Weaning from CPB

Dr. S. Parthasarathy MD., DA., DNB, MD (Acu),

Dip. Diab.DCA, Dip. Software statistics, Phd (physio)

Mahatma Gandhi Medical college and research institute , puducherry , India

• Weaning from CPB should represent a smooth transition from the mechanical pump back to the patient’s heart and lungs as the source of blood flow and gas exchange

• Discontinuation – better word !! • Coordinated --- surgeon, anaes, perfusionist • This is simple write up !! • Preop and intraop course – consider

What do we mean by that ??

When does it start ??• Remove cross clamp !! • Blood starts to flow to coronaries • Heart starts to beat ?? • It flushes out the metabolites and then start• De fib if needed – (10 or 20 J )• cold, decreased pressure , not protected well

--- fibrillate !!• Be ready for all the problems !• What is this readiness ??

Romannof Royster CVP pneumonic

• C V P

• Cold Ventilation Predictors • Conduction Visualization Pressure • Cardiac output Vaporizer Pressors• Cells Volume expanders Pacer Calcium

Protamine• Coagulation Potassium

The first “C” stands for “cold”

• patient's temperature at the time of weaning from CPB,

which should be 36°C to 37°C.

• Neither the temperature of the venous blood returning

to the CPB circuit nor nasopharyngeal temperature

should ever exceed 37°C because hyperthermia may

increase the risk for postoperative neurologic

complications

• Nasopharyngeal Temp --- brain

• Rectum 2 degrees lower• A larger than four degrees gradient between

the nasopharyngeal and rectal temperatures is indicative of inadequate rewarming or increased vasoconstriction

• Vasodilator ---- warming blankets – children

C for conduction – rate and the rhythm

• Rate - 80 to 100 beats/min

• Brady--- pacing or chronotropy with inotropy

• Need dromotropy also sometimes

tachycardia• 1) Hypoxia• (2) Hypercapnia• (3) Medications (inotropes, pancuronium, )• (4) Light anesthesia, awareness• “Fast track” anesthesia with its lower medication additional dose of narcotic and benzodiazepine, or

hypnotic (propofol infusion) should be given during the rewarming period or if tachycardia is present.

• (5) Anemia• (6) ST and T-wave changes indicative of ischemia

Rhythm

• Sinus rhythm is preferable, particularly in patients with poor LV

compliance, who are especially dependent on an “atrial kick”

to achieve adequate filling.

• If supraventricular tachycardia is present, direct synchronized

cardioversion is often warranted.

• In addition, pharmacologic therapy with amiodarone, esmolol,

verapamil, or adenosine may be used in the initial treatment of

or to prevent the reoccurrence of supraventricular tachycardia.

• Stabilize parameters

• Defib

• Pacing

• Then only anti arrhythmic drugs

Cells

• The hemoglobin concentration should be measured

after rewarming.

• If it is less than 6.5 to 7 g/dL before terminating CPB--

?? 10 gm is acceptable in many centres!

• 2 units of PRCs, 6 units ready

• Salvaged blood –ready.

• COPD, cyanosis ,residual stenosis, low output ---- aim

for higher hematocrit

“C” stands for “cardiac output” or “contractility.”

• Following unclamping ,an adequate reperfusion period must

be permitted.

• allows the heart to replenish metabolic substrates,

specifically high-energy phosphates (ATP), and “washes out”

the products of anaerobic metabolism,

• Contractility may be estimated from TEE and cardiac output

can be measured with a PA catheter. -- 3 minutes interval –

ok??

Commonly encountered risk factors for failure to wean from CPB include:

• poor preoperative ventricular function;• • urgent and emergency surgery;• • prolonged aortic cross-clamp time;• • inadequate myocardial protection; • • incomplete surgical repair.

DRUGS -------- ELECTRO-MECHANICAL SUPPORT

• • Adrenergic agonists• (Adrenaline,Dopamine ,Dobut

amine,)• • Phosphodiesterase inhibitors• (Milrinone)• • Calcium sensitizer• (Levosimedan)• • Systemic vasodilators NTG,• NPS) • • Pulmonary vasodilator (NO,• PGI2)

. • Bi-Ventricular pacing

• • Intra-Aortic Balloon Pump

• • Extra-Corporeal Membrane

• Oxygenation

• • Ventricular Assist Device

The fifth “C” stands for “coagulation

• the prothrombin time, • partial thromboplastin time, • platelet count• ACT ??• RISK :: • long CPB times; • extreme hypothermia,• chronic renal failure.

• Platelet function tests may be useful in patients taking platelet inhibitors such as clopidogrel or aspirin.

• See the field and drains – not the lab values alone

Calcium • The concentration of calcium in the plasma

may be reduced by large volumes of citrated blood, leading to impaired contractility and vasodilatation.

• Ionized calcium should be maintained above 1.0 mmol/l.

• Calcium – culprit in reperfusion injury – correct only after establishing serum values

ALL “C “

• Cold • Conduction • Contractility • Calcium • Cells • Coagulation

V

Ventilation

• slowly occlude venous line • blood into lungs • Manual ventilation 100 % oxygen few puffs 30 cm water

– open up alveoli • May continue ventilation as long as it doesnot hinder

surgeon • Suction pleural space • ICD in ?? • Anastamosis not stretched ??• Compliance and bronchodilators

A venous oxygen saturation of 75% and a minimum venous PO2 of 35mmHg are satisfactory to start weaning from CPB.

The second “V” is for “visualization

both directly in the surgical field (where the right-sided chambers are visible) and on TEE,

to estimate global and regional contractility

Blood volume

Air ??

Vaporizer • Awareness Vs• Contractility Vs• Hypotension• Use agent and vasopressors !! 0.7 MAC

isoflurane • Some use 3 % iso on bypass also • Analgesia , midazolam, relaxants

Volume

• When all products from the pump have been exhausted and if blood transfusion is not indicated,

• crystalloid and albumin or hetastarch should be readily available to rapidly increase preload if necessary.

• Usually blood in the tubes taken out by us earlier

• Read CVP and MAP

V• Ventilation • Vision • Vaporizer• Volume

P

Predictors

• Ejection is less • Cold • Long duration • Surgical repair ??

The second “P” is for “pressure.”

• Calibration and re zeroing are accomplished

shortly before starting to wean the patient

from CPB.

• Any discrepancy between distal (usually

radial) arterial pressure and central aortic

pressure should be recognized.

Pressors

• • Phenylephrine• • Norepinephrine• • Terlipressin• • Methylene Blue (1.5 mg/kg)

• Catecholamines

Pressors

• Low SVR -- norad or vasopressin

• Low cardiac output syndrome-

• Adrenaline , dopamine, dobutamine, milrinone and levosimendan

“potassium”• hypokalemia may contribute to dysrhythmias

• hyperkalemia may result in conduction abnormalities.

• Hypo more a common problem – patients on diuretics

• Off bypass – usually in the range of 2.5

• magnesium (2 to 4 g) is generally administered before CPB is terminated.

Parameters

• Administration of sodium bicarbonate solution, usually into the cardiotomy reservoir of the extracorporeal circuit, generates a substantial amount of intracellular carbon dioxide and is often associated with a reduction in systemic vascular resistance.

• K+, Ca 2+, Mg2+ and acidosis

pH• a pH of 7.4 and a PCO2 higher than 35 mmHg are

mandatory to safely disconnect a patient from the pump.

• Any degree of acidosis should promptly be corrected

because it depresses myocardial contraction, diminishes

the action of inotropes, and increases pulmonary vascular

resistance.

• Acidosis → sympathetic activity → beta blockers ( preop )

“protamine.”• 3-4 mg/kg

• Or 1 mg for 100 units of heparin administered

• Slow

• Vasodilation • Pulmonary vasoconstriction

pacing

• Epicardial pacing is commonly required in the immediate and early post-CPB period.

• Atrial (AV node ok) , / ventricular ( chronic AF)

• If cardiac function is adequate after weaning from CPB, pacing may not prove necessary.

P

• Predictors • Pressure • Pressors • Pacing• Potassium • pH • Protamine

SVR

• Systemic vascular resistance (SVR) values are usually assumed to be low following CPB

• because of the association between hemodilution and reduction in SVR and because of the SIRS

• During CPB • [MAP(mmHg)- RA (mmHg)]/pump flow (l/min) =

SVR (Wood Units) • 900–1200 dyn.s/cm 5 .

de-airing

• Direct cardiac massage and syringing of left -sided chambers

and venting of the aorta or left -sided chambers is best

undertaken in a head down position, prior to, and after,

aortic unclamping.

• It is customary to ventilate the lungs during the de-airing

process in order to displace air that accumulates in the

pulmonary veins.

Air seen as white specks

Glucose (4.0–7.8 mmol/l)

• Tight glucose control in the postoperative period has been shown by some investigators to improve outcome after cardiac surgery.

• Hypoglycemia is rare except in liver diseases

• Lactate may be high (> 2.5 mmol/l) – usually no treatment

Summarize

• Normal blood parameters - De airing – ACC off – ventilation • Support time – narrow complex, sinus, rate • Pressors • Load with progressive venous occlusion • No distension – load more • BP increase CVP no increase • Perfusionist – occlude aortic line – pump off • Protamine – protamine – assess • Remove venous line • Arterial line – ACT – blood

Separation

CPB : (v. cavae oxygenator aorta)

Partial bypass

(v. cavae oxygenator + RV/lungs/LV common

return to aorta)

Off CPB : (v. cavae heart/lungs aorta)

Transition should be smooth

• Any hiccups • We may need to go

back to bypass • More and more

complicated • Pre and intra op

Thank you all