Cardiogenic Shock: A Study Notes

Definition

• Cardiogenic shock occurs when the heart fails to pump enough blood to meet the body’s perfusion needs.

• The problem lies within the heart itself --not from a loss of blood volume.

Pathophysiology

• Primary issue: Decreased cardiac output (CO) → ↓ tissue perfusion → cellular hypoxia → organ failure.

• Cardiac output = Heart rate × Stroke volume (SV)

  • Normal CO: 4–8 L/min

  • Stroke Volume (SV) determined by:

    • Preload: Ventricular stretch at end-diastole

    • Afterload: Pressure the ventricle pumps against

    • Contractility: Strength of ventricular contraction

Causes

1. Systolic Dysfunction (contraction problem):

• Acute Myocardial Infarction (AMI) — especially involving the left ventricle.

• Myocardial ischemia → muscle cell death → ↓ contractility → ↓ stroke volume.

2. Diastolic Dysfunction (filling problem):

• Cardiac tamponade (fluid around the heart compresses chambers)

• Restrictive cardiomyopathy

3. Electrical or Structural Issues:

• Dysrhythmias

• Valvular defects (e.g., mitral or aortic regurgitation)

• Septal defects

Hemodynamic Concepts

Term	Normal	Cardiogenic Shock
CO	4–8 L/min	↓
Cardiac Index (CI)	2.5–4 L/min/m²	< 2.2 L/min/m²
Pulmonary Capillary Wedge Pressure (PCWP)	4–12 mmHg	> 18 mmHg
Central Venous Pressure (CVP)	2–8 mmHg	↑ (backflow)
Systemic BP	> 90 mmHg	↓ (< 90 mmHg)

Clinical Manifestations

Cardiac:

• Hypotension (SBP < 90 mmHg)

• Weak peripheral pulses

• Chest pain (poor coronary perfusion)

Respiratory:

• Pulmonary edema → dyspnea, crackles, tachypnea

• ↓ O₂ saturation

Neurological:

• Confusion, agitation (↓ cerebral perfusion)

Renal:

• ↓ Urinary output (< 30 mL/hr)

• ↑ BUN, ↑ Creatinine (↓ renal perfusion)

Skin:

• Cold, clammy, pale

• Delayed capillary refill (> 2 seconds)

Diagnostics

• Cardiac enzymes: ↑ Troponin, ↑ BNP

• Chest X-ray: Pulmonary edema

• Serum lactate: > 4 mmol/L (anaerobic metabolism → metabolic acidosis)

• ABG: ↓ pH (< 7.35)

Clinical Interventions

Goals:

1. Restore perfusion to myocardium

2. Improve cardiac output

3. Support oxygenation and ventilation

Monitor:

• Hemodynamic values (CO, PCWP, CVP)

• Urine output (> 30 mL/hr)

• LOC, vital signs, ECG, O₂ sat

• Skin color, temperature, cap refill

Medical Management

1. Reperfusion

• Coronary angioplasty / Stent placement for MI

2. Medications

Drug Class	Examples	Action	Key Notes
Diuretics	Furosemide (Lasix)	↓ pulmonary congestion	Monitor K⁺ (risk of hypokalemia), BP
Vasopressors	Norepinephrine	↑ preload & BP via vasoconstriction	Monitor perfusion & ischemia
Positive Inotropes	Dobutamine, Dopamine	↑ contractility → ↑ CO	Dobutamine may ↓ BP; dopamine ↑ HR
Vasodilators	Nitroglycerin, Nitroprusside	↓ afterload → easier ejection	Risk: hypotension
Fluids	NS cautiously	Restore perfusion only if hypovolemic	Avoid overload (pulmonary edema)

Advanced Support Devices

Intra-Aortic Balloon Pump (IABP)

• Catheter with balloon in aorta that inflates/deflates with cardiac cycle:

  • Inflates during diastole → ↑ coronary perfusion

  • Deflates during systole → ↓ afterload, assists ejection

• Goal: Improve CO and myocardial oxygen supply.

Key Lab & Monitoring Values

Parameter	Normal	Cardiogenic Shock
CI	2.5–4 L/min/m²	< 2.2
PCWP	4–12 mmHg	> 18
CVP	2–8 mmHg	Elevated
MAP	≥ 65 mmHg	Decreased
Urine Output	≥ 30 mL/hr	Decreased
Lactate	< 2 mmol/L	> 4

Summary

• Cardiogenic shock = Pump failure.

• Cardiac output drops, organs are not perfused, and pulmonary congestion develops.

• Management focuses on:

  • Restoring coronary perfusion

  • Enhancing CO (inotropes, vasopressors)

  • Reducing workload (diuretics, vasodilators)

  • Supporting ventilation and monitoring hemodynamics