What Is Obstructive Shock

Introduction

Shock is characterised by a circulatory collapse leading to insufficient cellular oxygen consumption. Shock can be classified into four different types, depending on the causative mechanism: distributive, obstructive, hypovolaemic and cardiogenic shock. An imbalance between the supply and consumption of oxygen causes poor perfusion and multiple organ failure, which is a common outcome of all forms of shock.¹ 

The body cannot receive adequate blood flow during any kind of shock, which inhibits it from getting enough oxygen. In obstructive shock, the blood flow in and out of the heart or large vessels is impeded by something. . Both blood pressure and the volume of blood being pumped out by the heart can rapidly decline as a result of this obstruction. This causes a lack of oxygen, which can have knock-on effects on all organs.²

Signs and symptoms

Individuals suffering from obstructive shock often have respiratory discomfort and can present with tachycardia, hypotension, tachypnoea, air hunger (an excessive need to breathe) and chest pain.

Dilated and engorged neck veins are caused by inadequate blood return to the heart and can be a symptom of causative illnesses such as pneumothorax and tamponade. There are multiple signs and symptoms which may point to potential underlying conditions. For example, hyperresonant noises on percussion, dilated neck veins and absence of breath sounds are the symptoms of cardiac tamponade. Tension pneumothorax can present in a similar way to cardiac tamponade, with swollen neck veins and hypotension.³ 

Causes 

Obstructive shock is often associated with decreased right ventricular output and is primarily caused by extracardiac factors such as cardiac pump failure.

There are two types of obstructive shock:

• Pulmonary vascular
• Mechanical

Pulmonary vascular

The main cause of obstructive shock is right ventricular failure, which is triggered by a haemodynamically substantial pulmonary embolism (PE) or severe pulmonary hypertension (PH). The right ventricle fails in these situations because it is unable to exert enough pressure to overcome the elevated pulmonary vascular resistance associated with PE or PH.

Although mechanical blockage is typically the cause of haemodynamic collapse in the context of PE, pulmonary vasoconstriction mediated by vasoactive mediators, such as thromboxane and serotonin, also influences these outcomes. Severe stenosis and acute tricuspid or pulmonary valve blockage may also occur as a result of pulmonary vasoconstriction.⁴

Mechanical

Since decreased preload rather than pump failure is the primary cause of both disorders, mechanical obstructive shock can occasionally appear clinically as hypovolemic shock. That is to say, even when the heart pumps normally, preload is reduced when the right ventricle fills up inadequately.⁴

Tension pneumothorax, pericardial tamponade, restrictive cardiomyopathy, and constrictive pericarditis are a few types of extrinsic mechanical compression.³

Tension pneumothorax

Pneumothoraces can be classified as open (air passing through an open chest wound), tension (where there is a shift in mediastinal structures) or simple (no mediastinal shift). Untreated tension pneumothorax can be fatal. It is an uncommon disorder with a malignant course. When air becomes trapped in the pleural space under positive pressure, it can compromise cardiac function and displace mediastinal structures.⁵

Risk factors of tension pneumothorax:⁹

1. Penetrating or blunt trauma
2. Barotrauma
3. Central venous catheter placement
4. CPR (Cardiopulmonary resuscitation)
5. Displaced spinal fracture

Tension pneumothorax treatment

To manage a tension pneumothorax, a large-bore (such as 14 or 16-gauge) needle is inserted into the second intercostal space in the midclavicular line as soon as possible. Usually, air will explode out. Then, a tube thoracostomy should immediately be inserted since needle decompression can result in a simple pneumothorax.¹⁰

Restrictive cardiomyopathy

The characteristic diastolic dysfunction in a non-dilated ventricle of restrictive cardiomyopathy (RCM) is apparent. There are numerous restrictive cardiomyopathies which differ in terms of their aetiology, clinical manifestation, diagnostic assessment, management, and prognosis. Cardiomyopathy, sarcoidosis and haemochromatosis are three of the main causes of restrictive cardiomyopathy.⁶

Causes of restrictive cardiomyopathy include:¹³

1. Cardiac amyloidosis
2. Carcinoid heart disease
3. Iron overload (haemochromatosis)
4. Sarcoidosis
5. Scarring after radiation or chemotherapy
6. Scleroderma
7. Tumours of the heart

Common symptoms of restrictive cardiomyopathy are:

1. Cough
2. Breathing problems that occur at night, with activity or when lying flat
3. Fatigue and inability to exercise
4. Loss of appetite
5. Swelling of the abdomen
6. Swelling of the feet and ankles
7. Uneven or rapid pulse

Other symptoms may include:

1. Chest pain
2. Inability to concentrate
3. Low urine output

Constrictive pericarditis

The fibro-elastic sac that envelops the heart is called the pericardium. It influences heart haemodynamics and acts as a protective barrier. Constructive pericarditis is a disorder in which there is the production of granulation tissue within the pericardium, which reduces its flexibility. Transitory and occult forms of this condition have been reported, and it typically has a chronic presentation.⁷

Types of constrictive pericarditis

There are a few different subtypes¹⁴ of constrictive pericarditis: 

1. Acute
2. Subacute
3. Effusive-constrictive pericarditis
4. Transient constrictive pericarditis

This initially manifests as acute pericarditis and then progresses to inflammatory constrictive pericarditis. It can be treated with anti-inflammatory drugs.

5. Occult constrictive pericarditis

The word "occult" insinuates that there is difficulty in diagnosing this particular kind of constrictive pericarditis. Occult constrictive pericarditis is often an incidental diagnosis, which is uncovered when testing for other conditions.

Complications of constructive pericarditis.

1. Pulmonary hypertension
2. Hepatomegaly
3. Renal failure
4. Metabolic acidosis
5. Hypoxia
6. Shock
7. Death

Pericardial tamponade

When blood, fluid or air accumulates in the pericardium, which is the double-walled sac surrounding the heart, this results in compression of the heart and leads to pericardial tamponade, also referred to as cardiac tamponade. This prevents the heart from expanding normally and puts strain on it. The blood supply to the body is subsequently reduced as less blood is pushed out with each heartbeat. Cardiac arrest and circulatory shock can develop quickly from pericardial tamponade.¹¹

Symptoms 

Symptoms¹² that rapidly develop in cardiac tamponade may include:

1. Sharp chest ache which may radiate to the shoulder, arm, back or neck. Pain may also be exacerbated by coughing, lying down or taking deep breaths
2. Difficulty breathing 
3. Rapid breathing 
4. Lightheadedness, dizziness, or fainting
5. Colour changes to the skin
6. Heart palpitations, characterised by an uncomfortable awareness of your pulse
7. Rapid heartbeat
8. Altered state of mind - for example, a patient suffering from cardiac tamponade may appear confused or agitated

Treatment of obstructive shock

IV crystalloids are used sparingly to treat obstructive shock. Vasopressors, such as vasopressin, should be started early if shock persists. Alternatively, norepinephrine can be trialled. Throughout treatment, IV fluids should be continued and the patient should be well-monitored.⁸

To identify obstructive shock, there are various tests and investigations² which can be conducted: 

1. Ultrasound
2. Echocardiogram
3. Computed tomography (CT)
4. Electrocardiogram (ECG)

Summary

In summary, obstructive shock is a serious condition in which adequate cellular oxygen consumption is impeded by circulatory collapse. This type of shock is caused by blockages to blood flow in and out of the heart or major veins, which results in a significant decrease in blood pressure and heart pump volume. There are many different forms of obstructive shock, each of which has its own distinct set of symptoms, causes, and diagnoses. Tension pneumothorax, restrictive cardiomyopathy, constrictive pericarditis, and pericardial tamponade are the main mechanical causes of obstructive shock. Early identification, made possible by imaging tests such as CT, ultrasound, echocardiograms, and electrocardiograms, is necessary to deliver early management. IV crystalloids and vasopressors are used in combination for the treatment, focusing on early management to avoid complications and multiple organ failure. 

The information provided highlights how critical it is to address obstructive shock as soon as possible in order to improve patient outcomes. This includes timely recognition, precise diagnosis, and focused treatment approaches.