The absence of a palpable pulse in a major peripheral artery (carotid, radial, or femoral), pulseless >10 seconds in an unconscious, unmonitored patient is diagnostic. Within the OR, monitoring equipment might show a precipitous drop in end-tidal CO2, loss of pulse oximetry waveform, a low or nondetectable noninvasive blood pressure, or a flattening and drop in the arterial pressure waveform. Nonperfusing cardiac rhythms on EKG include tachyarrhythmias such as VF and VT as well as nontachyarrhythmias such as asystole, pulseless electrical activity (PEA), or severe bradycardia.
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