Cardiac Output Monitoring - 6 How to use Wrexham s Cardiac Output Monitors. Wrexham Maelor Critical Care Version 02.05.16
Introduction Types of Devices: NICOM - Cheetah Oesophageal Doppler +/- Pulse Contour Analysis PiCCO LiDCO ECHO How to set device up: NICOM - Cheetah Oesophageal Doppler +/- Pulse Contour Analysis PiCCO LiDCO ECHO Management of Hypotension Using the right tool for the job!
Introduction: Shock comes in many guises and varies in severity. It is often not sufficient to use blood pressure as a surrogate for blood flow, especially when evidence of inadequate end organ delivery becomes obvious e.g. high lactate. HEART RATE PRELOAD CARDIAC OUTPUT CONTRACTILITY AFTERLOAD Types of Devices We are very fortunate on Critical Care to have access to a number of cardiac output devices. Some are more invasive than others. Some have different output values, but most are trying to provide surrogates for the above diagram. The advice with all is to observe and target the dynamic response to a system challenge (e.g. fluid, inotrope, vasopressor etc) as opposed to absolute figures.
Nicom Cheetah: The CHEETAH NICOM provides continuous, non-invasive hemodynamic monitoring it is based on a technology known as Bioreactance, essentially the use of time delay, or phase shifts in an alternating electrical current as it passes through the thorax during different phases of the cardiac cycle. Bioreactance technology is not the same as bioimpedance, an older technology that has certain limitations when used for assessing fluid responsiveness. The output data on the screen informs you of Cardiac Output (+indexed), Heart Rate, Stroke Volume (+indexed) Stroke Volume Variability (%) and TPR (+ indexed)
As stated earlier, a clinical impression can be made from the absolute values, however trends are more reliable. Deltex Oesophageal Doppler: This is also classed as a non-invasive continuous cardiac output monitor (although both those points can be debated!) It measures blood flow velocity in the descending aorta using a thin flexible ultrasound probe which is placed in the oesophagus via either the nose or the mouth. Calculations on blood velocity are made based on the Doppler Principle (a shift in ultrasound frequency occurs when the sound wave is reflected back from moving RBCs, with the shift in frequency proportional to the velocity of the blood flow). The measurement is then combined with the cross-sectional area of the descending aorta (using a nomogram based on age, weight and height) to give a quantitative output for stroke volume. The device can then be slaved to the arterial line to give continuous SV analysis. Obtaining an adequate signal can be difficult. Typical values obtained are: Cardiac Output (+indexed), Heart Rate, Stroke Volume (+indexed) Stroke Volume Variability (%) Flow Time corrected (FTc), Stroke Distance (SD) and Peak Velocity (PV).
Stroke distance (SD) is the distance in cm that a column of blood moves along the aorta with each contraction of the left ventricle of the heart and similar to stroke volume and is not often used in analysis. Flow time corrected (FTc) is the duration of flow during systole corrected for heart rate.typical values for FTc in a healthy adult are 330-360 ms. A low value for FTc may indicate hypovolaemia, or other causes of increased afterload. A high value for FTc may be seen in patients with low afterload. Peak velocity (PV) is the highest blood velocity detected during systole, and may be used as an indication of left ventricular contractility. Typical values for PV are: 90-120 cm/s for a 20 year old; 70-100 cm/s for a 50 year old; and 50-80 cm/s for a 70 year old. elearning: Iphone App: https://itunes.apple.com/gb/app/deltex-guide/id900086442?mt=8 Deltex Elearning : http://deltexmedical.education/en/ Oesophageal Doppler Workbook
PiCCO PiCCO is a cardiac output monitor that combines pulse contour analysis and calibrated with a transpulmonary thermodilution technique. It requires the presence of a central line and a PiCCO catheter which is a modified arterial line with a thermistor tip, this unfortunately requires placement of this specialised arterial line into the femoral artery (brachial arterial line is also available but not in our ICU). The calibration uses the change in blood temperature detected at the tip of the PiCCO Catheter (femeral arterial line) over time caused by the rapid injection of cold 0.9% saline into the blood via the central line. From this data the following parameters are derived: Cardiac Output (CO) Cardiac Index (Ci) Stroke Volume (SV) Stroke Volume index (SVi) Global end-diastolic volume (GEDV) (and GEDVi) - Blood in all 4 chambers of the heart Global Ejection Fraction - The ratio of 4 stroke volumes divided by GEDV Intrathoracic blood volume (ITBV) - Volume in the heart + pulmonary vessels Extravascular Lung Water (EVLW) - Water content of the lungs. PiCCO make a decision making algorithm based on these findings:
As with all the cardiac output monitoring machines the most useful information can be gained from the continuous analysis in this case, arterial pulse contour analysis which provides continuous beat-by-beat parameters obtained from shape of arterial pressure wave. Giving continuous: Pulse continuous cardiac output (PCCO) Systemic vascular resistance (SVR) Stroke volume variation (SVV) (dpmax slope of pressure vs time trace = closely approximates contractility of LV) More on the PiCCO including how to set it up on the Phillips Monitor can be found here. LiDCO Unity: Can be used in a number of different modes: Non-invasive Minimally invasive Fully Calibrated Although this system can utilise dual finger cuffs for non-invasive cardiac output monitoring, the two real options are a continuous uncalibrated pulse pressure analysis from a arterial line or a lithium dilution calibrated pulse pressure analysis. It comes as a separate monitor and uses a smart card to hold patients data and time limit the machine. Advantages over the PiCCO is that it can use the existing arterial line and central line for calibration and pulse analysis. The graphical displays range from complex to simple, and information provided includes: Stroke Volume Variation (SVV) Heart Rate Variation (HRV) Cardiac Output (CO) Cardiac Index (Ci) Systemic Vascular Resistance and index (SVR & SVRi)
Echocardiography: Echo gives a quantitative and qualitative view of both right and left sided cardiac function, preload and afterload, you can also measure the true stroke volume and cardiac output. For more information or if interested consider enrolling on the FICE (Focused intensive Care Echo) How to set devices up: Cheetah: PiCCO Please see accompanying document.
LiDCO - in development ECHO - in development Managing the Hypotensive Patient: There are many ways to approach a patient, and on the whole a fluid challenge may not be harmful. Fluid however does have the potential to be every bit has harmful as any other drug. So it is vital to observe the response to a challenge. Many algorithms have been adapted, but essentially for non cariogenic shock a reasonable starting point is initial 20 ml/kg of crystalloid, if MAP is still below 65 mmhg then start Noradrenaline, if this increases to above 0.15 ug/kg/min (about 10ml/hr) then Cardiac Output Monitoring is indicated. An example of Paul Marik s guide to fluid management in CHEST 2014.