18 - Respiratory Failure & ARDS Flashcards
What is the onset of acute vs. chronic respiratory failure? Which one is more serious?
Acute - rapid onset, life-threatening
Chronic - weeks-years
What are the physiologic responses to hypoxemia and hypercarbia from acute respiratory failure?
Hypoxemia
- increased catecholamines –> tachycardia
- increased carotid body stimulation –> tachypnea and hyperventilation
Hypercarbia
- decreased pH and increased intracranial pressure –> CO2 narcosis
- increased PaCO2 –> cerebral vasodilation
What is the equation for O2 delivery?
DO2 = CO * CaO2
What are the physiologic responses to hypoxemia and hypercarbia from chronic respiratory failure?
Hypoxemia
- increased erythropoietin –> increased hemoglobin
Hypercarbia
- increased bicarbonate –> less severe acidosis
How does pulse oximetry work?
2 wavelengths of light due to different absorption by reduced and oxygenated hemoglobin –> allows us to calculate the percentage of oxyhemoglobin
What are the complications of oxygen therapy?
- reactive O2 species are cytotoxic
- blindness or bronchopulmonary dysplasia in children
- decreased mucuciliary clearance
- tracheitis
- acute lung injury
- absorptive atelectasis (removing N2 from air will create a much stronger gradient, causing instantaneous alveolar collapse as gas quickly diffuses out of alveoli)
What are the nonspecific and specific therapies for respiratory failure?
Nonspecific
- hypoxemia –> supplemental oxygen (ineffective if hypoxemia is due to shunt)
- hypercapnia –> avoid/correct
Disease specific
- pneumonia: antibiotics, secretion clearance
- atelectasis: remove secretions
- COPD/asthma: bronchodilators, steroids
- drug overdose: antidote
What are the indications for mechanical ventilation? What are the complications?
Hypoxemic failure
- shunt
- inadequate lung expansion due to atelectasis
Hypercapnic failure
- elevated work of breathing
- respiratory muscle weakness
- insufficient respiratory drive
What are the advantages, disadvantages, and indications for non-invasive ventilation?
Advantages
- avoid endotracheal tube
- less sedation
- care can be given outside of ICU
Disadvantages
- may not tolerate mask or pressure
- no access to airway to remove secretions
Indications
- respiratory failure that can get better in a day or two
- chronic respiratory failure (neuromuscular disease, OHS)
What is the pathogenesis of acute respiratory distress syndrome?
Inflammatory injury to alveoli –> increased alveolar-capillary permeability –> non-cardiogenic pulmonary edema –> reduced compliance and increased shunt –> hypoxemia
What are the common pulmonary and extra-pulmonary causes of acute respiratory distress syndrome?
Pulmonary
- pneumonia
- gastric aspiration
- inhalation
- near drowning
- toxic gas inhalation
- thoracic trauma (pulmonary contusion)
Extra-pulmonary
- sepsis
- pancreatitis
- non-thoracic trauma
- fat embolism
- massive transfusion
- drugs (heroin)
Heterogeneity injury to the lung with areas of poor ventilation and areas of better ventilation is suggestive of ___.
acute respiratory distress syndrome
What is the pathogenesis of acute respiratory distress syndrome?
- Injured alveolar and capillary endothelium –> increased permeability –> fluid leaks into interstitium then alveolar space –> fluid filled alveoli have decreased compliance and cause a shunt
- injury causes significant inflammation and leaking of protein into alveolar space
- type II cells are injured –> reduction in surfactant
- existing surfactant is inhibited by inflammatory cells, oxidation, and proteolytic enzymes –> decreased compliance, alveolar collapse, and alveolar flooding
How is pulmonary circulation affected in acute respiratory distress syndrome? What causes it?
- abnormal
- increased pulmonary arterial pressure
- increased pulmonary vascular resistance
- increased dead space fraction
Results from:
- vasoconstriction
- microthrombi
- compression of vessels by edema
What are the complications of placing someone with ARDS on a ventilator with normal settings? How should ventilator settings be modified?
Normal settings –> all or much of volume will go to better-ventilated areas of lung, leading to:
- barotrauma (disruption of lung with air leaking into pleural space, causing pneumothorax)
- volutrauma (injury to alveolar/capillary interface –> inflammatory process)
- atelectrauma - alveolar injury from opening and closing of alveoli
- biotrauma (increase in cytokines, causing systemic dysfunction)
Modified settings:
- low tidal volumes (to avoid overdistension)
- PEEP (to keep alveoli from completely collapsing at end of expiration)
