A 52-year-old woman develops cardiac arrest while hospitalized for the treatment of a pulmonary embolism. Advanced cardiac life support (ACLS) measures, including external chest compressions and endotracheal intubation, are implemented. After the airway is secured, a waveform capnograph is attached to the endotracheal tube and shows that the end-tidal partial pressure of CO₂ (EtCO₂) is 16 mm Hg. Cardiopulmonary resuscitation is continued along ACLS guidelines. After approximately 5 minutes of resuscitation, the EtCO₂ rapidly increases to 38 mm Hg.
Which of the following is the most likely explanation for the change in this patient's capnography finding?

Question

Quizplus · Accepted Answer

Capnography is the measurement of the partial pressure of CO₂ in the exhaled breath over time. The maximum CO₂ concentration at the end of each tidal breath (end-tidal [Et] CO₂) can provide information about ventilation and perfusion in patients in cardiac arrest undergoing cardiopulmonary resuscitation (CPR). The increase in cardiac output with the return of spontaneous circulation (ROSC) causes rapid transport of CO₂ accumulated in tissues during cardiac arrest to the lungs. This is detected as a sudden rise in EtCO₂ on capnography and is the earliest indicator of ROSC, occurring even before a pulse can be palpated. This technology virtually eliminates the need to stop CPR to check for a palpable pulse, reducing interruptions in cardiac compressions. In addition, recent studies have indicated that EtCO₂ can help determine prognosis during cardiac arrest. Patients with an EtCO₂ of ≤10 mm Hg after 20 minutes of CPR are highly unlikely to achieve ROSC. (Choices A and B) Esophageal intubation or a kinked endotracheal tube leads to ineffective ventilation. The EtCO₂ fails to rise despite effective CPR or ROSC. (Choice C) EtCO₂ levels reflect pulmonary blood flow and can be used as a noninvasive measure of cardiac output during CPR. High-quality chest compressions increase cardiac output and systemic and pulmonary perfusion causing a rise in EtCO₂, although this change is gradual. Poor quality chest compressions would cause a fall rather than a sudden increase in EtCO₂. (Choice E) Signs of right mainstem endobronchial intubation include an asymmetric rise in the chest wall during inflation and the absence of left-sided breath sounds. Regardless of tube positioning, a sudden rise in EtCO₂ during CPR suggests ROSC. Educational objective: A sudden rise in end-tidal CO₂ is the earliest indicator of return of spontaneous circulation in patients in cardiac arrest undergoing cardiopulmonary resuscitation. __________

A 52-Year-Old Woman Develops Cardiac Arrest While Hospitalized for the Treatment