ARDS and ALI Flashcards
Define hypoxemic respiratory failure
Causes?
anything that limits diffusion or V/Q matching so O2 sat decr diffusion across alveolocapillary membrane (impaired gas diffusion)
–> V/Q mismatch
- -> high altitude (low PIO2)
- -> alveolar hypoventilation
What is alveolar hypoventilation
excess CO2
No room for O2
What are examples of V/Q mismatch diseases
1) pneumonia
2) pulm edema
3) obstructive airways
which conditions are more likely to have signif shunt
1) alveolar collapse or filling
PNA/ARDS
examples of decr diffusion across alveolocapillary membrane causing hypoxemia
1) interstitial fibrosis
2) amyloid
examples of alvolear hypoventilation causing hypoxemia
1) sedatives
2) alcohol
3) brain injury
4) neuromuscular disease
define hypercapneic resp failure
separated by?
any process that impairs ventilation (CO2 elimination) or elev CO2
can’t breathe vs. won’t breathe
hypercapneic resp failure
if you can’t breathe, causes…
lung diseases
1) asthma
2) COPD
3) upper airway obstruction
4) severe burn (chest wall restriction)
5) trauma
6) neuromuscular
hypercapneic resp failure
if you won’t breathe, causes
chronic lung disease
adapted to chronic ability to hypoventilate
1) central hypoventilation
2) oversedation
3) brain injury
4) seizure
2 determinants of ventilation
To incr ventilation, incr…
1) tidal volume (affects ventilation)
2) respiratory rate (affects ventilation)
To incr oxygenation on ventilation
3) incr FIO2 (0.21 vs. 1.00)
4) PEEP (more recruit alveolus)
what ultimately determines PaCO2
alveolar ventilation
Va = (Vt - Vd) x f
Define dead space ventilation
causes of deadspace
a process that decr perfusion to ventilated alveoli, incr physio dead space (air, but no blood flow)
1) hypovolemia (lower perfusing pressure –> alveolar collapse and need high vent pressures)
2) decr CO
3) PE (stopped blood flow)
4) high airway pressures (when alveolar pressure > capillary pressure = no ventilation = zone 1)
When evaluating respiratory failure,
procedure?
1) physical exam
2) CXR
3) ABG
Standard notation of ABG
pH/pCO2/pO2
Calculate A-a DO2
7.36/36/65 on room air in Denver
PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ
PAO2=(630-47)x 0.21-36/0.8
PAO2=77
A-a DO2= PAO2-PaO2
A-a DO2= 77-65
A-a DO2= 12
Normal A-a reflects ___
normal lung function in regards to oxygenation
Hypoxemia in setting of normal A-a DO2 is due to?
Low Pbar
Low FIO2
Low PaCO2
Compensation rules for acute respiratory acidosis
[HCO3-] ↑ 1 mEq/L : PaCO2 ↑ 10 mm Hg
∆ pH = 0.008 x (40- PaCO2)
Comepnsation rules for chronic respiratory acidosis
[HCO3-] ↑ 4 mEq/L : PaCO2 ↑ 10 mm Hg
∆ pH = 0.003 x (40- PaCO2)
Approach to classification of respiratory failure
1) calculate A-a DO2 to classify hypoxemia
- primary diffusion, V/Q or shunt
- hypercapnea
2) acute vs. chronic based on clinical
3) if respiratory acidosis is present, THERE IS A COMPONENT OF hypercapneic resp failure
4) determine acute vs chronic based on compensation rule
KNOW!!!!!!!!!!
for the exam,
if a patient has hypoxemic due to alveolar hypoventilation, THEY HAVE ____
they don’t have hypoxemic respiratory failure
THEY HAVE HYPERCAPNIC RESPIRATORY FAILURE
normal A-a gradient excludes ____
hypoxemic respiratory failure
Example 1
65 year old woman with mild emphysema, no home oxygen requirement, and 3 days of increasing cough and wheeze presents with shortness of breath.
ABG: 7.28/55/30 on room air.
Calculate A-a on room air in Denver
PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ
PAO2=(630-47)x 0.21-55/0.8
PAO2= 54
A-a DO2= PAO2-PaO2
A-a DO2= 54-30
A-a DO2= 24
∆pH = 0.12 (from 7.40)
∆pCO2=15 (from 40 normal)
0.12/15=0.008 (and ratio = 0.008) so pure acute mixed resp failure resp acidosis
(both acute hypoxemic and hypercapneic)
Example 1
65 year old woman with mild emphysema, no home oxygen requirement, and 3 days of increasing cough and wheeze presents with shortness of breath.
ABG: 7.28/55/30 on room air.
Diagnosis?
∆pH = 0.12 (from 7.40)
∆pCO2=15 (from 40 normal)
0.12/15=0.008
respiratory acidosis
hypercapneic resp failure
hypoxemia
we know she has hx of emphysema and she has no home O2
so likely just ACUTE
Long-term smoker who hasn’t seen a doctor in 40 years comes in with obvious emphysema on Xray, saturating 82% on room air, 92% on 4L?
has some chronic hypoxemia
feeling fine —> then came
down with cold (acute on chronic)
Example 2
42 y/o morbid obesity and chronic low back pain. Has had worsened low back pain the past few days, for which he has been taking oxycodone. Brought into ED after family found him very sleepy and confused.
ABG: 7.30/54/55 on room air.
Calculate the A-a DO2:
on room air in Denver
PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ
PAO2=(630-47)x 0.21-55/0.8
PAO2= 55
A-a DO2= PAO2-PaO2
A-a DO2= 55-55
A-a DO2= 0
∆pH = 0.09
∆pCO2=14
0.09/15=0.006 (between 0.003 and 0.008 since between acute and chronic = acute-on-chronic)
Example 2
42 y/o morbid obesity and chronic low back pain. Has had worsened low back pain the past few days, for which he has been taking oxycodone. Brought into ED after family found him very sleepy and confused.
ABG: 7.30/54/55 on room air.
what does he have?
∆pH = 0.09
∆pCO2=14
0.09/14=0.006
no hypoxemic
acute-on-chronic hypercapnea
PaCO2 is high, pH low
Patient with chronic lung disease on 2L per minute nasal cannula O2 at home
comes in with sat of 92% on 2L?
comes in with saturation of 82% on 2L, 92% on 6L
chronic hypoxemic at basleine
acute on chronic resp failure (when there is change in baseline and have chronic so manage the chronic)
Define PEEP
ET tube prevents glottis’ ability to maintain expiratory pressure and lung inflation
when vent goes into exhalation, provides an adjustable back pressure to stim glottic closure
–> MAINTAIN ALVEOLAR RECRUITMENT AND SURFACE AREA, PREVENT DERECRUITMENT
Without PEEP what happens?
1) atelectasis = deflation of alveoli causing alveolar de-recruitment, decr surface area
PEEP maintains surface area in hypoxemia
100% FIO2 AND 5 PEEP
and not oxygenating well then ____
turn up the PEEP
22 year old woman with history of asthma comes in with an acute attack, requiring intubation and mechanical ventilation.
What type of respiratory failure do you expect?
7.10/80/470
PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ
PAO2=(630-47)x 1-80/0.8
PAO2= 483
A-a DO2= PAO2-PaO2
A-a DO2= 483-470
A-a DO2= 13
∆pH = 0.3
∆pCO2=40
0.3/40=0.008
ACUTE HYPERCAPNEIC RESP FAILURE
need to incr ventilation
22 year old woman with history of asthma comes in with an acute attack, requiring intubation and mechanical ventilation.
Assuming her vent settings are VT 500, RR 20, FIO2 100%, PEEP 5, what next?
HYPERCAPNEIC RESP FAILURE
need to incr ventilation
Decrease FIO2 increase RR (or VT),
turn down FIO2 because 470 is too high and don’t have to worry about oxygenation
treat asthma with standard therapies (steroids, bronchodilators, ± antibiotics).
62 year old woman with history of chronic systolic heart failure comes in decompensated and volume overloaded. Despite diuresis, afterload reduction, and supplemental oxygen, she requires intubation and mechanical ventilation.
What type of respiratory failure do you expect?
7.50/28/45
PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ
PAO2=(630-47)x 1-28/0.8
PAO2= 578
A-a DO2= PAO2-PaO2
A-a DO2= 578-45
A-a DO2= 533
∆pH = 0.10
∆pCO2=12
0.10/12=0.008
hyperventilating and
hypoxemic respiratory fialure
acute resp alkalosis
pulm edema interstitial and alveolar space –> hypoxemia
62 year old woman with history of chronic systolic heart failure comes in decompensated and volume overloaded. Despite diuresis, afterload reduction, and supplemental oxygen, she requires intubation and mechanical ventilation.
Assuming her vent settings are VT 500, RR 20, FIO2 100%, PEEP 5, what next?
Ventilation is OK. Since our vents don’t go to 11, our only option is to increase PEEP.
since vent already maxed out at FIO2 = 100% can only change PEEP
Definition of ARDS
occurs within 1 week of known insult/worsening resp symptoms
2) diffuse bilateral pulm infiltrates
3) not explained by cardiac failure/fluid overload
4) severity classfiied by PaO2: FIO2 with > 5 cM-H2O PEEP
best if 201-300 = mild
ARDS pathogenesis
1) inflamm and macrophage infiltrate –> disrupt alveolar/capill barrier function –> alveolar flooding with fluid, red cells neutrophils, LOSS surfactant
histology of ARDS
hyaline membrane with hypoxemic resp failure
1) alveolar filling with protein edema
2) denuded basement membrane
3) HYALINE MEMBRANE (PROTEIN DEPOSITION)
4) neutrophils, hemorrhage
5) type II hyperplasia
radiology of ARDS
bilateral alveolar infiltrates
etiology of ARDS
1) Sepsis
2) pancreatitis
3) trauma
4) aspiration
5) transfusion = indirect
most likely pathogenesis of ARDS
UTI –> cytokines –> lungs –> oxidant damage
humoral
cytokines
activ neutrophils
functional disability after ARDS 5 yrs later
at 1 yr –> physiologic limitation
over 5 yrs physiology unchanged but return to work improved
how to treat ARDS
1) treat underlying cause
2) supportive care
3) ventilator management
6 cc/kg tidal voluem, plateau pressure
what is ventilator induced lung injury
high tidal volume ventilation can worsen lung injury and systemic inflamm
why is prone position better for ARDS ventilation
when to use?
more uniform transpulmonary pressure and distrib of alveolar stress
PaO2:FIO2
Before incr a patient’s tidal volume based on ABG, ___
make sure does not meet criteria for ARDS
ventilate patient with ___ ON EXAM!!!
LOW TIDAL VOLUME
CONSIDER PRONE IN SEVERE
