What is Pulsus paradoxus? Made Easy & Simple to understand!
Pulsus paradoxus is a misnomer.
The phenomenon is neither related to the pulse nor is there any paradoxical change in the described sign. Pulsus paradoxus, in fact, is related to blood pressure & there is an exaggerated drop in blood pressure during inspiration.
Definition of Pulsus Paradoxus?
Normally, there is a small drop in systolic pressure (<10 mmHg) during inspiration.
Pulsus paradoxus is, simply, >10 mmHg drop in systolic blood pressure during inspiration.
Mechanism of Pulsus Paradoxus
Normally, with chest expansion during inspiration in healthy individuals, intrathoracic pressure is reduced. This causes an increase in venous return and therefore increases right heart filling.
However, the same thing does not happen in the left heart during inspiration. This is because, during inhalation, the lungs expand and pull radial traction on the pulmonary vasculature. The capacitance of pulmonary vessels is therefore increased, momentarily sequestering blood in the chest and there is a drop in blood flow to the left heart. This decreases pre-load on the left side, and consequently reduced stroke volume and cardiac output. Normally, this blood pressure drop is <10 mmHg.
The opposite phenomenon occurs during expiration. So as you can infer, systolic pressure decreases during inspiration and increases during expiration.
In pulsus paradoxus, the drop in systolic pressure during inspiration exaggerates. This is because the external forces, like cardiac tamponade, do not let the right heart’s free wall expand during inspiration, in order to accommodate an increased venous return. The increased venous return in the right heart then is accommodated at the expense of the left heart chamber, because the interventricular septum pushes into the left chamber. This results in a further reduction in preload on the left side, and thus markedly decreased stroke volume and thus cardiac output. The result is pulsus paradoxes – the drop in systolic blood pressure >10 mmHg during inspiration.
Because the drop in blood pressure is secondary to a drop in left ventricular stroke volume, the change in pressure noted during pulsus paradoxus will primarily reflect a decrease in both systolic and pulse pressure. Diastolic pressure is usually minimally affected.
Conditions causing it?
Pulsus paradoxus can be noted in:
– Cardiac tamponade (most common cause)
– Constrictive pericarditis
– Right ventricular myocardial infarction
– Restrictive cardiomyopathy
– Severe COPD/Asthma
– Tension pneumothorax
– Pleural effusion (large & bilateral)
– Pulmonary embolism
– Sever hypovolemic shock
– Any condition resulting in cardiac compression – iatrogenic compression during surgery, marked obesity, and pectus excavatum
How to measure it?
1. Manually with sphygmomanometer & Stethoscope
Use a manual sphygmomanometer and stethoscope to measure pulsus paradoxus. Automated blood pressure cuffs cannot measure it accurately.
Step 1: Assessment is made by inflating the cuff until all Korotkoff sounds become absent. Then, gradually release cuff pressure.
Step 2: The first sounds auscultated will be heard only during expiration. Note this pressure reading.
Step 3: As the cuff pressure is further reduced, Korotkoff sounds become audible during both inspiration and expiration. Note this reading as well.
Step 4: If the difference between the 2 readings is >10 mmHg, this indicates the presence of pulsus paradoxus.
An important tip, while assessing for pulsus paradoxus, is to ensure normal tidal volume breathing in the patient. Do not instruct them to change their breathing pattern, as the depth of respiration influences the magnitude of pulsus paradoxus, and will be amplified in patients with pulmonary disease.
It shall be noted that severe pulsus paradoxus may also be appreciated as a weakening or even disappearance of the palpated pulse during inspiration. Under certain circumstances, you may also be able to note it in the patient’s pulse oximetry waveform during different respiratory phases.
2. If there is Indwelling Arterial Access
For patients with indwelling arterial access, measuring pulsus paradoxus does not need manual sphygmomanometer measurement. It is simply done by watching the waveform and noting the difference in systolic pressure during the respiratory cycle.
What is the management of pulsus paradoxus?
Pulsus paradoxus is not a disease but a sign. Therefore further evaluation is needed to search for and then treat the underlying cause.
As has already been mentioned, the most common cause of pulsus paradoxus is cardiac tamponade. So if there is known or suspected pericardial effusion, then a diagnosis of cardiac tamponade should be considered.
Do an ECG, chest radiography, and trans-thoracic echocardiography, if there is no hemodynamic compromise.
If hemodynamic instability is present, emergent drainage of pericardial fluid should be considered.
