Emergency Medicine · Shock States
The facts most likely to be tested
Hypovolemic shock is characterized by decreased preload, resulting in low pulmonary capillary wedge pressure (PCWP) and low cardiac output.
The body compensates for volume loss via sympathetic nervous system activation, leading to increased systemic vascular resistance (SVR) and tachycardia.
Hemorrhagic shock is the most common cause of hypovolemic shock, often presenting with tachycardia, hypotension, and cool, clammy extremities.
Class III hemorrhage involves a 30-40% blood volume loss, typically manifesting as marked tachycardia, tachypnea, and a significant drop in systolic blood pressure.
Initial resuscitation for hypovolemic shock requires two large-bore peripheral IV lines and the administration of isotonic crystalloids (e.g., Lactated Ringer's).
In cases of hemorrhagic shock, the massive transfusion protocol should be activated to maintain a 1:1:1 ratio of packed red blood cells, fresh frozen plasma, and platelets.
Base deficit and serum lactate levels are the most reliable markers for assessing the adequacy of tissue perfusion and the effectiveness of resuscitation.
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A 24-year-old male is brought to the emergency department following a high-speed motor vehicle collision. He is lethargic, his skin is pale and cool, and his capillary refill is delayed. Vital signs show a heart rate of 135 bpm, blood pressure of 82/50 mmHg, and a respiratory rate of 28/min. Physical examination reveals flat neck veins and absent breath sounds on the right side.
What is the most appropriate initial management step for this patient?
Needle thoracostomy followed by tube thoracostomy
While the patient is in hypovolemic shock, the presence of absent breath sounds and hypotension indicates a tension pneumothorax, which must be decompressed immediately before or concurrent with fluid resuscitation.
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Etiology / Epidemiology
Hemorrhage (trauma/GI bleed) and dehydration (vomiting/diarrhea) are the primary drivers. Hypovolemia results in decreased preload and cardiac output.
Clinical Manifestations
Classic presentation includes tachycardia, thready pulse, and hypotension. Look for cool, clammy skin and delayed capillary refill.
Diagnosis
Diagnosis is clinical. Lactate > 4 mmol/L and base deficit indicate tissue hypoperfusion. Bedside ultrasound (FAST) is the gold standard for trauma.
Treatment
Resuscitate with isotonic crystalloids (NS/LR). Avoid vasopressors until volume is restored. Use blood products for hemorrhagic shock.
Prognosis
Mortality correlates with base deficit severity. Monitor urine output > 0.5 mL/kg/hr to assess end-organ perfusion.
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Epidemiology & Etiology
Common causes include trauma (hemorrhagic) and gastrointestinal losses (non-hemorrhagic). Elderly patients are at high risk due to blunted compensatory mechanisms. Third-spacing in burns or pancreatitis also contributes to intravascular volume depletion.
Pertinent Anatomy
The venous capacitance system holds the majority of blood volume. Loss of this volume reduces venous return to the right atrium, directly limiting stroke volume via the Frank-Starling mechanism.
Pathophysiology
Decreased intravascular volume leads to reduced preload, causing a drop in cardiac output. The body compensates via sympathetic nervous system activation, increasing heart rate and systemic vascular resistance. Prolonged hypoperfusion leads to anaerobic metabolism and lactic acidosis.
Clinical Manifestations
Patients present with tachycardia, narrow pulse pressure, and oliguria. Altered mental status is a late, ominous sign of cerebral hypoperfusion. Physical exam reveals dry mucous membranes and poor skin turgor in non-hemorrhagic cases.
Diagnosis
Diagnosis is primarily clinical, supported by serum lactate levels. FAST exam is the gold standard for identifying free fluid in trauma. Monitor central venous pressure (CVP), which is typically low (< 5 mmHg).
Treatment
Initiate isotonic crystalloids (1-2L bolus) as the first-line intervention. Do not delay blood transfusion in hemorrhagic shock; use a 1:1:1 ratio of PRBCs, FFP, and platelets. Vasopressors are contraindicated until adequate volume resuscitation is achieved.
Prognosis
Failure to restore mean arterial pressure (MAP) > 65 mmHg leads to multi-organ failure. Continuous monitoring of urine output and serial lactate levels is required to guide resuscitation.
Differential Diagnosis
Cardiogenic shock: elevated JVP and pulmonary edema
Obstructive shock: Beck's triad (tamponade) or tension pneumothorax
Distributive shock: warm extremities and wide pulse pressure
Adrenal crisis: refractory hypotension despite fluids
Neurogenic shock: bradycardia and loss of sympathetic tone