ANESTHESIA FOR CARDIOVASCULAR SURGERY CARDIOPULMONARY BYPASS General Basic Circuit -resevoir -oxygenator -heat exchanger -main pump roller pumps centrifugal pumps pulsatile flow -arterial filter -accessory pumps and devices cardiotomy suction left ventricular vent cardioplegia pump ultrafilter Systemic Hypotension Myocardial Preservation -potassium cardioplegia Physiologic Effects of CPB -hormonal and humoral responses -altered pharmokinetics- Anesthetic Management of Cardiac Surgery preoperative management -premedication -preparation -venous access -monitoring induction of anesthesia -primarily inhalational techniques -primarily intravenous technique -muscle relaxants prebypass period -anticoagulation -bleeding prophylaxis -cannulation -flow and pressure -monitoring -hypothermia and cardioplegia -ventilation -management of respiratory gases -anesthesia -cerebral protection -termination of CPB -weaning of CPB postbypass period -reversal of anticoagulation -persistant bleeding -anesthesia -transportation -postoperative period Off-Pump Coronary Artery Bypass Surgery Cardiac Transplantion -preoperative consideration -anesthetic management -pericardial diseases Anesthesia for surgery on the Aorta -preoperative considerations -specific lesions of the aorta aortic dissection aortic aneursym occlusive disease of the aorta aortic trauma coarctation of aorta -anesthetic management surgery on the ascending aorta surgery involving the aorta arch surgery involving the descending aorta surgery of the abdominal aorta -postoperative consideration Anesthesia for Carotid Artery Surgery -preoperative considerations -preoperative anesthetic evaluation and history -general anesthesia -monitoring cerebral function -regional anesthesia CARDIOPULMONARY BYPASS General Cardiopulmonary bypass involves: -divert venous blood away from the heart -add oxygen to the diverted blood -remove C02 from the diverted blood -return the diverted blood to a large artery (ex. aorta) Cardiopulmonary bypass results in cessation of blood flow to: -heart -lungs Cardiopulmonary bypass provides: -artificial ventilation -artificial perfusion methods of myocardial protection involve: -systemic hypothermia: (20-32°C) -topical hypothermia: (ice slush solution) -cardioplegia (chemical solution to decrease myocardial electrical activity) basic circuit -venous resevoir -oxygenator -heat exchanger -main pumps -arterial filter Priming cardiopulmonary bypass circuit -prime with balanced salt solution: ex. Plasmalyte-A other components which may be added to the priming salt solution includes: -colloids: (albumin or hetastarch) -mannitol: (for renal protection) -heparin: (500-5000 units) -bicarbonate: (if cardioplegia not chosen) Priming the cardiopulmonary bypass circuit may result in: -hemodilution which results in hematocrit levels of about 22 - 25% -method to prevent hemodilution is priming with blood instead of standard priming solution VENOUS RESEVOIR -recieves blood from the patient through venous cannulas from the right atrium (or SVC or IVC) gravity drainage allows blood: -flow from the heart to the venous resevoir -directly proportional to the height difference between the patient and venous resevoir -inversely proportional to the resistance of the cannula and tubing resevoir fluid level is critical: -if becomes empty because air embolus may enter the main pump -may cause a fatal air embolus -therefore recommended to have a low resevoir alarm OXYGENATOR -blood drains from the bottom of the venous resevoir into the oxygenator -blood is driven by gravity -membrane oxygenator allows independant control of Pa02 and PaC02 -upon entering into the oxygenator, blood passes through a blood gas interface blood gas interface: -allows blood to equilibriate with the gas mixture -very thin gas-permeable silicone membrane arterial oxygenation: -inversely related to the thickness of the blood filter in contact with the membrane arterial C02 tension: -dependant on total gas flow HEAT EXCHANGER -blood either cooled or warmed depending on the temperature of water filling through the exchanger -water temperature flowing through the exchanger varies from 4°C to 42°C -conduction provides heat transfer between blood and water -as blood temperature increases, gas solubility decreases -upon rewarming, bubbles which may form are caught by a filter MAIN PUMP -roller pumps -centrifugal pumps -pulsatile flow Roller Pumps: -turning heads produce flow by compressing large-bore tubing within the main pumping chamber -excessive red blood cell trauma is prevented by subtotal occlusion of the tubing -produces a continuous nonpulsatile flow by constant speed of the rollers -flow of blood is directly proportional to the number of revolutions per minute of the rollers Centrifugal Pumps: -consists of a series of cones in a plastic housing -centrifugal forces generated by spinning cones propel blood from the central inlet into the periphery -less red blood cells trauma due to nonocclusion -generally located between the venous resevoir and the oxygenator pressure sensitive: -monitored by an electromagnetic flowmeter ex. increased distal pressure results in decreased flow therefore compensated by increased pump speed ex. decreased distal pressure results in increased flow therefore compensated by decreased pump speed Pulsatile Flow -instantaenous variations in the rate of rotation of the roller heads creates pulsations pulsatile flow may: -improve tissue perfusion -facilitate oxygen extraction -minimize release of stress hormones -lower systemic vascular resistance ARTERIAL FILTER -neccesary to prevent systemic embolism -usually 27 - 40 uM -filtered blood returns to the patient via cannula -filtered blood generally returns to the ascending aorta helps filter: -thrombi -fat globules -calcium -tissue debris ACCESSORY PUMPS AND DEVICES -cardiotomy suction -left ventricle vent -cardioplegia pump -ultrafilter Cardiotomy Suction: -aspirates blood flow from the surgical field and returns the blood to the main pump resevoir during cardiopulmonary bypass Left Ventricle Vent: -helps remove acculumated blood within the left ventricle -helps aspirate blood from the left ventricle catheter inserted into the left ventricle from: -right superior pulmonary vein -left atrium blood reaccumulates within the left ventricle from: -bronchial arteries -thebesian vessels -aortic regurgitation left ventricle distention results in: -compromise of myocardial preservation -requirement of decompression/venting Cardioplegia Pump: -commonly administered through an accessory pump on the cardiopulmonary bypass machine cardioplegia pump provides well control of: -infusion pressure -infusion rate -infusion temperature Ultrafilter: ultrafiltration: -increases patients hematocrit without transfusion -hemultrafiltration allows separation of aqueous phase of blood from cellular and protienaceous elements blood can be directed to pass through fibers by either: -arterial side of the main pump -venous resevoir using an accessory pump Systemic Hypothermia -core body temperature is commonly reduced to 20°C - 32 °C -reduction of myocardial metabolic oxygen requirements with decreased core body temperature -half myocardial oxygen demand with every decrease of 10 °C in core body temperature Profound hypothermia -core body temperature of 15 - 18 °C -allows for total circulatory arrest -indicated for complex repairs -effective for upto 60 minutes adverse effects of hypothermia include: -platelet dysfunction -possible citrate toxicity -decreased serum ionized calcium -coagulopathy (reversible) -myocardial depressant (decreased contractility) Myocardial Preservation -helps reverse myocardial damage which normally occurs during cardiopulmonary bypass -myocardial damage occurs due to imbalance between myocardial oxygen supply and oxygen demand factors which reduces basal metabolic oxygen demand include: -systemic hypothermia -topical cardiac hypothermia factor which reduces both electrical and mechanical energy expenditure includes: -cardioplegia purpose of myocardial preservation is to: -prevent myocardial damage -maintain normal cellular integrity and function myocardial damage results in: -myocardial ischemia -myocardial injury -myocardial infarction patients who are at increased risk of myocardial damage during cardiopulmonary surgery are: -symptomatic heart disease with manifestions at rest -ventricular hypertrophy -severe CAD manifestations of inadequate myocardial preservation are: -low cardiac output -ECG signs of ischemia -cardiac dysrhythmia aortic cross-clamping during cardiopulmonary bypass surgery: -abolishes coronary blood flow -generally should not be longer than 120 minutes myocardial ischemia may occur during cardiopulmonary bypass before or after cross-clamping due to: -low arterial pressures -coronary embolism -coronary vasospasm -graft vasospasm -excessive surgical manipulation of the heart Cellular changes during ischemia may involve: -depletion of high energy phosphate compounds (ex. ATP) -alterations in Na+/K+ ATPase channels -accumulation of intracellular calcium Cellular energy when coronary blood flow ceases is derived from: -creatine phosphate -anaerobic metabolism -impaired fatty acid oxidation important causes of myocardial damage involves: -ventricular fibrillation: may double myocardial oxygen demand -ventricular distention: increases myocardial oxygen demand, reduces oxygen supply by restricting subendocardial blood flow -ionotropic administration -excessive calcium administration POTASSIUM CARIOPLEGIA -commonly used method of myocardial arrest of electrical activity -administration of potassium rich crystalloids -increases extracellular potassium concentration -reduces transmembrane potential therefore less negative intracellular -alteration of Na+ current during depolarization potassium cardioplegia affects action potentials by: -decrease in the rate of rise -decrease in amplitude -decrease in conduction velocity complete inactivation of sodium channels results in: -abolished action potential -resultant heart arrested in diastole components of cardioplegia solutions generally include: potassium 15 -40 mEq/L sodium 100 - 120 mEq/L chloride 110 - 120 mEq/L calcium 0.7 mEq/L magnesium 15 mEq/L glucose 28 mEq/L bicarbonate 27 mEq/L general guidelines for cardioplegia: potassium -is generally kept below 50 mEq/L -greater than 50 mEq may paradoxically increase myocardial oxygen demand sodium -generally sodium within the cardioplegia should be less than plasma sodium because ischemia may increase intracellular sodium content calcium -small amounts of calcium is required to maintain cellular integrity magnesium -may control an excessive influx of calcium intracellularly bicarbonate -helps protect excessive build up of acidic metabolites other components which may be contained within cardioplegia include: -hypertonic agents: ex. mannitol to control cellular edema -glucocorticosteroids: membrane stabilizing effects -prostacyclins: antiplatelet effects -calcium channel blockers: reduce myocardial oxygen demand -beta adrenergic blockers: reduce myocardial oxygen demand -free radical scavenger: ex. mannitol -alkalotic buffers: ex. histidine and tromethamine (THAM) -energy substituents ex. glucose, glutamate, aspartate Reperfusion injury may involve: -extensive cell injury -rapid accumulation of intracellular calcium -oxygen derived free radicals Protection of reperfusion injury involves: -free radical scavengers ex. mannitol -minimize metabolic requirements of the heart with cardioplegia for the first 10 minutes of reperfusion -avoid hypercalcemia -10 -30 minutes before weaning the patient from cardiopulmonary bypass, keep the heart empty and beating -correct any existing acidosis -correct and existing hypoxia Possible complications involved with excessive cardioplegia include: -absence of electrical activity -atrioventricular conduction block -poor myocardial contractility in conclusion of bypass Physiological Effects of Cardiopulmonary Bypass: Inititaion of Cardiopulmonary Bypass Increases levels of stress hormones include: -catecholamines -cortisol -arginine vasopressin -angiotensin Hormonal system effects include the activation of: -complement system via alternative pathway (C3) and classic pathway (Hageman factor XII) -coagulation system -fibrinolytic system -kallikrein system Mechanical trauma stimulates: -platelets -neutrophils Classic pathway stimulates: -coagulation cascade -platelets -plasminogen -kallikrein ALTERED PHARMACOKINETICS onset of cardiopulmonary bypass: -plasma concentrations of must drugs are acutely decreased -some drugs unbound fraction may remain unchanged altered pharmacokinetics may be due to: -sudden increase in volume of distribution Vd -hemodilution -decrease in protien binding -changes in perfusion to vital organs -change in redistribution between peripheral and central compartments other factors which may affect drug activity during cardiopulmonary bypass: -drugs binding to cardiopulmonary bypass components ex. fentanyl -competitive inhibition of drug binding to plasma protiens constant drug infusion during cardiopulmonary bypass may cause an increase in drug levels due to: -decreased hepatic perfusion -decreased renal perfusion -hypothermia increased alpha acidic glycoprotien may increase after cardiopulmonary bypass ANESTHETIC MANAGEMENT OF CARDIAC SURGERY Determine the adequacy of cardiac reserve: -exercise/activity tolerance -myocardial contractility measurements ex. EF = systolic function -myocardial diastolic function ex. flow velocity across MV during diastole = diastolic function -severity of coronary occlusion -location of coronary stenosis -ventricular wall motion abnormalities -left ventricular end diastolic pressure -cardiac output -valvular areas/gradients ex. valve area = flow across valve/ K (sqaure root of mean transvalvular gradient) Preoperative Management -premedication -preparation -venous access -monitoring Premedication + 02 NC 2 - 3 L/min benzodiazepines ± opiods opiods +antimuscarinic/sedation Benzodiazepine ± opiods -midazolam: 5 - 10 mg IM -morphine: 5 - 10 mg IM -diazepam: 5 - 10 mg PO -lorazepam: 2 - 4 mg PO opiods +antimuscarinic/sedation -morphine: 0.1 - 0.15 mg/kg IM -scopolamine: 0.2 - 0.3 mg (avoid scolpolamine in patients > 70 yrs) Preparation check list: -anesthetic machine -monitors -infusion pumps -anesthetic drugs -vasoactive drugs -airways -suction Venous Access two large bore intravenous access required due to: -cardiac surgery often involved with rapid and large fluid shifts -multiple drug infusions -one of the two large bore intravenous lines should be placed centrally (RIJ, subclavian, external jugular) -drug infusion preferably given into the central line -blood should be available for immediate infusion especially for a redo-surgery Monitoring ELECTROCARDIOGRAM -continuous monitoring of II and V5 -order of most senstive to least sensitive for monitoring ischemia : V5, V4, II, V2, V3 -assess ST segment analysis ARTERIAL BLOOD PRESSURE -generally use nondominant radial artery radial arterial line may provide falsely low reading due to: -compression of the subclavian artery during sternal retraction -compression between the clavicle and 1st rib -left radial more vulnerable than right radial Avoid radial arterial line on the same side the brachial artery was performed on during cardiac catherization due to: -high incidence of arterial thrombosis -wave distortion other catherization sites which may be useful: -brachial artery -femoral artery -axillary artery PULMONARY ARTERY CATHERIZATION generally used for patients with any of the following -compromised ventricular function -ejection fraction < 40 - 50% -pulmonary hypertension Useful information obtained from a pulmonary artery cathether include: -pulmonary artery pressure -pulmonary artery occlusion pressure (PAOP) -thermodilution cardiac output with specialized catheters may provide: -extrainfusion ports -continuous mixed venous oxygen saturation measurements -cardiac output -ability to pace the right ventricle or atrioventricular sequential pacing Pulmonary Artery Catherter routinely pulled back approx. 2 -3 cm due to: -common distal migration during cardiopulmonary bypass -may spontaneously wedge despite the balloon being deflated -risk of pulmonary artery rupture -risk of lethal pulmonary hemorrhage due to pulmonary artery rupture -cathether wedges the pulmonary artery with less than 1.5 ml of air within the balloon Site to approach for central venous catherization -internal jugular vein: preferred approach -external jugular vein -subclavian vein external jugular vein and subclavian vein on left side less desirable due to: -vulnerability of kinking -during sternal retraction URINE OUTPUT -monitor hourly urine output ( > 0.5 ml/kg/hr) -monitor bladder temperature sudden red urine may be due to: -cardiopulmonary bypass -transfusion reaction TEMPERATURE: multiple temperature monitors include: -bladder temperature: represents average body temperature -rectal temperature: represents average body temperature -esophageal temperature: represents core body temperature -pulmonary artery temperature: represents core body temperature -nasopharyngeal temperature: represents brain temperature -tympanic membrane temperature: represents brain temperature -direct cardiac measurement during CPB represents myocardial temperature LABORATORY PARAMETERS -blood gases -hematocrit -serum potassium -ionized calcium -glucose -magnesium -ACT: monitors anticoagulation -thromboelastography SURGICAL FIELD -when the sterum is open: lung expansion is able to be directly visualized -when the pericardium is open: heart is able to be directly visualized Helps to assess: -cardiac rhythm -ventricular volume -ventricular contractility -blood loss TRANSECHOCARDIOGRAPHY Helps assess the anatomy and function during cardiac surgery such as: -regional ventricular wall abnormalities -global ventricular wall abnormalities -ventricular chamber dimensions -valvular anatomy -presence of intracardiac air -cannulation of coronary sinus for cardioplegia multiple views include: -upper esophagus -lower esophagus -transgastric Different planes include: -transverse -sagittal -inbetween planes Most commonly used views of TEE during cardiac surgery: -transverse four chamber view -transgastric (short axis) view Most important uses for intraoperative TEE are to assess: -ventricular function -valvular function -residual intracardiac air -other cardiac structural abnormalities Ventricular Function includes: Global systolic function: -ejection fraction -left ventricle end diastolic volume (LVEDV) Global diastolic function: -flow velocity through the MV during diastole -visualizing abnormal ventricular relaxation Regional systolic function: -ventricular wall motion abnormality Hypokinesia: (mild, moderate, severe) Akinesia: Dyskinesia: -ventricular thickening abnormality Valvular Function assessed by: -Doppler Echocardiogram -Color Flow Imaging Valvular function parameters which are monitored include: -pressure gradients -stenotic valve area -severity of stenosis -severity of valvular regurgitation -prosthesis valve dysfunction ex. valvular obstruction ex. regurgitation ex. endocarditis Images most useful in assessing aortic valve and ascending aorta include: TEE images in the upper esophagus at: 40 - 60 ° 110 - 130 ° Views most useful in assessing doppler across the aortic valve: -transgastric view Position used to assess the mitral valve: -midesophageal position -with/without color 0 through 150° view Assessment of cardiac structural abnormalities include: -congenital heart disease: ex. patent foramen ovale, ASD, VSD -pericardial disease: ex. pericardial tamponade, constrictive pericarditis -cardiac tumors Doppler Color-Flow imaging helps determine: -abnormal intracardiac blood flow -abnormal intracardiac shunts Transesophageal echocardiography helps assess: -extent of myomectomy in patients with idiopathic hypertrophic subaortic stenosis -diagnosis of an acute disease process ex. aortic dissection: extent of dissection and involvement ( ascending/descending aorta) ex. aortic aneursym: ex. artheroma: helps assess protrussion of artheroma into the ascending aorta helps assess the risk of postoperative CVA ELECTROENCEPHALOGRAPHY -useful in assessing anesthetic depth during cardiac surgery -ensure complete electrical silence prior to circulatory arrest Detecting neurological insults during cardiopulmonary bypass is limited due to the effects of: -anesthetic agents -hypothermia -hemodilution Progressive hypothermia is generally associated with: -EEG slowing -burst suppression -isoelectric recording Most strokes during cardiopulmonary bypass surgery involves: -small emboli -not likely to be detected by EEG TRANSCRANIAL DOPPLER -noninvasive measurement of blood flow velocity in the basal arteries of the brain -usually measures blood flow through the middle cerebral artery -helps detect cerebral emboli -emboli detected by transcranial doppler often associated with postoperative neurological changes INDUCTION OF ANESTHESIA Induction of anesthesia for cardiac surgery involves: -general anesthesia -endotracheal intubation -controlled mechanical ventilation "cardiac induction" implies: -slow: slow and small increments of administered anesthetic agents -smooth stable hemodynamics -controlled fashion each series of challenges correlate with controlled heart rate and blood pressure -each series of challenges may help to evaluate anesthetic depth -continuous monitoring of blood pressure and heart rate Light anesthesia indicated by: -sudden increase in heart rate -sudden increase in blood pressure therefore requires more anesthetic prior to next challenge if no increase in blood pressure or heart rate, then ready for next stimulus ex. insertion of naso/oropharyngeal airway insertion of urinary cathether insertion of endotracheal tube Decrease in blood pressure after intubation often occurs because: -anesthetised state associated with: vasodilation and decreased systemic vascular resistance -lack of surgical stimulation -volume depletion due to: preoperative fasting, diuretic treatment Baseline measurements commonly obtained after intubation and controlled ventilation include: -hemodynamic parameters -baseline ACT -arterial blood gas -hematocrit -serum potassium concentration Anesthetic agents patients with relatively good ventricular function: inhalational anesthetic agents patients with severely poor ventricular function: total intravenous anesthetic agents Volatile anesthetic agents -allows for careful titration according to hemodynamics -allows ability to change concentrations rapidly -may cause dose dependant direct cardiodepression -may cause intracoronary steal most commonly used volatile anesthetic agent in cardiac surgery: -isoflurane Intravenous anesthetic techniques: high dose opiod technique other techniques High dose opiod technique Rarely used due to: -patient awareness/recall of surgery -postoperative prolonged respiratory depression -does not consistently control hypertensive responses to surgical stimuli Methods to help control hypertensive response to surgical stimuli during cardiac surgery includes: -vasodilation ex. NTG, NTP -beta adrenergic blockers ex. propanolol, esmolol -volatile anesthetic agents Fentanyl and sufenanil when used alone generally provide: -stable hemodynamics -minimal cardiac depression Fentanyl or sufetanil when used with benzodiapines or barbiturates may cause: Hypotension due to: -vasodilation -cardiac depression Sufentanil compared to fentanyl may compromise hemodynamics more especially in: -elderly patients -patients with poor ventricular function -possibly due to decreased sympathetic tone Patients who recieve high dose sufentanil compared to high dose fentanyl may: -regain consciousness sooner -may be intubated sooner secondary to regained consciousness High dose opiods may cause: -bradycardia -muscle (chest wall) rigidity Muscle rigidity due to high dose opiods may be prevented by: -administration of small dose NDMR prior to induction ex. pancuronium 1 mg Opiods may generally be administered by: -boluses -loading dose then continuous infusion ex. fentanyl induction and intubation: slow bolus of 15 - 40 ug/kg ex. 70kg patient: 1050 ug - 2800 ug Maintenance: additional boluses as needed: 3 - 5 ug/kg or continuous infusion of : 0.3 - 1 ug/kg/min total dose of fentanyl generally used is: 50 - 100 ug/kg ex. sufentanil induction and intubation bolus of: 5 - 10 ug/kg Maintenance small bolus as needed: 1 ug/kg or continuous infusion: 0.075 ug/kg/min total dose of sufentanil generally used is: 15 - 30 ug/kg Other techniques: combination technique of ketamine + midazolam -used for induction and maintenance -relatively stable hemodynamics -good amnesia -good analgesia -minimal postoperative respiratory depression -may be useful in patients with poor ventricular function ex. induction: slow intravenous bolus of: ketamine: 1 - 2 mg/kg midazolam: 0.05 mg/kg ex. maintenance: continuous infusion of: ketamine: 1.4 mg/kg/hour midazolam: 0.07 mg/kg/hour muscle relaxants: -generally NDMR are used for intubation unless anticipation of a difficult airway -if anticipating a difficult airway intubation may be facilitated with succinylcholine most commonly used muscle relaxant during cardiac surgery include: -rocuronium -vecuronium: may enhance opiod induced bradycardia -pancuronium may offset opiod induced bradycardia PREBYPASS PERIOD -period after induction and intubation but before bypass may involve moments of minimal stimulation to intense stimulation Minimal stimulation may include: -skin preparation -draping -often associated with hypotension Intense stimulation may include: -skin incision -sternotomy -sternal retraction -opening of the pericardium -aortic dissection -often associated with hypertension Increased vagal response may occur during: -sternal retraction -opening of pericardium increased vagal response may cause: -bradycardia -hypotension may be more pronounced in patients with: -beta adrenergic blockers -diltiazem -verapamil Progressive decline of cardiac output may occur once: -chest is open Due to: Decrease in venous return due to: -normally negative intrathoracic pressure becoming atmospheric -intravenous fluids may minimize the effects of decreased venous tone Myocardial ischemia within the prebypass period often is associated with: Hemodynamic fluctuations such as: -tachycardia -hypertension -hypotension prophylactic infusion of NTG may relieve the incidence of ischemic events ex. NTG 1 -2 ug/kg/min Anticoagulation Anticoagulation prior to cardiopulmonary bypass helps prevents: -acute disseminated intravascular coagulation -formation of clots in cardiopulmonary pump Adequacy of anticoagulation is confirmed and determined by: -activated clotting time ACT (celite-ACT for heparin, kaolin-ACT for aprotinin) -ACT greater than 400 - 450 seconds is considered adequate and accepted in most surgical centers HEPARIN -heparin 300 - 400 Units/kg often given during cannulation -if given by the surgeon: administered into the right atrium -if given by the anesthesiologist: administered rhrough the central line Measure ACT -within 3 - 5 minutes after giving the heparin -if ACT < 400 seconds, give an additional heparin dose of 100 Units/kg Heparin resistance may occur: -antithrombin III deficiency (acquired, congenital) normal function of antithrombin III -circulating serine protease -irreversibly binds and inactivates thrombin heparin + antithrombin III -increases antithrombin III's anticoagulant effects 1000 x's Adequate coagulation with antithrombin III deficiency achieved by either of the following: -infusion of 2 units of FFP -infusion of antithrombin III concentrate -synthetic antithrombin III Heparin Induced Thrombocytopenia (HIT) due to: -production of heparin-dependant antibodies -platelet agglutinates -results in thrombocytopenia -may/maynot have thromboembolic phenomena if history of HIT is minimal or remote and no detection of antibodies -may safely use heparin only for cardiopulmonary bypass If significant history of HIT and antibody titers are detected: -plasmaphoresis may help transiently to eliminate the antibodies -then normal heparinization may occur Alternative anticoagulants include: -hirudin -ancrod Patients with HIT undergoing emergency cardiac surgery may also attempt inactivation of platelets prior to heparization with: -asprin -dipyrimadole -iloprost (prostacyclin analog) Bleeding Prophylaxis -antifibrinolytics agents may be started before or after anticoagulation possible benefits of initiating antifibrinolytics after heparinization include: -reduced incidence of thrombotic complications -reduced efficacy due to delayed administration Aprotinin therapy often considered for: -patients undergoing repeat operation ex. myocardial revascularization -patients who refuse blood products ex. Jehovahs witness -patietnts at high risk od postoperative bleeding ex. recent asprin ingestion, coagulopathy, long/complicated procedure Aprotinin -inhibitor of serine proteases (ex. plasmin, kallikrein, trypsin) May preserve platelet function by: -increased adhesiveness -increased aggregation Benefits of aprotinin therapy involve -reducing perioperative blood loss -reduces transfusion requirements -blunts the intense inflammatory response to cardiopulmonary bypass Allergic reactions involved with aprotinin include: -more likely to occur with repeat exposure -possible serious allergic reactions including anaphylxis Test dose of aprotinin: -aprotinin 1.4 mg (10,000KIU) prior to loading dose loading dose of aprotinin -aprotinin 280 mg ( 2million KIU) over 20 - 30 minutes -given central line Infusion of aprotinin -70 mg/hr ( 500,000 KIU/hr) -duration of cardiac surgery -cardiopulmonary bypass pump also primed with 280 mg aprotinin ( 2million KIU) alternative to aprotinin -bolus of €- aminocaproic acid 5 -10 gram -infusion of €- aminocaproic acid 1 mg/hr -bolus of tranexamic acid 10 mg/kg -infusion of tranexamic acid 1mg/kg/hr both €- aminocaproic acid and tranexamic acid -do not affect the ACT -less likely to produce allergic reactions -do not preserve platelet function Cannulation: critical period during cardiopulmonary bypass aortic cannulation: occurs before venous cannulation and after heparinization venous cannulation: frequency associated with hemodynamic problems AORTIC CANNULATION -usually performed before venous cannulation and after heparinization -if neccessary, provides for rapid fluid infusions -ascending aorta most commonly used site for aortic cannulation jet stream may occur if: arterial cannulation not positioned correctly and may possibly result in: -aortic dissection -preferential blood flow to the innominate artery during cardiopulmonary bypass facilitation of aortic cannulation: -reduction of systemic arterial pressure -90 - 100 mmHg systolic blood pressure is prefered prior to the induction of cardiopulmonary bypass, arterial cannulation should be: -completely removed of air bubbles in the arterial cannulation -demonstrate a backflow of blood into the arterial line failure to remove all the air bubbles from the arterial cannula may result in: air emboli often within: -coronary circulation -cerebral circulation method which may decrease the chance of cerebral embolism during aortic cannulation: -temporary compression of the carotid arteries during aortic cannulation VENOUS CANNULATION: -either one or two venous cannulas are placed into the right atrium -common site of venous cannulation is the right atrial appendage single venous cannula: -often adequate for most coronary artery bypass surgery -aortic valve operation often has two ports (two stage) -one port in the right atrium -one port in the IVC separate caval cannulas -used for open heart surgical procedures manipulation of the venae cavae may lead to: -impaired ventricular filling -resultant hypotension venous cannulation may precipitate: -atrial dysrhythmias -premature atrial contractions -ventricular dysrhythmias -supraventricular tachycardia sustained paroxysmal astrial tachycardia or atrial fibrillation may lead to: -hemodynamic compromise requiring: -pharmacologic treatment -electrical treatment -immediate anticoagulation -initiation of bypass malpositioning of the venous cannula may lead to: -impaired venous return: manifested as poor venous return to the resevoir -impaired venous drainage from the head and neck SVC syndrome manifested as edema of head and neck BYPASS PERIOD prior to initiation: -cannulas must be properly placed and secured -an acceptable ACT level -perfusionist ready Initiation of cardiopulmonary bypass involves: -removal of clamps across the cannulas -venous clamps removed before arterial clamps -start of cardiopulmonary bypass main pump establish adequate venous return to the venous resevoir demonstrated by: -decreasing resevoir level -quick emptying of pump prime -air entry into the pump circuit Malpositioning of the venous cannula or aortic regurgitation may lead to: -progressive distention of the heart -aortic regurgitation requires immediate aortic cross-clamping and cardioplegia Flow and Pressure -pump flow slowly increased to 2 - 2.5 L/min/m² systemic arterial blood pressure often decreased suddenly at the onset of cardiopulmonary bypass due to: -abrupt hemodilution -reduced blood viscosity -decreased systemic vascular resistance Causes of excessive and persistent decreases in systemic arterial blood pressure may include: -aortic dissection -poor venous return -pump malfunction -pressure transducer error Relationship between the following: -pump flow -systemic vascular resistance -systemic mean arterial pressure MAP = (pump flow) ( systemic vascular resistance) Constant SVR: MAP is proportional to pump flow goal is to maintain adequate: -MAP: between 50 - 80 mmHg -blood flow 2 - 2.5 L/min/m² by manipulating: -pump flow -SVR: may be increased with phenylephrine or methoxamine flow requirements usually proportional to the core body temperature: ex. deep hypothermia ( 20 - 25°C) adequate cerebral blood flow may be maintained with MAP as low as 30 mmHg systemic blood pressure greater than 100 mmHg -treated with decreasing pump flow -adding isoflurane to the oxygenator gas inflow -vasodilation ex. NTP if other methods fail Increased systemic blood pressure greater than 150 mmHg may promote: -aortic dissection -cerebral hemorrhage Monitoring additional monitors include: -pump flow rate -venous resevoir level -pressure of arterial in line -blood temperature -myocardial temperature -in line arterial and venous oxygen saturation -in line pH sensor -C02 tension sensor -oxygen tension sensors Inadequate flow rates may be indicated by: -low venous oxygen saturation < 70% (in absense of hypoxia) -progressive metabolic acidosis -low urinary output Difference in pressure between arterial inflow in line pressure and systemic arterial pressure may be due to pressure drop across: -arterial filter -arterial tubing -narrow opening of the aortic cannula Normal arterial in line pressure should be below: 300 mmHg elevated arterial in line pressure may be due to: -clogged arterial filter -obstruction of arterial tubing/cannula -aortic dissection Serial laboratory measurements during cardiopulmonary bypass include: -serial ACT: immediately after bypass then every 20 - 30 minutes -serial hematocrit: kept between 20 - 25% -serial [potassium]: elevated [K+] treated with furosemide Hypothermia Routinely used for most procedures involve: -moderate hypothermia: 26 - 32°C -severe hypothermia: 20 - 25°C Lower temperature involves: -longer time for cooling -longer time for rewarming -allows for lower adequate cardiopulmonary bypass flows ex. temperature 20°C: allows for cardiopulmonary bypass flows of 1.2 L/min/m² temperature between 28 - 29 °C may potentiate ventricular fibrillation Cardioplegia -should be established immediately after cooling -hypothermia induced ventricular fibrillation consumes high energy phosphate -resultant impaired cardiac protection -therefore cardioplegia must be initiated cardioplegia achieved by: -cross-clamping the ascending aorta proximal to the aortic inflow cannula -cardioplegia solution infused through a small catheter proximal to the cross clamp Ventilation pulmonary ventilation generally continued until: -adequate pump flows are reached -heart stops ejecting blood discontinuing ventilation prematurely may: -promote hypoxemia due to: -blood remaining in the pulmonary circulation passing through a nonventilated lung -related to pulmonary blood flow: pump flow ratio ventilation may resume: -at the conclusion of cardiopulmonary bypass -heart begins to eject blood adequately Management of Respiratory Gases -solubility of gas increases with hypothermia -therefore partial pressures of gas decrease as temperature of blood decreases clinical significance on: C02 tension due to: -arterial pH -cerebral blood flow decreased temperature: -decreases arterial 02 tension -resultant increase in pH -alkalotic blood environment ex. @ 37°C pH =7.40/ PaC02 =40mmHg @ 25°CpH =7.60/ PaC02= 23mmHg pH stat management -method of temperature correcting gas tensions -maintenance of a normal C02 tension of 40 mmHg and pH of 7.4 in the setting of hypothermia during hypothermia cardiopulmonary bypass: -may require adding C02 to the oxygen gas inflow -increases total blood C02 content cerebral blood flow: becomes more dependent on: -C02 tension -MAP becomes less dependent on: -CMR02 Anesthesia hypothermia has some anesthetic effects light anesthesia: -occurs by failure to provide adequate anesthetic agents during cardiopulmonary bypass -contributes to awareness of surgical procedure may lead to: -hypertension -movement if paralysis is worn off light anesthesia may require: -additional dose of muscle relaxant -additional dose of anesthetic agents ex. isoflurane administered through the oxygenator residual myocardial depression: -avoided by discontinuing the volatile anesthetic agent prior to termination of cardiopulmonary bypass providing additional anesthesia upon initiation of rewarming may be with either of: -benzodiazepine: ex. midazolam 5 - 10 mg IV -antimuscarinic: ex. scopolamine 0.2 - 0.4 mg other options include either: -opiods -ketamine-midazolam infusion Cerebral Protection -neurologic complications may be as high as 40% following cardiopulmonary bypass surgery complications consist of: -transient neuropsychiatric dysfunction (subtle cognitive changes to intellectual changes) -delirium -oraganic brain syndrome -cerebral vascular accident factors which may be associated with neurological sequelae include: -intracardiac procedures (ex. valvular procedures) -advanced age -pre existing cerebral vascular disease prophylactic thiopenthal infusion: -controversial to what extent it provides cerebral protection -completely supresses EEG activity -used immediately prior to and during intracardiac procedures -been reported to decrease both incidence and severity of neurologic deficits -may increase the requirement of ionotropic support upon termination of cardiopulmonary bypass methods and agents usually administered before cardiac arrest include: -very deep hypothermia -corticosteroids: (methyprednisolone 30 mg/kg) -mannitol: ( 0.5 mg/kg) -phenytoin ( 10 - 15mg/kg) -cover head with ice bags other possible agents used before cardiac arrest include: -magnesium -calcium channel blockers ( nimodipine, nifedipine) -N-methyl-D-aspartate ( ketamine) Termination of Cardiopulmonary Bypass procedures and conditions neccessary for discontinuing cardiopulmonary bypass: -completion of rewarming -complete evacuation of air from the heart and bypass grafts -removal of aortic cross clamp -resume of pulmonary ventilation decision of rewarming: -time is required for adequate rewarming rewarming too soon: -abolishes the protective effects of hypothermia rewarming too rapidly -creastes a large temperature gradient between the well perfused organs and the tissue subjected to vasoconstriction -vasodilation (NTG/NTP) may reduce the temperature gradient -may result in the formation of gas bubbles -due to decreased solubility of gas in blood with increasing temperature decreased chance of fibrillation upon rewarming may occur with: -lidocaine 100 - 200 mg -magnesium sulfate 1 -2 grams before removing aortic cross clamp removing intracardiac air: -helps to reduce the risk of cerebral emboli -may be accomplished by head down position -lung inflation may assist in removing intracardiac air from the left side of the heart guidelines for separation from cardiopulmonary bypass include: -core body temperature at least 37°C -stable rhythm -adequate heart rate (preferred between 80 - 100 bpm) -normal lab values -adequate pulmonary ventilation with 100% FI02 -check all monitors for optimal function Weaning From Cardiopulmonary Bypass slow discontinuation of cardiopulmonary bypass with constant monitoring of: -systemic arterial blood pressure: central aortic root pressure estimated by the surgeon via palpation -ventricular volume: assessed visually or measured by CVP, PAOP, TEE -ventricular pressure: assessed by CVP, PAOP -cardiac output: assessed by thermodilution correlation between: -central aortic pressure -radial artery pressure -noninvasive blood pressure cuff reversal of normal systolic pressure gradient: -monitored by aortic pressure becoming higher than the radial artery pressure weaning from the cardiopulmonary bypass accomplished by: -releasing any remaining tapes around the vena cava -clamping the venous return line -allowing the beating heart to fill -ventricular ejection will begin -gradual decrease in pump flow as the arterial pressure increases pump flow is stopped when: -total occlusion of venous line -adequate systolic blood pressure ( SBP > 80 - 90 mmHg) -patient is then re-evaluated Four general categories patients often fall into when coming off the cardiopulmonary bypass: -patients with good ventricular function -patients who are hypovolemic with normal ventricular function -patients who are hypovolemic with ventricular impairment -patients who are hyperdynamic with decreased SVR but normal ventricular function hypovolemic patients with normal ventricular function may display: -respond quickly to 100 ml aliquots of pump blood infused into the aortic cannula -increase in blood pressure and cardiac output with each bolus of blood -eventual sustained increase in blood pressure and cardiac output with boluses -adequate blood pressure and cardiac output with LVEDP less than or equal to 10 - 15 mmHg hypovolemic patients with impaired ventricular function may display: -increased LVEDP during volume infusion despite any changes in blood pressure and cardiac output -LVEDP > 15 mmHg pump failure patients coming off cardiopulmonary bypass often have: -sluggish heart -poorly contracting heart -progressive dilation of the heart -re-institute going back on cardiopulmonary bypass -initiate inotropic treatment if systemic vascular resistance is elevated, afterload reduction may be useful by: -vasodilation with NTP/NTG -inodilator ex. milrinone evaluation of unrecognized ischemia includes: -kinked graft -coronary vasospasm -valvular dysfunction -shunting -right ventricular failure Intra-aortic Balloon Pump is used after cardiopulmonary bypass surgery if: patients who experience heart failure and do not improve with: -inotropic therapy -reduction of afterload Intra-aortic Balloon Pump: -efficacy primarily dependant on proper timing of inflation and deflation of the balloon -inflation of the balloon: immediately after the dicrotic notch which helps augment the diastolic BP and coronary blood flow -deflation of the balloon: just before left ventricular ejection which prevents excessive afterload commonly used inotropes after weaning from cardiopulmonary bypass include: -dopamine -dobutamine -amrinone -milrinone -epinephrine -norepinephrine agents used for patients experiencing pulmonary hypertension: -inhalational nitric oxide -PGE POSTBYPASS PERIOD postbypass period involves: -control of bleeding: systolic BP maintained at 90 - 110 mmHg helps to minimize bleeding. -removal of bypass cannulas: atrial cannula removed before the aortic cannula -removal of anticoagulation: -closure of chest: upon termination of bypass: -patients may require additional blood volume (ex. blood, colloid, crystalloid) fluid administration should be guided by: -LVEDP (ventricular filling pressures) -post bypass hematocrit (preferred hematocrit approx. 25 - 30%) ventricular ectopy may occur due to: -electrolyte abnormalities (ex. hypokalemia, hypomagnesemia) -residual ischemia ventricular ectopy may be treated with: -lidocaine -procainamide -amiodarone