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Respiratory Failure
Critical Care
| Question | Answer |
|---|---|
| Describe and explain the two major classification of acute respiratory failure (hypoxemic) | Hypoxemic: PaO2 ≤60mmHg on ≥60% FiO2 → Oxygenation failure (inadequate O2 transfer at alveoli and pulmonary capillary bed) – Causes: V/Q mismatch, shunt, impairing diffusion, and alveolar hypoventilation |
| Describe and explain the two major classification of acute respiratory failure (hypercapnic) | PaCO2 >45 with pH <7.35 → Ventilation failure (respiratory system unable to remove sufficient CO2: to maintain normal PaCO2) – Causes: airways and alveoli (airway obstruction and air trapping), CNS (dec. drive to breathe), chest wall, N/M conditions |
| Ventilation/Perfusion mismatch | secretions in airway (ex: COPD), secretions in alveoli (ex: pneumonia, bronchospasm/asthma), Alveolar collapse (atelectasis), Pain |
| Intrapulmonary shunting | blood moves from r-heart to l-heart without oxygenating in the lungs |
| Impaired diffusion | alveolar capillary membranes are damaged > stiff > compromises gas exchange |
| Conditions affecting pulmonary vascular bed | Emphysema and recurrent PE |
| Cause membrane to become more fibrotic (glow gas transport) | ARDS, pulmonary fibrosis, interstitial lung disease |
| Alveolar Hypoventilation | Low ventilation leads to high CO2 and low PaO2 as a result of restrictive lung diseases, CNS diseases, chest wall dysfunction, acute asthma, and N/M disease |
| Renal compensation | Kidneys reabsorb/retain HCO3 as needed, to compensate for state of acidosis (takes days to take effect) → minimizes change in arterial pH |
| Cardiovascular Compensation | Heart + lungs attempting to compensate for increased O2 delivery! Hypercapnia → vasodilation → cerebral blood flow → mild ICP → HA! Slower RR @ night → severe morning HA! Cyanosis = late sign! |
| Interpret signs of impaired ventilatory function. | a. Restlessness, changes in LOC (confusion → coma) b. Tachypnea / dyspnea / cough c. Auscultation of lungs d. Tachycardia e. Substernal retractions f. Diaphoretic (+ g-k) |