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
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 ??
RomannofRoyster 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 ,Dobutamine,) • • 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
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 hetastarchshould 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
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 • hyperkalemiamay 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.
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