Cardiac output monitoring


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Cardiac output monitoring

  1. 1. Cardiac output monitoring Dr Karen Orr ST6 anaesthetics/ICM Altnagelvin ICM study day 7/11/13
  2. 2. Cardiac output • Volume of blood ejected from the left ventricle per minute • Depends on preload, contractility, heart rate and afterload • CO = HR x SV • MAP = CO x SVR
  3. 3. Methods of measuring CO • Clinical • Minimally-invasive • Invasive
  4. 4. Clinical • Assess adequacy rather than "numbers" • End organ perfusion • • Kidney (UO) • Tissues (lactate) • • Brain (confusion, altered consciousness) Skin (CRT) BP correlates poorly...but...narrowed pulse pressure may have some value
  5. 5. • Increased intrathoracic pressure during inspiration • Reduced venous return therefore reduced SV and BP • More pronounced during MV
  6. 6. Minimally invasive
  7. 7. Efficacy compared to PAFC?????
  8. 8. Fick principle • Amount of a substance taken up by an organ per unit time is equal to the arterial minus the venous concentration multiplied by blood flow • CO = VCO2/ CaCO2- CvCO2 • CO2 production can be measured via sensors on breathing circuit • CO2 content in mixed venous and arterial blood • Reduced accuracy in sicker patients, severe chest trauma, intra pulmonary shunt, low MV and high CO
  9. 9. Thoracic bio-impedance • Ejection of blood from LV into aorta is associated with changes in electrical impedance of the thoracic cavity • High frequency, low voltage AC is applied • Adv- minimally invasive • Correlates relatively well in healthy people but not in unwell patients (0.29L/min) • Reduced reliability in advanced age, perioperative fluid shifts, pulmonary oedema, MI, patient movement and electrical interference
  10. 10. Oesophageal Doppler • Continuous, real time monitoring • Shift in frequency of reflected sound waves changes proportionally with change in velocity • V = 2 x transmitted frequency/ velocity of US in blood x Doppler shift x cosine theta
  11. 11. Assumptions • 70% of blood enters descending aorta • Blood flow is uniform and maximal • Cross sectional area is constant (calculated using formula dependent on age, sex and height)
  12. 12. Measured variables • CO • SV (stroke distance x aortic root diameter) • Stroke distance is AUC x HR • FTc (corrected flow time): indicates preload • Peak velocity: indicates contractility • HR
  13. 13. Contraindications • Oesophageal varices • IABP • Severe coarctation • Known oesophageal pathology
  14. 14. Limitations • Intubated patients • Probe must be as close as possible to parallel to aorta • Operator dependent • Learning curve for operator • Probe displacement
  15. 15. Evidence for use • Reduced post operative complications, cost, CVC use and hospital LOS when used in high risk surgical patients • No change in mortality in either surgical or ICU pts • Recommended by NICE for high risk surgical pts
  16. 16. • Small study (12 pts) comparing PAFC and OD in adult sepsis in ICU: good correlation with CI but poor with preload and SVR
  17. 17. Pulse contour analysis • Relate the contour of the arterial pressure waveform to SV and SVR • An algorithm is use to determine CO and produce a continuous readout • Provide info on CO/ SVR etc but also SVV as a measure of fluid responsiveness • SVV is the difference between max and min SV across the respiratory cycle
  18. 18. PiCCO • Thermistor tipped femoral arterial line • Standard central line is used to calibrate using thermodilution • Correlates strongly with PAFC readings in both controls and patients with abnormal physiology (less than 0.29L/min)
  19. 19. FloTrac • Standard arterial catheter • Algorithm is used based on age, height, gender, weight and waveform characteristics • No external calibration • Conflicting evidence for accuracy compared with PiCCO and PAFC • One study showed CO underestimated by up to 2L/min in 40% of readings • Main advantage is ease of use
  20. 20. LiDCO • Pulse power analysis (based on law of conservation of mass) • Assumes that net power equates to net flow • Standard arterial line +/- CVL • Calibrated using lithium dilution • Good correlation with PAFC across a range of values (error of <0.11L/min) • Contraindicated in chronic lithium use, recent NDNMB, early pregnancy
  21. 21. Limitations • Rely on optimal arterial signal • Arrhythmias • IABP • Severe aortic regurg • Changes in SVR
  22. 22. Invasive
  23. 23. Pulmonary artery flotation catheter • Dye dilution (known quantity of indocyanine green with timed samples) • Thermodilution (continuous- heated coil or intermittentknown volume of cold saline injected via RA with distal thermistor at the tip) • PACWP (surrogate for LVEDP) • Modified Stewart Hamilton equation
  24. 24. Limitations • Right and left ventricular output may differ in the presence of an cardiac shunt • Tricuspid or pulmonary valve regurg may cause underestimation of CO • MV causes variation in CO depending on point in respiratory cycle • Tip of catheter in west zone 1 or 2 • Mitral stenosis
  25. 25. Advantages • Right and left sided pressures • SvO2 • Core temperature • Multi lumen infusion port • Provides angiographic access
  26. 26. Complications • Associated with CVL (arterial puncture, nerve injury, embolism, pneumothorax) • Associated with catheterisation (arrhythmias, RV rupture) • Associated with prolonged catheter insertion (PA rupture, pulmonary infarction, thrombosis, stenosis) • PACMAN trial 10% incidence, ESCAPE trial 5%
  27. 27. The evidence • No effect on mortality, LOS, or cost of care in either general ICU or high risk surgical patients • No effect on surgical outcomes when used preoperatively to optimise haemodynamics
  28. 28. What about cardiac surgery? • Increased mortality and end organ complications in propensity matched obs study • Authors recognise need for RCT
  29. 29. Device comparison