From the Guidelines
The workup for acute hypoxia leading to respiratory failure should begin with immediate supplemental oxygen therapy, targeting an oxygen saturation range of 94-98% for patients without risk of hypercapnic respiratory failure, or 88-92% for those with risk factors, as recommended by the BTS guideline for oxygen use in adults 1. The initial assessment should include a thorough clinical evaluation, vital signs, oxygen saturation, and physical examination to identify potential causes of hypoxia.
- Initial diagnostic tests should include: + Arterial blood gas analysis to assess pH, PaO2, PaCO2, and bicarbonate levels + Complete blood count to evaluate for infection or anemia + Comprehensive metabolic panel + Chest X-ray to identify pulmonary infiltrates, effusions, or pneumothorax + Electrocardiogram to rule out cardiac causes
- Additional testing may be necessary based on the suspected etiology, such as CT chest for suspected pulmonary embolism, echocardiogram to assess cardiac function, or specific tests like D-dimer, BNP, troponin, or sputum cultures. For patients with saturation below 85%, treatment should be started with a reservoir mask at 15 L/min, as per the BTS guideline 1. If the patient shows signs of respiratory distress despite oxygen therapy, consider high-flow nasal cannula, non-invasive ventilation (CPAP or BiPAP), or endotracheal intubation with mechanical ventilation for severe cases.
- Specific treatments should address the underlying cause, such as: + Antibiotics for pneumonia + Diuretics for heart failure + Bronchodilators for COPD/asthma exacerbations + Anticoagulation for pulmonary embolism This systematic approach helps identify and treat the underlying cause while supporting oxygenation and preventing further deterioration, as outlined in the BTS guideline for oxygen use in adults 1.
From the Research
Workup for Acute Hypoxia
The workup for acute hypoxia leading to respiratory failure involves several steps, including:
- Assessing the patient's oxygenation status, with a definition of acute hypoxemic respiratory failure as PaO2 < 60 mm Hg or SpO2 < 90% on room air, or PaO2/FiO2 ≤ 300 mm Hg 2
- Administering supplemental oxygen according to the monitoring of SpO2, with the aim of maintaining SpO2 above 92% and below 98% 2
- Using noninvasive respiratory supports, such as high-flow nasal cannula oxygen (HFNC), noninvasive ventilation (NIV), and continuous positive airway pressure (CPAP), to relieve dyspnea and improve oxygenation 3, 2
Noninvasive Respiratory Supports
The use of noninvasive respiratory supports in acute hypoxemic respiratory failure is a topic of ongoing debate, with some studies suggesting that:
- HFNC may be superior to conventional oxygen therapy (COT) in avoiding intubation 2
- NIV may not have beneficial effects compared to HFNC 2
- CPAP cannot currently be recommended as a first-line noninvasive respiratory support due to uncertain benefits on intubation 2
- Awake prone positioning may have potential benefits in reducing the risk of intubation, but more studies are needed to confirm this 2
Predictors of Intubation
Several factors have been identified as predictors of intubation in patients with acute hypoxemic respiratory failure, including:
- Respiratory rate greater than or equal to 30 breaths/min under standard oxygen 4
- Increased heart rate after HFNC initiation 4
- PaO2/FIO2 ratio less than or equal to 200 mm Hg and tidal volume greater than 9 mL/kg of predicted body weight after NIV initiation 4
- Tidal volume above 9 mL/kg during NIV, which is also associated with 90-day mortality 4
Oxygenation Targets
The optimal oxygenation targets for acute hypoxemic respiratory failure are still unclear, with ongoing research aiming to determine the best approach, including: