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Oxygenation and ventilation problems are assessed by how many abnormal variables?
one
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Acid-Base disorders are assessed by how many variables?
2+
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pH is _____ related to [H+]
inversely
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What does a negative base excess (base deficit) indicate?
metabolic acidosis
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What is a normal value for base excess?
-2 - 2
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What determines the acidity of a solution?
[H+]
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What is the normal pH and number of hydrogen ions in arterial blood and ECF?
- 35-45 nmol/liter
- 7.45 - 7.35
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What is the normal pH and number of hydrogen ions in the ICF?
6.9, ~ 160 nmol/liter
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What is pH?
- the power to which number 10 must be raised to find the exact number of H+ that exist in a liter of solution
- - exponent of the number 10
- - negative logarithm of H+
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If H+ are 1000, pH is ____
6
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If H+ are 100, pH is ____
7
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If H+ are 10, pH is ____
8
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What are the 4 buffer systems?
bicarbonate, hemoglobin, phosphate, protein
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What are the 3 ways the body regulates pH?
buffer systems, ventilatory response system, renal response system
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What does it mean to be a weak acid?
it readily gives up a H+
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What is pKa?
A value that tells us the pH at which a solution is 50% ionized (deprotonated) and 50% non-ionized (protonated)
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If you have 2 solutions, one with a pKa of 8 and one with a pKa of 6, which one will more easily give up a hydrogen ion?
pKa 8, it is a weaker acid
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What are the 5 components of the bicarbonate buffer system?
- carbon dioxide
- water
- carbonic anhydrase
- carbonic acid
- bicarbonate
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What is the formula for the bicarbonate buffer system?
CO2 + H2O <--> H2CO3 <--> H+ + HCO3-
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What does the Henderson-Hasselbach equation define?
the hydrogen ion concentration in terms of pH (HCO3-/H2CO3 or pCO2)
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Where/how is most of the body's carbonic acid stored?
in the blood as dissolved CO2
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What is quantitatively the largest buffering system in the ECF?
bicarbonate buffer system
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What are the 3 variables of the H-H equation?
measured HCO3, measured PaCO2, calculated pH
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How does a Hgb molecule accept a H+?
by releasing O2
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What are the different percentages of blood CO2 transport?
- 7% stays in plasma
- 23% binds to Hgb
- 70% converts to carbonic acid and then to H+ and HCO3- where HCO3- is pushed into the blood by a Cl- moving on to the cell
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What is the exchange of a Cl- for a HCO3- ion on a RBC called?
hamburger shift or chloride shift
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What is the haldane effect?
deoxygenated Hgb has a higher affinity for CO2
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Where are the 3 chemoreceptors located that are involved in the Ventilatory Response System?
- 1) carotid bodies
- 2) aortic arch
- 3) ventral surface of the medulla oblongata
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What % of response is the central chemoreceptor responsible for?
85%
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Where are the carotid body chemoreceptors located? What nerve do they use?
- bilateral bifurcation of the carotid arteries
- use glossopharyngeal (CN IX)
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What are the 3 mechanisms utilized by the renal response system?
- 1) reabsorption of bicarb
- 2) secretion of H+ (NH3-->NH4-> excretion)
- 3) intracellular bicarb production
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Where is bicarb reabsorbed?
the proximal tubules
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How does Acetazolamide (diamox) work?
- carbonic anhydrase inhibitor
- creates a non-AGAP acidosis
- used to correct chloride-resistant metabolic alkalosis
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What are the causes (general) of Resp Acidosis?
- 1) increased production
- 2) Decreased elimination
- 3) Increased rebreathing or absorption
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What causes an increased production of CO2?
- malignant hyperthermia
- hyperthyroidism
- sepsis
- overfeeding
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What causes decreased elimination of CO2?
- pulmonary disease (PNA, ARDS, fibrosis, edema)
- upper airway obstruction (laryngospasm, foreign body, OSA)
- lower airway obstruction (asthma, COPD)
- Chest wall restriction (obesity, scoliosis, burns)
- CNS depression (anesthetics, opiods, CNS lesions)
- decreased skeletal muscle strength
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What causes increased rebreathing or absorption?
- exhausted soda lime
- incompetent one way valve
- laparoscopic surgery
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What causes Respiratory Alkalosis? (general)
- Increased minute ventilation
- decreased production
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What are causes of an increased minute ventilation?
- hypoxia
- mechanical ventilation
- anxiety, pain
- CNS disease (tumor, infection, trauma)
- Fever, sepsis
- drugs (salicylate, progesterone, doxapram)
- liver disease
- pregnancy
- restrictive lung disease
- pulmonary embolism
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What are causes of a decreased production of CO2?
- hypothermia
- skeletal muscle paralysis
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What are causes of AGAP metabolic acidosis?
- M - methanol, ethylene glycol
- U - uremia
- L - lactic acidosis (decreased perfusion)
- E - ethanol
- P - paraldehyde
- A - aspirin, INH
- K - ketones
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What are causes of a non-AGAP acidosis?
- NaCl administration > 30ml/kg/hr
- GI losses (diarrhea, ostomy, pancreatic fistula)
- Renal losses - RTA
- acetazolamide
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What are the causes of metabolic alkalosis?
- Chloride responsive:
- - renal loss (diuretic therapy)
- - GI loss (vomiting, NG suction)
- - Alkali administration (citrate in blood products, acetate in TPN, bicarb)
- Chloride resistant:
- - hyperaldosteronism
- - refeeding syndrome
- - profound hypokalemia
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What are the dangers in over ventilating someone in reps acidosis?
- You can create a metabolic alkalosis
- - CNS irritability and seizures
- - hypocapnia causes vasoconstriction --> cerebral and myocardial ischemia
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What happens if respiratory alkalosis is prolonged?
- HCO3- ions are transported our of the CSF --> resetting of central chemoreceptors to a lower PaCO2 level
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What role does phosphotructokinase play in alkalosis?
- alkalosis -->
- stimulation of phosphotructokinase -->
- glycolysis and generation of lactic acid
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Does alkalosis cause relative hypo or hypercalcemia? how? what symptom is associated?
hypo - alkalosis increases the affinity between plasma proteins and calcium (so you can potentially see tetany)
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What is AGAP primarily used for?
differential diagnosis of metabolic acidosis
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What is the formula to calculate AGAP?
Na - (Cl + HCO3)
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If you have a metabolic acidosis but a normal AGAP, what does that mean? what is it called?
- Cl- has replaced your HCO3- loss
- hyperchloremic metabolic acidosis
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Where are common buffers found? what implication does this have?
in the bone. chronic acidosis --> loss of bone mass
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How do you calculate how much bicarb someone needs? and how much do you administer?
base deficit x weight in kg x 0.3
administer half of this calculation and then recheck
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