What is Distributive Shock?
Distributive shock, also referred to as vasodilatory shock, is one of the four main types of disorders that result in poor blood flow to the body’s tissues. This condition causes the blood vessels to widen, which decreases blood flow to key organs like the brain, heart, and kidneys and can result in organ damage. Additionally, distributive shock allows fluid to leak from tiny blood vessels called capillaries into surrounding tissues, making the situation even more complicated. Because this disease is complex, the causes and treatments for distributive shock involve various approaches.
What Causes Distributive Shock?
Distributive shock, which often happens in emergency situations, is typically caused by conditions such as sepsis (a serious infection) or anaphylaxis (a severe allergic reaction). Cases involving trauma might lead to what’s called neurogenic shock. Other, less common triggers range from adrenal insufficiency (when the body doesn’t produce enough hormones) to capillary leak syndrome (when fluids leak out of blood vessels). If a patient has overdosed on certain types of medication, particularly ones that widen blood vessels like calcium channel blockers and hydralazine, it can also lead to distributive shock.
Sepsis-induced distributive shock is a result of an immune reaction gone haywire in response to infection, which leads to the release of molecules called cytokines. These cytokines cause blood vessels to widen and fluids to leak out of blood vessels. They can also lead to a decrease in heart function, known as septic cardiomyopathy, which can contribute to a state of shock.
Distributive shock can also be triggered by the body’s inflammatory response to non-infectious issues, such as pancreatitis (inflammation of the pancreas) or burns.
In a case of anaphylactic shock, the patient normally has a history of exposure to a allergen, which has caused their body to form allergy-causing antibodies (IgE molecules). These IgE molecules bind to certain cells in the body which then causes the release of histamine when the allergen is encountered again, leading to widening of blood vessels and fluid leak.
Distributive shock can also be due to toxic shock syndrome, a severe illness caused by bacterial toxins (from Staphylococcus aureus and group A streptococci) that trigger the release of cytokines, leading to widened blood vessels and fluid leak. This condition has historically been associated with the use of vaginal and nasal tampons.
Neurogenic shock, which typically happens in trauma cases involving the neck portion of the spinal cord, is due to damage to the part of the nervous system that controls the blood vessels and heart. This leads to widening of blood vessels, low blood pressure, and unusually slow heart rate.
If someone has been on steroids for a long time and suddenly stops, it can cause distributive shock due to adrenal insufficiency, because it decreases the number of certain receptors on small arteries, causing the blood vessels to dilate.
Rare conditions such as capillary leak syndrome might be at play in cases of distributive shock. When the protein albumin is low in the blood, it can lead to fluid leaking from the blood vessels into the tissues. This condition should be considered in patients who are experiencing distributive shock and appear swollen.
Risk Factors and Frequency for Distributive Shock
Septic shock is the most common type of distributive shock seen in emergency departments. Around one million people are admitted each year with severe sepsis, a condition that has a mortality rate of around 50%. It’s important to highlight that almost 50% of septic patients have something called cryptic shock. This means that they don’t have enough blood flow to their tissues, even though their blood pressure appears normal.
Anaphylaxis is probably the second most common cause of distributive shock. It can happen to anyone, no matter their age or whether they’ve had it before. Having a nut allergy or a history of asthma are both risk factors for death in patients suffering from anaphylaxis, so these patients need to be carefully monitored.
Signs and Symptoms of Distributive Shock
When a patient arrives in emergency care, it’s vital to quickly gather as much information as possible. Sometimes the patient can provide this information, but if they can’t, it may need to come from emergency service teams, family members, or witnesses. Key things to note include:
- Symptoms like shortness of breath, cough, fever, chills, nausea, vomiting, stomach pain, or painful urination. These could suggest an infection leading to sepsis.
- If the patient has a weakened immune system or recent hospital stays.
- Any known allergies and a history of severe allergic reactions.
- Possible exposure to things the patient is allergic to.
- The patient’s medications, particularly steroids and blood pressure drugs. Also, note any drug misuse, as this could contribute to their condition.
Though a physical exam might not pinpoint the source of the patient’s shock, it can provide some helpful clues. Warm limbs could suggest an underlying issue causing blood vessels to widen. A thorough skin exam can help identify potential skin infections like cellulitis, skin ulcers, or abscesses. If the patient has hives, this could point towards a serious allergic reaction.
In cases where a patient has low blood pressure, doesn’t show signs of infection, and normal resuscitation methods aren’t working, adrenal gland problems should be considered.
A physical exam might reveal:
- Changes in mental state
- Rapid heart rate and breathing
- Low blood pressure
- Warm skin with strong, fast pulses in early shock
- Abnormally high or low body temperature
- Decreased urine production
- Low blood oxygen levels
Testing for Distributive Shock
When patients come to the emergency room with shock and the cause isn’t immediately clear, the first step is always to check their airway, breathing, and circulation. This primary check also includes setting up a reliable vein (or ‘intravenous’) access for fluids or medications and monitoring the heart and blood pressure. It’s also important to quickly do a full head-to-toe examination.
Some patients might need help managing their breathing, but doctors try to stablize the heart function before proceeding with this, to avoid causing a heart attack. An ECG, a test that records the heart’s activity, is done as soon as possible to check for any abnormal rhythms or signs that the heart muscle isn’t getting enough oxygen, which can sometimes appear like shock.
Doctors also perform a chest x-ray on the spot to check for conditions such as pneumonia, fluid in the lungs, or air in the chest cavity outside the lungs. Alongside, an ultrasound exam, called the RUSH (Rapid Ultrasound for Shock) exam, is performed at the bedside. This provides a quick evaluation of the heart’s function and how much fluid is in the body, and can also detect problems such as fluid around the heart, fluid in the lungs, air outside the lungs, or hidden bleeding within the abdomen.
Additionally, a comprehensive set of lab tests are conducted. These include measuring lactate, a substance that can build up in the body during shock; collecting blood and urine samples for culture, to identify any infections; checking the blood gases, to understand how well oxygen is being delivered and used in the body; and for women who could be pregnant, doing a pregnancy test.
Treatment Options for Distributive Shock
Most people experiencing shock can benefit from an initial boost of 250-500 mL of fluids. Distributive shock patients, in particular, are more likely to need help from a vasopressor, a drug that narrows blood vessels and raises blood pressure. The goal of treatment is to optimize blood flow within the body. This is achieved by aiming for a mean arterial pressure (average blood pressure) above 65 mmHg, which is the ideal blood pressure for heart and kidney health. Healthcare providers monitor this using physical exams, lab tests, and other methods.
In septic shock, a critical type of blood infection, the first line of treatment is norepinephrine. This drug can boost blood pressure without significantly affecting heart function. If more intervention is needed, vasopressin – another vasoconstrictor – might be used. The patient should also be given plenty of fluids and administered antibiotics as soon as possible.
In anaphylactic shock, which occurs from a severe allergic reaction, epinephrine is the treatment of choice. It boosts blood pressure and also helps open up airways and stabilize cells involved in allergic reactions. Other treatments can include antihistamines, steroids, albuterol (a medication which helps open up the airways), and fluids. In some cases, glucagon may be given if the patient is taking beta-blockers, a type of blood pressure medication.
If a patient’s shock doesn’t respond to fluids or vasopressors, they may have adrenal insufficiency. In this case, steroids could be administered to help boost alpha-1 receptors which help regulate blood pressure. Hydrocortisone 100 mg is commonly used for this purpose.
In urgent situations where vasopressor drips aren’t immediately available and the patient’s blood pressure is critically low (a mean arterial pressure below 50 mmHg can potentially damage the brain), quick injection of vasopressors can be used. Common choices for this are epinephrine and phenylephrine.
Once the patient has been resuscitated, they should start to receive nutrition as soon as possible. This could involve feeding through a tube or intravenous nutrition, depending on the patient’s needs.
What else can Distributive Shock be?
- Severe allergic reaction (Anaphylaxis)
- Carbon Monoxide (CO) poisoning
- Bad reactions to medications (Adverse drug reaction)
- Shock due to spinal cord injury (Neurogenic shock)
- Severe bacterial infection resulting in low blood pressure (Toxic shock syndrome)
- Cyanide poisoning
- Shock due to poor heart function (Cardiogenic shock)
- Shock due to severe blood loss (Hemorrhagic shock)
- Fluid build-up around the heart constraining its function (Tamponade)
What to expect with Distributive Shock
The death rate from distributive shock, a serious medical condition in which blood isn’t distributed properly in the body, varies greatly depending on its cause. It could range from 20% to 80%. Survival rates tend to improve greatly when the condition is identified early.
Certain factors are associated with a higher risk of mortality from distributive shock. These include the presence of bacteria in the blood, being of an advanced age, an increase in lactate levels in the blood or inability to lower these levels, infection due to a certain type of bacteria called pseudomonas aeruginosa, alcohol consumption, having a weakened immune system, and having a poor overall health before the onset of the condition.
