Pulsus Paradoxus

Definition: Exaggerated drop in systemic blood pressure during inspiration that can cause weakening of peripheral pulses

Causes:
1) Cardiac: tamponade, shock, pericardial effusion
2) Pulmonary: PE, tension pneumothorax, asthma, COPD
3) Misc: anaphylactic shock, SVC obstruction

Measurement:
1) Inflate a sphygmomanometer cuff as if measuring BP. As the cuff is deflating, measure the systolic pressure at which Korotkoff sounds become audible during expiration and inspiration. The difference between these 2 pressures is the pulsus paradoxus.
2) Decrease in the pulse wave amplitude during inspiration seen on an arterial tracing or pulse oximeter waveform
3) Severe pulsus paradoxus can be palpated in the radial, brachial, or femoral pulses as a weakening or disappearance of the pulse during inspiration