Respiratory Failure Flashcards
- Define hypoxemia and hypercapnic respiratory failure.
PaO2 less than 60 mmHg or PaCO2 greater than 45-50 mmHgwhen breathing room air
- Describe the etiology of mechanisms of respiratory failure, including CNS depression, neuromuscular, chest wall/pleural space abnormality, airway abnormalities, parenchymal disease and vascular disorders.
CNS: drug overdose, brainstem lesion or bulbar poliomyelitis
NM: malnutrition, cord injury, MS, Guillain-Barre, MG, tetanus
Chest wall/Pleural abnormality: pleural effusion, post-op, obesity, COPD, kyphoscoliosis, flail chew, restrictive chest wall burn
airway abnormality: Chronic bronchitis, emphysema, asthma, upper airway obstruction
parenchymal disease: pulm. edema, pneumonia, ARDS, interstitial fibrosis, pneumothorax
vascular disorders: PE, pulm. HTN
- Demonstrate the pathophysiologic classification of hypoxemic respiratory failure.
characterized by increase in venous admixture- low V/Q and or shunt; good examples include (acute) pneumonia and ARDS (chronic) pulmonary fibrosis
tx. can include supplemental oxygen; patients often hyperventilate with increased work of breathing, which may require assisted ventilation
- Demonstrate the pathophysiologic classification of hypercapnic respiratory failure.
represents an imbalance between the demand for and supply of alveolar ventilation
Increased CO2 production,
decrease in TV,
decreased RR (drive or strength)
or increased dead space can all contribute
pure examples include CNS depression and neuromuscular diseases; both which call ventilation assistP
- Examine the physiology of supplemental oxygen as a therapy for respiratory failure.
therapy aims PaO2 of around 60mmHg for saturation at or above 90% via supplemental oxygen
2 major side effects: paradoxical increase in PaCO2 in select patients (central depression of the CO2 dependent drive to breath esp. in decompensated) and oxygen toxicity due to ROS
remember hypoxemia related to shunting will be more refractory to supplemental oxygen
- Define assisted ventilation.
particularly helpful in low compliance states where transpulmonary pressure may not be adequate to fill lungs
most methods decreased the work of breathing also increase the distending pressure to improve hypoxemia
mechanical ventilation does not always ensure respiratory muscle at rest, particularly if breathing is dyssynchronus with ventilator and muscle rest may contribute to muscle atrophy
- Contrast advantages and disadvantages of different methods of non-invasive ventilation, NPV and CPAP.
negative pressure ventilation (iron lung, rarely used now) doesnt require intubation and can perform work of breathing, but is cumbersome, limits access to the patient
Continuous positive airway pressure: deliver of high flow gas so airway and alveolar pressure is always positive, improving lung compliance; no intubation, minimal CV effects; patient must protect their airway and has a relatively small impact on work of breathing, prolonged use may dry upper respiratory tract
- Contrast advantages and disadvantages of different methods of non-invasive ventilation, IPPV.
intermittent positive pressure ventilation (both BPAP and through endotracheal tube): decreases work of breathing, improves ventilation and may diminish hypoxemia by cyclical application of positive pressure to the lung
BPAP can be delivered with a “back up rate”; no intubation, minimal CV effects; patient must protect their airway and has a relatively small impact on work of breathing, prolonged use may dry upper respiratory tract
- Compare advantages and disadvantages of different methods of invasive ventilation.
requires endotracheal or tracheostomy tube, ventilator mode defined by trigger, (usually time or patient effort) and the cycle (defined by volume or pressure)
commonly volume assist/control: clinicians determine VT and min RR
intubation allows for good tracheobranchial “toilet” and fine control of ventilatory pattern, rate, volume, FiO2 and PEEP although intervention is invasive, and holds the potential for trauma, infection, baro trauma, negative CV (decreased CO) and interferes with communication
PEEP is often added
- Assess factors involved in weaning of mechanical ventilation.
scheduled, daily interruption of sedation to assess radiness for liberation from mechanical ventilation
passing of 5 screening items predicts successful extubation at rate of 80-90%
- RR/Vt < 105 during spontaneous breathing, with greatly reduced mechanical support
- PaO2/FiO2>200 - the trajectory of improvement is more important than the value
- absence of sedation
- absence of continuous infusion of vasoactive drugs
- reasonable cough and estimated strength and overall capacity to clear respiratory secretions
- Describe epidemiological characteristics of acute respiratory failure.
ARF is one of the most common indications for admission to ICU, and incidence has been increasing in recent decades
risk increases exponentially with each decade until age 85
30-day mortality for patients hospitalized for acute respiratory failure requiring mechanical ventilation exceeds 30%
20% deaths in US take place after short ICU stay
historically patients with ARF either recovered or died, increasing number of those requiring prolonged mechanical ventilation (outcomes are poor) 1 year mortality well over 50%
Describe the unwanted side effects of positive pressure ventilation.
increasing dead space ventilation through overdistension of some alveoli which can divert blood flow from ventilated regions (can be countered b reducing Vt)
decrease blood return to the thorax, thus reducing ventricular preload and cardiac output (may be countered with volume infusion)
baro or volotrauma— over distension of alveoli can result in alveolar rupture, causing air to leak into the pleural, pericardial, mediastinal or subcutaneous spaces and possibly worsen inflammatory response
