blood gases Flashcards
blood gases rely on
circulation of buffers in the blood, pulmonary, and renal systems that act together
what is the air we breath in consist of
nitrogen, oxygen, small amount of water and CO2
At sea level: atmospheric pressure is 760 mg and all the gases contribute the pressure in the proportion of contribution
partial pressure
partial pressure depends on
diffusion
When you breath in through your nose, vapor in your nose is added to bring relative humidity to 100% at RT
brings vapor pressure to 47 mm Hg
when blood leaves the lungs have parital pressure of 100 mmHg the pressure in the lungs is now
40 mm Hg
blood away from heart and tissues
arteries
-more oxygen rich, darker red
RBCs let go of oxygen and pick up CO2
blood back to the heart
venial blood
where is the biggest exchange of oxygen and CO2?
lungs
____ has greater affinity for Hgb
CO2
what factors affect movement across the membrane
- Partial pressure
- How well it can diffuse
- Affinity for oxygen
Number of RBCs
In normal person 95% of Hgb in arterial blood is bound to oxygen
oxygen saturation rate
if saturation rate dips below 95%=
hypoxia
-not enough oxygen
-not enough RBCs
-too much functional Hgb
cyanotic
blue person
what makes up total CO2
Bicarb, dissolved CO2, other small components
-if total CO2 is increased this also means bicarb
hypercapnia
increased CO2 in arterial blood, not normal
-breath in too much CO2
hypocapnia
decreased in CO2 in arterial blood
-due to hyperventilation
partial pressure of oxygen
amount of oxygen in our blood stream
partial pressure of CO2
amount of carbon dioxide in bloodstream
% of Hgb that is carrying oxygen
oxygen saturation
too much alkaline products
base excess
deficient of acid products
base defect
every gram of Hgb can carry ______ mL of oxygen
1.93
oxygen disassociation curve
Plots oxygen saturation against partial pressure of oxygen
as you go to the right=
acid
Hgb will share more of its oxygen to the tissues
as you move to the left =
alkaline
hgb tends to keep oxygen and is less willing to share
what can cause shifts to left or right of curve
pH
what is the dissociation curve called
Bohr’s effect
another factor affecting Hgb affinity for oxygen
2,3 BPG- bisphosphoglycerate
what is 2,3 BPG- biphosphoglycerate
byproduct of glucose, center of Hgb molecule
when 2,3 BPG is increased
T form- tight binding
decreased oxygen affinity- give oxygen away
when 2,3 BPG is decreased
relaxed form
increased oxygen affinity- more work
when there is a increase in CO2, H and Cl
decrease Hgb affinity for oxygen
Increases in temp, will make Hgb want to
get rid of oxygen
Decreases in temp will make Hgb want to
keep oxygen
shift to the right - share oxygen
- Decrease in pH
- Increase in temp
- Increase in BPG
- Increase in Hydrogen ions
in cases of anemia there are less RBCs to shift to right
fewer cells to carry oxygen and body needs it so RBCs willing to give up
shift to the left (overall)
- Increase in pH
- Decrease temp
- Decrease BPG
what shift has a more negative impact on a person , especially long term
left
parameters for blood transfusions
- Blood that sites on shelf loses 2,3 BPG (lowered) = Hgb keeps oxygen
- Only give blood if Hct <7
normal hydrogen con
35-45
normal pH
7.35- 7.45
2 main ways body gets ride of hydrogen; blood gases maintained
kidney and lungs
recongize Henderson-Hasselbalch equation
notes
normal ratio fo bicarb to carbonic acid
20:1
carbonic acid formula
(0.03 x PCO2)
formation of CO2
using fats, CHO, and protein
CO2 + H2O<—> H2CO3 <—> H+ + HCO3- driven by
carbnoic anhydrase enzyme
excretion of 20,000 moles of CO2/day
what is incomplete oxidation
nonvolatile acids
get rid through the kidney 50 mm of acid/day
what convert carbonic acid to Co2 so we can breath it out
lungs
most important buffering system in plasma
Bicarbonate/ carbonic acid system
-because of high concentration of bicarb
Bicarbonate/ carbonic acid system controlled by
lungs and kidneys
intercellular Hgb most important buffer
Hgb buffer system
how does Hgb buffer system work
As CO2 produced in tissues get picked by RBC combines with h2o through carbonic anhydrase and converted into hydrogen and bicarb
bicarb out and Cl in
what buffer system involves in chloride shift
Hgb buffer system
-negative out, negative in
in acidosis uses a lot of bicarb (negative), body will try to
get rid of negative - chlordie
phosphate buffer system
Uses phosphate to minimize pH changes in plasma and RBCs
most important buffering system in urine
phosphate buffer system
-exchange of hydrogen adn sodium ions
protein buffer
○ Plasma proteins to minimize pH changes in blood
○ At 7.4 most proteins negatively charged; bind with excess hydrogen ions to help keep us out of acidosis
in the lungs what is a normal byproduct
CO2
if more carbonic acid, more ___will be formed
CO2
body regulates this by breathing out
lungs respond to CO2 by either
increasing or decreasing breathing
if CO2 can’t be expelled you will form
carbonic acid, put body into acidosis
if too much carbonic acid =
more CO2
increase respiration
if hyperventilate too long=
put into alkalosis
CO2 being removed faster than hydrogen ions are being formed
if you do this too long, increase in carbonic acid
what is the first response for acidosis/ alkalosis
respiratory
-either breath faster or slower
-will change depth of breath
SHORT TERM
how does kidney respond to acidosis/ alkalosis
excreting or retaining bicarb
when in acidosis the kidney
retains bicarb (keep)
in alkalosis in the kidney
get rid of bicarb
where do you collect blood gases
arterial site
how should a specimen be kept until sample run
anaerobically- no air bubbles
areas to draw for gases
radial, brachial, femoral artery
most common area to draw
radial artery
best site to draw but most complications
femoral artery
what is allen’s test
determine what hand is better for draw
thumbs press down
-release one side and hand returns pink= good
if not color returns= can’t draw, decreased blood flow
what is blood gas drawn into
premeasured lithium, heparin syringe
-mixed to avoid clots
-immediately run or put on ice
if blood gas left at RT
cells will continue to use oxygen and produce CO2
-pH also decreased
if there is exposure to air
O2 increases
CO2 decrease
pH increase
when patients hyperventilate about getting blood gas drawn
decrease amount of CO2
pH increase
respiratory acidosis
pH of less than 7.35, CO2 greater than 45, Bicarb decreased
what causes respiratory acidosis?
○ Inability to get rid of CO2 (exhale)
§ Anything that stops my breathing
§ Pneumonia
§ Emphysema
§ COPD
Fluid in lungs
SHALLOW breathing
what does respiratory acidosis have an effect on
cardiovascular, nervous system, drowsy
treat by whatever is causing it ; give oxygen
when respiratory acidosis kidney compensates by
keep bicarb
Respiratory Alkalosis
pH greater than 7.45, CO2 less than 35
causes of Respiratory Alkalosis
Hyperventilating
○ Stress, anxiety, fear
○ Anxiety drugs
Pregnancy
in Respiratory Alkalosis kidneys
get rid of bicarb
treatment: breath in paper bag, CO2 coming right back at you
characteristics of metabolic acidosis
pH less than 7.35, bicarb less than 22
involves kidney
what metabolic processes can put you into acidosis?
diabetic keto acidosis
destruction of RBC, overdose aspirin, renal failure
seen in diabetic keto acidosis
anion gap increased
ketones
what specifically are you overdosing on when you overdose on aspirin
overdose on salicylates, lactic acid, salicylic acid
how to treat metabolic acidosis
treat the cause
if diabetic in DKA, give insulin
If in metabolic acidosis, respiratory system may try to help
body will try to hyperventilate and try to get rid of CO2
metabolic alkalosis
pH greater than 7.45, bicarb greater than 26
causes of metabolic alkalosis
losing too much acid
-prolong vomiting and/or diarrhea
-ingestion of antacids
-hyperaldosteronism
what is hyperaldosteronism
doesn’t allow for sodium-hydrogen exchange, no buffering system
how will respiratory try to fix metabolic alkalosis
shallow breathing
-most difficult acid-base imbalance to fix
correction
when parameters are back to normal, we corrected
degrees of compensation
primary disorder is continuing but opposing system is beginning to adjust
compensation example
pH is within normal limits
only time we call compensation is when the pH is within normal limits
partially compensation
pH is not within normal limits but both components are in opposite directions
uncompensated
pH is not in normal limits, 1 component is abnormal and the other one is within normal limits
mixed component
both components are causing the problem
blood gas analyzers measures
PO2, PCO2, and pH
bicarb is measured as
total CO2
TCO2-1
what does blood gas calculates
carbonic acid and base excess
what do blood gas analyzers need to be set at to be accurate
37 degrees
every degree above 37- pH decreases by 0.015
every degree below 37, pH increase by 0.015
PO2 measurement
amperometric- currrent flow
based on same principle as ISE- selective membrane
PO2 electrode called
Clark electrode
reference solution KCL
sources of error on blood gas analyzer
protein buildup on membrane, O2 decrease
pre-analytical errors for blood gas analyzers
not left on ice
-cells use O2
-CO2 increase
-pH increase
bubble
-increase O2
-CO2 decrease
-ph increased
hyperventilating
-CO2 decrease
pH measurement in blood gas analyzer
glass electrode
potentiometric measurement- change in voltage
electrode used for pH measurement
calomel electrode
-mercury chloride in ti
PCO2 measurement in blood gas analyzer
potentiometric
severinghaus electrode
how is bicarb calcularted
HH equation
pKa assumed= 6.1 at 37 degrees
how is base excess/ deficiency calculated
Ph, CO2, Hgb
normal range -2 to +2
parameter of metabolic
above 2+ indicated
excess of bicarb = metabolic alkalosis
below -2 indicates
deficiency of bicarb = metabolic acidosis
when to do venial draws
emergency situations
patient’s in ICU
differences in venial draws
oxygen saturation rate
pH- slightly lower
bicarb and CO2 -similar
