Pulsatile vs non pulsatile perfusion
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This document discusses pulsatile versus non-pulsatile perfusion during cardiopulmonary bypass. Pulsatile perfusion is considered more physiologic as it simulates the pulsatile blood flow generated by the human heart. Pulsatile flow is associated with better organ function outcomes and increased microcirculation. It works through increasing surplus hemodynamic energy, maintaining capillary patency above the critical closing pressure, and stimulating neuroendocrine reflexes. Systems that can generate pulsatile flow include ventricular pumps, compression plate pumps, and pulsatile assist devices. However, transmitting pulsatile flow through the cardiopulmonary bypass circuit can be challenging due to pressure losses across components.
Pulsatile vs non pulsatile perfusion
- 2. Pulsatile vs non- pulsatile (Continuous) Flow • Why use pulsatile flow? Inherently more physiologic (simulates the human heart). • What is flow like in our vessels?? • Is there a difference between pulsatile and non-pulsatile flow? • Theories behind pulsatile perfusion • Effects of pulsatile perfusion • Benefits • Systems delivering pulsatile perfusion • Setting pulsatile mode in HLM • Conclusion
- 3. Pulsatile Flow in Vessels
- 4. • Pulsatility is an intrinsic aspect of the human cardiovascular systems, as the beating heart generates periodically alternating blood pressure and flow. • Pulsatility is emerging as the preferred perfusion method for CPB. • Clinical evidence show better cardiac, renal, and pulmonary outcomes in patients receiving pulsatile perfusion • Better cytokine, endothelin, and hormone levels and a higher respiratory index are shown in pulsatile perfusion modes compared with non-pulsatile perfusion modes
- 5. Theories of Pulsatile Flow • Energy Equivalent Pressure • Capillary Critical Closing Pressure • Neuroendocrine reflex mechanisms effected by baroreceptor discharge
- 6. • Pulsatile flow lacks a universal definition, and quantification of arterial pressure and pump flow-waveforms is imprecise. • Adequate quantification depends on an energy gradient rather than a pressure gradient.
- 7. Energy Equivalent Pressure • EEP can be used to calculate the total hemodynamic energy (THE), and, in conjunction with the mean arterial pressure (MAP), the surplus hemodynamic energy (SHE). • SHE represents the extra energy generated caused by pulsatility. • Theoretical advantage that the production of pulsatile flow depends not on a pressure gradient, but on an energy gradient. • EEP formula, which precisely quantifies hemodynamic energy, is defined as the ratio between hemodynamic work during time (∫fpdt) and the volume of blood pumped in that same period of time (∫fdt).
- 8. In 1966, Shepard et al. introduced pulsatile blood flow in terms of energy equivalent pressure (EEP). • EEP represents the energy content of the pulsatile arterial wave. EEP = ∫pfdt/ ∫fdt P = pressure (mmHg) f = flow rate (ml/sec) dt =change in time at a specific point • Using this formula it was determined that the energy needed to deliver pulsatile flow was up to 2.3 x that required to produce non-pulsatile flow for the same levels of mean pressure and flow.
- 9. • SHE values correlate with the existence of pulsatility. • If the pump flow were completely nonpulsatile, then the SHE values would be zero. • What does this extra energy mean? - The extra energy generated by a pulsatile or nonpulsatile device is the difference between the mean arterial pressure and EEP. - Thought to be available to the tissues by capillary patency - Increased lymph flow - Oscillatory movements at the cell level
- 11. Capillary Critical Closing Pressure Studies have suggested a reduction in capillary blood flow and a significant reduction in cerebral capillary diameter with non-pulse as opposed to pulsed flow. (1) Suggests that capillary patency is preserved longer by the peaks of systolic pressure. (2) That non-pulsatile flow produces more microcirculatory shunting and reduced capillary perfusion
- 13. Capillary Critical Closing Pressure: (although never seen under microscope) The belief that when the pressure in the capillary system goes below a certain point the capillaries will close…reducing the gas exchange between the blood and the tissues
- 14. Endocrine reflex mechanism effected by baroreceptor discharge • Transition from pulsatile to non-pulsatile flow results in: Marked increase in discharge frequency from baroreceptor in carotid sinus -This may initiate reflex neuroendocrine responses which remain operative throughout the non-pulsatile phase.
- 15. Release of baroreceptors in aorta and carotid artery Critical Closing Pressure Neuroendrocrine reflex mechanism
- 16. EFFECTS OF PULSATILE PERFUSION
- 17. Hemodynamic Effects of Pulsatile Flow • Non-pulse flow is associated with progressive elevation in SVR - Renin angiotensin activation - Continues into the post CPB period • Pulsatile perfusion is associated with significantly lower levels of vascular resistance in all regional vascular beds Benefits: - Improved tissue perfusion - Lower afterload for ventricle at the end of the perfusion period
- 18. Effect on Microcirculation , lymph flow and Metabolism • Improves microcirculation and tissue metabolism • Inhibits edema formation by increasing lymph flow • Lactate production is reduced as a result of aerobic metabolism.
- 19. Metabolic Effects of Pulsatile Flow • Cellular level Pulsed flow is associated with higher rates of oxygen consumption and reduced metobolic acidosis - ??enhanced energy may maintain microcirclatory patency and optimize tissue perfusion. • Organ Level - Kidney: Improved kidney function is the result of better gas exchange at the capillary level together with the maintenance of normal lymph flow. - Brain: reduced cerebral acidosis/markers of brain injury - Hepatic, gut, pancrease: functions better preserved possibly because of reduction of mucosal ischemia which can induce endotoxemia
- 20. Effect on Brain: • Better preservation of regional cerebral blood flow causing reduction in cerebral acidosis • Pulsatile flow reduces cerebral vascular resistance by as much as 25%. The improvement in regional blood flow distribution causes reduced cerebral lactate production . • Anaerobic metabolism is suppressed with pulsatile blood flow, particularly during the critical cooling and rewarming phases. • No difference in cerebral oxygen saturation.
- 21. Effect on Pancreas & Liver: • Preserves pancreatic function better than nonpulsatile CPB. • Reduced incidence of elevated amylase levels in patients undergoing CPB with pulsatile flow. • Hepatic function is also preserved as reflected in postoperative SGOT level. Hepatic blood flow shows a vasoconstrictive response to nonpulsatile CPB with decrease in hepatic oxygen consumption.
- 22. Pulsatile blood flow and the gut; • Postoperative gastrointestinal morbidity occurs in undergoing CPB. The cause is mesenteric hypoperfusion leading to ischemia CPB associated with endotoxemia which in turn cause increase in gut permeability. • Pulsatile blood flow results in improved blood flow to the gut ,reducing mucosal ischemia by increasing oxygen delivery.
- 23. Systems Producing Pulsatile Flow • Roller Pump Pump-head accelerates in systolic phase and decelerates during diastole - Sub-optimal waveform • Centrifugal pumps - EEP and SHE is very minimum. - Heat generation is more - Afterload dependance makes them unreliable for this purpose.
- 24. • Physiologic pulsatile pumps create the most hemodynamic energy levels whereas some roller pumps produce only a quarter of the hemodynamic energy generated by these physiologic pumps, and non-pulsatile pumps do not generate adequate SHE at all. • Pulsatile flow is a more complex procedure for minimal benefits.
- 25. VENTRICULAR PUMPS Physiologic method for generating pulsatile blood flow Operate in a similar manner to the ventricle of the heart. Consist of compressible sac and two one-way valves permitting blood to flow into and out of the ventricle in only one direction.
- 26. COMPRESSION PLATE PUMPS A length of tubing of known diameter is placed on a rigid back plate and compressed by a moving plate that descends for a preselected stroke length, thereby ejecting a volume of perfusate from the tube .The direction of blood flow is ensured by valves positioned at the inlet and outlet of the ventricle or sac.
- 28. What the Natural Pulse Does • Steep front (blood acceleration) induces a pressure wave • Pressure wave creates a wave phenomenon which: - expands walls of blood vessels, allowing more blood flow to move with lower pressure - reinforces muscles of blood vessels - removes obstacles inside the blood vessels - pushes blood through tiny capillaries
- 29. PULSATILE ASSIST DEVICE • Is an intermittent occlusive device that employs an intraaortic balloon pump apparatus to produce pulsatile blood flow in the arterial line of the CPB circuit. • The pulse is generated by occluding the arterial line of the circuit under flowing conditions, thereby creating a large pressure and volume delay within the arterial side of the circuit. On deflation of the balloon in the arterial line, the pressure and volume are released in the aorta to the patient as a pulse.
- 31. • Base flow -- continuous flow without the pulsatile component • Start time -- time when the pump flow starts from the base flow • Stop time -- the time when the flow returns to base flow. • Start and stop time points reflect the time between the two R waves of ECG, must be atleast 20% of cycle. • Internal frequency --70 to 80 PEDIATRIC CIRCULATORY SUPPORT - LOW BASE FLOW AND SHORT SYSTOLIC PERIOD PRODUCES BETTER PULSATILITY. - Hemolysis and GME is a concern.
- 32. BASE FLOW, FREQUENCY, WIDTHSETTINGS OF HLM:
- 34. • Beneficial in - elderly patients - high risk group - patients with pre existing renal disease. - Cardiac surgery in pregnancy
- 35. Release of GME Comfort level with non pulsatile flow Difficult to understand the pressure curves and energy generated Fear of shear stress/ hemolysis/intimal damage Diminished pulsatility
- 36. Pulsatility over CPB circuit components • In developing a model that can best predict the behavior of pressure- flow waveforms in the ECC, - component design must be first optimized. • The ECC presents an entirely different hemodynamic environment than human circulation. • Because blood is pumped through the oxygenator, the arterial filter, and several feet of arterial tubing, significant pressure drops occur. • It is important to select satisfactory circuit components, so that energy loss is minimized.
- 37. Obstacles to Transmitting Pulsatile Flow • Length of tubing • Resistance and damping of the: - Membrane - Arterial line filter - Cannula The small size of the aortic cannula creates the equivalent of AS resulting in circuit stresses and possibly hemolysis
- 38. Clinical Outcomes of Pulsatile Perfusion • Facilitate aerobic metabolism due to increases in vital organ blood flow and microcirculation • Increases renal, cerebral, pancreatic flow • Increase capillary perfusion • Increase RBC transit • Increase in Lymphatic function • Positively affect the recovery process, by reducing - systemic inflammatory response syndrome - inotropic support - intubation periods - duration of hospitalization.
- 39. • Reduced markers of endothelial damage • Decrease release of baroreceptor reflex hormones, limiting vasoconstriction • Attenuation of hormonal responses : Catecholamine, Renin Angiotensin Aldosterone, Antidiuretic hormone, Cortisol, Thromboxane, Prostacyclin. • Improved gastric mucosal oxygenation
- 40. THANK YOU
Editor's Notes
- #13: Windkessel principle explains the elastic properties of the aorta and the large arteries. During diastole some amount of blood is retained because of the elasticity properties in the aorta and other arteries.
- #16: In continuous flow
- #33: ideo
- #34: 32 years female for MV repair in her second trimester.