Respiratory failure and ARDS

Question 1

two basic types of respiratory failure

Answer 1

hypoxemic (Low PaO2 and/or SaO2) and hypercapneic (high CO2)

Question 2

Hypercapneic respiratory failure etiology

Answer 2

Any process that acutely impairs ventilation (inadequate CO2 removal) Differentiate from chronic hypercapneic respiratory failure

Question 3

What causes hypercapneic respiratory failure

Answer 3

Cant breathe: Asthma, COPD, upper airway obstruction, severe burn (chest wall restriction), trauma, neuromuscular. Wont breathe: Respiratory drive issues central hypoventilation, oversedation, brain injury, seizure
Cant breathe: Asthma, COPD, upper airway obstruction, severe burn (chest wall restriction), trauma, neuromuscular. Wont breathe: Respiratory drive issues central hypoventilation, oversedation, brain injury, seizure

Question 4

Hypoxemic respiratory failure etiology

Answer 4

¡Any process that limits diffusion or V/Q matching to the point that oxygen saturation is <55.

Question 5

Hypoxemic respiratory failure causes

Answer 5

¡any alveolar filling process (pneumonia, blood, water, aspiration, inflammation, tumor), atelectasis, pulmonary embolism, pulmonary contusion, progression of chronic hypoxemic diseases, such as pulmonary hypertension, COPD, ILD.

Question 6

Causes of hypoxemia

Answer 6

ventilation/perfusion (V/Q) mismatch, impaired gas diffusion across alveolocapillary membrane, alveolar hypoventilation, altitude

Question 7

explain V/Q mismatch

Answer 7

A shunt occurs when there is perfusion without ventilation. Dead space occurs when there is ventilation without perfusion.

Question 8

Examples of V/Q mismatch and which are more likely to have a shunt

Answer 8

Pneumonia, pulmonary edema, obstructive airways disease (examples of V/Q mismatch). Conditions with alveolar collapse or filling are most likely to have more shunt
Pneumonia, pulmonary edema, obstructive airways disease (examples of V/Q mismatch). Conditions with alveolar collapse or filling are most likely to have more shunt

Question 9

causes of decreased gas diffusion

Answer 9

interstitial fibrosis, amyloid

Question 10

Causes of alveolar hypoventilation

Answer 10

Excess CO2 leaves no room for O2. - sedatives, alcohol, brain injury, neuromuscular disease
Excess CO2 leaves no room for O2. - sedatives, alcohol, brain injury, neuromuscular disease

Question 11

What 3 things are done for evaluation of respiratory failure

Answer 11

physical exam, chest imaging, arterial blood gas

Question 12

What are the 4 important parameters of mechanical ventilation

Answer 12

1. FIO2 - the fraction of inspired oxygen between 21% (room air) and 100% (pure oxygen). 2. PEEP - Positive end-expiratory pressure. 3. Respiratory rate . 4. Tidal volume
2. FIO2 - the fraction of inspired oxygen between 21% (room air) and 100% (pure oxygen). 2. PEEP - Positive end-expiratory pressure. 3. Respiratory rate . 4. Tidal volume

Question 13

2 determinants of ventilation

Answer 13

respiratory rate and tidal volume

Question 14

2 determinants of oxygenation

Answer 14

FIO2 and PEEP

Question 15

What is positive end expiratory pressure

Answer 15

Maintains alveolar recruitment (thus diffusion surface area) and prevent derecruitment by limiting lug deflation at end-expiration. Naturally the glottis maintains expiratory pressure

Question 16

What is atelectasis

Answer 16

complete deflation of alveolar units (occurs without PEEP). This results in alveolar de-recruitment, which decreases the effective alveolar/capillary surface area.

Question 17

clinical definition of Acute Lung Injury and Acute respiratory distress syndrome

Answer 17

ALI/ARDS are diagnosed based on: 1. Diffuse bilateral radiographic infiltrates, 2. PaO2:FIO2 ratio < 300 (ALI) or <200 (ARDS), 3. No evidence of a cardiogenic etiology (i.e. left heart failure)

Question 18

Histology of ARDS

Answer 18

alveolar flooding, neutrophil influx, epithelial cell damage and death, hemorrhage, proteinaceous edema, hyaline membranes(intra-alveolar accumulation of protein deposits), and systemic inflammation

Question 19

Common causes of ARDS

Answer 19

sepsis, pancreatitis, trauma, aspiration, acute CNS processes, amniotic fluid embolism, and transfusion.

Question 20

How does mechanical ventilation affect ARDS

Answer 20

Can cause or worsen ARDS

Question 21

What is the only intervention that improves survival in ARDS

Answer 21

1. low tidal volume ventilation (6 cc/kg), even if the patient develops hypercapnea and respiratory acidosis (permissive hypercapnea). Possibly consider using a prone position if PaO2:FIO2 <150

Question 22

How do you calculate the alveolar/arterial oxygen difference

Answer 22

A-a DO2= PAO2-PaO2. Where PAO2= alveolar oxygen pressure, PaO2= afterial oxygen pressure.

Question 23

How do you calculate alveolar oxygen pressure

Answer 23

PAO2=(Pbar-PH2O) x FIO2-PaCO2/RQ. Where Pbar= 760 (sea level) or 630 (Denver), RQ= 0.8, FIO2 = 21% at room air, PH2O= 47

Question 24

standard notation for arterial blood gas

Answer 24

pH/pCO2/PO2

Question 25

What does a normal A-a DO2 reflect

Answer 25

normal lung function

Question 26

Hypoxemia in setting of normal A-a DO2 is due to what?

Answer 26

Lung function is normal, so it must be due to barometric pressure, FIO2, or arterial CO2 pressure

Question 27

Acute vs chronic respiratory acidosis

Answer 27

acute: [HCO3-] ↑ 1 mEq/L : PaCO2 ↑ 10 mm Hg and ∆ pH = 0.008 x (40- PaCO2). Chronic: [HCO3-] ↑ 4 mEq/L : PaCO2 ↑ 10 mm Hg and ∆ pH = 0.003 x (40- PaCO2)

Question 28

Respiratory acidosis indicates what?

Answer 28

Hypercapneic respiratory failure component

Question 29

What ultimately determines the PaCO2?

Answer 29

alveolar ventilation