hypoxia
-usually due to kidney secretion H+ ions
-MC cause is volume depletion from diuretics or vomiting
-kidney attempts to maintain plasma vol by reabsorbing Na in exchange for H+
-check urine chloride -> <10 (volume depletion); >10 (not volume depletion) -> dont need to know value
-if NOT volume depletion (Cl>10) -> assess for HTN
-if urine Cl > 10 and have HTN -> adrenal cortical over activity-conn syndrome or renal artery stenosis
-urine Cl > 10 and no HTN think -> genetic disorder-Bartter and Gitelman syndromes
metabolic alkalosis examples
-diuretics
-dehydration
-emesis
-NG suction
-genetic disease- bartter or giteiman
-hyperaldosterone- renal artery stenosis // conn syndrome
respiratory acidosis compensation
-for every 10 change in CO2 -> HCO3- increases by:
1 mmol/L (in ACUTE resp. acidosis)
4 mmol/L (in CHRONIC resp. acidosis)
-dont need to know!
respiratory alkalosis compensation
-for every 10 change in CO2 -> HCO3- decrease by
2 mmol/L (in ACUTE resp. acidosis)
5 mmol/L (in CHRONIC resp. alkalosis)
-dont need to know
-ABG:
-pH = 7.25
-PCO2 = 60
-HCO3- = 26
-PO2 = 55
-respiratory acidosis
-no compensation
