Hemodynamically unstable patients require emergency care or admission to the intensive care unit. This lesson will discuss the tools and methods required for monitoring hemodynamic instability.
What to Monitor for Hemodynamic Instability
Todd is a sixty-year old man who is admitted to the intensive care unit (ICU) for a change in mental status and possible shock.
He is being monitored closely for any signs of hemodynamic instability so he can be treated quickly.Todd’s son is present in the room and asks the nurse, Carla, about his condition.Carla begins to explain to Todd’s son about the complications of hemodynamic instability. Hemodynamic instability, or unsteady blood pressure, happens when there is a decrease in blood pressure that leads to poor blood flow to organs and organ failure, or an inadequate cardiac output.Carla is continuously monitoring Todd’s heart rate, blood pressure, respiration, urine output, central venous pressure, and venous oxygen saturation.
Todd’s blood pressure has been slowly dropping, so the doctor wants to begin monitoring him for hemodynamic instability to make sure he does not go into organ failure. Other signs of hemodynamic instability consist of:
- Change in mental status
- Decreased urinary output
- Slow capillary refill
- Abnormal heart rate
- Respiratory distress
Hemodynamic instability monitoring can also help determine which type of shock is present in a patient. The four different types of shock are hypovolemic, cardiogenic, obstructive, and distributive.
How is Hemodynamic Instability Monitored?
The doctor is trying to determine the best way to monitor Todd’s hemodynamic instability because there are many invasive, less invasive and non-invasive methods. The most important parts of monitoring is to identify:
- Cardiac output – the measure of blood volume pumped by the heart per minute.
- Pulmonary arterial occlusion pressure – pressure in the arterial system when a catheter is in the branch of one of the pulmonary arteries.
- Pulmonary arterial pressure – pressure in the blood vessel that moves blood from the heart to the lungs.
- Mixed venous oxygen saturation – the amount of oxygen in the blood that returns to the right side of the heart.
- Stroke volume variation – the amount of blood pumped from the left ventricle during each heart beat.
- Extravascular water – water in the lungs.
The doctor begins to look over the various types of monitoring choices so she can make a decision on how she wants to monitor Todd’s hemodynamic status.
She reviews whether the techniques are calibrated or non-calibrated.
- Calibrated techniques involve adjustments to the equipment to ensure accuracy of the measurements.
- Non-calibrated techniques use patient demographic factors to adjust measurements.
Hemodynamic Instability Monitoring Techniques
While the pulmonary artery catheter is the considered the gold standard for measuring hemodynamic instability, it carries the highest risk of complications.
A pulmonary catheter is placed through the subclavian, jugular, or femoral artery and goes from the right atrium to the right ventricle of the heart until it reaches the pulmonary artery.The following table summarizes various monitoring techniques.
|Pulmonary artery catheter||Invasive/calibrated||Provides direct measurements in the right atrium and pulmonary artery but has risks since it is invasive|
|Transpulmonary thermodilution (PiCCO, VolumeView/EV1000)||Less invasive/calibrated||Provides intermittent or continuous measurement of cardiac output but needs an arterial or central line|
|Transpulmonary dye dilution (LiDCO)||Less invasive/calibrated||Provides intermittent or continuous measurement of cardiac output but needs an arterial or central line|
|Ultrasound flow dilution (COstatus)||Less invasive/calibrated||Continuously measures cardiac output and can detect shunts in the heart|
|Pulse contour and pulse pressure analysis (FloTrac, Vigileo, ProAQT, Pulsioflex, LiDCOrapid, pulseCO, Most Care, PRAM||Less invasive/non-calibrated||Provides continuous measurement of cardiac output but can be inaccurate in unstable patients or with patients on vasoactive medication|
|Respiratory derived cardiac output monitoring system (NiCO)||Less invasive/non-calibrated||Does not require intravascular monitoring but is limited to use on sedated patients on ventilation|
|Transesophageal echocardiogram||Less invasive/needs person to operate||Provides images of cardiac anatomy and blood flow in real time with minimal risks|
|Esophageal Doppler||Less invasive/needs person to operate||Provides information about afterload and cardiac output in real time but has a risk of dislocation|
|Transthoracic echocardiogram||Non-invasive/needs person to operate||Provides images of the cardiac anatomy and direct cardiac output but is difficult to get accurate information in critically ill patients|
|Non-invasive pulse contour system (T-line, ClearSight, Nexfin, Physiocal, CNAP, VERIFY||Non-invasive/non-calibrated||Easy to use but is not as accurate as other techniques|
|Bioimpedance||Non-invasive/non-calibrated||Simple to use while providing cardiac output measurements and detects fluid overload|
|Estimated continuous cardiac output (esCCO)||Non-invasive/non-calibrated||Estimates cardiac output by using variables but can be inaccurate|
|Ultrasonic cardiac output monitoring system (USCOM)||Non-invasive/non-calibrated||Easy to use with little risk but only provides an estimated cardiac output measurement|
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