Cardiogenic Shock and Reduced Perfusion

Clinical Orientation

A 62-year-old man with an anterior STEMI is in the cardiac ICU. Despite successful LAD stenting, his BP is 78/48 on high-dose vasopressors. His lactate is 8.2 and rising. His extremities are cold and mottled. His urine output is 5 mL/hour. His cardiac index is 1.6 L/min/m2. He has cardiogenic shock. This chapter answers: What mechanism links cardiogenic shock to bedside findings, tests, red flags, and nursing priorities?

Cross-reference: Book 10 provides the complete shock integration volume. This chapter focuses on the cardiogenic mechanism.

What Goes Wrong?

Cardiogenic shock: Severe pump failure → cardiac output inadequate to meet tissue oxygen demand despite adequate intravascular volume. The defining hemodynamics: low cardiac output, elevated filling pressures (high PCWP), high SVR (vasoconstriction). This distinguishes it from distributive shock (low SVR) and hypovolemic shock (low filling pressures).

The downward spiral:

Severe pump dysfunction → reduced CO → hypotension → reduced coronary perfusion pressure → worsened myocardial ischemia → further reduced contractility → further reduced CO

Plus, systemic hypoperfusion → lactic acidosis (depresses myocardium) + release of inflammatory mediators (cause vasodilation and further myocardial depression). This is why mortality is so high (40-50%).

Causes: Most commonly acute MI (especially large anterior MI → >40% LV mass). Also: acute severe mitral regurgitation (papillary muscle rupture), ventricular septal defect, acute aortic regurgitation, end-stage cardiomyopathy, myocarditis, post-cardiotomy.

What the Nurse May See

Hemodynamic profile:

• Hypotension: SBP <90 mmHg or MAP <65 mmHg, or drop >30 mmHg from baseline.
• Low cardiac output: Tachycardia, weak pulses, narrow pulse pressure, cool/mottled extremities, delayed capillary refill.
• Elevated filling pressures: Pulmonary congestion (crackles, hypoxia, frothy sputum), JVD, hepatomegaly.
• End-organ hypoperfusion: Altered mental status, oliguria (<0.5 mL/kg/hr), rising lactate, rising creatinine.

Key distinction from other shock types:

• Hypovolemic: Low filling pressures (flat JVD, dry), usually responds to fluids.
• Distributive (septic): Warm extremities (early), bounding pulses, wide pulse pressure, low SVR.
• Cardiogenic: Elevated filling pressures (JVD, crackles), cold extremities, narrow pulse pressure, high SVR.

Tests and Monitoring

• Echocardiogram: EF, wall motion, mechanical complications (papillary muscle, VSD, tamponade).
• Invasive hemodynamics (PA catheter): Cardiac output/index, PCWP (wedge), PAP, CVP, SVR.
• Lactate: Rising = inadequate oxygen delivery. Trend is key.
• Mixed venous oxygen saturation (SvO2): Low (<60%) = increased oxygen extraction (inadequate delivery). Continuously falling = worsening.
• End-organ function: Renal (BUN/Cr, urine output), hepatic (LFTs), neurologic (mental status).

Nursing Priorities

1. ABC assessment: May need intubation (respiratory failure from pulmonary edema, altered mental status). Mechanical ventilation also reduces oxygen consumption of respiratory muscles.

1. Hemodynamic optimization:
   • Inotropes (dobutamine, milrinone): Increase contractility. Milrinone also vasodilates → reduces afterload. Monitor for hypotension and arrhythmias.
   • Vasopressors (norepinephrine): Increase SVR to maintain perfusion pressure. But they increase afterload → increase myocardial oxygen demand.
   • Afterload reduction (nitroprusside if BP allows): Reduces ventricular workload.
   • This is the tightrope: you need enough pressure to perfuse but not so much afterload that the failing heart cannot eject.

1. Fluid management: Unlike other shock types, fluids may worsen cardiogenic shock (increase filling pressures, worsen pulmonary edema). However, RV infarction is volume-dependent. Assessment is key.

1. Mechanical support (if available): Intra-aortic balloon pump (IABP), Impella, ECMO. Bridge to recovery, transplant, or LVAD.

1. Continuous monitoring: HR, BP (arterial line), SpO2, urine output (hourly), lactate, cardiac rhythm, PA catheter parameters.

1. Family communication: Cardiogenic shock has high mortality. Keep family informed. Facilitate provider-family discussions about goals of care.

Red Flags