Acid Base Physiology Flashcards
what are the three variables of the Henderson Hasselbach equation? which two organs have effect on these variables?
pH, bicarbonate and PCO2
the kidney sets the level of bicarbonate and the lung sets the partial pressure of CO2
on the davenport graph, what are the x and y axes? what are the lines called that relate pH and bicarbonate at constant PCO2?
the x axis are values of pH and bicarbonate is on the y axis
isobars or metabolic lines
what is the henderson hasselback equation when solving for bicarbonate?
[HCO3-}= 0.03 x PCO2 x 10^(pH-6.1)
what is the davenport graph used for?
to find one of three variables when given the other two (pH, bicarbonate and PCO2)
what do isobars or metabolic lines describe?
the changes in pH and bicarbonate that occur when an acid or base is added at constant PCO2
if a person was on a ventilator to keep constant PCO2 and acid or base would do what to the blood pH and bicarbonate levels? would this follow the davenport graph?
it would cause immediate changes in blood pH and bicarbonate before compensatory responses. the initial changes are not represented on the graph but the compensatory ones are.
what is represented within the hexagon on the Davenport graph? which PCO2 isobar is included in this hexagon?
represents the range of values for normal healthy individuals. PCO2=40 (normal ventilation
what does the CO2 absorption curve demonstrate? what line does this create when plotted on the Davenport graph?
total CO2 ([CO2] + [H2CO3] + [HCO3-] vs PCO2 and the pH that would ensue creates respiratory lines
what do respiratory lines represent?
the effect of pulmonary ventilation on blood pH and bicarbonate
why does pH decrease as PCO2 increases?
because there is a resultant increase in carbonic acid which dissociates into bicarbonate and H+
describe what determines PCO2
set by rate of alveolar ventilation which is in equilibrium with alveolar gas
what does the respiratory line describe on the Davenport graph? what determines the slope of the respiratory line?
how PCO2, [HCO3-] and pH changes with increased ventilation. slope determined by Hb concentration
when Hb is greater, what is the effect on bicarbonate with a change in pH?
more HCO3- is produced per change in pH because the H+ is buffered by the Hb.
what are some causes of hypoventilation?
COPD, asthma, airway obstruction, pneumonia, depression of respiratory control centers or weakness of respiratory muscles
what is created by the intersection between the normal metabolic line and the respiratory line?
four quadrants that describe the four primary acid base disturbances
what are the four acid base disturbances?
resipiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis
what is the mechanism of immediate compensation for pH change? slower change?
immediate- respiratory changes
slow acting- renal mechanisms
what is the normal point on the Davenport graph?
pH is 7.4 with [HCO3-] at 24 mM and PCO2 at 40 mmHg
what is respiratory acidosis in terms of the Davenport graph? what is it caused by?
decreased pH with increased PCO2
caused by hypoventilation
at what point does hypercapnea result in stupor and coma?
when it exceeds 80 mmHg
where is respiratory acidosis represented on the Davenport graph?
upward and to the left on the respiratory line
when pH is falling during respiratory acidosis, what is happening to bicarbonate levels?
they are increasing
how does the kidney compensate for respiratory acidosis? what happens to pH with this compensation?
acid is being secreted bicarbonate is being resorbed by the kidney, further increasing levels while pH is now rising
what explains the phenomenon that pH can either rise or fall when bicarbonate is increasing?
that pH of blood depends on proton concentration, not concentration of bicarbonate.
what is the pulmonary compensation for respiratory acidosis?
increasing frequency or depth of breathing
what is one electrolyte side effect of renal compensation for chronic respiratory acidosis?
the excretion of NH4Cl will lead to hypochloremia and the blood will be mildly acidic
what causes hyperventilation? what does it lead to?
ventilator set too high, anxiety attack, trauma to respiratory center or brain tumor.
leads to respiratory alkalosis
how is respiratory alkalosis represented on the davenport graph?
by moving downward and to the right on the respiratory line
what does respiratory alkalosis lead to?
decrease in cerebral blood flow resulting in lightheadedness and tinglign with increased neuromuscular excitability
above what pH do cardiac arrhythmias and seizures occur?
7.7
what are the pulmonary and renal compensations for respiratory alkalosis?
cessation of hyperventillation
decrease reabsorption of HCO3- and retention of acid by decreasing excretion of NH4Cl and other titratable acids
what is the only acid base disorder that renal compensation can completely correct in respect to blood pH?
respiratory alkalosis
how is metabolic alkalosis represented on the davenport graph?
high pH with high bicarbonate. represented in the upper right hand quadrant of the graph
what causes metabolic alkalosis?
excessive vomiting, overdose of antacid, hypertensive patients on excess of diuretics or dehydration
how do excess diuretics cause metabolic acidosis?
diuretics cause an increase in loss of NaCl and fluid, activating the renin/angiotensin/aldosterone system. This increases renal proton secretion and plasma bicarbonate
what is the pulmonary compensation for metabolic alkalosis? why is it ineffective? what is the renal response?
decrease ventilation- ineffective because of need for O2
renal- decrease reabsorption of HCO3-
what causes metabolic acidosis?
excessive overproduction of acid or exogenous overload, undersecretion of acid by kidney, excessive renal excretion of bicarbonae and GI bicarbonate loss (diarrhea)
acid accumulation occurs in which types of patients often? why does this occur?
uncontrolled diabetes mellitis or normal individuals during prolonged starvation. lowered insulin levels with increased glucagon causes ketogenesis and ketoacidosis
what is the anion gap? how does it change with ketoacidosis?
anion gap= [Na+]-([Cl-]+[HCO3-])
increases the gap from normal value of 12
overdoses of what compounds cause metabolic acidosis? what is the mechanism?
poison associated anion gap acidosis
overdoses of methanol, ehtylene glycol or aspirin
what is the liver metabolism of methanol? what is an antidote for methanol intoxication?
it is converted to formaldehyde and formic acid
ethanol competatively inhibits alcohol dehydrogenase
what do uremias cause? what are the subtypes?
they compromise the ability of the kidneys to excrete acid leading to metabolic acidosis
proximal tubular acidosis- reabsorption of bicarbonate is decreased. distal tubular acidosis- acid secretion is decreased
how is metabolic acidosis represented on the Davenport graph?
there is a decrease in bicarbonate with a decrease in pH. this is represented in the lower left hand quadrant of the graph
what is the primary response to metabolic acidosis? what secondary conditions does this cause?
hyperventilation (primary) imposes a respiratory alkalosis on top of the metabolic acidosis
also reduces PCO2 to the minimum amount
what is the renal response to metabolic acidosis?
reabsorption of bicarbonate
what does a PCO2 higher than the predicted range indicate in a patient with metabolic acidosis?
indicates a mixed metabolic and respiratory acidosis
what do points in the corners of the quadrants (x/y not those formed by the respiratory and metabolic lines) of the davenport graphs represent?
uncomponsated acid base disorders
where are all of the types of acidosis represented on the davenport graph?
metabolic acidosis has low bicarbonate with lowered pH as well. acute respiratory acidosis exists with lower pH and normal bicarbonate. chronic respiratory acidosis exhibits high bicarbonate with slightly lower to normal pH
where are all of the types of alkalosis represented on the davenport graph?
metabolic alkalosis exists with high bicarbonate and increased pH. acute respiratory alkalosis has regular to low bicarbonate with increased pH. chronic respiratory alkalosis has higher pH with lower bicarbonate.
what is base excess?
the amount of bicarbonate that should be added or subtracted to bring the patient back to normal (positive in alkalosis and negative in acidosis) (=[HCO3-]-24)
