ANESTHESIA FOR CARDIOVASCULAR SURGERY

Part I…after Part II…whatever

What to look forward to…

Overview of Cardiopulmonary Bypass

Overview of On-Pump CABG

TEE will not be covered.

Cardiopulmonary Bypass

General

Functions include: 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 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 exchang

er

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 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

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 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 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

WeaningGroup I: Vigorous

Group II: Hypo-volemic

Group IIIA LV Failure

Group IIIBRV Failure

Group IVHyper-dynamic

BP Normal Low Low Low Low

CVP Normal Low Normal or high

High Normal or low

PA pressure

Normal Low High Normal or high

Normal or low

Wedge Normal Low High Normal or low

Normal or low

CO Normal Low Low Low High

SVR Normal Normal or high

High Normal or high

Low

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