Acute Respiratory Failure

Question 1

Hypoxemia ?

Answer 1

Causes include ventilation-perfusion (V/Q) mismatch, right-to-left shunt, hy- poventilation, low inspired O2 content (important at altitudes), and diffusion impairment.

Question 2

history/PE of Hypoxemia ?

Answer 2

Findings depend on the etiology. ↓ HbO2 saturation, cyanosis, tachypnea, shortness of breath, pleuritic chest pain, and altered mental status may be seen.

Question 3

Diagnosis of Hypoxemia ?

Answer 3

• Pulse oximetry: Demonstrates ↓ HbO2 saturation.
• CXR: To rule out ARDS, atelectasis, or an infiltrative process (e.g., pneumonia) and to look for signs of pulmonary embolism.
• ABGs: To evaluate PaO2 and to calculate the alveolar-arterial (A-a) oxy-
  gen gradient

Question 4

TREATMENT of hypoxia ?

Answer 4

• Address the underlying etiology.
• Administer O2 before initiating evaluation.
• If the patient is on a ventilator, ↑ O2 saturation by increasing FiO2, posi-
  tive end-expiratory pressure (PEEP), or the I/E ratio.
• Hypercapnic patients: ↑ minute ventilation.

Question 5

Acute Respiratory Distress Syndrome (ARDS) ?

Answer 5

Acute respiratory failure with refractory hypoxemia, ↓ lung compliance, and noncardiogenic pulmonary edema.

Question 6

Causes of Acute Respiratory Distress Syndrome (ARDS) ?

Answer 6

The pathogenesis is thought to be endothelial injury. Common triggers include sepsis, pneumonia, aspiration, multiple blood transfusions, inhaled/ingested toxins, and trauma.
- Overall mortality is 30–40%.

Question 7

HISTORY/PE of Acute Respiratory Distress Syndrome (ARDS) ?

Answer 7

Presents with acute-onset (12–48 hours) tachypnea, dyspnea, and tachycardia +/− fever, cyanosis, labored breathing, diffuse high-pitched rales, and hypox- emia in the setting of one of the systemic inflammatory causes or exposure.

Question 8

Phases of Acute Respiratory Distress Syndrome (ARDS) ?

Answer 8

• Phase 1 (acute injury): Normal physical exam; possible respiratory alkalosis.
• Phase 2 (6–48 hours): Hyperventilation, hypocapnia, widening A-a oxygen gradient.
• Phase 3: Acute respiratory failure, tachypnea, dyspnea, ↓ lung compliance, scattered rales, diffuse chest infiltrates on CXR
  Phase 4: Severe hypoxemia unresponsive to therapy; ↑ intrapulmonary shunting; metabolic and respiratory acidosis.

Question 9

The criteria for ARDS diagnosis ?

Answer 9

• Acute onset of respiratory distress.
• PaO2/FiO2 ratio ≤ 200 mmHg.
• Bilateral pulmonary infiltrates on CXR.
• No evidence of cardiac origin (capillary wedge pressure < 18 mmHg or
  no clinical evidence of elevated left atrial pressure).

Question 10

TTT for ARDS?

Answer 10

■ There is no standard treatment.
■ Treat the underlying disease and maintain adequate perfusion to pre-
vent end organ damage.
■ Minimize injury induced by mechanical ventilation by ventilating with low tidal volumes.
■ Use PEEP to recruit collapsed alveoli and titrate PEEP and FiO2 to achieve adequate oxygenation. Goal oxygenation is PaO2 > 60 mmHg or SaO2 > 90% on FiO2 ≤ 0.6.
■ Slowly wean patients from ventilation, and follow with extubation trials (see Table 2.15-6).