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Cardiovascular Hemodynamics

Cardiovascular Hemodynamics. Michael J. Lazar, MD. The Big Picture. What is our goal in the ICU for cardiac surgery patients? End-organ perfusion Keeping the blood pressure high enough to perfuse the tissues Keeping the delivery of oxygen adequate Oxygen Consumption Oxygen Delivery.

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Cardiovascular Hemodynamics

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  1. Cardiovascular Hemodynamics Michael J. Lazar, MD

  2. The Big Picture • What is our goal in the ICU for cardiac surgery patients? • End-organ perfusion • Keeping the blood pressure high enough to perfuse the tissues • Keeping the delivery of oxygen adequate • Oxygen Consumption • Oxygen Delivery Cardiac Inotropes

  3. Topics of the Day • Blood Pressure • Cardiac Output- why do we really care • What is and how do you fix Oxygen Delivery • When, why and how to use pressors • What medications do cardiac patients go home on Cardiac Inotropes

  4. General Range of Blood Pressure • Postop SBP < 130 secondary to concerns for suture lines and bleeding • Aneurysms SBP around 100 • Preop levels +/- 10% • Gradual decrease to “normal” levels • Why do we care? Cardiac Inotropes

  5. Blood Pressure and Flow • Organs are able to autoregulate blood flow within a given range of pressures • Outside this range they loose the ability to control their local environment and depend entirely on the systemic pressure • The brain and kidneys are particularly sensitive to alterations in blood pressure Cardiac Inotropes

  6. Obviously pressure is only part of the story • The body will maintain blood pressure at all costs • When cardiac output is low, pressure is increased by peripheral vasoconstriction • This allows a driving pressure to certain organs but reduces flow to others • How does this occur? Cardiac Inotropes

  7. Distribution of Cardiac Output • Increases in cardiac output are regulated by individual organs • Within limits the flow can be modified by local changes in vascular tone • At extremes of blood pressure, both high and low, local regulation is ineffective. Cardiac Inotropes

  8. Flow By Organ System Organs vary in range of blood flows and these are generated by adjustments in the tone of the resistance arteries and arterioles of the organ vessels Brain Heart Gut Renal Muscle Skin Bone ml/min per 100 g -------------------------------------------------------------------------------- Basal 60 75 100 400 5 10 3 Maximal 120 400 150 420 200 350 5 Minimal 55 70 30 30 3 3 2 Several patterns: high basal, little further at max: kidney low basal, high max: skeletal muscle, skin basal near minimal: heart, brain Cardiac Inotropes

  9. Detecting a problem • blood pressure • compensatory sympathetic stimulation • tachycardia • sweating • vasoconstriction • organ dysfunction • mental state • urine output • tissue hypoxia • pH • lactate Cardiac Inotropes

  10. Expected values following cardiac surgery Mean arterial pressure (MAP) 70–95 mm Hg Systolic blood pressure (SBP) 90–140 mm Hg Right atrial pressure (RAP) 5–15 mm Hg Left atrial pressure (LAP) 5–15 mm Hg Cardiac index (CI) = CO/BSA 2.0– 4.4L/min Systemic vascular resistance (SVR) SVR = (MAP - RAP/CO) x 80 SVRI = (MAP - RAP / CI) x 80 1400–2800 dyn·s·cm5/m2 Cardiac Inotropes

  11. Topics of the Day • Blood Pressure • Cardiac Output- why do we really care? • What is and how do you fix Oxygen Delivery • When, why and how to use pressors • What medications do cardiac patients go home on? Cardiac Inotropes

  12. Oxygen Delivery • The body needs oxygen to live • Oxygen delivery is the body’s capacity to deliver this oxygen • The delivered oxygen must be more than the oxygen consumed • SVO2 as the gold standard for delivery consumption mismatch • Ideally we would rather increase oxygen delivery rather than decrease consumption -- How? Cardiac Inotropes

  13. Oxygen Delivery (DO2) Cardiac Output (CO) Oxygen Content Oxygen Delivery Cardiac Inotropes

  14. Oxygen Delivery DO2 = Oxygen Content x Cardiac Output =(1.38 x Hgb x SaO2 + Pa02 x .0031) x HR x SV x 10 Things to fix : • Hemoglobin • Saturation • Cardiac Output Cardiac Inotropes

  15. Oxygen Delivery (DO2) Cardiac Output (CO) Oxygen Content Heart Rate (HR) Stroke Volume (SV) Hemoglobin (Hgb) Hemoglobin Saturation (PaO2) Oxygen Delivery Cardiac Inotropes

  16. Oxygen Content • Hemoglobin – Transfuse to ≈ 10 g/dL • Most efficient delivery of oxygen through capillary beds • pAO2 contributes little to oxygen delivery • Oxygen Saturation ≈ 100% • Concern for oxygen toxicity • Increased PEEP can decrease CO (best PEEP) Cardiac Inotropes

  17. Oxygen Delivery (DO2) Cardiac Output (CO) Oxygen Content Heart Rate (HR) Stroke Volume (SV) Hemoglobin (Hgb) Hemoglobin Saturation (PaO2) Importance of Hemodynamics Cardiac Inotropes

  18. Cardiac Output (CO) Heart Rate Stroke Volume Preload Contractility Afterload Importance of Hemodynamics Cardiac Inotropes

  19. The Starling Curve • Different lines represent different contractile states • Volume status moves the patient along each line Cardiac Inotropes

  20. How do we measure LV preload? Wedge Pressure • The wedge is an estimate of the End Diastolic Pressure of the Left Ventricle • This is in turn an estimate of the End Diastolic Volume of the LV • This is the preload from the startling curve. Cardiac Inotropes

  21. The Gold Standard • TTE – Transthoracic echocardiogram • TEE – Transesophageal echocardiogram • Direct visualization of the Left Ventricle Cardiac Inotropes

  22. Cardiac Inotropes

  23. Mitral Regurgitation Cardiac Inotropes

  24. Aortic Stenosis Cardiac Inotropes

  25. Cardiac Output (CO) Heart Rate Stroke Volume Preload Contractility Afterload Importance of Hemodynamics Cardiac Inotropes

  26. The Starling Curve • Afterload is the force the heart beats against • No blood is ejected until vascular resistance is overcome • As afterload is reduced, more of the cardiac energy is used to eject blood. Cardiac Inotropes

  27. How do we measure Afterload? • Systemic vascular resistance • SVR = (MAP - RAP/CO) x 80 • This is a calculated number depends on each of the parameters of the equation. Cardiac Inotropes

  28. Cardiac Output (CO) Heart Rate Stroke Volume Preload Contractility Afterload Importance of Hemodynamics Cardiac Inotropes

  29. Topics of the Day • Blood Pressure • Cardiac Output- why do we really care • What is and how do you fix Oxygen Delivery • When, why and how to use pressors • What medications do cardiac patients go home on Cardiac Inotropes

  30. Commonly Used Postoperative Medications Dopamine Cardiac Inotropes

  31. Commonly Used Postoperative Medications Epinephrine Cardiac Inotropes

  32. Commonly Used Postoperative Medications Norepinephrine Cardiac Inotropes

  33. Commonly Used Postoperative Medications Phenylephrine Cardiac Inotropes

  34. Commonly Used Postoperative Medications Milrinone Cardiac Inotropes

  35. Commonly Used Postoperative Medications Nitroprusside Cardiac Inotropes

  36. Commonly Used Postoperative Medications Nitroglycerin Cardiac Inotropes

  37. Commonly Used Postoperative MedicationsCalcium Cardiac Inotropes

  38. Commonly Used Postoperative Medications Triiodothyronine Cardiac Inotropes

  39. Hmmm • That’s way too much information to remember • Lets look at how these drugs work Cardiac Inotropes

  40. Alpha receptors • alpha1 receptors: • post synaptic cardiac - stimulation causes significant increase in contractility without an increase in rate • effect more pronounced at low heart rates • slower onset and longer duration than beta1 response • alpha2 receptors: • presynaptic in heart and vasculature • appear to be activated by norepinephrine released by sympathetic nerve itself and mediate negative feedback • inhibition of further norepinephrine release • post synaptic alpha1 and alpha2 receptors in peripheral vessels mediate vasoconstriction Cause Vasoconstriction Cardiac Inotropes

  41. Beta receptors • post synaptic beta1 receptors are predominant adrenergic receptors in heart • Stimulation causes increased rate and force of cardiac contraction. • post synaptic beta2 receptors in vasculature mediate vasodilatation Increase Contractility Increase Rate Reflex Vasodilation Cardiac Inotropes

  42. Dopamine receptors • peripheral DA1 receptors mediate renal, coronary and mesenteric arterial vasodilatation and a natriuretic response • DA2 receptors: • presynaptic receptors found on nerve endings • inhibit norepinephrine release from sympathetic nerve endings • inhibit prolactin release and may reduce vomiting • stimulation of either DA1 or DA2 receptors suppresses peristalsis and may precipitate ileus Increase Renal Blood Flow More Urine output Cardiac Inotropes

  43. Receptor pharmacology Agent Alpha1 Alpha2 Beta1 Beta2 Dopamine Dobutamine + + ++++ ++ 0 Dopamine ++/+++ ? ++++ ++ ++++ Epinephrine ++++ ++++ ++++ +++ 0 Norepinephrine +++ +++ ++ + 0 Phenylephrine ++++ +++ + + 0 Cardiac Inotropes

  44. Receptor pharmacology Dopamine Dobutamine Epinephrine Norepinephrine Phenylephrine Milrinone Vasopressin Little bit of everything Beta Alpha, Beta Apha, small beta Alpha Like beta Like alpha Cardiac Inotropes

  45. Putting It All Together

  46. Treatment of low cardiac output (CI < 2.0–2.2 L/min/m2) • Consider surgical complications, including • Coronary graft occlusion • Valve malfunction • Tamponade • Bleeding • Coronary spasm Cardiac Inotropes

  47. Treatment of low cardiac output (CI < 2.0–2.2 L/min/m2) • Optimize heart rate and rhythm • Increase rate to 90–100 beats per minute • Atrial pacing if no heart block • A-V pacing if heart block exists Cardiac Inotropes

  48. Treatment of low cardiac output (CI < 2.0–2.2 L/min/m2) • Low blood pressure(SBP <100 mm Hg or MAP <70 mm Hg) • If LAP * <15 mm Hg and HCT 25, administer Ringer's lactate or hetastarch • If LAP <15 mm Hg and HCT <25, administer PRBCs • If LAP 15 mm Hg, start dopamine or other inotropic agent, then add nipride when MAP >70 mm Hg Cardiac Inotropes

  49. Treatment of low cardiac output (CI < 2.0–2.2 L/min/m2) • Normal or high blood pressure (SBP >100 mm Hg or MAP >70 mm Hg) • If LAP <15 mm Hg and HCT 25, administer Ringer's lactate or hetastarch, plus nipride or other vasodilator • If LAP <15 mm Hg and HCT <25, administer PRBCs, plus nipride or other vasodilator • If LAP 15 mm Hg, administer nipride/other vasodilator and consider diuretic Cardiac Inotropes

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