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Cardiopulmonary bypass questions

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pilacede's version from 2016-06-09 17:42

MACHINE BASICS

Question Answer
Describe the two primary types of cardiopulmonary bypass (CPB) pumps?Roller and kinetic (centrifugal) pumps.
What are the advantages of roller pumps?Simple, effective, low-cost, low priming volume, and reliable output, which is afterload independent.
What are the disadvantages of roller pumps?(1) Because output is afterload independent, if the arterial line becomes occluded, high pressure will develop, which may cause rupture of connections in the arterial line. (2) If inflow is obstructed, roller pumps can generate high negative pressures creating microbubbles (cavitation) and RBC damage.
What are the advantages of centrifugal pumps?Non-occlusive and afterload dependent (an increase in downstream resistance or pressure decreases forward flow).
A reputed advantage of _______ pumps over _______ pumps is less risk of pumping massive air emboli into the arterial line.centrifugal pumps; roller pumps
What is the action of cardioplegia?Deliberate arrest of the action of the heart, as by hypothermia or the injection of chemicals, to enable complex heart surgery to be carried out.
The antegrade technique is achieved by administering cardioplegia solution into the ______ between the _______ and aortic clamp.aortic root; aortic valve
Cardioplegia may also be administered retrograde through a catheter in the _________.coronary sinus
In patients with ___________, administration of cardioplegia directly into the left and right coronary ostia may be required.aortic regurgitation
Cardioplegia is typically given intermittently every ___ to ___ min, but may be given continuously.20-30
What steps may the perfusionist take to improve venous return to the CPB machine (with appropriate venous drainage, the CVP should be low (0 to 5 mm Hg)?(1) adjustment of the venous cannula or cannulas by the surgeon; (2) raising the operating table height; (3) suction applied to the venous reservoir.
What are the three places cardioplegia may be administered: The antegrade technique is achieved by administering cardioplegia solution into the (1) ________ between the aortic valve and aortic clamp. Cardioplegia may also be administered retrograde through a catheter in the (2) _________; however, it may provide inferior protection of the RV. In patients with aortic regurgitation, administration of cardioplegia directly into the (3) __________ may be required.(1) aortic root; (2) coronary sinus; (3) left and right coronary ostia
When is retrograde cardioplegia used?(1) Valvular procedures (aortic, mitral); (2) during arterial grafting with in situ arteries (internal mammary, gastroepiploic); (3) in the presence of severe occlusive coronary artery disease.
What is the purpose of using a hemoconcentrator?(1) Used to eliminate excess crystalloid and potassium, (2) to raise hematocrit, and (3) to remove inflammatory mediators.
What is the purpose of the low-level alarm?If the blood level drops below the sensor, an alarm sounds and a light flashes.
What CPB pump can be used to generate pulsatile flow?Pulsations can be produced by roller pumps, and to a lesser degree by centrifugal pumps, designed to rotate at varying speeds.
Why may it be important for CPB pumps to generate pulsatile flow?(1) Transmission of more energy to the microcirculation, which improves tissue perfusion, lymphatic flow, and cellular metabolism. (2) Reduction of adverse neuroendocrine responses (mainly vasoconstrictive) to non-pulsatile flow that emanate from baroreceptors, the kidneys, and the endothelium.
How is the blood oxygenated while the patient is on CPB?Currently only MOs are used in most parts of the world. MOs function similarly to natural lungs, imposing a membrane between the ventilating gas and the flowing blood and eliminating direct contact between the blood and the gas.
How is dosing of cardioplegia decided and how often is it administered?The frequency of cardioplegia administration is determined by several factors, most importantly the temperature of the myocardium. (a) Warm myocardium requires a constant supply of oxygen and thus constant administration of cardioplegia. (b) With cold myocardium, visualization can be maximized with intermittent administration of cardioplegia. (c) Single-dose cardioplegia can be used with cold myocardium if the duration of the operation will be limited and if there is no significant coronary artery disease to limit the distribution of cardioplegia. (d) Multidose regimens are preferable in most circumstances. Some surgeons monitor the myocardial temperature with a probe and re-dose the cardioplegia with a rise in temperature, but more commonly cardioplegia is re-dosed at time intervals or with the return of electrical or mechanical myocardial activity.
What effect on BP should you expect when cardioplegia is being administered?Cardioplegia solution entering the circulation also reduces SVR and is a common cause of hypotension.
What is “pump prime” and what different types of prime may be used?The ECC (including venous and arterial lines) must be filled with fluid (“primed”) before use and all air in the circuit eliminated. Circuits are usually primed with asanguineous fluids (p. 607). Many formulations are in use. Most use a balanced electrolyte solution without glucose. Much controversy surrounds the need to add colloid, and use of both albumen and hydroxyethyl starches have been advocated (although use of high-molecular-weight HES is not recommended by the FDA in the U.S.). Many add mannitol to the prime and most include heparin (about 2,500 units/L).
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CLINICAL APPLICATION

Question Answer
What are the causes of the adverse systemic effects of CPB?(1) Microemboli (gas and particulate matter); (2) Activation of the inflammatory and coagulation systems; (3) Altered temperature, cooling, and warming; (4) Exposure of blood to foreign surfaces; (5) Reinfusion of shed blood and transfusion of blood products; (6) Hemodynamic alterations (abnormal flow rate and pattern, abnormal arterial and venous pressures); (7) Ischemia and reperfusion (especially of heart, lungs, and gut); (8) Hyperoxia; (9) Hemodilution (with anemia and reduced oncotic pressure)
What circulatory changes occur during the onset of CPB? Why?Hypotension due to a decrease in SVR. This phenomenon results from the following: (a) decreased blood viscosity secondary to hemodilution by the pump-priming fluid; (b) decreased vascular tone secondary to dilution of circulating catecholamines, temporary hypoxemia, and low pH and low calcium and magnesium levels in the priming fluid.
What circulatory changes occur during hypothermic arrest? Why?Increased and decreased SVR. The observed increase in SVR during the course of CPB is due to several factors: (1) decreased vascular cross-sectional area from closure of portions of the microvasculature; (2) vasoconstriction brought on by hypothermia, increasing levels of circulating catecholamines, AVP, endothelin, and angiotensin II; (3) increase in blood viscosity secondary to hypothermia and rising hematocrit (due to urine output or translocation of fluid into the interstitial compartment). Transient decreases in SVR may be observed shortly after infusion of cardioplegic solutions.
What temperature is the goal for moderate hypothermia?As low as 28°C, but is more often 32°C or above.
What changes may be seen in RBCs and WBCs during CPB?(1) RBCs become stiffer and less deformable during CPB, which may interfere with microcirculatory blood flow and increase susceptibility to hemolysis; RBCs are exposed to nonphysiologic surfaces and shear stresses, which may cause their destruction. (2) Leukocytes. CPB affects primarily neutrophils (polymorphonulcear leukocytes [PMNs]) and, to a lesser degree, monocytes. Shortly after the onset of CPB there is a marked decrease in circulating PMNs. This is due to sequestration in the pulmonary circulation and intravascular and extravascular accumulation in the microcirculation of heart and skeletal muscle. Blockage of vessels by PMNs or microcirculatory derangements induced by substances released from PMNs may contribute to organ dysfunction after CPB. Circulating PMN levels increase dramatically with rewarming. Neutrophils released from the pulmonary circulation and younger cells released from the bone marrow contribute to the observed neutrophilia.
What determines cardiac output during CPB?“Cardiac output” on CPB is the pump flow rate, which can be set at any level desired, but is limited by the amount of venous return.
What determines arterial pressure during CPB?As in the normal state, arterial pressure is the product of cardiac output (i.e., pump flow during CPB) and systemic vascular resistance (SVR). The latter is determined by blood viscosity and by smooth muscle tone in the arterioles. Viscosity is principally influenced by hematocrit and temperature, both of which often change considerably during CPB.
What measurement does the perfusionist use during CPB to evaluate global oxygen delivery?Oxygen delivery (DO2 = CaO2 x pump flow) may be one of the most important determinants of adequacy of perfusion. The DO2 calculation incorporates two critical variables that determine tissue oxygenation (arterial oxygen content and pump flow rate) into a single measure.
What is the role of hemodilution during CPB?Although oxygen-carrying capacity is decreased from hemodilution, oxygen delivery may be improved due to decreased viscosity and enhanced microcirculatory flow.
In which direction does the oxyhemoglobin dissociation curve shift during hypothermia? What are the clinical implications?As the temperature decreases, the affinity of oxygen for hemoglobin increases (i.e., the oxygen-hemoglobin dissociation curve is shifted to the left).
Why does “third spacing” of fluid occur during CPB?(1) Membrane permeability is increased by activation of the SIR and intermittent ischemia/reperfusion; (2) plasma oncotic pressure falls due to the use of asanguineous priming fluids; (3) inadequate venous drainage may increase mean capillary hydrostatic pressure, whereas immobility, lack of pulsatile flow, and loss of negative intrathoracic pressure impede lymphatic flow (p. 621).
During full CPB, is the heart ever completely empty?Yes, if suction is used.
Where should IV medications be administered during CPB?Drugs should be administered directly into the heart-lung machine.
What is the effect on the vascular system of the following mediators: cytokines, nitric oxide, leukotrienes, arachidonic acid metabolites, bradykinin, and endothelin?a. Cytokines: Cytokines are small proteins and polypeptides that mediate and regulate immunity, inflammation, and hematopoiesis.; b. Nitric oxide: The effects of NO include regulation of vasomotor tone, inhibition of platelet and neutrophil aggregation, and immunomodulation.; c. Leukotriene: Leukotrienes act as chemokines and potent vasoconstrictors of smooth muscle.; d. Arachidonic acid metabolites: Arachidonic acid mediates or modulates inflammatory reactions.; e. Bradykinin: increases vascular permeability and release of tissue plasminogen activator.; f. Endothelin: Endothelin-1 is a potent vasoconstrictor that has been associated with pulmonary and systemic hypertension and myocardial dysfunction.
What happens to plasma levels of magnesium and calcium during CPB?Both ionized calcium and total and unfiltratable fractions of magnesium commonly fall, whereas potassium levels may fluctuate widely during CPB.
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