What is Paco2 (partial pressure of carbon dioxide) post cardiac arrest?

From the Guidelines

Paco2 (partial pressure of carbon dioxide) post cardiac arrest should be targeted at 35-45 mm Hg.

Rationale

• This target range is based on the consensus of multiple studies, including the 2024 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1, which suggests targeting normocapnia (a partial pressure of carbon dioxide of 35–45 mm Hg) in adults with ROSC after cardiac arrest.
• The evidence from RCTs and observational studies is inconsistent, but the task forces deemed it reasonable to target normocapnia, generally defined as a PaCO2 of 35 to 45 mm Hg, in both RCTs and observational studies 1.
• Other studies, such as the 2019 pediatric post-cardiac arrest care scientific statement from the American Heart Association 1, also support targeting normocapnia (ie, normal for the child, or Paco2 35–45 mm Hg) or a Paco2 specific for the patient’s condition, limiting exposure to severe hypercapnia and hypocapnia.
• The 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1 also recommend avoiding hyperventilation and targeting normocapnia, as hyperventilation may worsen global brain ischemia by excessive cerebral vasoconstriction.
• The 2024 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1 and the 2015 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1 also support maintaining Paco2 within a normal physiological range as part of a post-ROSC bundle of care.

Key Points

• Target Paco2 range: 35-45 mm Hg
• Avoid hyperventilation and hypocapnia
• Avoid hypercapnia
• Maintain normocapnia as part of a post-ROSC bundle of care
• Consider individual patient factors, such as chronic CO2 retention, when adjusting PaCO2 targets 1

From the Research

Paco2 Post Cardiac Arrest

• The normal range for Paco2 is between 30 and 50 mmHg, with normocapnia associated with good neurological function 2, 3, 4
• Hypocapnia (Paco2 < 30 mmHg) and hypercapnia (Paco2 > 50 mmHg) are common after cardiac arrest and are independently associated with poor neurological outcome 2, 3, 4
• Studies have shown that maintaining normal levels of Paco2 is important for reducing morbidity and improving survival of cardiac arrest survivors 5, 4
• The optimal target for Paco2 after cardiac arrest is still uncertain, but current evidence suggests that targeting a normal range (35-45 mmHg) may be beneficial 6, 4

Association with Neurological Outcome

• Normocapnia has been associated with good neurological function, with an odds ratio of 4.44 (95% CI 1.33 to 14.85) 2
• Hypocapnia and hypercapnia have been independently associated with poor neurological outcome, with odds ratios of 2.43 (95% CI 1.04-5.65) and 2.20 (95% CI 1.03-4.71), respectively 3
• A systematic review and meta-analysis found that normocarbia was associated with increased hospital survival and good neurological outcome 4

Clinical Implications

• Maintaining normal levels of Paco2 is important for reducing morbidity and improving survival of cardiac arrest survivors 5, 4
• Targeting a normal range (35-45 mmHg) for Paco2 after cardiac arrest may be beneficial, but further research is needed to determine the optimal target 6, 4