At face value, pulsus paradoxus is a significant decrease in an individual’s blood pressure when they breathe in. However, this relatively simple clinical sign points us to far more complicated medical problems. Pulsus paradoxus can be an indicator of many underlying medical conditions, ranging from those with a better prognosis, such as asthma, and chronic obstructive pulmonary disease (COPD), to those more sinister, including cardiac tamponade, and pulmonary embolism.

Another more sinister culprit is hypovolemic shock - a medical emergency in which sudden blood volume loss means that tissue throughout the body does not receive enough oxygen, so organs cannot perform their normal function. Studies have shown almost half of the shock patients present with pulsus paradoxus, yet shock is often otherwise asymptomatic, initially. Therefore, identifying pulsus paradoxus can be a lifesaving first indication that a patient is in hypovolemic shock and requires higher-level medical attention. Pulsus paradoxus is unlikely to be spotted by an individual, and instead, it is picked up in medical examinations.

• So, what symptoms can you look out for, to point you to getting a medical examination? 
• What is this sinister condition earning pulsus paradoxus its foreboding name?
• And what can be done for those with severe hypovolaemic shock and pulsus paradoxus?

Reading on, these questions will be answered, and you will uncover the events that take place within the body for hypovolaemic shock to manifest as pulsus paradoxus.

Definitions

• CT scan - A Computed Tomography Scan
• Cardiac Output - the volume of blood pumped by the heart in a given period
• Hypovolaemia - a decreased volume of circulating blood in the body
• Hypoperfusion - a reduced blood flow
• Hypotension - low blood pressure
• Systemic – throughout the body
• Systemic Vascular Resistance – resistance in the circulatory system allowing for blood pressure

What is pulsus paradoxus?

For a drop in blood pressure to be classed as pulsus paradoxus, the decrease must be of 10 mmHg in the systolic pressure and must occur upon inspiration. The systolic blood pressure reflects the pressure in the left ventricle when the heart is contracting to pump blood around the body and is the top number read on a blood pressure monitor (Sphygmomanometer). It is normal for systolic blood pressure to decrease slightly during inspiration, due to the mechanism by which we inspire. Upon inspiration, our ribs move upwards and outwards, and the diaphragm flattens, decreasing the pressure within the thorax to below atmospheric level so that air can be drawn into our airways. In the same instance, there is less pressure upon the blood vessels, which also exist within the thorax. This causes blood to be drawn into thoracic vessels as part of normal venous return to the heart.
In pulsus paradoxus, this decrease in pressure within the blood vessels is amplified, usually because of abnormalities with venous return, meaning the blood drawn into thoracic vessels and subsequently the heart, does not maintain normal blood pressure. One such problem is our example of hypovolaemia. 

How is pulsus paradoxus presented?

Pulsus paradoxus is usually uncovered during a medical examination, which is performed because patients present with symptoms of an underlying condition. The associated symptoms which may lead a health professional to investigate for pulsus paradoxus include: a cough, chest pain, and dizziness. If you notice any of these symptoms you should seek advice from a medical professional.

Pulsus paradoxus doesn’t in itself cause any identifiable symptoms, its identification and subsequent identification of its underlying causes relies heavily on the investigations a health professional performs. Initial pulse palpation may indicate the need for further investigation if volume appears reduced during inspiration over several cycles, but to definitively diagnose pulsus paradoxus, blood pressure measurement is key. In primary care settings such as your general practice, blood pressure is read using a Sphygmomanometer. However, it can be difficult to specifically identify pulsus paradoxus by this method, as noting differences in Korotkoff (pulse) sounds between inspiration and expiration is highly subjective. This introduces the requirement for a more accurate approach - the arterial line.

Arterial lines are flexible tubes inserted by cannulation into peripheral arteries, most commonly the radial artery of the wrist. From here, changes in blood pressure can be measured with respect to the change in the flow of blood within the tube. This allows blood pressure to be calculated with every heartbeat, unlike using a Sphygmomanometer and creates a waveform on a graph. During inspiration, the amplitude of the wave will decrease in patients with pulsus paradoxus, when compared to expiration. Arterial lines are only used in secondary care settings such as hospitals, so patients may be referred from primary care settings to receive this specialist reading.
If found to have pulsus paradoxus, the next question is. What is causing it? Could it be an indicator of disease progression such as in the case of severe hypovolaemic shock?

What is hypovolaemic shock?

As already mentioned, severe cases of hypovolaemic shock are one of the underlying causes of pulsus paradoxus. Shock is a state of systemic tissue hypoperfusion, meaning cells of tissues around the body are not receiving enough oxygen. In shock, hypoperfusion is due to low blood pressure, either resulting from a low cardiac output, low systemic vascular resistance, or both. The body’s sympathetic nervous system can compensate for shock initially by increasing the heart rate, to pump more blood around the body, and constricting the blood vessels, to increase the pressure known as systemic vascular resistance. In more severe cases of shock, as the causative agent persists, the body can no longer compensate and tissues become necrotic, meaning their cells die and the organs they comprise fail to function. This is termed multiple organ failure and is fatal if left untreated.
In hypovolemic shock, the drop in blood pressure is the result of a sudden depletion in blood volume of greater than 15%. Causes of such sudden blood volume loss can be haemorrhagic, meaning they are due to a bleed, and non-haemorrhagic, commonly accounting for cases of dehydration such as extreme burns, vomiting, and diarrhoea.

The common symptoms of shock include: low urine output, dry mucous membranes, decreased skin elasticity, cold peripheries, cyanosis (which is a blue discoloration of the skin), nausea, and dizziness. Particularly in hypovolemic shock, additional signs are sometimes noted such as blood when going to the toilet or in vomit. If you notice any of these symptoms you should seek advice from a medical professional. A medical professional will also notice the increased heart rate and breathing rate as the body tries to compensate for the shock, and in some cases, they may note a change in a patient’s pulse and blood pressure. One such change being pulsus paradoxus.

How does hypovolemic shock cause pulsus paradoxus?

The blood volume depletion observed in hypovolemic shock triggers pulsus paradoxus as it causes an exaggerated normal physiological drop in inspiratory systolic blood pressure.
This occurs because the volume of blood in vessels is low already, and when thoracic pressure decreases during inspiration, the pressure in thoracic blood vessels becomes so low that there is no force to drive blood into the left side of the heart adequately. As a result, there is less blood in the left side of the heart upon contraction, reducing cardiac output, and therefore lowering systolic blood pressure to a greater extent than in a healthy individual.

Managing hypovolemic shock

If hypovolemic shock is suspected, it is treated as a medical emergency and patients are sent for further examinations. A medical professional will check a patient’s fluid outputs, to understand what is causing a loss in blood volume, and blood, including lactate, which will be raised if cells are respiring anaerobically, and a full blood count to check for anaemia. To check whether hypovolemic shock has caused end-organ damage, organ function is assessed using liver and kidney function blood tests, echocardiograms to assess the heart’s function, and CT scans to examine the brain.

Once detected, hypovolemic shock is managed by fluid resuscitation to rescue a normal blood volume, or using blood transfusions and coagulant medication in the case of hemorrhagic hypovolemia. Vasopressors such as norepinephrine can also be given, which increases systemic vascular resistance to recover blood pressure, and if patients have low oxygen levels they will be ventilated.

Summary

Hypovolemic shock is a medical emergency that has a high fatality risk if left undetected. Originally, the condition is often asymptomatic, and so indicators such as pulsus paradoxus are essential to identify,  so effective treatment can begin early and improve prognosis. Pulsus paradoxus can also be a clinical manifestation of many other conditions so medical professionals must perform the appropriate investigations to decipher what the specific cause in each individual is and how best it can be managed.