Card Set Information
IHS Acid-Base/Blood Gas Analysis
Oxygenation and ventilation problems are assessed by how many abnormal variables?
Acid-Base disorders are assessed by how many variables?
pH is _____ related to [H+]
What does a negative base excess (base deficit) indicate?
What is a normal value for base excess?
-2 - 2
What determines the acidity of a solution?
What is the normal pH and number of hydrogen ions in arterial blood and ECF?
7.45 - 7.35
What is the normal pH and number of hydrogen ions in the ICF?
6.9, ~ 160 nmol/liter
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+
If H+ are 1000, pH is ____
If H+ are 100, pH is ____
If H+ are 10, pH is ____
What are the 4 buffer systems?
bicarbonate, hemoglobin, phosphate, protein
What are the 3 ways the body regulates pH?
buffer systems, ventilatory response system, renal response system
What does it mean to be a weak acid?
it readily gives up a H+
What is pKa?
A value that tells us the pH at which a solution is 50% ionized (deprotonated) and 50% non-ionized (protonated)
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
What are the 5 components of the bicarbonate buffer system?
What is the formula for the bicarbonate buffer system?
CO2 + H2O <--> H2CO3 <--> H+ + HCO3-
What does the Henderson-Hasselbach equation define?
the hydrogen ion concentration in terms of pH (HCO3-/H2CO3 or pCO2)
Where/how is most of the body's carbonic acid stored?
in the blood as dissolved CO2
What is quantitatively the largest buffering system in the ECF?
bicarbonate buffer system
What are the 3 variables of the H-H equation?
measured HCO3, measured PaCO2, calculated pH
How does a Hgb molecule accept a H+?
by releasing O2
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
What is the exchange of a Cl- for a HCO3- ion on a RBC called?
hamburger shift or chloride shift
What is the haldane effect?
deoxygenated Hgb has a higher affinity for CO2
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
What % of response is the central chemoreceptor responsible for?
Where are the carotid body chemoreceptors located? What nerve do they use?
bilateral bifurcation of the carotid arteries
use glossopharyngeal (CN IX)
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
Where is bicarb reabsorbed?
the proximal tubules
How does Acetazolamide (diamox) work?
carbonic anhydrase inhibitor
creates a non-AGAP acidosis
used to correct chloride-resistant metabolic alkalosis
What are the causes (general) of Resp Acidosis?
1) increased production
2) Decreased elimination
3) Increased rebreathing or absorption
What causes an increased production of CO2?
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
What causes increased rebreathing or absorption?
exhausted soda lime
incompetent one way valve
What causes Respiratory Alkalosis? (general)
Increased minute ventilation
What are causes of an increased minute ventilation?
CNS disease (tumor, infection, trauma)
drugs (salicylate, progesterone, doxapram)
restrictive lung disease
What are causes of a decreased production of CO2?
skeletal muscle paralysis
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
What are causes of a non-AGAP acidosis?
NaCl administration > 30ml/kg/hr
GI losses (diarrhea, ostomy, pancreatic fistula)
Renal losses - RTA
What are the causes of metabolic alkalosis?
- renal loss (diuretic therapy)
- GI loss (vomiting, NG suction)
- Alkali administration (citrate in blood products, acetate in TPN, bicarb)
- refeeding syndrome
- profound hypokalemia
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
What happens if respiratory alkalosis is prolonged?
- HCO3- ions are transported our of the CSF --> resetting of central chemoreceptors to a lower PaCO2 level
What role does phosphotructokinase play in alkalosis?
stimulation of phosphotructokinase -->
glycolysis and generation of lactic acid
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)
What is AGAP primarily used for?
differential diagnosis of metabolic acidosis
What is the formula to calculate AGAP?
Na - (Cl + HCO3)
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
Where are common buffers found? what implication does this have?
in the bone. chronic acidosis --> loss of bone mass
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