Shock — Types and Management

Hypovolemic — loss of intravascular volume

• Hemorrhagic: trauma, GI bleeding, ruptured abdominal aortic aneurysm, ruptured ectopic pregnancy, postpartum hemorrhage, retroperitoneal bleed on anticoagulation
• Non-hemorrhagic: vomiting/diarrhea, burns (plasma loss across denuded skin), diabetic ketoacidosis with osmotic diuresis, third-spacing in pancreatitis or bowel obstruction

Distributive — pathologic vasodilation and capillary leak

• Septic: pneumonia, urinary tract, intra-abdominal, and skin/soft-tissue sources predominate; endotoxin-driven nitric oxide release drops systemic vascular resistance
• Anaphylactic: IgE-mediated and non-IgE (direct mast cell activation) triggers — foods, hymenoptera venom, beta-lactams; contrast media and neuromuscular blockers act largely through direct mast cell activation
• Neurogenic: spinal cord injury above roughly T6 interrupts sympathetic outflow → vasodilation plus unopposed vagal tone
• Endocrine/toxic: adrenal crisis, myxedema coma, liver failure, vasodilator or sedative overdose

Cardiogenic — pump failure

• Acute MI with large territory of injured myocardium (the most common cause), mechanical complications (papillary muscle rupture, ventricular septal rupture, free wall rupture), fulminant myocarditis, decompensated cardiomyopathy, tachy- or bradyarrhythmias, acute valvular regurgitation, beta-blocker or calcium channel blocker overdose

Obstructive — mechanical impedance to filling or ejection

• Tension pneumothorax, cardiac tamponade, massive pulmonary embolism, auto-PEEP in severe asthma/COPD on the ventilator, aortic dissection with tamponade

Cellular and Tissue-Level Mechanisms

• Tissue hypoperfusion → inadequate oxygen delivery relative to demand; cells shift from aerobic to anaerobic metabolism, producing lactate and causing metabolic acidosis
• Mitochondrial dysfunction → impaired ATP production, failure of Na+/K+ ATPase pumps, cellular swelling, and loss of cellular integrity leading to apoptosis and necrosis
• Inflammatory cascade activation → release of cytokines (TNF-α, IL-1, IL-6), activation of complement and coagulation pathways, increased vascular permeability, and progression to SIRS (Systemic Inflammatory Response Syndrome) and MODS (Multiple Organ Dysfunction Syndrome)

Compensatory Mechanisms (Early/Compensated Shock)

• Sympathetic nervous system activation → increased heart rate, vasoconstriction, and increased contractility to maintain cardiac output and blood pressure
• Renin-angiotensin-aldosterone system (RAAS) activation → fluid retention and further vasoconstriction to restore intravascular volume and perfusion pressure
• Baroreceptor reflex → maintains mean arterial pressure (MAP) through increased peripheral vascular resistance

Decompensated Shock (Late/Irreversible)

• Vascular collapse → loss of compensatory vasoconstriction, severe hypotension, and inability to maintain perfusion despite maximum catecholamine stimulation
• Myocardial depression → cytokine-induced reduction in contractility (especially in septic shock); further decreases cardiac output
• Disseminated intravascular coagulation (DIC) → widespread microthrombi formation consumes clotting factors and platelets, causing bleeding and further ischemia
• End-organ ischemia → acute kidney injury, hepatic dysfunction, acute respiratory distress syndrome (ARDS), and bowel ischemia with bacterial translocation

Universal Signs of Shock (Present in All Types)

• Tachycardia — compensatory response to maintain cardiac output; may be absent in severe bradycardia or with certain medications (beta-blockers, vasodilators)
• Hypotension — systolic BP <90 mmHg or MAP <65 mmHg (critical threshold for organ perfusion); late finding indicating decompensated shock
• Altered mental status — confusion, agitation, lethargy from cerebral hypoperfusion and acidosis; often the earliest sign of shock in at-risk patients
• Cool, clammy skin and peripheral cyanosis — sympathetic vasoconstriction shunting blood to core organs; indicates poor peripheral perfusion
• Tachypnea — compensatory response to metabolic acidosis and tissue hypoxia; respiratory rate often >20 breaths/min

Lactate Elevation and Oliguria

• Serum lactate >2 mmol/L — reflects anaerobic metabolism and tissue hypoperfusion; lactate >4 mmol/L indicates severe shock
• Oliguria (urine output <0.5 mL/kg/hour) — reflects renal hypoperfusion and acute tubular necrosis risk

Type-Specific Presentations

• Pulmonary edema (crackles, orthopnea, pink frothy sputum)
• Elevated jugular venous pressure (JVP), peripheral edema
• Weak or absent pulses; cold extremities

• Dry mucous membranes, poor skin turgor, flat neck veins
• Severe thirst
• Postural vital sign changes (orthostatic hypotension) in early stages

• Fever or hypothermia with source of infection (e.g., pneumonia, UTI, intra-abdominal source)
• Warm extremities initially ("warm shock") due to vasodilation; progresses to cold shock
• Rapid capillary refill despite hypotension

• Tension pneumothorax: severe respiratory distress, unilateral absent breath sounds, tracheal deviation
• Massive PE: severe dyspnea, unilateral leg swelling (DVT signs)
• Cardiac tamponade: Beck's triad (hypotension, elevated JVP, muffled heart sounds) plus pulsus paradoxus

Clinical Diagnosis

• Systolic BP <90 mmHg OR MAP <65 mmHg (or >40 mmHg drop from baseline) with signs of hypoperfusion
• Presence of at least 2 of: altered mental status, cool extremities, oliguria, lactate >2 mmol/L
• Note: Shock can exist with "normal" BP in early/compensated phases; clinical assessment of perfusion takes precedence

Laboratory Tests

• Arterial or venous blood gas — assess pH, lactate, bicarbonate; metabolic acidosis with elevated lactate confirms tissue hypoperfusion
• Serum lactate — prognostic marker; serial lactate measurement (lactate clearance) predicts outcome better than single value
• Complete metabolic panel — assess renal function (creatinine, BUN), electrolytes, glucose; hyperglycemia common in stress response
• Complete blood count — assess for anemia (bleeding), thrombocytopenia (DIC)
• Coagulation studies (PT/INR, PTT, fibrinogen) — screen for DIC
• Blood cultures — obtain before antibiotics in suspected sepsis
• Troponin, BNP — assess for myocardial ischemia/infarction in cardiogenic shock
• Lactate clearance — >10% improvement in 6 hours associated with better prognosis than persistent elevation

Imaging and Monitoring

• 12-lead ECG — assess for MI, arrhythmia, signs of PE (S1Q3T3, right axis deviation)
• Chest X-ray — assess for pneumothorax, ARDS, pulmonary edema, pneumonia
• Focused ultrasound (POCUS) — assess for pericardial effusion (tamponade), free fluid (hemorrhage), IVC distension (volume status), pneumothorax
• Central venous pressure (CVP) monitoring — helps guide fluid resuscitation and distinguish shock types (elevated in cardiogenic/obstructive, low in hypovolemic)
• Cardiac output monitoring — advanced hemodynamic assessment (Swan-Ganz catheter, non-invasive methods) in refractory cases

Type-Specific Diagnostic Findings

• Cardiogenic: elevated CVP, low cardiac output, pulmonary edema on imaging, elevated troponin, reduced ejection fraction on echocardiogram
• Hypovolemic: low CVP, normal cardiac output until late stages, clear lung fields, source evident (hemorrhage, GI loss, insensible loss)
• Distributive/Septic: low CVP initially, normal or elevated cardiac output, lactate elevation, infection source identifiable, systemic inflammatory markers elevated
• Obstructive: variable CVP depending on etiology; imaging diagnostic (tension pneumothorax on CXR, PE on CT angiography, pericardial fluid on ultrasound)

Immediate Initial Management (First Minutes)

1. 1.Positioning — place patient supine, elevate lower extremities (passive leg raise or Trendelenburg); improves venous return

Complications of shock itself

• Acute kidney injury / acute tubular necrosis: sustained renal hypoperfusion causes ischemic tubular death; signaled by oliguria, rising creatinine, and muddy brown granular casts on urine microscopy (KDIGO staging)
• ARDS: cytokine-mediated alveolar-capillary leak; bilateral opacities with hypoxemia not explained by cardiac failure — requires low-tidal-volume ventilation per ATS/ESICM/SCCM
• **Ischemic hepatitis (shock liver)**: centrilobular necrosis from low hepatic blood flow; transaminases in the thousands within 24–48 hours, out of proportion to bilirubin
• Mesenteric ischemia and bacterial translocation: pain out of proportion to exam, rising lactate that fails to clear — a surgical emergency
• DIC: consumption of factors and platelets; prolonged PT/PTT, low fibrinogen, schistocytes, simultaneous oozing and microthrombosis
• Anoxic brain injury and PEA arrest: the terminal common pathway — immediate emergency; the shockable rhythms to look for are ventricular fibrillation and pulseless VT (AHA ACLS)
• Sheehan syndrome after postpartum hemorrhagic shock: pituitary infarction presenting with failure of lactation

Complications of treatment

• Volume overload from over-resuscitation: worsening hypoxemia, new crackles, rising oxygen requirement — particularly hazardous in cardiogenic and right-ventricular-failure shock
• Hyperchloremic metabolic acidosis with large-volume 0.9% saline; balanced crystalloids are favored in the Surviving Sepsis Campaign 2021 guidance
• Abdominal compartment syndrome: massive resuscitation raises intra-abdominal pressure → oliguria plus high airway pressures — decompression emergency
• Massive transfusion sequelae: citrate-induced hypocalcemia, hyperkalemia, hypothermia, and dilutional coagulopathy; also TRALI and TACO
• Distinguish these from the classic trauma lethal triad — hypothermia, acidosis, and coagulopathy — to which hypocalcemia is added in the newer diamond of death framing
• Vasopressor injury: peripheral extravasation of norepinephrine causes tissue necrosis — treat with local phentolamine; digital and mesenteric ischemia occur even with correct central delivery; dopamine and epinephrine are the most arrhythmogenic
• Procedural: central line pneumothorax and CLABSI; single-dose etomidate transiently suppresses adrenal cortisol synthesis

• The hemodynamic grid is the single most tested concept: cardiogenic = low cardiac output, high PCWP, high SVR; hypovolemic = low CO, low PCWP, high SVR; distributive = high CO, low PCWP, low SVR; obstructive = low CO with SVR high and PCWP dependent on the lesion. Mixed venous O₂ saturation is low in all except distributive, where impaired extraction keeps it high.
• **Neurogenic shock = hypotension with bradycardia and warm, dry, well-perfused skin** after cord injury. The distractor is spinal shock, which is a neurologic phenomenon (flaccid paralysis, areflexia, loss of bulbocavernosus reflex), not a hemodynamic one.
• Tension pneumothorax is a clinical diagnosis: the best next step is immediate needle decompression followed by tube thoracostomy — never a chest x-ray first.
• Anaphylaxis: epinephrine 0.3 mg IM into the anterolateral thigh is first-line with no absolute contraindication (AAAAI/ACAAI parameter). Antihistamines and glucocorticoids are adjuncts and never substitutes; delayed epinephrine is the modifiable factor in fatal cases.
• Septic shock: obtain blood cultures, then give broad-spectrum antibiotics promptly (within one hour for shock per Surviving Sepsis Campaign 2021), at least 30 mL/kg balanced crystalloid, and norepinephrine as the first-line vasopressor targeting MAP ≥65 mmHg. Add vasopressin as a norepinephrine-sparing second agent; consider hydrocortisone for pressor-refractory shock.
• Inferior MI with hypotension after nitroglycerin = right ventricular infarction. Confirm with right-sided leads (V4R); the RV is preload-dependent, so treat with fluids and avoid nitrates and diuretics.
• Cardiogenic shock from MI: early revascularization improves survival (SHOCK trial); CULPRIT-SHOCK supports culprit-lesion-only PCI rather than immediate multivessel intervention. Avoid beta blockers and large boluses in the acutely decompensated patient (ACC/AHA 2022).
• Toxicologic look-alikes: beta-blocker overdose responds to glucagon; calcium channel blocker overdose to IV calcium plus high-dose insulin euglycemic therapy. A refractory hypotensive patient with hyponatremia, hyperkalemia, and eosinophilia has adrenal crisis — give hydrocortisone.