What are considered the most reliable indicators of cardiac arrest?

The most reliable indicators of cardiac arrest are ECG readings and waveform capnography. An electrocardiogram (ECG) provides direct and real-time information about the electrical activity of the heart, allowing responders to identify lethal arrhythmias and confirm the absence of cardiac activity. Waveform capnography measures the concentration of carbon dioxide in exhaled air, providing insight into the patient’s ventilatory status and circulation. In cardiac arrest, this measurement often shows a sudden drop in end-tidal carbon dioxide (ETCO2), which can be a critical indicator of the effectiveness of chest compressions and overall perfusion.

Other indicators, such as visual assessments and patient history, can provide context but lack the specificity and immediacy required in emergency situations. Pulse oximetry and respiratory rate offer important information about a patient’s oxygenation and ventilation, but they are not definitive indicators of cardiac arrest. Similarly, while electrolyte levels and blood pressure can inform a clinician's understanding of the patient's condition, they are not direct indicators of cardiac arrest and can often be affected by various factors that occur post-arrest. Therefore, ECG and waveform capnography stand out as the most objective and definitive indicators.