Anesthesia for Cardiovascular Surgery Part I…after Part II…whatever Anesthesia for Cardiovascular Surgery

What to look forward to… Overview of Cardiopulmonary Bypass Overview of On-Pump CABG TEE will not be covered.

Cardiopulmonary Bypass

General Functions include: Non-physiologic Diverting venous blood away from the heart Adding oxygen Removing CO2 Returning blood to arterial side Non-physiologic Requires steps to minimize organ damage

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

CPB Circuit Additional parts Accessory pump for Cardiotomy suction Accessory pump for left ventricular vent Cardioplegia line Circuit primed with 1200-1800 mL for adults Balanced salt solution Colloid Heparin Dilutes hematocrit to 22-25%

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

Reservoir Receives blood from the patient via Driving force is GRAVITY One cannula in right atrium Two cannulas in superior and inferior vena cava Driving force is GRAVITY Reservoir on the floor Flow proportional to difference in height Must monitor fluid level If reservoir empties air can enter pump and cause air embolism Frowned upon

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

Oxygenator Blood drained from bottom of reservoir Blood-gas interface allows blood to equilibrate with gas mixture Oxygen Volatile anesthetic Thin gas-permeable membrane Oxygenation inversely related to thickness of blood film over the membrane CO2 tension dependent on gas flow

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

Heat Exchanger Water (heated or cooled) runs through exchanger Heat transfer by conduction As temperature rises, gas solubility decreases Bubbles created Caught by filter

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

Main Pump Roller Pump Centrifugal Pump Rotating pump produces flue by compressing tubing Flow directly related to revolutions per minute Centrifugal Pump Series of cones spin causing centrifugal force Flow is pressure sensivitve: Increase in distal pressure requires an increase in the pump speed to maintain flow Nonocclusive: Less daming to RBCs Often placed between reservoir and oxygenator Organs accustomed to pulsatile flow Not possible with centrifugal pumps, some roller pumps Possibly improves perfusion, oxygen extraction

CPB Circuit Patient Venous Reservoir Oxygenator Heat exchanger Main Pump Arterial Filter

Arterial Filter Particulate matter common with CPB circuit Thrombi Fat globules Debris Filter placed to prevent systemic embolism Filter contructed with bypass limb in case of clogging and to extract air

Accessory Devices Cardiotomy Suction Left Ventricular Vent Suctions blood from surgical field Left Ventricular Vent Blood reaccumulates in LV due to residual pulmonary flow Aortic regurgitation Distention of LV increases wall tension thereby compromising myocardial preservation Cardioplegia pump Ultrafilter Ultrafiltration to increase hematocrit Hydrostatic pressures force water and electrolytes across membrane

Hypothermia Core body temperature to 20-32°C. Metabolic oxygen requirements are CUT IN HALF FOR EVERY 10°C reduction Profound hypotension for total circulatory arrest: 15-18° Adverse effects Platelet dysfunction Potentiation of citrate toxicty Coagulopathy Depression of contractility

Myocardial Preservation Cardiac Surgery is tough on the heart Goal is to accomplish surgery efficiently while minimizing damage to the organ Damage results from imbalance between myocardial oxygen demand and supply Reperfusion injury Oxygen-derived free radicals Intracellular calcium overload Abnormal endothelial-leukocyte interactions Myocardial cellular edema Symptoms post-bypass Low Cardiac Output ECG signs of ischemia Arrythmias

Myocardial preservation At aortic cross-clamp, clock starts ticking CPB times longer than 120 minutes undesirable Ischemia causes depletion of ATP and accumulation of intracellular calcium Preventing ischemic damage requires maintaining normal cellular integrity Reducing energy expenditure Preserving availability of high-energy phosphate compounds

Myocardial Preservation Reduce Basal metabolic oxygen consumption Hypothermia Reduce energy expenditure Cardioplegia Prevent ventricular fibrillation

Cardioplegia Potassium-rich solution Additional components K: 10-40 mEq/L Additional components Sodium (<140) Calcium to maintain cellular integrity Magnesium to prevent excessive calcium influx Buffer to prevent buildup of acidic metabolits Bicarbonate THAM (histidine and tromethamine) Energy substrate (glucose, glutamine, aspartate)

Cardioplegia Increased extracellular potassium reduces transmembrane potential Interferes with normal sodium current during depolarization Decreases rate of rise, amplitude and conduction velocity of action potential With time sodium channel is inactived, action potentials cease, heart arrests in diastole Washout necessitates redosing after 30 minutes Where is cardioplegia given? Anterograde cardioplegia (through aortic root) may not reach areas distal to occlusion Retrograde cardioplegia given through coronary sinus Excessive cardioplegia result in absence of eletrical activity, AV block, poor contractility

Effects of CPB Non-physciologic Increase in stress hormones Inflammatory response similar to sepsis or trauma Complement system by contact with circuit Coagulation Platelet dysfunction Fibrinolysis kallikrein Elevated levels of Catecholamines Cortisol Arginine vasopressin Angiotensin Plasma concentration of drugs acutely decrease with CPB

CABG We are going to make this interactive…hopefully won’t crash and burn. Let’s talk through a CABG 65 year-old man with remote history of right knee history presents for 3-vessel CABG. History significant for 3 months worsening chest pain during Saturday morning walks at the mall.

Preoperative evaluation What do you want to know?

Anesthetic Management Premedication Anesthetic Plan? Lines?

Note on Pulmonary Artery Catheters In general, utilized in patients: Compromised ventricular function Pulmonary hypertension Complicated procedures Information provided PA pressures Wedge pressures Cardiac output TEE provides opportunity to assess function

Prebypass Periods of intense stimulation Skin incision Sternotomy Sternal retraction Aortic dissection Vagal response during sternal retraction or opening of pericardium Fluid management goal to keep under 1000cc

Anticoagulation Heparin 3000-4000 U/kg Resistance to heparin Acts upon Antithrombin III to enhance activity 1000-fold Should be given via central line Monitored by ACT, confirm >375 before cannulation Resistance to heparin Antithrombin III deficiency Give FFP or antithrombin III Patient with Heparin-induced Thrombocytopenia Heparin-dependent antibodies agglutinate platelets Remote history, no antibodies  heparin Antibodies present  alternative anticoagulation, usually hirudin

Pre-bypass checklist Anticoagulation? Anesthesia adequate? Cannulation correcct? Infusions off? Monitors in place?

Cannulation Anticoagulation confirmed Blood pressure decreases to systolic of 100 for aortic cannulation Closed heart procedures utilize one cannula in RA Open heart procedures use two cannula: SVC, IVC Malpositioning manifested by poor venous return or edema of head and neck Initiation of CPB Unclamp venous line first Flow starts slow to ensure venous return, then increased Failure of heart to empty signifies malpositioning

On Bypass Initial arterial pressure falls Prolonged decrease pressure may indicate aortic dissection If dissection, must cannulate aorta distally On CPB, arterial mean pressure = pump flow x SVR At Tulane, perfusionist controls hemodynamics during CPB Muscle relaxant may be required Light anesthesia may result in awareness, especially during rewarming

Weaning from Bypass Core body temperature at least 37°C Stable rhythm, atrioventricular pacing may be required Adequate heart rate between 80-100 Labs within limits, treat acidosis, hypocalcemia, hyperkalemia Adequate ventilation with 100% oxygen

Weaning from bypass Venous return line progressively clamped allowing blood to fill heart Ventricular ejection resumes Pump flow decreased Once venous line is occluded and arterial pressure adequate, pump flow is stopped Patient’s hemodynamics are evaluated

Weaning Group I: Vigorous Group II: Hypo-volemic Group IIIA LV Failure Group IIIB RV Failure Group IV Hyper-dynamic BP Normal Low CVP Normal or high High Normal or low PA pressure Wedge CO SVR Tx None (yay) Volume (duh) Inotrope; reduce afterload; IABP; LVAD Pulmonary vasodilator; RVAD Increase hematocrit

So… Patients flying off bypass or hyperdynamic can be weaned quickly If patient is hypovolemic, coordinated bolus from bypass pump in 100cc doses (This is what’s going on when you are standing there and the attending keeps on asking, “What do you have for me? Ok, give me 100. Give 100 more. Etc.”) Pump failure is more difficult For LV, inotropes +/- vasodilator if SVR is high Evaluate TEE Intraaortic balloon pump Timing is vital: Inflation just afte dicrotic notch  augments diastolic BP and coronary flow Deflation just prior to LV ejection

Reversal of anticoagulation Protamine (1.3mg per 100 units of heparin) Highly positive charged protein that inactivates heparing Heparin-protamine complexes removed by reticuloendothelial system Infuse slowly over 5-10 minutes Allergic reactions Men with previous vasectomies Diabetics who received NPH insulin Allergy to fish Prior reaction Type I Hypersensitivity reaction

Catastrophes Aortic dissection due to malposition of aortic cannula Cannula within wall, not in true lumen Clues Occlusion of true lumen cause profound decrease in arterial pressure High pressure on pump Organ hypoperfusion Management Discontinue CPB Reposition arterial cannula Place arterial cannula distally

Reversed Cannulation Blood drained from aorta, return under pressure to venous Great risk for air entrapment in in aorta causing air embolism upon correction Clues Arterial hypotension Severe facial edema High CVP Flaccid aorta Management Discontinue CPB Steep head down De-air the aorta and pump line Exchange cannulas

Gas embolism High risk of MI, stroke, or death Common causes include emptied reservoir, clotted oxygenator, opening a beating heart, disconnection of lines during CPB Management Head down Vent Retrograde CPB through SVC line Carotid compression Hypothermia Ventilate with 100% oxygen