Types of Shock: Hypotensive Patients and Gas Pumps
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Example Case
A patient arrives to the emergency department by ambulance with unstable vital signs. You walk into the room to find the patient profoundly hypotensive and tachycardic.
The patient appears ill and you are concerned that if action is not taken quickly, then they may arrest. You don’t have a patient name yet, and there is no time to look through their chart. They are too altered and confused to provide a history.
You begin to think about what could be causing their hypotension and what your next steps will be to manage this patient.
Types of Shock
Whenever there is a patient with unstable vital signs, the initial thoughts are why and what can be done to fix it?
Unfortunately those answers are not always obvious immediately.
To further complicate matters, hypotension can quickly become life threatening. As a result, critical decisions may have to be made despite having little information about the patient and not knowing the cause of their hypotension.
The need to make these quick management decisions in a busy environment with little information can be challenging.
Sound stressful?
Fortunately, it doesn’t have to be and this lecture will help provide you the tools to better understand the different types of shock.
Having a solid understanding of each type of shock will help you determine why the patient may be hypotensive and what needs to be done to correct the underlying problem.
As with every EZmed post, you will learn a simple method to remember the material. The 4 main types of shock can be easily explained using a gas pump analogy described below.
There will be future posts on anaphylaxis, septic shock, and other disease states within each of the 4 categories of shock, and also future posts on vasopressors. This post will serve as a strong foundation and reference for those topics.
What is shock?
Shock is circulatory failure causing inadequate perfusion to vital tissues and organs.
Inadequate oxygenated blood flow can lead to tissue hypoxia, cellular death, and organ failure (potentially multi organ).
If left untreated for prolonged periods of time critically low perfusion could lead to cardiac arrest and even death.
However, successfully identifying the type(s) of shock the patient is in will help target your treatment to that particular cause and hopefully prevent a code situation from occurring.
The patient’s body will also produce several physiological responses to improve blood pressure and perfusion.
The sympathetic nervous system will act on alpha adrenergic receptors to facilitate vasoconstriction and beta adrenergic receptors to augment cardiac output to improve blood pressure.
The renin-angiotensin-aldosterone system will also be activated to facilitate vasoconstriction and sodium/water reabsorption from the renal tubules. The system also stimulates the release of vasopressin/antidiuretic hormone and aldosterone.
The sympathetic nervous system and renin angiotensin aldosterone system (RAAS) work together as compensatory mechanisms to improve blood pressure in a shock state.
Increased sympathetic activity increases catecholamine levels that lead to vasoconstriction and increased cardiac output.
Activation of the RAAS will increase angiotensin II levels which will lead to vasoconstriction, aldosterone release, antidiuretic hormone release, and sodium/water reabsorption from the kidneys.
Shock Analogy
Now that we know what shock is, what are the potential causes of it?
The different types of shock can be easily explained using a gas pump analogy.
The gas pump represents the heart, the hose is the vasculature, the gasoline is the intravascular blood volume, and the vehicle is the tissues/organs.
Now if you think about it, there are 4 problematic scenarios in which it will be difficult to fill the car up with gas.
In other words, there are 4 main circulatory situations in which tissues/organs will not receive adequate oxygenated blood perfusion.
There is a problem with the gas pump (Cardiogenic Shock)
There is no gas (Hypovolemic Shock)
Something is blocking the gas (Obstructive Shock)
There is a problem with the hose (Distributive Shock)
Practical Correlation
The analogy is helpful because the 4 scenarios in which it will be difficult to fill up the car with gas also represents the 4 major classifications of shock in which oxygenated blood will not perfuse tissues and organs.
Let’s translate this to practical terms:
The patient’s heart (gas pump) is not adequately functioning leading to poor cardiac output (Cardiogenic Shock).
The patient’s intravascular volume (gasoline) is depleted (Hypovolemic Shock).
There is something obstructing (gas blockage) the ability to deliver the oxygenated blood to tissues and organs (Obstructive Shock).
The blood vessels are too permeable (leaky hose) and/or too dilated (big hose) to allow for adequate oxygenated blood delivery and perfusion (Distributive Shock).
Practical Application
Gas Pump Doesn’t Work = Cardiogenic Shock = Poor Cardiac Output
There Is No Gas = Hypovolemic Shock = Depleted Intravascular Volume
Gas Blockage = Obstructive Shock = Obstructing Tissue Perfusion
Problem with Hose = Distributive Shock = Vascular Permeability/Vasodilation
You can now appreciate how understanding and identifying the underlying problem will help tailor management and treatment specific to that cause.
If it is cardiogenic shock, management will be focused on improving cardiac output. If it is hypovolemic shock, management will be focused on repleting volume. If it is obstructive shock, management will include treating the obstruction. If it is distributive shock, management will include improving vascular tone.
Let’s discuss each type of shock in more detail.
Cardiogenic Shock
Gas pump is not functioning properly.
As discussed above, cardiogenic shock occurs when there is some underlying process involving the heart that causes decreased cardiac output and inadequate tissue perfusion.
Cardiac output is one of the variables to blood pressure and therefore directly impacts blood pressure and perfusion.
Cardiogenic shock can result from a number of etiologies including acute coronary syndrome, dysrhythmia, CHF, valvulopathy, drug toxicity, myocarditis, and myocardial contusion.
Point being, there is some underlying cardiac etiology that is deleterious to cardiac output.
Diagnostic investigation pertaining to cardiogenic shock should include cardiac work up to further investigate any of the underlying causes listed above.
Below are just a few example considerations for working up cardiogenic shock.
An EKG and troponin can be used to assess for acute coronary syndrome, myocardial ischemia, myocarditis, dysrhythmias, or drug toxicity.
Chemistry can be used to assess for electrolyte disturbances that could cause arrhythmia.
A BNP can be used to assess for heart failure.
A chest x-ray can assess for signs of cardiomegaly or pulmonary edema.
A bedside ultrasound can be used to assess overall squeeze of the heart and for B lines that could suggest pulmonary edema, along with other views discussed below.
Often with a strong history and physical exam, you can delineate what type of shock the patient is presenting in.
Findings and symptoms of cardiogenic shock may include but are not limited to chest pain, shortness of breath, edema, palpitations, JVD, cardiac murmurs, chest trauma, history of ingesting a bottle of beta blockers, etc.
However, unless there is an obvious etiology as to why the patient is hypotensive then work up should be broad to include the other types of shock as well.
Treatment of cardiogenic shock will be focused on correcting the underlying cause: cardiac catheterization, toxicology management, electrolyte corrections, valvular repair, inotropes, etc.
Underlying process is causing gas pump/heart dysfunction.
Hypovolemic Shock
There is no gas.
As discussed above, hypovolemic shock occurs when there is depletion of intravascular volume.
Without gas in the tank, tissues will not adequately be perfused.
This could be due to intractable vomiting and diarrhea leading to significant dehydration, hemorrhage from trauma, a ruptured abdominal aortic aneurysm, a GI bleed, etc.
Point being, there is some underlying process that is causing decreased intravascular volume. It will be imperative to replace the patient’s volume with appropriate crystalloid, blood products, and/or colloid depending on what they are losing and require.
It is also important to be mindful that more than one type of shock can be present.
For example, a patient who is in septic shock (form of distributive shock discussed below) may also have a hypovolemic component from vomiting and decreased oral intake due to being ill.
Again, this is why it is important to investigate all forms of shock when managing the undifferentiated patient.
Diagnostic investigation pertaining to hypovolemic shock should be used to assess the etiologies listed above.
Below are just a few example considerations when working up hypovolemic shock.
CBC, coagulation studies, and type and screen will help if there is concern for hemorrhage, GI bleed, etc.
Chemistry can be used to assess BUN and creatinine ratios, although decreased perfusion to kidneys could be from any of the types of shock and not just from hypovolemia.
Assessing mucous membranes, checking urine ketones and specific gravity, and asking about urine output/monitoring urine output can be helpful if there is concern for dehydration.
Asking the patient about volume loss such as bleeding, vomiting, diarrhea is important.
Ultrasound of the IVC can be useful to assess intravascular volume.
Treatment as mentioned above will include replacement of whatever volume is being lost.
Underlying process is causing decreased gas/intravascular volume levels.
Obstructive Shock
Gas blockage.
As discussed above, obstructive shock occurs when there is some underlying process obstructing the ability to adequately perfuse tissues.
The gas pump may be working and there could be gas, but something is blocking the gas from coming out.
Unlike cardiogenic shock and hypovolemic shock, the patient may have a well functioning heart and adequate intravascular volume but oxygenated blood delivery is being obstructed.
This can occur from a tension pneumothorax (increased intrathoracic pressure causing decreased venous return to the heart, thereby decreasing stroke volume and cardiac output), cardiac tamponade (fluid around the heart is becoming deleterious to the filling of the heart during diastole and contraction of the heart during systole), or a pulmonary embolism (thrombus in pulmonary artery preventing blood flow from the heart to the lungs).
Keeping these in the differential is important in the undifferentiated patient as they can quickly be assessed.
For example, chest X-ray or ultrasound can show tension pneumothorax. There may also be decreased lung sounds on auscultation.
Bedside ultrasound could show a pericardial effusion with tamponade physiology.
CT PE can be ordered to assess for pulmonary embolism (PE). Ultrasound may also show evidence of right heart strain.
Treatment will be geared toward correcting the underlying process. For example, oxygen or chest tube for pneumothorax, preload support and possible pericardiocentesis for cardiac tamponade, and anticoagulation or direct thrombolytics for PE.
Underlying process is preventing gas/oxygenated blood from coming out.
Distributive Shock
There is a problem with the hose.
As mentioned above, distributive shock occurs when there is a problem with the vasculature in delivering oxygenated blood to tissues usually due to vasodialtion and/or increased vascular permeability.
The hose may have a hole (vascular permeability) and/or be too big (vasodilation) to deliver the gas.
Causes of distributive shock include sepsis, anaphylaxis, neurogenic, adrenal crisis, or toxicologic.
As always, history and physical can help to guide you through the undifferentiated patient.
Diagnostic work up pertaining to distributive shock should include investigating the etiologies listed above.
Some considerations and examples are listed below.
Blood cultures, lactate, urine and urine cultures (along with other basic labs and labs mentioned in other forms of shocks) should be ordered for sepsis.
The other forms of distributive shock are typically more obvious based on history: neurogenic shock from trauma, anaphylaxis from allergen exposure, toxicologic from an overdose or exposure.
Adrenal crisis can be more tricky as it is often forgotten about and should at least be in your differential for hypotension. Always consider this as a possibility in those taking exogenous steroids.
Treatment will be tailored to whatever etiology is causing the distributive shock state. For example, epinephrine/steroids/antihistamines for anaphylaxis, antibiotics for sepsis, antidotes or supportive care for toxicologic causes, steroids for adrenal crisis, etc.
Of note, treatment discussions up to this point have been focused on treating the underlying cause. However, this may take time and any of these shock states may require temporary blood pressure support with pressor medications.
Underlying process is causing problems with the gas hose, either too leaky and/or too big.
Conclusion
4 types of shock:
Cardiogenic - Poor cardiac output and/or function (gas pump)
Hypovolemic - Intravascular volume depletion (gasoline)
Obstructive - Tissue perfusion obstruction (gas blockage)
Distributive - Vascular permeability and/or vasodilation (hose)
Hopefully this was useful to better understand the different types of shock.
Understanding the various types of shock will allow you to think through a differential as to why the patient is hypotensive, followed by appropriately working them up and targeting your management.
Below is a type of shock table for your convenience.
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