Lippincott Nursing Pocket Card - March 2021

Hemodynamic Monitoring

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What is hemodynamic monitoring?

Hemodynamic monitoring is a mainstay in the care of critically ill patients. It involves using invasive and non-invasive methods to provide information about pump effectiveness, vascular capacity, blood volume and tissue perfusion. The precise data obtained from hemodynamic monitoring helps to identify the type and severity of shock (cardiogenic, hypovolemic, distributive, or obstructive). When paired with clinical evaluation, hemodynamic monitoring is helpful in guiding the administration of fluids, in selecting and titrating vasoactive drugs, and in deciding when mechanical support might be necessary to treat refractory shock. It allows for evaluation of the effectiveness of treatment in real time. 

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The Cardiac Cycle & Key Definitions

A thorough understanding of the cardiac cycle and key definitions provide a foundation for the interpretation of hemodynamics.

The Cardiac Cycle
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Key Definitions
  Definition Clinical Considerations
Cardiac output (CO)
 
The volume of blood pumped through the heart per minute (L/min) Normal range is 4-8 L/minute.
 
Calculation
CO = Stroke Volume (SV) X Heart Rate (HR)
Cardiac index (CI)
 
CO adjusted for body surface area (BSA) Normal range is 2.8-4.2 L/min/m2.

Calculation
CI = CO/BSA
Stroke volume (SV) The volume of blood pumped out of the left ventricle (LV) per heart beat Normal range is 60-90 mL.

Calculation
SV = End-diastolic volume (EDV) – end-systolic volume (ESV)
End diastolic volume (EDV) Volume of blood in the right ventricle (RV) or LV at the end of diastole (filling) Normal is about 120 mL.
End systolic volume (ESV) Volume of blood in the RV or LV at the end of systole (contraction) Normal is about 50 mL.
Preload The amount of ventricular stretch at the end of diastole Also known as the left ventricular end-diastolic pressure (LVEDP)
Afterload The amount of resistance the heart must overcome to open the aortic valve and push the blood volume out into the systemic circulation Also known as the systemic vascular resistance (SVR)
Contractility The ability of the heart to contract and generate force  
Central venous pressure (CVP)

The blood pressure in the vena cava and an estimate of right atrial pressure

Used to assess preload and volume status

Normal is 2-6 mm Hg.

Measuring Hemodynamics

Hemodynamic instability causes a mismatch between oxygen delivery and demand, leading to organ failure. Hemodynamic instability can often be managed with regular clinical examination and monitoring of vital signs (heart rate, blood pressure, oxygen saturation, and respiratory rate) and urine output.  However, when the patient does not improve or deteriorates further, invasive hemodynamic monitoring is needed to guide fluid management and vasopressor/inotropic support. 

Clinical Assessment
A clinical examination is the fastest and least invasive hemodynamic monitor available.
  • A patient with inadequate global perfusion often presents with signs of organ dysfunction, such as tachypnea, tachycardia, confusion, weak peripheral pulses, skin mottling, and oliguria.
  • Capillary refill time (CRT) can be rapidly tested and is the time required for blood flow (and color) to return to the distal capillaries after the release of fingertip compression sufficient to cause blanching of the skin (10 seconds of compression time). The upper limit of normal is 3 seconds in adults; a longer CRT indicates reduced capillary perfusion.
Non-invasive Monitoring
Electrocardiogram (ECG)
  • Heart rate is an important determinant of cardiac output (CO = HR X SV).
  • A 12-lead ECG confirms cardiac rhythm and provides baseline information on ST segments and T waves.
  • Continuous monitoring of heart rate, rhythm and ST segments allows early recognition of hypovolemia and myocardial ischemia.
  • Tachyarrhythmias are a common finding in certain shock states. Bradycardia and/or heart block may indicate cardiogenic shock.
Blood pressure (BP)
  • The definition of hypotension (low BP) is patient-specific and interpreted in the context of the patient’s usual BP.
  • Hypotension is a common feature of most shock states.
  • Mean arterial blood pressure (MAP) is an approximation of organ perfusion pressure.
  • Severely elevated BP, especially if acute, is associated with increased vascular resistance and may be associated with inadequate tissue perfusion, for example hypertensive encephalopathy or acute renal failure.
 Pulse oximetry (SpO2)
  • Continuous SpO2 monitoring enables rapid detection of even a small reduction in arterial oxygen saturation, which is an integral part of oxygen delivery.
  • The SpO2 signal is often inaccurate in the presence of altered skin perfusion. The inability to measure SpO2 is itself an indicator of abnormal peripheral perfusion.
 Echocardiography
  • An echocardiogram provides visualization of the cardiac chambers, valves, pericardium, and overall cardiac function.
  • It allows for measurement of left ventricular ejection fraction (LVEF) and estimates of SV and CO based on measurement of LV outflow tract (LVOT), LVOT velocity and heart rate.
 Fluid responsiveness
  • Fluid resuscitation is a critical component of the treatment of hemodynamically unstable patients. Although rapid optimization of volume status has been shown to improve outcomes, volume overload is associated with increased morbidity and mortality.
  • A fluid challenge is necessary to determine whether fluid administration will benefit the patient.
  • Fluid responsiveness is frequently defined as an increase in cardiac output (≥ 10% from baseline) with a fluid challenge (250-500 mL administered over 10-15 minutes).
  • An alternative to a fluid challenge is to perform a ‘passive leg raise’ maneuver. This produces an ‘autotransfusion’ of blood from the venous compartments in the abdomen and lower limbs.
    • Position the patient in the semi-recumbent position with the head and torso elevated at 45 degrees.
    • Obtain a baseline blood pressure measurement.
    • Lower the patient's upper body and head to the horizontal position and raise and hold the legs at 45 degrees for one minute.
    • Obtain subsequent blood pressure measurement.
    • The expected response to this maneuver in those that are fluid responsive is a 10% or greater increase in cardiac output (CO). Although not considered a validated measure, we often use blood pressure as a surrogate marker of CO in evaluating response to the PLR.
    • Only patients who are fluid responsive after a fluid bolus or passive leg raise should receive additional fluids.
 Invasive Monitoring
Intra-arterial blood pressure
  • Arterial cannulation (usually the radial artery) allows for accurate continuous blood pressure measurement. Arterial line BP monitoring is the standard of care for patients on vasopressor/inotrope infusions.
  • Arterial lines facilitate frequent blood draws for blood gases or other lab studies.
 Central venous pressure (CVP)
  • The CVP is the blood pressure in vena cava/right atrium; normal range is 2-6 mm Hg.
  • The CVP reflects right ventricular (RV) function and venous return to right side of heart.
  • It is measured via a catheter positioned in the vena cava.
 Pulmonary artery pressure (PAP)
  • PAP is the blood pressure in pulmonary artery; normal systolic PAP range is systolic 15-30 mm Hg and normal diastolic PAP is 5-15 mm Hg.
  • It may be measured during right heart catheterization or via introduction of a catheter into the pulmonary artery (i.e., Swan Ganz Catheter).
 Mixed venous oxygen saturation (SvO2)
  • SvO2 reflects the balance between oxygen delivery and oxygen consumption (VO2).
  • It depends on arterial blood saturation (SaO2), the balance between VO2 and CO, and hemoglobin (Hgb) levels.
    • Normal SvO2 is greater than or equal to 70% (drawn from a pulmonary artery catheter).
    • Central venous oxygenation (ScvO2) is normally greater than or equal to 65% (drawn from a central venous catheter).

Novel Cardiac Output Monitoring Devices

The gold standard for cardiac output monitoring is using periodic measurements derived from a pulmonary artery catheter (PAC). However, there are safety concerns with PACs (e.g., infection, pneumothorax, pulmonary artery rupture) and evidence suggests that there is no mortality benefit. Devices for minimally invasive cardiac output monitoring using arterial pressure tracings and pulse-contour analysis or chest bioreactance have been developed. Esophageal doppler monitoring utilizes a flexible trans-esophageal doppler ultrasound probe to estimate cardiac output and stroke volume.  These techniques perform better to monitor trends in cardiac output as opposed to providing absolute cardiac output values.

References:
Bridges, E. (2017). Assessing Patients During Septic Shock Resuscitation. American Journal of Nursing, 117(10), 34-40. https://www.doi.org/10.1097/01.NAJ.0000525851.44945.70

Bridges, E. (2013). Using Functional Hemodynamic Indicators to Guide Fluid Therapy. American Journal of Nursing, 113(5), 42-50. https://www.doi.org/10.1097/01.NAJ.0000429754.15255.eb

Clement, R.P., Vos, J.J. & Scheeren, W.L. (2017). Minimally Invasive Cardiac Output Technologies in the ICU: Putting It All Together. Current Opinion in Critical Care, 23(4), 302-309. https://www.doi.org/10.1097/MCC.0000000000000417

Kerstens, M.K., Wijnberge, M., Geerts, B. F., Vlaar, A.P., & Veelo, D.P.  (2018). Non-invasive cardiac output monitoring techniques in the ICU. Netherlands Journal of Critical Care, 26(3), 104-110.

Marino, P. (2014). The ICU Book, 4th edition. Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia.

Mikkelsen, M.E, Gaieski, D.F., & Johnson, N.J. (2020, September 28). Novel Tools for Hemodynamic Monitoring in Critically Ill Patients with Shock. UpToDate. https://www.uptodate.com/contents/novel-tools-for-hemodynamic-monitoring-in-critically-ill-patients- with-shock

Silvestry, F. (2020, July 15). Pulmonary Artery Catheterization: Interpretation of Hemodynamic Values and Waveforms in Adults. UpToDate. https://www.uptodate.com/contents/pulmonary-artery-catheterization-interpretation-of-hemodynamic-values-and- waveforms-in-adult