Respiratory Failure Flashcards
What is the definition of respiratory failure?
Inability of the lungs to meet the metabolic demands of the body
-> failure of tissue oxygenation or CO2 homeostasis
What is the difference between hypoxemic and hypercapnic respiratory failure?
In both cases, PaO2 is low
In hypercapnic respiratory failure, PaCO2 is also increased. Generally, PaCO2 is decreased in hypoxemic respiratory failure.
What is acute vs chronic vs acute on chronic respiratory failure?
Acute - minutes to hours
Chronic - develops over several days or weeks
Acute on chronic - Overlap between acute and chronic (i.e. patient with COPD develops pneumonia)
What type of respiratory failure results from problems with CNS, peripheral nerves, muscles of respiration, upper airway, or bronchial tree obstruction?
Hypercapnic respiratory failure
-> hypoventilation = low O2 high CO2
What does defect in pulmonary gas exchange (alveoli or pulmonary vasculature) cause?
Hypoxemic respiratory failure
-> generally low PCO2 due to hyperventilation
Other than lung problems, what other issues can contribute to respiratory failure?
Decreased O2 delivery due to low hemoglobin, decreased cardiac output, or shoack
Metabolism at cellular level may be affected (CN poisoning, endotoxin)
What are the five mechanisms of hypoxemia?
- Low environmental O2
- Hypoventilation
- Diffusion defect
- V/Q mismatch
- Right to left shunt
Which of the five mechanisms of hypoxemia are associated with an increased A-a gradient? Why?
- Diffusion defect - gas can’t diffuse
- V/Q mismatch - ventilation is generally adequate but flow is too poor to well oxygenate the blood
- Right to left shunt - ventilation is adequate but there is too mush blood to fully oxygenate it
Which of the five mechanisms of hypoxemia are not associated with an increase A-a gradient?
- Low environmental O2 - high altitudes, lower oxygen concentration inspired
- Hypoventilation
See notes for calculation of A-a gradient. Pg 263 in coursepack 2.
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What are two overall causes of increased A-a gradient?
- Age
- Lung disease - hypoxemic respiratory failure
= pulmonary embolism, pneumonia, pulmonary edema
What is FiO2 and what is it useful for calculating?
Fraction of inspired O2
-> useful for recalculating A-a gradient when patient is on 100% inspired O2
Aka (760-47)1.00 rather than (760-47)0.21 = PiO2
What are some common causes of decreased environmental O2? Treatment?
High altitude
High risk patients travelling in airplanes (pressured to 10000 feet)
Carbon monoxide poisoning
Treatment is O2 supplementation or hyperbaric O2 for CO
How is minute ventilation calculated?
Ve = Vt * RR
Minute ventilation = tidal volume * respiratory rate
What are some common causes of hypoventilation and what will be the A-a gradient? What type of respiratory failure is this?
A-a gradient = normal
Respiratory center depression, neuromuscular diseases, chest wall abnormalities, airway diseases
This is hypercapnic respiratory failure
What equation describes the PaCO2?
PaCO2 is proportional to:
CO2 production rate / (minute ventilation * (1- dead space volume / tidal volume))
Based on the PaCO2 equation, what things can cause an increase in PaCO2?
Increased CO2 production - catabolic states and high caloric intake
Low minute ventilation - decreased respiratory drive
Dead space volume / tital volume ratio is high - respiratory diseases like COPD / asthma
Give examples of CNS / neuromuscular diseases causing hypercapnic respiratory failure (hypoxemia).
CNS: CVA’s affecting brainstem, TBI’s, CNS depressants like opioids, cervical spinal cord injury,
Neuromuscular: ALS, Guillain-Barre syndrome, poliomyelitis, myasthenia gravis, muscular dystrophies
What are some chest wall abnormalities which can cause hypercapnic respiratory failure?
Kyphosis, scoliosis
What airway diseases other than asthma and COPD can cause hypoventilation?
Foreign bodies or tumors, vocal cord diseases
What are the symptoms of hypercapnic respiratory failure? What’s the treatment?
Somnolence, lethargy, headache, restlessness, slurred speech, asterixis, coma
Supplemental O2, and mechanical ventilation may be needed
What is a very common cause of V/Q mismatch?
Pulmonary embolism -> lack of blood supply despite adequate ventilation
What is the definition of shunting?
Movement of blood past the lungs or through the lungs without adequate oxygenation
-> often occurs due to low V/Q ratio
What are some causes of low ventilation V/Q mismatch with widening of the A-a gradient? How does CO2 generally respond?
CO2 generally decreases or stays the same because ventilation is occurring fast enough to blow off CO2, but there is not enough gas exchange to allow total uptake of O2 (all around the lung)
- > diseases include pneumonia, atelectasis, pulmonary edema, COPD exacerbation, pneumothorax
- > upper portions of the lung blow off CO2, but lower portions fail adequate gas exchange
What is right to left shunt basically?
An extreme form of V/Q mismatch, where Q is very high and V is basically 0
-> blood passes from right to left circulation without passing thru alveoli
What are some common causes of right to left shunt?
ASD / VSD with Eisenmenger syndrome
Large arteriovenous malformations in lungs -> connections between pulmonary artery and veins
Can right to left shunt be corrected with oxygen?
No -> blood is not reaching the lungs to get oxygenated
A-a gradient will remain elevated due to hypoxemia
In what types of diseases do you have diffusion defect in the lungs?
Interstitial and fibrotic lung diseases
What type of respiratory failure is acute respiratory distress syndrome? How does it look on CXR?
Hypoxemic respiratory failure
-> bilateral pulmonary filtrates and hypoxemia
How can left heart failure cause hypoxemic respiratory failure?
Pulmonary edema (fluid in alveoli), or low cardiac output
What are common etiologies of ARDS? One of these relates to why you must fast before surgery?
Pneumonia Aspiration of gastric contents (as in surgery) Trauma (pulmonary contusion) Sepsis Severe trauma with shock Inhalation injury, severe burns Pancreatitis Emboli
What is pathogenesis of ARDS?
Release of cytokines and inflammatory mediators which lead to influx of inflammatory cells and activation of macrophages
- > damage to endothelium, causing fluid leak into interstitium and alveoli
- > pulmonary edema, atelectasis
- > development of hyaline membranes and thrombosis
What are the symptoms of hypxoemia?
Tachyacrdia, tachypnea, cyanosis, hypertension initially followed by hypotension, diaphoresis, AMS, seizures /coma
What blood count indicates probable chronic hypoxemia? What can anemia indicate
Polycythemia (elevated hematocrit)
Note: ANEMIA can actually indicate decreased O2 carrying capacity and be a cause of hypoxemic respiratory failure
Why is echocardiogram important in evaluation of acute respiratory failure?
Can point to left heart failure or right heart failure as the most likely cause
What patient is in better shape:
- Patient has PaO2 of 70 mmHg on 100% oxygen
- Patient has PaO2 of 60 mmHg on 21% oxygen
- PaO2/FiO2 = 70/1.00 = 70
- PaO2/FiO2 = 60/0.21 = 300
Patient 2 is in a much better spot
A patient is in respiratory failure but pulse ox is 93%, and their lips are cherry red. Why?
CO poisoning most likely
What are general treatments for managing ARDS? When must mechanical ventilation be used?
Small tidal volumes and prone ventilation
Mechanical ventilation must be used when patients cannot protect airway, are uncooperative, need restraints, are hemodynamically unstable, or have excessive excretions, do not approve to alternate ventilation in first 1-2 hours
What is the non-invasive ventilator which is probably better than putting an ET tube down most patients? What can it be used?
Non-invasive positive pressure ventilation (face mask)
-> do no need to be sedated, fewer complications, no intubation
Can be used in COPD, hypoxemic respiratory failure, neuromuscular disorders
If a patient has altered mental status or ventilatory failure characterized by apnea, how should they be ventilated?
Mechanical ventilation
