Exam

Cardiac Output

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Cardiac Output, Cardiac Index, Stroke Volume, Stroke Index, Clinical Assessment of Cardiac Output, Cardiac Function

  • Definitions
  1. Cardiac Output (CO)
    1. Quantity of blood pumped per minute through the aorta and into the peripheral circulation
    2. Cardiac Output is proportional to (arterialPressure / totalPeripheralResistance)
    3. CO = SV * HR
      1. Where SV = Stroke Volume
      2. Where HR = Heart Rate
    4. Normal Adult
      1. Range: 4-8 L/min (typical 70 kg male = 5.25 L/min)
  2. Cardiac Index (CI)
    1. Average stroke output of heart per minute (Cardiac Output) adjusted for body surface area
    2. CI=CO/BSA
      1. Where CO = Cardiac Output
      2. Where BSA = Body Surface Area
    3. Normal Adult
      1. Range: 2.4 - 4 L/min/m2 (60% of csardiac output in the normal, average sized adult)
  3. Stroke Volume (SV)
    1. Volume of blood pumped from the heart in one cycle of diastole and systole
    2. Stroke Volume is affected by Preload, contractility and Afterload
    3. SV = EDV - ESV
      1. Where EDV = End-diastolic volume
      2. Where ESV = End-systolic volume
    4. Normal Adult
      1. Range: 55-100 ml (typical 70 kg male = 70 ml)
  4. Stroke Index
    1. Average stroke output of heart per cycle (Stroke Volume) adjusted for body surface area
    2. SI = CI/HR
      1. Where CI = Stroke Index
      2. Where HR = Heart Rate
    3. Normal Adult
      1. Range: 20-40 ml/m2
  • Physiology
  1. Stroke Volume components
    1. Preload (based on venous return and ventricular compliance)
      1. End-diastolic volume (EDV)
    2. End-systolic volume (ESV) depends on ejection fraction (percentage of EDV ejected from left ventricle)
      1. Ventricular Contractality
        1. Force of ventricular contraction or inotropy
      2. Ventricular Afterload
        1. Force against which the left ventricle pumps
  2. Cardiac Output components
    1. Product of Heart Rate and Stroke Volume
    2. Heart Rate is the first compensatory mechanism to increase Oxygen Delivery to the tissues
  • Diagnostics
  • Clinical Assessment of Cardiac Output (and SV, Preload, Afterload and Contractility)
  1. Heart Rate and rhythm
    1. Palpated pulse
    2. Pulse Oximetry
    3. Telemetry or Electrocardiogram
  2. Right Preload
    1. Central Venous Pressure
    2. IVC Ultrasound for Volume Status (Caval Aorta Index)
  3. Left Preload
    1. Symptoms (Orthopnea or Dyspnea on exertion)
    2. Signs (pulmonary edema, rales)
    3. Imaging (Lung Ultrasound)
  4. Right Afterload
    1. Mean pulmonary artery pressure or wedge pressure
  5. Left Afterload
    1. Mean arterial pressure
  6. Contractility
    1. Echocardiogram (ejection fraction, Stroke Volume)
  7. Cardiac Output
    1. Pulmonary artery catheter
    2. Arterial catheter (arterial waveform analysis)
    3. Esophageal doppler (descending aorta flow)
  • Resources
  • References
  1. Killu and Sarani (2016) Fundamental Critical Care Support, p. 93-114
  2. Marino (2014) ICU Book, 4th Ed Wolters-Kluwer p. 144-6