From the Guidelines
Respiratory failure type 1 and 2 can be identified on venous blood gas (VBG) with Type 1 showing hypoxemia and normal or low PvCO2, and Type 2 demonstrating hypercapnia with elevated PvCO2 and often hypoxemia. When interpreting VBG results, it is essential to consider the differences between venous and arterial blood gas values, as venous CO2 is typically 4-6 mmHg higher than arterial values, while venous O2 is 5-10 mmHg lower 1. The British Thoracic Society guidelines suggest that blood gases should be checked in critically ill patients, those with unexpected or inappropriate falls in SpO2, and patients with risk factors for hypercapnic respiratory failure who develop acute breathlessness or deteriorating oxygen saturation 1. For patients with Type 2 respiratory failure, the BTS/ICS guidelines recommend starting non-invasive ventilation (NIV) when a pH <7.35, a PaCO2 of ≥6.5 kPa, and RR >23 breaths/min persist or develop after an hour of optimal medical therapy 1. Key points to consider when evaluating respiratory failure on VBG include:
- Normal venous PO2 is 35-40 mmHg and normal venous PCO2 is 45-50 mmHg
- Type 1 respiratory failure on VBG typically shows hypoxemia with a PvO2 significantly lower than expected and normal or low PvCO2
- Type 2 respiratory failure on VBG demonstrates hypercapnia with elevated PvCO2 (>50 mmHg) and often hypoxemia
- VBG can be useful for trending pH and PCO2 in patients with known respiratory failure, but arterial sampling remains the gold standard for definitive diagnosis 1. Treatment of respiratory failure depends on the underlying cause, but generally includes oxygen therapy for Type 1 and ventilatory support (non-invasive or invasive) for Type 2 respiratory failure, along with addressing the primary condition causing the respiratory compromise.
From the Research
Respiratory Failure Type 1 and 2 on VBG
- Respiratory failure is categorized into two types: Type 1 and Type 2, which can be identified through arterial blood gas (ABG) analysis, but also through venous blood gas (VBG) with some limitations 2, 3.
- Type 1 respiratory failure is characterized by hypoxemia (low oxygen levels in the blood) without hypercapnia (elevated carbon dioxide levels in the blood), whereas Type 2 respiratory failure involves both hypoxemia and hypercapnia 3.
- The study by 3 defines acute hypoxemic respiratory failure as PaO2 < 60 mm Hg or SpO2 < 90% on room air, which can be related to Type 1 respiratory failure.
- For Type 2 respiratory failure, non-invasive ventilation (NIV) has been shown to be effective in managing acute type 2 respiratory failure in patients with chronic obstructive pulmonary disease (COPD) 2.
- The use of high-flow nasal cannula oxygen (HFNC) is recommended as a first-line noninvasive respiratory support in patients requiring more than 6 L/min of oxygen or PaO2/FiO2 ≤ 200 mm Hg and a respiratory rate above 25 breaths/minute or clinical signs of respiratory distress 3.
- Continuous positive airway pressure (CPAP) and NIV may not be recommended as first-line treatments if HFNC is available, due to uncertain benefits on intubation and lack of evidence supporting their use over HFNC 3.