Anesthesia for Cardiac Surgery Part 1 Terms in this set (179) How is coronary perfusion pressure calculated? (Aortic DBP - LVEDP)/coronary vascular resistance What is the most useful indicator of CoPP? MAP Under normal conditions, what MAP is CoPP autore

Anesthesia for Cardiac Surgery Part 1 Terms in this set (179) How is coronary perfusion pressure calculated? (Aortic DBP - LVEDP)/coronary vascular resistance What is the most useful indicator of CoPP? MAP Under normal conditions, what MAP is CoPP autoregulated between? MAP 60 - 110 How does CAD affect CoPP? Flow is no longer autoregulated after it passes the partial obstruction CoPP becomes pressure dependent, especially when MAP <70 What is total coronary blood flow determined by with CAD? Perfusion pressure gradient Time allotted for flow Coronary anatomy Coronary vascular resistance Which region of the heart is at most risk for ischemia with CAD? Subendocardium = exposed to the highest LVEDP What two factors decrease myocardial blood supply and increase myocardial oxygen demand? Tachycardia Increases in LVEDP What is the most significant cause of perioperative ischemia? Tachycardia What is tachycardia an independent predictor of? Cardiac & all-cause mortality in men and women with and without CAD What is the goal in improving myocardial oxygen supply & demand? Maintain adequate MAP Avoid tachycardia What is the difference between eccentric and concentric hypertrophy? Eccentric Dilated Systolic dysfunction Concentric Thickening Diastolic dysfunction What are factors that affect myocardial supply and/or demand? How does autoregulation differ between the subendocardium and subepicardium? In the subendocardium, autoregulation is exhausted and flow becomes pressure-dependent when pressure distal to a stenosis declines to less than 70 mmHg In the subepicardium, autoregulation persists until perfusion pressure declines to <40 mmHg Autoregulatory coronary reserve is less in the subendocardium How does blood flow differ between the right and left coronary artery? The RV is perfused throughout the cardiac cycle Flow to the LV is largely confined to diastole What are common causes of decreased O2 supply? Tachycardia (decreased diastolic time) Hypotension Increased pulmonary artery EDP Decreased O2 content Anemia What is the perioperative management strategy for tachycardia? Keep HR relatively low (<70 bpm) Deepen anesthesia during stimulating periods What is the perioperative management strategy for hypotension? Maintain high normal MAP Consider phenylephrine Decrease anesthetic depth during less stimulating periods and surgical manipulation that causes decreased MAP What is the perioperative management strategy for increased PaEDP?? Consider NTG Evaluate LV volume with TEE (PaEDP increased in patients with concentric LVH & increased LVEDV) What is the perioperative management strategy for decreased O2 content? Maintain SaO2 >95% What is the perioperative management Maintain adequate hemoglobin Anesthesia for Cardiac Surgery Part 1 What are common causes of increased O2 demand? SNS stimulation Tachycardia Increased preload Increased contractility Increased afterload What is the perioperative management strategy for SNS stimulation? Maintain adequate depth of anesthesia Anticipate stimulating events and treat preemptively What is the perioperative management strategy for increased preload? Consider NTG or diuretic What is the perioperative management strategy for increased contractility? Consider agents that depress contractility = beta-blockers or VAs What is the perioperative management strategy for increased afterload? Avoid HTN Consider vasodilator What is the ischemia cascade? Diastolic dysfunction precedes systolic dysfunction Stiff and less compliant ventricle What is the most sensitive intra-op indicator of myocardial ischemia? TEE Wall motion abnormalities on ECHO seen before ECG changes What is the role of ECG in monitoring for intra-op ischemia? Monitor 5 lead with lead V3, V4, V5 with ST analysis What is stunning? Brief periods of ischemia (<20 min) causes reversible contractile dysfunction Can last for several hours What is the effect of stunning seen in post- op? Many CABG patients require 12-24 hr of inotropic support What is ischemic preconditioning? Short periods of ischemia improve the heart's ability to tolerate longer periods of ischemia How do VAs provide ischemic preconditioning? Protect myocardium from ischemic and reperfusion injury & reducing infarct size What is hibernation? Stable coronary plaques cause chronic reductions in coronary perfusion Steady-state ischemia occurs with results in LV perfusion-contraction mismatching What is the effect of hibernation? LV function is reduced to match the amount of O2 available These patients usually have significantly improved LV function post-CPB What are significant findings of ECG on cardiac preoperative testing? ST-T wave changes and presence of significant Q waves If recent ACS, STEMI vs NSTEMI vs UA Presence of significant arrhythmia BBB (concern if placing PAC) and LVH Presence of pacemaker What are significant findings of chest X-ray on cardiac preoperative testing? Cardiomegaly Pulmonary vascular congestion/pulmonary edema Pleural effusion Presence of pacemaker or implantable cardioverter defibrillator What are significant findings of TEE on cardiac preoperative testing? LV ejection fraction (systolic dysfunction) Presence and grade of diastolic dysfunction Amount and type (concentric or eccentric) of LVH RV function Pericardial effusion/tamponade Presence of PFO (extra concern for air R to L) Presence of plaque on the ascending aorta (problem cannulating and/or clamping) What are significant findings of exercise stress test on cardiac preoperative testing? Level and severity of ischemic changes & leads involved Patient characterization of symptoms Maximum heart rate (target >85% of predicted) What are significant findings of pharmacologic stress test on cardiac preoperative testing? Adenosine and dipyridamole cause vasodilation in normal coronaries leading to steal or supply ischemia in areas with CAD -- used to identify viable myocardium Dobutamine increases HR and contractility inducing demand ischemia; also used for stress ECHO What are significant findings of nuclear imaging on cardiac preoperative testing? Radionuclides with varying tracer actions and kinetics are used to evaluate myocardial perfusion and function What are significant findings of SPECT on cardiac preoperative testing? Two sets of images are obtained = after stress & after rest Defects that are initially seen (ischemic area) and fill later indicate viable myocardium, whereas fixed defects indicate scar What are significant findings of PET on cardiac preoperative testing? Ischemia shifts metabolism from fatty acids to glucose An isotope is given that attaches to glucose The scan can show flow as well as identify areas of uptake Anesthesia for Cardiac Surgery Part 1 What are significant findings of stress ECHO (exercise or dobutamine) on cardiac preoperative testing? Segments with new wall motion abnormalities during stress are considered ischemic and therefore viable What are significant findings of coronary CTA on cardiac preoperative testing? Advanced CT technology and angiography are used to obtain high-resolution, 3D images of the moving heart and great vessels Able to identify extent and location of plaque in coronaries and aorta What are significant findings of cardiac catheterization on cardiac preoperative testing? LVEDP Cardiac index Presence of L main, triple vessel disease, or equivalent Quality of targets Type and timing of PCI Type, location, and timing of coronary stents Presence of pulmonary HTN What are forms of extracorporeal circulation? CPB LHB (left heart bypass) ECMO What is the purpose of CPB? To provide a motionless, bloodless heart for the surgical procedure What is a general overview of what CPB is doing? Venous blood is removed from the heart to the "pump" O2 is added, CO2 is removed, and blood is filtered before returning it to the arterial system Provides artificial ventilation, perfusion, and temperature regulation What occurs to blood flow during CPB? Stops nearly all blood flow to heart and lungs What does cardioplegia do? Stops electrical activity of the heart and protects it during the procedure What is performed along with cardioplegia during CPB? Intermittent perfusion Cooling How is cardiac index maintained during CPB? With an arterial flow of 2 - 2.4 L/min/m2 How is blood flow different during CPB? Nonpulsatile What is MAP maintained at during CPB? No less than 50-60 mmHg Which patients undergoing CPB require a higher MAP? Elderly Those with known carotid disease (60-70 mmHg) to ensure adequate cerebral perfusion pressure What are risks of CPB? Blood and blood components exposed to non-endothelial surfaces = increased incidence of platelet dysfunction & coagulopathy Anesthesia for Cardiac Surgery Part 1 What are the 5 basic components of the CPB pump? Venous reservoir Main pump Oxygenator Heat exchanger Arterial filter What is the general steps for blood flow within the CPB circuit? Deoxygenated blood drained from a cannula in the right side of the heart (atrium or vena cava) Carried by tubing to a reservoir The main pump (arterial pump/artificial heart) propels the blood to an oxygenator (artificial lung) and heat exchanger The oxygenated blood flows through an arterial line filter before returning to the arterial circulation via cannula (usually in the ascending aorta) to perfuse the rest of the body Besides blood flow, what are other function of the CPB circuit? Delivers cardioplegia via accessory pump Heart is vented Blood is salvaged from the field by suction devices What is the CPB blood tubing? Medical grade PVC tubing used to connect the assorted components of the CPB machine and conduct blood into and out of the patient vascular system What is a complication of the CPB blood tubing? Because of the extensive blood contact with tubing, the pump, and the membrane oxygenator, activation of plasma protein cascade occurs Intrinsic and extrinsic clotting cascade, complement system, & fibrinolytic protein system What are benefits of newer generation CPB blood tubing? They have surface coatings to reduce bioactivity These coatings help to reduce coagulation markers of subclinical coagulation, attenuate cytokine elevation (and other inflammatory markers), and shorten intubation time What are the two major types of surface coating in newer generation CPB blood tubing? Heparin coated Poly 2-methoxy-ethylacrylate (PMEA) -- not shown to be as effective in reducing platelet activation as heparin coating What fluid is used to prime the CPB circuit and its components? Isotonic balanced electrolyte solution = LR, plasmalyte-A, or normosol-R Circuit must be carefully de-aired How much volume is used to prime the CPB circuit? What is the effect? 1-2 L = 20-35% decrease in HCT What medications can be added to the CPB prime? What are their effects? Colloid -- decrease postop edema Blood -- treat anemia Mannitol -- diuresis Heparin -- anticoagulation Bicarbonate -- acidosis What physiologic effect occurs upon institution of CPB due to the priming of the circuit? What is its effect? Causes dilutional anemia upon institution Offsets increase in blood viscosity that occurs when blood cools during CPB What method of priming can control the risk of dilutional anemia? Retrograde autologous priming (RAP) Where is the venous reservoir positioned in the CPB circuit? Between the venous cannula and the arterial pump What are two types of venous reservoirs? Collapsible plastic bag Hard-shelled plastic canister What are benefits of using a hard-shelled plastic canister for venous reservoir? Allow the incorporation of a venous filter Have negative & positive pressure valves to allow for suction application to augment venous drainage What is the purpose of the venous reservoir? Facilitates the displacement of large volumes of blood out the vasculature during strategic surgical points Also contains cardiotomy reservoir How is blood drained to the venous reservoir? Usually by gravity What are factors that affects the rate of gravity drainage of blood into the venous reservoir? Size and placement of the cannula Height of the bed Patient's intravascular volume status When is gravity an ineffective method of draining blood to the venous reservoir? Minimally invasive procedures = small cannula & tubing What is used if gravity drainage of blood isn't effective for filling the venous reservoir? Vacuum-assisted venous drainage (VAVD) = >60 mmHg What are the risks of VAVD? Hemolysis -- increases with strength of suction Air embolism What are the 2 types of arterial pumps used in CPB? Roller pump Centrifugal pump How does the roller pump work? Positive displacement pumps = occlude a piece of tubing and roll the occlusive point along the length of the tubing Causes forward fluid movement in front of the occlusive point and draws fluid in behind the occlusive point What are pros & cons of the roller pump? Pro = more economical and simpler to use Con = increased destruction of blood elements How does the centrifugal pump work? Motor is used to generate high-speed revolutions inside of a constrained vortex Blood is propelled out through an opening in the cone while blood is drawn in to the center of the cone This produces a non-pulsatile flow Backflow is possible How does the hemodynamic status of the patient affect the centrifugal pump? What is the benefit? Varies with changes in preload and afterload = afterload dependent This protects against arterial line rupture and/or microemboli formation What are pros and cons of the roller pump? Pros Capable of generating high positive and negative pressure d/t occlusive properties Backflow isn't possible Pulsatile flow is possible Cons Can inadvertently pump massive quantities of air into the arterial cannula Roller pump machines now must be servoregulated (reduce pump speed when high pressure air is detected in the path of blood) More traumatic mode of blood circulation vs centrifugal pumps What are pros and cons of the centrifugal pump? Pros Less trauma (platelet/cytokine activation) to blood If air is introduced into the cone, the pump will de- prime (unable to pump large air volumes into the arterial cannula) Cons Unable to generate high positive and negative pressures Lack of an occlusive point potentially allows retrograde flow from the arterial cannula to the filter, oxygenator, and low-pressure venous reservoir (one-way valve or computer activated clamp can be positioned in the arterial line to prevent inadvertent exsanguination) Anesthesia for Cardiac Surgery Part 1 What are the two types of oxygenators? Bubble -- not common anymore Membrane What is the role of the membrane oxygenator during CPB? Performs gas exchange during CPB, thus replacing the patient's lungs What are similarities between the oxygenator and the patient's lungs? Gas and blood phase are present Driven by passive diffusion gradients Membrane used to separate blood from gas interface What are characteristics of the membrane used in the oxygenator? Made from microporous polypropylene Polypropylene is extruded into thin straws to increase surface area for gas exchange (total surface area = 2-4 m2) Straw outer diameter typically 200-400 micrometers with thickness of 20-50 micrometers What are benefits of a membrane oxygenator vs bubble oxygenator? Less SIRS Better control of gases Less microemboli What is the priming volume of the oxygenator? 135-340 mL How much blood is the oxygenator capable of oxygenating? Up to 7 L/min of venous blood How does gas flow occur within the oxygenator? Has separate gas inlet and outlet to allow refreshment of gas inside oxygenator What are the gas and blood components of the oxygenator? Gas component is the internal lumen of the polypropylene fibers (straws) Venous blood is directed to the outside of these fibers How does gas exchange occur within the oxygenator? Microscopic pores (0.5-1 micrometers) allow for O2/CO2 exchange, but prevent solutes from entering the fibers from the blood What may occur if gas pressure is too high within the oxygenator? If the pressure exceeds that of the blood, gaseous emboli may form How are blood gas levels adjusted via the oxygenator? Oxygen level can be changed by increasing FiO2 Amount of CO2 removed can be changed by changing the liter gas flow rate or "sweep" of gas through the oxygenator VA can be added to the fresh gas inlet (oxygenator sweep gas) to maintain depth of anesthesia How does the heat exchanger work? Usually made of stainless steel tubes with heated or cooled water flowing through them Blood enters separately or in combination with the oxygenator What is heat exchange important during 20-35% of the patient's circulating blood volume is exposed to ambient OR Anesthesia for Cardiac Surgery Part 1 What temperature is induced mild hypothermia and profound hypothermia? Mild = 35 Celsius Profound = 18 Celcius What must occur to blood temperature before discontinuing CPB? Must be returned to normal to facilitate separation from the CPB machine