From the Guidelines
Hypoxemia is present on arterial blood gas (ABG) when the oxygen saturation is less than 90% on room air, or in cases where the PaO2 is less than 60 mmHg 1.
Clinical Scenarios
- In patients with respiratory failure, hypoxemia may be present with an oxygen saturation of less than 90% on room air 1.
- In patients with chronic obstructive pulmonary disease (COPD), hypoxemia may be present with an oxygen saturation of less than 92% on supplemental oxygen, due to impaired gas exchange 1.
- In cases of carbon monoxide poisoning, carboxyhemoglobin levels may be elevated, leading to decreased oxygen saturation 1.
Management
- The therapeutic goal is to maintain SpO2 ≥ 94% during rest, sleep, and exertion 1.
- In patients with COPD, long-term oxygen therapy (LTOT) may be necessary to improve survival, exercise, sleep, and cognitive performance 1.
- Arterial blood gas (ABG) assessment is the preferred method to determine oxygen need, as it includes acid-base information 1.
- Pulse oximetry is adequate for trending oxygen saturation, but ABG is necessary for accurate diagnosis of hypoxemia 1.
From the Research
Definition of Hypoxemia
Hypoxemia is defined as an arterial oxygen tension (PaO2) of less than 60 mmHg or a PaCO2 of greater than 50 mmHg, or both, whilst breathing room air 2.
Arterial Blood Gas (ABG) Analysis
ABG analysis is used to assess the metabolic and oxygen status of patients with acute exacerbation of chronic obstructive pulmonary disease (COPD) 3. The analysis measures parameters such as pH, partial pressure of carbon dioxide (PCO2), partial oxygen pressure (PO2), bicarbonate (HCO3), and venous and arterial blood oxygen saturation (SO2).
Presence of Hypoxemia on ABG
Hypoxemia is present on ABG when the PaO2 is less than 60 mmHg 2. This can occur in various conditions, including:
- Acute respiratory failure
- Chronic obstructive pulmonary disease (COPD)
- Pneumonia
- Acute exacerbation of COPD
- Status asthmaticus
Key Points
- Hypoxemia can be detected using ABG analysis 3, 2, 4, 5
- Pulse oximetry can be used as a surrogate to invasive ABG analysis, but it may overestimate oxygen saturation in COPD patients 6
- Venous blood gas (VBG) values can be used to predict ABG levels in patients with acute exacerbation of COPD, but not for oxygen status 3
- Blood oxygen equilibration time after cessation of supplemental oxygen is around 6-20 minutes in patients with chronic respiratory disease 4
- Silent hypoxemia can occur in COVID-19 patients, and prompt detection is crucial to prevent rapid deterioration and higher mortality rates 5