From the Guidelines
A CO2 level of 20 indicates hypocapnia, which can be associated with unfavorable outcomes, including decreased cerebral blood flow and potentially increased risk of delayed cerebral ischemia (DCI) in certain patient populations, such as those with aneurysmal subarachnoid hemorrhage (aSAH) 1.
Clinical Implications
- A PaCO2 level of 20 mmHg is considered low and may indicate hypocapnia, which can have significant effects on cerebral blood flow and oxygenation 1.
- Studies have shown that hypocapnia can be associated with unfavorable outcomes, including decreased cerebral blood flow and potentially increased risk of DCI in patients with aSAH 1.
- However, it is essential to consider the clinical context and other factors that may influence the interpretation of this CO2 level, such as the presence of an external ventricular drain (EVD) or other multimodality monitoring 1.
- The relationship between CO2 levels and cerebral blood flow is complex, and further research is needed to fully understand the effects of permissive hypercapnia as a therapy in patients with brain injuries 1.
Management Considerations
- In patients with aSAH, maintaining a PaCO2 level between 35-45 mmHg may be beneficial to ensure optimal cerebral blood flow and oxygenation 1.
- However, the optimal CO2 level may vary depending on individual patient factors, such as the presence of cerebral autoregulation and the risk of increased intracranial pressure (ICP) 1.
- Clinicians should carefully consider the potential risks and benefits of permissive hypercapnia and adjust ventilator settings accordingly to minimize the risk of adverse outcomes 1.
From the Research
Carbon Dioxide Levels
Effects of Low CO2 Levels
- Hypocapnia can occur in various disease states, including early asthma, high-altitude pulmonary edema, and acute lung injury 2.
- It can also be a result of hyperventilation, which can be caused by pulmonary congestion in patients with congestive heart failure 3.
- Low CO2 levels can lead to respiratory alkalosis, characterized by decreased Paco2, increased pH, and compensatory decreases in blood HCO3- levels 5.
Clinical Implications
- Hypocapnia is generally underappreciated and can have negative effects on the body, including organ injury 4.
- Permissive hypercapnia, or acceptance of raised CO2 concentrations, may be associated with increased survival in mechanically ventilated patients 4.
- Therapeutic hypercapnia might be tested in severely ill patients to reduce the adverse effects of hypocapnia and promote the beneficial effects of hypercapnia 4.