Acid Base II Flashcards
Describe the isohydric principle.
Do we measure acid/base on arterial or venous side? Why?
Isohydric Principle-in plasma space. body contains many buffer systems- each of which competes for the same H ions. how many types of protons are there in plasma space? ONE. “iso” … how many protein buffers? multiple
- so when loading plasma w protons, they’re buffered by 3 diff systems (or more)
- only one buffer system needs to be closely examined to understand the H in the plasma space- possible bc all buffer systems are linked together through a common H (isohydric principle)
acid/base measure arterial side, not venous
in exercise pour CO2 and H into venous blood but lungs take care of that. so look at arterial blood for assessment
Describe protons in the plasma and interstitial space and intracellular.
Is pH slighly higher or lower in intracellular space?
(plasma perfuses all body tissues) by regulation of plasma proton conc we then regulate the interstitial H ion conc. then regulate intracellular.
bottom line is regulation of intracellular (gradient from intercell to interstitial to plasma) 7.4 is usually less in intracellular spaces (lower pH in cells, higher proton conc. and takes time for protons to diffuse out of cells into interstitium)
How is intracellular pH affected when one hyperventilates or holds their breath?
transfer of protons from cell to interstitium to plasma (motion from intracellular to interstitium is slow-means when hyperventilate and blow off CO2 and pH high or hold breath and pH falls…doesnt affect intracellular pH that much bc of the slow transfer…means can’t hyperventilate yourself to death in terms of status… protected!
slow transfer is important
Describe the bicarbonate buffer system. Open/closed? How is the hydrogen ion conc. calculated?
What is the pK? Why is the bicarb system so useful?
open system in communication with the external environment
[H+] =Kal x (0.03 x PaCO2)/[HCO3-]
main focus is bicarb system -OPEN system.. so we can excrete CO2 by breathing…goes out to environment, pK is 6.1 which is more than 1 unit away from pH of 7.4 still a VERY useful system bc we breathe out CO2 and secrete protons and reabsorb bicarb
Describe the phosphate and protein buffer systems.
Open/closed?
Equation?
closed systems within the body -
closed system (buffering protons while in transit from tissue space and back to lungs and so forth) picking up protons and buffer them, take care of at lung and also kidney space to bring back to normal value protein system is closed system bc when buffers protons we don't bleed and lose that proton to environment
phosphate is sorta closed bc its in plasma space at low concentration. secrete/excrete phosphate salts so partially open to environment
[H+]=Ka2 x [H2PO4-]/[HPO42-]
Which buffer system is the most important to look at to understand the H in the plasma space?
Which is of second/third importance?
bicarb is most important…
[H+]=24 x (PaCO2)/[HCO3-]
- hemoglobin buffer is of secondary importance
- phosphate buffer is of tertiary importance
Draw a diagram of the isohydric principle.
Figure 8
Describe how a malfunctioning respiratory system can lead to acid-base disturbances.
insufficient CO2 removal- respiratory acidosis –acidemia
excessive CO2 removal-
respiratory alkalosis -alkalemia
alveolar ventilation is inadequate for metabolic demands - means alveolar ventilation is either too low (COPD) or too high (panic attack, over ventilated)
alveolar ventilation is geared to perfectly match metabolic processes in body so maintain constant PaCO2 at 40mmHg…so insufficient removal of CO2 is respiratory acidosis (my patient has “acidemia” or is “acidotic” NOT “acidic” …) if body fluids at 7.0 that is severe acidosis.. excessive removal of CO2 alveolar ventilation too high
Describe malfunctioning metabolic systems. (2 types)
renal (improper processing of H+ or HCO3-)
extra-renal (excessive metabolic CO2 and H+ production)
renal component and extra-renal component (everything else except lungs)
renal -improper processing of protons, (not secreted right) bicarb (not being reabsorbed)
extra-renal processes- prod. of ketoacids, can have aldosterone tumors leaking to alkalosis..
if acid based problem, get hint by differential diagnosis, look at anion gap to see if problem lies in kidney or else place.
What are the compensations for dysfunctional lungs or kidneys or extra-renal? Which are fast/slow compensations?
Describe HOW.
kidneys can compensate for dysfunctional lungs (renal system responds after a couple of days- slow) if lungs retain CO2, kidney takes that CO2 convert its to bicarb, secrete the proton, increase base-load and work as a buffer.
the lungs can compensate for dysfunctional kidneys (respiratory system responds within minutes- fast) if kidneys retaining protons, that proton conc. will stimulate kidney receptors and alveolar ventilation will go up and ventilates off as a volatile acid, CO2. responds in minutes
lungs and kidneys can both compensate for acid-base disturbances of extra-renal origin
How can the origin of acid- base disturbances and presence of compensations be determined?
measurement of bicarb buffer system components and pH (simple)
- looking at bicarb buffer system variables (bicarb, PaCO2, pH) …can calculate one by using other 2
interpretation of plasma electrolytes concentrations (Na, HCO3-, Cl-) (more complicated)
(anion gap is imp. K conc. are important) esp bc of proton/K exchange
Describe the anion gap. What does it account for. What does it differentiate between?
anion gap… accounts for unmeasured anions that must be present to neutralize the charge of the measured Na+ (plasma electroneutrality maintained)
anion gap differentiates between acid/base disorders due to renal/GI systems (normal A- gap) vs other metabolic disorders (high A- gap)
How do you rearrange the pH Henderson/H eq. to solve for a missing value. Solve for HCO3-, pH, PaCO2 and A-.
pH = 6.1 + log10 [HCO3-]/(0.03 x PaCO2))
HCO3- (mM) = 0.03 x PaCO2 x 10^(pH-6.1)
PaCO2 (mmHg) = [HCO3-]/(0.03 x 10^(pH-6.1))
[A-] (mEq/L) = [Na+] - [HCO3-] - [Cl-]
What are the normal limits for pH, PaCO2, [HCO3-], [H+], [A-]?
pH- 7.35 to 7.45 PaCO2 - 35mmHg to 45mmHg [HCO3-] 22mM to 28mM [H+] 35 nM to 45nM A- 10meq/L to 15meq/L
When does an uncompensated acid-base disturbance exist?
What values cause acidemia or alkalemia?
exists if pH is out of its normal range
acidemia - pH less than 7.35 or H+ greater than 45nM
alkalemia - pH greater than 7.45 or H+ less than 35nM
If an uncompensated acid-base disturbance exists, how can the primary cause be determined?
metabolic acidosis
respiratory acidosis
metabolic alkalosis
respiratory alkalosis
can be determined from the one bicarbonate system variable that is not normal
metabolic acidosis- HCO3 less than 22 mM
respiratory acidosis -PaCO2 greater than 45mmHg, retaining CO2, suppressed alveolar ventilation
metabolic alkalosis HCO3- greater than 28nM
respiratory alkalosis -PaCO2 is less than 35mmHg
When would a double acid-base disturbance exist?
When would a mixed acid-base disturbance exist?
double acid-base disturbance- if plasma pH is abnormal and both bicarbonate system variables are abnormal on the same side of pH
severe acidosis- HCO3 is less than 22mM and PaCO2 is greater than 45mmHg
When does a mixed acid-base disturbance exist?
Give examples using HCO3 and PaCO2.
if plasma pH is within its normal range (compensatory situation) but both bicarb system variables are not normal
HCO3- less than 22mN and PaCO2 is less than 35mmHg
HCO3- greater than 28mM and PaCO2 greater than 45mmHg
large anion gaps also are mixed disorders (A- is greater than 15mEq/L
Evaluate/work through Figure 10.
Figure 10.
compensation does not CURE. kidney can compensate for acid/base disturbances introduced by sick lung. just compensates, does not correct it..
If a compensatory situation exists, how can primary disturbance be determined?
by examining which side of normal the pH value resides
Figure 11
Given the following case, what is the diagnosis?
data:
pH= 7.35 units
PaCO2= 30mmHg
[HCO3-] =16mmol/L
primary disturbance?
compensation?
full/partial compensation?
diagnosis:
pH-normal, acid
PaCO2- low, pul. alkalosis
HCO3– low, metabolic acidosis
primary metabolic acidosis (since pH resides on acid side of normal
secondary respiratory alkalosis (compensation)
full compensation
Given the following case, what is the diagnosis?
data:
pH= 7.45 units
PaCO2= 30mmHg
[HCO3-] =20mmol/L
primary disturbance?
compensation?
full/partial compensation?
pH-normal, alk
PaCo2, low pul alk
HCO3- low metabolic acid
primary respiratory alkalosis
secondary metabolic acidosis
full compensation
Clinical observations:
are acidotic or alkalotic problems more common?
are respiratory or metabolic disorders more complicated?
acidotic more common and more easily regulated
respiratory less complicated than metabolic
Describe primary respiratory acidosis.
What is the initiating event? (Possible causes)
What are the resultant effects on CO2, PaCO2, H+, and pH
What are compensations?
What would suppress alveolar ventilation? bronchitis, emphysema, COPD (fibrosis NO bc its low compliance disease), barbiturate poisoning (CNS depression), weak respiratory muscles (neuromuscular disease
retain CO2, PaCO2 goes up, proton conc. in blood goes up, pH down
compensation - actually have increase at kidney level of more bicarb being reabsorbed, if PaCO2 higher in blood.. (CO2 rep. in blood in bicarb, carbamino-compounds and dissolved CO2 which filters)
if excess CO2 load in renal filtrate, then excess renal reab. of bicarb… secrete the proton. PCO2 response. kidney can take the CO2, keep the bicarb and secrete the proton (good thing) secondary metabolic alkalosis..nothing wrong, its compensating
