Respiratory failure and ARDS Flashcards
two basic types of respiratory failure
hypoxemic (Low PaO2 and/or SaO2) and hypercapneic (high CO2)
Hypercapneic respiratory failure etiology
Any process that acutely impairs ventilation (inadequate CO2 removal) Differentiate from chronic hypercapneic respiratory failure
What causes hypercapneic respiratory failure
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
Hypoxemic respiratory failure etiology
¡Any process that limits diffusion or V/Q matching to the point that oxygen saturation is <55.
Hypoxemic respiratory failure causes
¡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.
Causes of hypoxemia
ventilation/perfusion (V/Q) mismatch, impaired gas diffusion across alveolocapillary membrane, alveolar hypoventilation, altitude
explain V/Q mismatch
A shunt occurs when there is perfusion without ventilation. Dead space occurs when there is ventilation without perfusion.
Examples of V/Q mismatch and which are more likely to have a 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
Pneumonia, pulmonary edema, obstructive airways disease (examples of V/Q mismatch). Conditions with alveolar collapse or filling are most likely to have more shunt
causes of decreased gas diffusion
interstitial fibrosis, amyloid
Causes of alveolar hypoventilation
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
What 3 things are done for evaluation of respiratory failure
physical exam, chest imaging, arterial blood gas
What are the 4 important parameters of mechanical ventilation
- 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
- 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 determinants of ventilation
respiratory rate and tidal volume
2 determinants of oxygenation
FIO2 and PEEP
What is positive end expiratory pressure
Maintains alveolar recruitment (thus diffusion surface area) and prevent derecruitment by limiting lug deflation at end-expiration. Naturally the glottis maintains expiratory pressure
What is atelectasis
complete deflation of alveolar units (occurs without PEEP). This results in alveolar de-recruitment, which decreases the effective alveolar/capillary surface area.
clinical definition of Acute Lung Injury and Acute respiratory distress syndrome
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)
Histology of ARDS
alveolar flooding, neutrophil influx, epithelial cell damage and death, hemorrhage, proteinaceous edema, hyaline membranes(intra-alveolar accumulation of protein deposits), and systemic inflammation
Common causes of ARDS
sepsis, pancreatitis, trauma, aspiration, acute CNS processes, amniotic fluid embolism, and transfusion.
How does mechanical ventilation affect ARDS
Can cause or worsen ARDS
What is the only intervention that improves survival in ARDS
- 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
How do you calculate the alveolar/arterial oxygen difference
A-a DO2= PAO2-PaO2. Where PAO2= alveolar oxygen pressure, PaO2= afterial oxygen pressure.
How do you calculate alveolar oxygen pressure
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
standard notation for arterial blood gas
pH/pCO2/PO2
What does a normal A-a DO2 reflect
normal lung function
Hypoxemia in setting of normal A-a DO2 is due to what?
Lung function is normal, so it must be due to barometric pressure, FIO2, or arterial CO2 pressure
Acute vs chronic respiratory acidosis
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)
Respiratory acidosis indicates what?
Hypercapneic respiratory failure component
What ultimately determines the PaCO2?
alveolar ventilation
