Acid Base Physiology

Question 1

what are the three variables of the Henderson Hasselbach equation? which two organs have effect on these variables?

Answer 1

pH, bicarbonate and PCO2

the kidney sets the level of bicarbonate and the lung sets the partial pressure of CO2

Question 2

on the davenport graph, what are the x and y axes? what are the lines called that relate pH and bicarbonate at constant PCO2?

Answer 2

the x axis are values of pH and bicarbonate is on the y axis

isobars or metabolic lines

Question 3

what is the henderson hasselback equation when solving for bicarbonate?

Answer 3

[HCO3-}= 0.03 x PCO2 x 10^(pH-6.1)

Question 4

what is the davenport graph used for?

Answer 4

to find one of three variables when given the other two (pH, bicarbonate and PCO2)

Question 5

what do isobars or metabolic lines describe?

Answer 5

the changes in pH and bicarbonate that occur when an acid or base is added at constant PCO2

Question 6

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?

Answer 6

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.

Question 7

what is represented within the hexagon on the Davenport graph? which PCO2 isobar is included in this hexagon?

Answer 7

represents the range of values for normal healthy individuals. PCO2=40 (normal ventilation

Question 8

what does the CO2 absorption curve demonstrate? what line does this create when plotted on the Davenport graph?

Answer 8

total CO2 ([CO2] + [H2CO3] + [HCO3-] vs PCO2 and the pH that would ensue 
creates respiratory lines

Question 9

what do respiratory lines represent?

Answer 9

the effect of pulmonary ventilation on blood pH and bicarbonate

Question 10

why does pH decrease as PCO2 increases?

Answer 10

because there is a resultant increase in carbonic acid which dissociates into bicarbonate and H+

Question 11

describe what determines PCO2

Answer 11

set by rate of alveolar ventilation which is in equilibrium with alveolar gas

Question 12

what does the respiratory line describe on the Davenport graph? what determines the slope of the respiratory line?

Answer 12

how PCO2, [HCO3-] and pH changes with increased ventilation. slope determined by Hb concentration

Question 13

when Hb is greater, what is the effect on bicarbonate with a change in pH?

Answer 13

more HCO3- is produced per change in pH because the H+ is buffered by the Hb.

Question 14

what are some causes of hypoventilation?

Answer 14

COPD, asthma, airway obstruction, pneumonia, depression of respiratory control centers or weakness of respiratory muscles

Question 15

what is created by the intersection between the normal metabolic line and the respiratory line?

Answer 15

four quadrants that describe the four primary acid base disturbances

Question 16

what are the four acid base disturbances?

Answer 16

resipiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis

Question 17

what is the mechanism of immediate compensation for pH change? slower change?

Answer 17

immediate- respiratory changes

slow acting- renal mechanisms

Question 18

what is the normal point on the Davenport graph?

Answer 18

pH is 7.4 with [HCO3-] at 24 mM and PCO2 at 40 mmHg

Question 19

what is respiratory acidosis in terms of the Davenport graph? what is it caused by?

Answer 19

decreased pH with increased PCO2

caused by hypoventilation

Question 20

at what point does hypercapnea result in stupor and coma?

Answer 20

when it exceeds 80 mmHg

Question 21

where is respiratory acidosis represented on the Davenport graph?

Answer 21

upward and to the left on the respiratory line

Question 22

when pH is falling during respiratory acidosis, what is happening to bicarbonate levels?

Answer 22

they are increasing

Question 23

how does the kidney compensate for respiratory acidosis? what happens to pH with this compensation?

Answer 23

acid is being secreted bicarbonate is being resorbed by the kidney, further increasing levels while pH is now rising

Question 24

what explains the phenomenon that pH can either rise or fall when bicarbonate is increasing?

Answer 24

that pH of blood depends on proton concentration, not concentration of bicarbonate.

Question 25

what is the pulmonary compensation for respiratory acidosis?

Answer 25

increasing frequency or depth of breathing

Question 26

what is one electrolyte side effect of renal compensation for chronic respiratory acidosis?

Answer 26

the excretion of NH4Cl will lead to hypochloremia and the blood will be mildly acidic

Question 27

what causes hyperventilation? what does it lead to?

Answer 27

ventilator set too high, anxiety attack, trauma to respiratory center or brain tumor. leads to respiratory alkalosis

Question 28

how is respiratory alkalosis represented on the davenport graph?

Answer 28

by moving downward and to the right on the respiratory line

Question 29

what does respiratory alkalosis lead to?

Answer 29

decrease in cerebral blood flow resulting in lightheadedness and tinglign with increased neuromuscular excitability

Question 30

above what pH do cardiac arrhythmias and seizures occur?

Answer 30

7.7

Question 31

what are the pulmonary and renal compensations for respiratory alkalosis?

Answer 31

cessation of hyperventillation | decrease reabsorption of HCO3- and retention of acid by decreasing excretion of NH4Cl and other titratable acids

Question 32

what is the only acid base disorder that renal compensation can completely correct in respect to blood pH?

Answer 32

respiratory alkalosis

Question 33

how is metabolic alkalosis represented on the davenport graph?

Answer 33

high pH with high bicarbonate. represented in the upper right hand quadrant of the graph

Question 34

what causes metabolic alkalosis?

Answer 34

excessive vomiting, overdose of antacid, hypertensive patients on excess of diuretics or dehydration

Question 35

how do excess diuretics cause metabolic acidosis?

Answer 35

diuretics cause an increase in loss of NaCl and fluid, activating the renin/angiotensin/aldosterone system. This increases renal proton secretion and plasma bicarbonate

Question 36

what is the pulmonary compensation for metabolic alkalosis? why is it ineffective? what is the renal response?

Answer 36

decrease ventilation- ineffective because of need for O2 | renal- decrease reabsorption of HCO3-

Question 37

what causes metabolic acidosis?

Answer 37

excessive overproduction of acid or exogenous overload, undersecretion of acid by kidney, excessive renal excretion of bicarbonae and GI bicarbonate loss (diarrhea)

Question 38

acid accumulation occurs in which types of patients often? why does this occur?

Answer 38

uncontrolled diabetes mellitis or normal individuals during prolonged starvation. lowered insulin levels with increased glucagon causes ketogenesis and ketoacidosis

Question 39

what is the anion gap? how does it change with ketoacidosis?

Answer 39

anion gap= [Na+]-([Cl-]+[HCO3-]) | increases the gap from normal value of 12

Question 40

overdoses of what compounds cause metabolic acidosis? what is the mechanism?

Answer 40

poison associated anion gap acidosis | overdoses of methanol, ehtylene glycol or aspirin

Question 41

what is the liver metabolism of methanol? what is an antidote for methanol intoxication?

Answer 41

it is converted to formaldehyde and formic acid | ethanol competatively inhibits alcohol dehydrogenase

Question 42

what do uremias cause? what are the subtypes?

Answer 42

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

Question 43

how is metabolic acidosis represented on the Davenport graph?

Answer 43

there is a decrease in bicarbonate with a decrease in pH. this is represented in the lower left hand quadrant of the graph

Question 44

what is the primary response to metabolic acidosis? what secondary conditions does this cause?

Answer 44

hyperventilation (primary) imposes a respiratory alkalosis on top of the metabolic acidosis also reduces PCO2 to the minimum amount

Question 45

what is the renal response to metabolic acidosis?

Answer 45

reabsorption of bicarbonate

Question 46

what does a PCO2 higher than the predicted range indicate in a patient with metabolic acidosis?

Answer 46

indicates a mixed metabolic and respiratory acidosis

Question 47

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?

Answer 47

uncomponsated acid base disorders

Question 48

where are all of the types of acidosis represented on the davenport graph?

Answer 48

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

Question 49

where are all of the types of alkalosis represented on the davenport graph?

Answer 49

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.

Question 50

what is base excess?

Answer 50

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)