Pulmonary Pathophysiology Flashcards
What is the flow of bulk gases to the alveolar sacs
trachea
bronchi
bronchioles
terminal bronchioles
respiratroy bronchioles
alveolar ducts
alveolar sacs
the bulk flow of blood depends on
relies on the cardiovascular system
blood delivers oxygen throughout systemic circulation
lung -> peripheral tissues -> lung
What increases the oxygen carrying capacity of blood by 70x
Hemoglobin
1 gram Hb can carry 1.34 mL of O2
the percent of hemoglobin that has oxygen bound to it
Hemoglobin saturation (%)
measured via pulse ox (SpO2) or Arterial blood gas
What might cause the oxyhemoglobin dissociation curve to shift to the right
if it shifts to the right that means there is a decreased hemoglobin affinity for oxygen
1) Increased PCO2
2) Increased H+ (decreased pH)
3) Increased temperature
4) Increased 2,3 DPG
*Harder to load, easier to unload O2
What does it mean when the oxyhemoglobin dissociation curve shifts to the right
if it shifts to the right that means there is a decreased hemoglobin affinity for oxygen
1) Increased PCO2
2) Increased H+ (decreased pH)
3) Increased temperature
4) Increased 2,3 DPG
*Harder to load, easier to unload O2
What is the Bohr effect
hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and/or decreased blood pH
if it shifts to the right that means there is a decreased hemoglobin affinity for oxygen
1) Increased PCO2
2) Increased H+ (decreased pH)
3) Increased temperature
4) Increased 2,3 DPG
*Harder to load, easier to unload O2
What 4 factors decrease hemoglobins lower affinity for oxygen
1) Increased PCO2
2) Increased H+ (decreased pH)
3) Increased temperature
4) Increased 2,3 DPG
*Harder to load, easier to unload O2
What might cause the oxyhemoglobin dissociation curve to shift to the left
Increased Hb affinity for Hb
1) Decreased PCO2
2) Decreased H+ (increased pH)
3) Decreased temperature
4) Decreased 2,3 DPG
*Easier to load, harder to unload O2
What factors increase Hb affinity for Hb
1) Decreased PCO2
2) Decreased H+ (increased pH)
3) Decreased temperature
4) Decreased 2,3 DPG
*Easier to load, harder to unload O2
Trace the oxygen molecule to the mitochondria
Room air (21%)
Trachea
Primary bronchus
terminal bronchioles
respiratory brionchioles
alveolar sacs
Alveolus (gas exchange- passive diffusion)
Pulmonary capillaries- dissolved in plasma and bound to Hb
Tissues
Cells
Mitochondria
What drives simple diffusion of O2 (from the alveolus to blood and then tissues) and Co2 (From tissues to blood and then alveolus)
pressure gradients
Partial pressure = concentration x total pressure
Partial pressure =
Concentration x Total pressure
partial pressure of alveolar oxygen
PAO2
partial pressure of arterial oxygen (dissolved oxygen)
PaO2
Oxygen saturation (oxyhemoglobin)
SaO2
low arterial partial pressure of oxygen (PaO2)
Hypoxemia
What constitutes hypoxemia vs severe hypoxemia
Hypoxemia= PaO2 <80mmHg
Severe Hypoxemia= PaO2 <60mmHg
What is the difference between hypoxemia and hypoxia
Hypoxemia = low PaO2
Hypoxia = low tissue oxygen levels
What is the fraction of inspired oxygen
FiO2
21% on room air, 100% if under anesthesia
What is the barometric pressure
Pb
760mmHg at sea level
640mmHg at Fort Collins
What is the partial pressure of inspired oxygen
PiO2 = FiO2 (Pb- PH20)
at room air at sea level
0.21 (760-47) =150mmHg
partial pressure of alveolar CO2
PACO2
partial pressure of arterial CO2 (dissolved)
PaCO2
Why is PACO2 and PaCO2 about the same
because CO2 is really good at dissolving so it is about the same
is PvCO2 or PaCO2 higher
the partial pressure of venous CO2 (PvCO2) is about 5mmHg higher than PaCO2
How much higher is PvCO2 from PaCO2
about 5mmHg higher than PaCO2
What is hypercarbia
high CO2, we see hypoventilation instead
PaCO2>40mmHg
What value tell you that your patient is hypoventilating
When there is a PaCO2 > 40mmHg
Whaat value tells you that your patient is hyperventilating
When there is a PaCO2 <36mmHg
“Hypocarbia” or low PaCO2
When an animal is panting, are they hyperventilating
No. they are only moving the dead space in their longs and they are not hyperventilating
you can also only determine this with a blood gas to look at PaCO2
How do you estimate the alveolar oxygen, the amount of oxygen in the alveolus
Must be estimated (PAO2) using the alveolar gas equation
PAO2= FiO2 (Pb-PH20)- (PaCO3/R)
What is the partial pressure of water vapor
PH20; Always 47mmHg
What is the respiratory quotient in the alveolar gas equation
R = 0.8
You have a patient at sea level with a PaCO2 of 40mmHg, breathing room air. What is the PAO2
PAO2= FiO2 (Pb-PH20)- (PaCO2/R)
PAO2= 0.21(760mmHg-47mmHg)- (40/0.8)
PAO2= 150-50
PAO2=100mmHg
You have a patient in Fort Collins with a PaCO@2 of 35mmHg, breathing room air. What is the PAO2
PAO2= FiO2 (Pb-PH20)- (PaCO2/R)
PAO2= 0.21(640mmHg-47mmHg)- (35/0.8)
PAO2= 125-44
PAO2=81mmHg
What is a normal A-a gradient
<10mmHg
Pa)2 is typically 5-10mmHg less than PAO@
What does it mean if the A-a gradient is >10mmHg
there is gas exchange impairment
T/F: A-a gradient can be calculated on a patient receiving oxygen supplementation
False- and you cannot perform this with oxygen supplementation
What are the 5 causes of hypoxemia *
1) Decreased PiO2 (= FiO2(Pb-PH20))
2) Hypoventilation (Increased PaCO2)
3) Ventilation- perfusion mismatch (V/Q)
4) Diffusion impairment
5) Shunt
What are the 5 causes of hypoxemia *
1) Decreased PiO2 (= FiO2(Pb-PH20))
2) Hypoventilation (Increased PaCO2)
3) Ventilation- perfusion mismatch (V/Q)
4) Diffusion impairment
5) Shunt
Which of the following values on an arterial blood gas (sea level, FiO2 21%) is consistent with a patient with severe hypoxemia
a. PaO2= 76mmHg
b. PaCO2= 52mmHg
c. PaO2= 53mmHg
d. PaCO2= 38mmHg
c. PaO2= 53mmHg
Severe hypoxemia= PaO2 <60mmHg
Which of the following values on an arterial blood gas (sea level, FiO2 21%) is consistent with a patient that is hypoventilating
a. PaO2= 76mmHg
b. PaCO2= 52mmHg
c. PaO2= 53mmHg
d. PaCO2= 38mmHg
b. PaCO2= 52mmHg
Hypoventilation= PaCO2>40 mmHg
You have a dog under surgery with PaCO2: 23mmHg and PaO2: 40mmHg. What is the most likely cause of hypoxemia?
PaCO2: nx= 36-40mmHg
PaO2: nx= 90-100mmHg
Decreased FiO2 -> Decreased PiO2 -> hypoxemia
oxygen flow is not on
No oxygen is entering the alveolus so none will diffuse into the blood
increase the oxygen supplementation (Normal A-a gradient so its oxygen responsive)
Frenchie presents in repsiratory distress after playing ball outside.
PaCO2: 65mmHg
PaO2: 70mmHg
What is the likely cause of the hypoxemia
PaCO2: nx= 36-40mmHg
PaO2: nx= 90-100mmHg
Hypovenitaltion causing the hypoxemia
Alveolus is full of CO2 and oxygen cannot get in
*Yes this cause is responsive to oxygen (normal A-a gradient) . fixes the hypoxemia but does not fix the cause
What is a good sedative to use in a patient with respiratory distress
opioid (ie butorphanol) bc it has limited respiratory effects and then you can intubate
For every 1mmHg increase in PaCO2, PaO2 _______- by ________
decreases by 1mmHg
8yo MC golden present for 3 days of vomiting. Placed on oxygen but prior to, this arterial blood gas was achieved
PaCO2: 25mmHg
PaO2: 58mmHg
What is likely cause of hypoxemia
PaCO2: nx= 36-40mmHg
PaO2: nx= 90-100mmHg
Aspiration pneumonia: V/Q mismatch
normally the lung matches ventilation and perfusion perfectly
but this has compromised ventilation with adequate perfusion (aspiration pneumonia, pulmonary contusions, pulmonary edema)
might be oxygen responsive? because youre increasing gradient but it depends how severe it is
What is the most common cause of hypoxemia in vet med
V/Q mismatch
What might lead to a low V/Q mismatch
compromised ventilation with adequate perfusion
most common cause is something in alveoli impairing gas exchange
-aspiration pneumonia
-pulmonary contusions
How does aspiration pneumonia cause V/2 mismatch
if alveolus is filled with pus from the infection
then it can fill with oxygen
Low V/Q mismatch from low ventilation
Is hypoxemia due to aspiration pneumonia (V/Q mismatch) responsive to oxygen
might be oxygen responsive? because youre increasing gradient but it depends how severe it is
With a low V/Q mismatch, is there an elevated A-a gradient
Yes. Less is about to perfuse due to the low ventilation
(ie aspiration pneumonia- pus or edema in the lungs)
How does high V/Q mismatch cause hypoxemia
there is adequate ventilation and compromised perfusion (ie. PTE or hypovolemic)
blood cant get to the lungs
elevated A-a gradient
*oxygen supplementation may be effective but it depends on how much of the lung is affected.
+/- mildly responsive
Why might there be a high V/Q mismatch
-PTE (most common cause)
-Hypovolemic patient
-Anesthesia- compression
With high V/Q mismatch is there an elevated A-a gradient
Yes, there is adequate ventilation and compromised perfusion (ie. PTE or hypovolemic)
blood cant get to the lungs
elevated A-a gradient
*oxygen supplementation may be effective but it depends on how much of the lung is affected.
+/- mildly responsive
With V/Q mismatch, patients are never responsive to oxygen
False- there is variable response to oxygen. depends on how much of the lung or blood flow to the lung is affected
Elevated A-a gradient
You have a 8yo FS West Highland White Terrier with chronic cough and acute dypsnea after a hike. Short breathing pattern. What is likely cause
Diffusion impairment via pulmonary fibrosis
West highland white terriers randomly get thickening on alveolar membranes (Pulmonary fibrosis)
What breed of dog commonly get pulmonary fibrosis (thickening of the alveolar membranes) resulting in hypoxemia from diffusion impairement
West Highland White Terriers
an infrequent cause of hypoxemia in vet med
usually silent until the animal is exercising
-Decreased alveolar surface area (emphyema in people)
-thickening of alveolar membranes (pulmonary fibrosis in West Highland White terriers)
-Interstitial pulmonary edema
Diffusion Impairment
How might you get diffusion impairment leading to hypoxemia
-Pulmonary fibrosis (West Highland White Terriers)
-Interstitial Pulmonary edema
-emphysema
*Anything where there is thickening of alveolar membranes and oxygen cant diffuse across that thicker membrane
Fick’s Law
Diffusion is proportional to
1) Solubility of gas
2) Surface area
3) Differences in partial pressure between compartments
Inversely proportional to
1) thickness of membrane
2) molecular weight
Fick’s law state that diffusion is proportional to
_______
_______
_______
while inversely proportional to
_______
_______
_______
Diffusion is proportional to
1) Solubility of gas
2) Surface area
3) Differences in partial pressure between compartments
Inversely proportional to
1) thickness of membrane
2) molecular weight
Are diffusion impairments response to oxygen
yes
Diffusion is proportional to
1) Solubility of gas
2) Surface area
3) Differences in partial pressure between compartments
*Increasing oxygen partial pressure
Do you see an elevated A-a gradient with diffusion impairment
Yes
increase differences in O2 partial pressure -> increases in diffusion and elevated A-a gradient
What causes the most severe hypoxemia
Shunt reversal
not oxygen responsive
Is a reversed shunt responsive the oxygen
No
Is there an A-a gradient with shunts?
Yes, increased
Which of the 5 causes of hypoxemia is responsible for hypoxemia associated with aspiration pneumonia
V/Q mismatch
Which of the 5 causes of hypoxia are responsive to 100% oxygen
-Decreased PiO2
-Hypoventilation
-Diffusion Impairment
*Variable: V/Q mismatch
Which of the 5 causes of hypoxemia are not responsive to 100% oxygen supplementation
Diffusion impairment
Variable: V/Q mismatch
Which of the 5 causes of hypoxemia have an elevated A-a gradient
Diffusion impairment
Shunt
V/Q mismatch
Which of the 5 causes of hypoxemia have a normal A-a gradient
-Decreased PiO2
-Hypoventilation
Respiratory failure can be due to
-Oxygenation failure
-Ventilatory failure
-Fatigue
What is the gold standard for assessing oxygenation
Measuring PaO2
Advantages: reliable/precise, als oget acid-base information
Disadvantages: must get arterial sample, not continuous, maintenance, expensive machine
PaO2 is roughly ___________ FiO2
4-5x FiO2
21% x 5= 105mmHg
100% x 5= 500mmHg
Why might you not see cyanosis
You need to have >5g/dL deoxygenated hemoglobin
if anemic (ex: Hb=5 g/dL ) then youll never see cyanosis
if Hb= 15g/dL -> PaO2= 37mmHg and already very low
disadvantages is the cyanosis is unreliable, late indicator and subjective
Should you use cyanosis to diagnose hypoxemia in your patient
NO- it is unreliable, very late indicator, and subjective
depends on >5g/dL deoxygenated hemoglobin to be present
so if anemic, you might never see it
or even if Hb- 15g/dL, you still wont see it until 37mmHg PaO2 which is severely low
indirect measurement of oxygen content in blood
relies on detecting the difference in absorption of particular wavelengths of light by oxygenation and reduced hemoglobin
pulse oximetry
Oxygenated Hb absorbed _____________ (940nm) while deoxygenated /reduced Hb absorbs _____________ (660nm)
Infrared light (940nm)
red light (660nm)
What are the disadvantages of pulse ox for SpO2 measurement
relies on pulse of arterial system to discriminate between arterial blood saturation and venous
cannot distinguish dysfunctional hemoglobin
only reads up to 100% which may not be helpful when patient is on 100% FiO2 but might not reflect PaO2 under general anesthesia (misleading)
Adversely affected by: bright overhead lighting, vasoconstriction, dark pigmenet, hypothermia, hypoperfusion
What factors adversely affect SpO2 reading via pulse ox
bright overhead lighting
vasoconstriction
dark pigment
hypothermia
hypoperfusion
dysfunctional hemoglobin
T/F: SpO2 reading via pulse ox is affected by icterus
false
What SpO2 readings tell you normal, hypoxemic, and severely hypoxemic
Normal >95%
Hypoxemia <95%
Severe hypoxemia <90%
Why is SpO2 reading under general anesthesia not helpful
Because when you are supplying 100% oxygen (100% FiO2) you cannot distinguish a PaO2 of 100mmHg vs 400mmHg
Helps you differentiate different types of hemoglobin using 4-8 wavelengths of light
Co-oximetry
measures:
1) oxygenated hemoglobin
2) Deoxygenated hemoglobin
3) Carboxyhemoglobin
4) Methemoglobin
5) Oxygen content
What does co-oximetry tell you
differentiate different types of hemoglobin using 4-8 wavelengths of light
1) oxygenated hemoglobin
2) Deoxygenated hemoglobin
3) Carboxyhemoglobin
4) Methemoglobin
5) Oxygen content
*expensive
What has a 200x greater affinity for Hb than O2 and can falsely elevate SpO2 to 100%
Carbon monoxide forming Carboxyhemoglobin
*Housefires
Why might patients in a house fire have a falsely elevated SpO2 reading (100%)
Carbon monoxide has a greater than 200x greater affinity for Hb than O2 and can form Carboxyhemoglobin
Carboxyhemoglobin
Carbon monoxide has a greater than 200x greater affinity for Hb than O2 and can form Carboxyhemoglobin
falsely high SpO2- usually 100%
What is methemoglobinemia
seen in acetaminophen (chocolate colored mucous memebranes and SpO2 of 85%) Fe3+ is oxidized
also in topical benzocaine products
Pheazopyridine products
Phenazopyridine ingestion (urinary tract analgesic)
Nitrites
Nitrates
Skunk musk
Hydroxycarbamide
Methb reductase deficiency
Why might you have brown/chocolate looking mucous membranes
acetaminophen toxicity
also in topical benzocaine products
Pheazopyridine products
Phenazopyridine ingestion (urinary tract analgesic)
Nitrites
Nitrates
Skunk musk
Hydroxycarbamide
Methb reductase deficiency
What will the pulse ox read in an animal with memthemoglobinemia
always 85%
You have a patient with chocolate colored gum and an SpO2 of 85%. What do you think?
Methemoglobinemia
causes:
acetaminophen toxicity
topical benzocaine products
Pheazopyridine products
Phenazopyridine ingestion (urinary tract analgesic)
Nitrites
Nitrates
Skunk musk
Hydroxycarbamide
Methb reductase deficiency
You cant calculate the A-a gradient when on 100% oxygen. What can you do instead
P/F ratio= PaO2/FiO2
normal >400mmHg
acute lung injury (ALI)= 200-300mmHg
acute repsiratory distress syndrome (ARDS)= <200mmHg
What is the P/F ratio
P/F ratio= PaO2/FiO2
can be used when animal is on supplemental oxygen
normal >400mmHg
acute lung injury (ALI)= 200-300mmHg
acute respiratory distress syndrome (ARDS)= <200mmHg
What is the P/F ratio of animals with acute lung injury
200-300 mmHg
What is the P/F ratio of animals with acute respiratory distress syndrome (ARDS)
<200mmHg
The P/F ratio is _______ / _______
PaO2 / FiO2
What are methods to monitor ventilation
1) PaCO2
2) PvCO2
3) ETCO2
4) Capnography
PvCO2 is usually ________ ________ than PaCO2
5mmHg higher than PaCO2
PvCO2 is a reflection of arterial CO2 inflow, local tissue CO2 production, and tissue blood flow
ETCO2 is normally ________ ________ than PaCO2 and it varies due to _____________
ETCO2 is normally 5mmHg lower than PaCO2 and it is increased in the presence of dead space
What are the uses of capnography
1) Confirm endotracheal intubation
2) Assess ventilation
3) Estimate alveolar dead space ventilation
4) Monitor efficacy of CPCR
What are the different phases of capnography
0: inspiration, no CO2 measured (low)
I: early expiration, emptying of anatomic dead space, no CO2 is measured
II: expiraton, alveolar and dead-space gas, steep increase in CO2
III: alveolar plateau, alveolar CO2 measured
IV: ETCO2
What is the peak of a capnograph
the end-tidal CO2 (phase IV)
what is the plateau on a capnograph
the alveolar CO2 is being measured (phase III)
What is the upslope of the capnograph
expiration of alveolar and dead-space gas (phase II) leading to a steep increase in CO2
What is the flat low parts of capnograph
phase o: inspiration, no CO2 measured
What are the different techniques to deliver oxygen to a patient?
1) Flow by oxygen
2) Face mask
3) Nasal oxygen
4) Oxygen cage
5) High flow nasal oxygen
6) Intubation and ventilation
How much oxygen is supplied by flow-by, facemask, O2 cage, and nasal
Flow by: 2-3L/min (25-40%)
Facemask: 8-12L/min (50-60%)
O2 cage (21-60%)
Nasal: 50-150mL/kg/min (30-70%)
What are the pros and cons of flow by and face mask
Pros: fast, easy, able to handle patient
Cons: not long term, waste, not able to provide high FiO2 (only 25-40% or 50-60%, respectively)
What are the pros and cons of nasal prongs for O2 delivery
Pros: long-term, higher FiO2 (30-70%), easy to place, generally well tolerated
Cons: discomfort, may fall out, must be humidified
What are the pros and cons of O2 cage
Pros: long term, higher FiO2 (21%-60%), vented to prevent CO2 buildup
Cons: Expensive, hyperthermia, cannot handle patients, cannot hear patient
What are the pros and cons of high flow nasal oxygen
Pros: can deliver up to 100% oxygen at high flow rate, air is humidified, and warmed
Cons: not made for out patient’s face, expense
What are the pros and cons of intubation and mechanical ventilation
Pros: Allows for FiO2 100%, can control ventilation, can provide positive and expiratory pressure
maximal support that you can provide
Cons: expensive, technically challenging, 24 hour
What are the 4 indications for mechanical ventilation *
1) Severe hypoxemia despite therapy (PaO2 <60mmHg)
2) Severe hypoventilation despite therapy (PaCO2 >60mmHg) “rule of 60s at sealevel, 50s at altitude”
3) Increased work of breathing- maintaining normoxemia/ normocapnea at the expense of increased respiratory rate and effort
4) Severe hemodynamic instability
Increased work of breathing puts a patient at risk for ______________ and may be identified by ____________
puts patient at risk for fatigue
may be identified by
-Increasing PaCO2
-Decreasing chest wall excursions
-Physical appearance
*Treat with sedation and mechanical ventilation
a 10yo FS Lab in Fort Collins has a 2-3 day history of vomiting with a 1 day history of respiratory distress, coughing, and fever
pH: 7.480
PaCO2= 24mmHg
PaO2= PaO2
HCO3-= 22mmol/L
What is the patient in. and what is cause
Primary respiratory alkalosis without metabolic compensation
hypoxemia
PAO2= FIO2 (Pb-PH20) - PaCO2/0.8
=0.21(640-47)-24/0.8
=44mmHg (elevated)
Can be due to V/Q mismatch, Diffusion impairment or shunt
response to oxygen will tell you underlying cause of disease and it will also decrease work of breathing for the dog
can also fo P/F ratio to tell the repsonse
You have a dog on 40% oxygen and take arterial blood.
PaO2= 120mmHg
PaCO2= 30mmHg
What is the P/F ratio
P/F= 120/0.4= 300 mmHg
since they are on 40% oxygen- the PaO2 should be 160-200mmHg but its not (4-5x the % oxygen)
Normal >400 mmHg
ALI 200-300mmHg
ARDS <200mmHg
If you have a dog on 40% oxygen what should the estimated PaO2 be
about 4-5x the % oxygen
example: 160-200mmHg PaO2
