AssessmentsShock: Clinical practice
USMLE® Step 2 style questions USMLE
A 30-year-old primigravid woman at 28 weeks' gestation comes to the emergency department because of severe abdominal pain for 2 hours. Her last visit to the physician was 2 weeks ago. Her pregnancy had been uncomplicated. Her temperature is 37.1°C (98.8°F), pulse is 112/min, respirations are 22/min, and blood pressure is 94/58 mm Hg. Abdominal examination shows diffuse tenderness with board-like rigidity. Ultrasound shows a large subcapsular mass within the liver. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Shock is most commonly due to hypotension, which is a systolic blood pressure less than 90 mm Hg, or a mean arterial pressure less than 65 mm Hg, that leads to inadequate tissue perfusion and injury to various organ systems, like the brain, heart, kidneys, and liver.
If left untreated, shock can cause irreversible multi-organ failure and death.
Cardiogenic shock is when the decline in cardiac output is secondary to a decrease in contractility, such as in congestive heart failure, myocardial infarction, myocardial contusion, or due to dysrhythmias.
Okay, on the other hand of the equation, we have things that decrease the systemic vascular resistance, or in other words result in peripheral vasodilation. These include anaphylactic, septic, and neurogenic shock, as well as certain disease states like acute adrenal insufficiency.
Okay, the approach to an individual with suspected shock starts with the ABCs; airway, breathing and circulation. The goal here is to detect life-threatening emergencies and address them immediately.
The airway is evaluated for patency, and the easiest way to do this is to ask the individual to speak to you.
A clear, coherent voice usually means that they can protect their own airway.
Also, signs like lip and tongue swelling or inspiratory stridor suggest anaphylactic shock.
As for breathing, ventilation and oxygenation are assessed.
For example, hypoxemia, decreased air entry, hyperresonance on percussion, and tracheal deviation to the opposite side may be seen in a tension pneumothorax. In such a case, immediate needle decompression is performed by inserting a needle in the 2nd intercostal space on the affected side, which alleviates the compression of the inferior vena cava.
Alright, as for the circulation, IV access should be obtained by inserting two large-bore peripheral intravenous lines.
A small bolus of IV crystalloid fluid may be given initially as a “fluid challenge”, which assesses the person’s response to fluids.
Parameters like the mean arterial blood pressure or the urine output may be used to assess responsiveness.
Shock caused by decreased cardiac output usually leads to a narrow pulse pressure, like a pressure of 70 over 60 for example.
On the other hand, shock caused by a decreased systemic vascular resistance usually manifests as a wide pulse pressure, like a pressure of 100 over 30.
It’s also important to know a person’s baseline blood pressure. For example, a blood pressure of 110 over 80 is actually low for someone with uncontrolled hypertension who has a baseline of 180 over 120.
A shock index greater than 0.8 usually indicates shock, and the higher the number, the worse the shock, but a normal shock index value doesn’t exclude shock.
On physical exam, cold extremities usually signify shock caused by a decreased cardiac output, because the body attempts to redirect blood flow away from the skin to more vital organs like the brain and heart.
On the other hand, in shock caused by a decreased systemic vascular resistance, the extremities are usually warm due to peripheral vasodilation.
Other common findings include signs of decreased end-organ perfusion, such as oliguria, which is defined as a urine output less than 0.5 CCs per kilogram per hour.
Other signs are an altered mental status, which indicates decreased brain perfusion, and a prolonged capillary refill time, which indicates decreased skin perfusion.
So “H” is for heart, and here we’re mainly looking for a pericardial tamponade, which is immediately treated by doing a pericardiocentesis. It’s also possible to look at the way the heart is beating which may be abnormal in someone with cardiogenic shock.
In addition, a significantly enlarged right side of the heart may be due to right heart strain from a pulmonary embolism.
Okay, “I” is for the inferior vena cava, which provides an idea about the volume status and the central venous pressure, or CVP, which reflects the amount of blood returning to the right heart.
A dilated IVC means that the CVP is high, which points towards obstructive or cardiogenic shock.
A flat and collapsed IVC tells us that the CVP is low, which points towards hypovolemic or distributive shock.
“M” is for Morrison’s pouch, or the hepatorenal recess, which is where fluid or blood can collect in the setting of trauma. We also look for free fluid in the splenorenal recess and in the pelvis - any signs of trauma might mean needing to go directly to surgery for exploration.
The “A” is for the aorta, where we measure the aortic diameter looking for any signs of an aortic aneurysm. It’s crucial that we look at the entire aorta, beginning from the xiphoid process all the way down the abdomen until you see the aorta bifurcate into the common iliacs, which is usually just under the umbilicus.
Finally, there’s “P”, which is a reminder to look for a pneumothorax.
Hemorrhagic shock may initially show a normal hematocrit, because a person loses red blood cells and a proportional amount of plasma with it. But later, only after they’re resuscitated with fluid, does the anemia appears.
Lactate levels are quite helpful in identifying shock, especially in individuals who have a normal blood pressure, and serial lactate levels can be used to assess response to therapy.
While high lactate levels are abnormal, low lactate levels should not reassure you if there are other concerning signs of shock.
In shock, there’s also usually a high anion-gap metabolic acidosis.
An ECG may show ischemic changes, electrical alternans which is alternating amplitudes of the QRS complex, a sign of pericardial effusion, or even signs of right ventricular strain in pulmonary embolism like the S1Q3T3 pattern.
If a myocardial infarction is suspected, then troponin levels may be obtained, and if congestive heart failure is suspected, then a chest x-ray and brain-natriuretic peptide, or BNP levels can be checked.
Management depends on the cause of shock. So let’s start with hypovolemic shock, which may be non-hemorrhagic or hemorrhagic.
Non-hemorrhagic hypovolemic shock may result from gastrointestinal losses like vomiting or diarrhea, renal losses such as excessive diuresis in diabetic ketoacidosis or diabetes insipidus, excessive sweating like in hyperthermia or hyperthyroidism, or third-spacing.
Treatment includes replacing the lost fluids, usually with IV crystalloids like normal saline, correcting any electrolyte abnormalities, and addressing the underlying cause.
Hemorrhagic shock usually results from trauma, and can be obvious such as bleeding from the scalp or a long-bone fracture, or it could be occult such as intraperitoneal or retroperitoneal bleeding. It can also be non-traumatic, such as gastrointestinal or genitourinary bleeding, or a ruptured ectopic pregnancy.
Management includes applying direct pressure to the bleeding if possible, and providing blood products.