Overview
This lecture reviews cardiogenic shock, including its pathophysiology, causes, clinical presentation, diagnostics, and key nursing interventions, with a focus on understanding cardiac output and treatment strategies.
Pathophysiology of Cardiogenic Shock
- Cardiogenic shock occurs when the heart fails to pump enough blood to meet the body's perfusion needs.
- It results from problems with heart filling (diastolic dysfunction), contraction (systolic dysfunction), dysrhythmias, or structural defects.
- Unlike other types of shock, blood volume is adequate; the heart simply cannot maintain cardiac output.
Cardiac Output & Stroke Volume
- Cardiac output (CO) is the amount of blood the heart pumps per minute (normal: 4–8 L/min).
- CO = Heart Rate × Stroke Volume (SV); SV is the blood ejected by the left ventricle per beat (normal SV: 50–100 mL).
- SV is determined by preload (ventricular stretch at end of diastole), afterload (resistance heart pumps against), and contractility (strength of contraction).
- Manipulating preload, afterload, or contractility with medications can improve CO.
Causes of Cardiogenic Shock
- The main cause is acute myocardial infarction (heart attack), especially if the left ventricle is affected.
- Other causes: pericardial tamponade, myocarditis, endocarditis, severe valve or septal defects, and dysrhythmias.
Signs and Symptoms
- Pulmonary: Pulmonary edema, dyspnea, increased respiratory rate, low oxygen, crackles on lung exam.
- Hemodynamic: Weak pulses, systolic BP < 90 mmHg, cardiac index < 2.2 L/min/m², elevated pulmonary capillary wedge pressure (>18 mmHg), and elevated central venous pressure.
- Brain: Confusion, agitation from decreased cerebral perfusion.
- Renal: Oliguria (<30 mL/hr), increased BUN/creatinine due to poor kidney perfusion.
- Skin: Cool, pale, clammy, delayed capillary refill.
- Other: Jugular venous distension, chest pain.
Diagnostic & Laboratory Findings
- Elevated troponin (heart injury) and BNP (ventricular stretch).
- Chest X-ray may show pulmonary edema.
- Serum lactate >4 mmol/L (anaerobic metabolism).
- Arterial pH <7.35 (acidosis).
- Hemodynamic monitoring: High pulmonary capillary wedge pressure (>18 mmHg), high central venous pressure.
Nursing Interventions & Treatment Goals
- Restore perfusion to heart muscle (e.g., cardiac catheterization, stents).
- Increase cardiac output with medications targeting SV factors.
- Manage pulmonary edema with diuretics and ventilation support.
- Monitor hemodynamics (central lines, pulmonary artery catheter/Swan-Ganz).
- Assess for adequate perfusion: BP >90 mmHg, urine output >30 mL/hr, mental status, kidney function, lung sounds, capillary refill.
- Monitor and correct electrolyte imbalances, especially potassium.
Medications & Devices
- Diuretics (e.g., furosemide): Remove excess fluid but monitor for hypokalemia and hypotension.
- Vasopressors (e.g., norepinephrine): Increase preload and blood pressure via vasoconstriction.
- Inotropes (e.g., dobutamine, dopamine): Increase contractility but may cause hypotension (dobutamine) or tachycardia (dopamine).
- Vasodilators (e.g., nitroglycerin): Decrease afterload, improve coronary perfusion, risk of hypotension.
- Intra-aortic balloon pump: Temporarily increases coronary blood flow and cardiac output by inflating/deflating in the aorta.
Key Terms & Definitions
- Cardiac Output (CO) — Amount of blood pumped by the heart per minute.
- Stroke Volume (SV) — Blood volume pumped with each ventricular contraction.
- Preload — Ventricular stretch at end-diastole; determined by venous return.
- Afterload — Resistance the ventricle must overcome to eject blood.
- Contractility — Strength of heart muscle contractions.
- Cardiac Index — Cardiac output adjusted for body surface area.
- Pulmonary Capillary Wedge Pressure (PCWP) — Reflects left atrial pressure; elevated in cardiogenic shock.
- BNP (B-type Natriuretic Peptide) — Marker of ventricular stretch/failure.
- Troponin — Marker of cardiac muscle injury.
Action Items / Next Steps
- Take the free quiz on cardiogenic shock.
- Review previous lectures on shock, especially stages of shock.
- Study cardiac output formulas and factors affecting stroke volume.
- Be familiar with normal ranges for key hemodynamic values and lab markers.