From the Guidelines
A hypoxia workup should begin with immediate oxygen supplementation, using a reservoir mask at 15 L/min if the initial SpO2 is below 85%, or nasal cannulae at 2–6 L/min or simple face mask at 5–10 L/min, while investigating the underlying cause. The initial oxygen therapy should be guided by the patient's saturation level, with a target range of 94–98% unless the patient has COPD or other risk factors for hypercapnic respiratory failure, in which case the target range should be 88–92% pending blood gas results 1. A thorough history and physical examination should be performed, focusing on cardiopulmonary symptoms.
- Order arterial blood gases to assess the severity of hypoxemia and determine if respiratory acidosis or alkalosis is present.
- Obtain a chest X-ray to identify potential causes such as pneumonia, pulmonary edema, pneumothorax, or pleural effusions.
- Complete blood count may reveal anemia or infection. Additional tests should include:
- Electrocardiogram to evaluate for cardiac causes
- Pulmonary function tests to assess for obstructive or restrictive lung diseases
- CT pulmonary angiography if pulmonary embolism is suspected Consider echocardiography to evaluate cardiac function and rule out intracardiac shunts. Bronchoscopy may be necessary if airway obstruction is suspected. For patients with suspected sleep-related hypoxia, overnight pulse oximetry or polysomnography should be performed. The workup should be tailored to the clinical presentation, with more specialized tests like ventilation-perfusion scans, right heart catheterization, or lung biopsy reserved for cases where initial evaluation is inconclusive, as recommended by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.
From the Research
Hypoxia Workup
- Hypoxia is a common presentation in critically ill patients, with the potential for severe harm if not addressed appropriately 2
- The management of hypoxia involves ascertaining the severity of hypoxaemia, the underlying diagnosis, and implementing the most appropriate treatment 2
- Oxygen therapy can be delivered by variable or fixed rate devices, and non-invasive ventilation; if patients deteriorate, they may require tracheal intubation and mechanical ventilation 2
Treatment Options
- High-flow nasal cannula (HFNC) oxygen therapy is an emerging option for respiratory failure, providing oxygen at high flows with an optimal degree of heat and humidification 3
- HFNC has been shown to be effective in reducing dyspnoea and improving oxygenation in respiratory failure from a variety of aetiologies, thus avoiding escalation to more invasive supports 3
- Non-invasive ventilation (NIV) is also a treatment option, but it can be poorly tolerated by patients and requires specific expertise 3
- Conventional oxygen therapy (COT) can be insufficient in severe hypoxaemia 3
Comparison of Treatment Options
- HFNC has been compared to COT and NIV in several studies, with results showing that HFNC may be superior to COT in terms of oxygenation, patient comfort, and work of breathing 4
- HFNC has also been shown to be comparable to NIV in preventing reintubation after extubating in COPD patients, with improved tolerance, comfort, and less complications 5
- However, NIV with active humidification may be more effective than HFNC in avoiding reintubation in patients who are at extremely high risk for extubating failure 5
Physiological Effects
- HFNC reduces the anatomical dead space and improves carbon dioxide wash-out, reduces the work of breathing, and generates a positive end-expiratory pressure and a constant fraction of inspired oxygen 3
- Helmet NIV has been shown to improve oxygenation, reduce dyspnea, inspiratory effort, and simplified pressure-time product, with similar transpulmonary pressure swings, PaCO2, and comfort compared to HFNC 6