Anesthetic Management During Cardiopulmonary

Bypass

Dr.N.Kanagarajan

Preparations for Cardiopulmonary Bypass

CPB CIRCUIT

Function

Oxygenation and Carbon dioxide elimination

Circulation of blood

Systemic Cooling

Diversion of blood from the heart to provide a bloodless

surgical field

CIRCUIT DESIGN

Venous circuit

Venous blood drained by gravity from the right side of the

heart into the reservoir

Most commonly single venous cannulation followed.

Arterial Cannula

Returns oxygenated blood from pump to aorta

Usually placed in ascending aorta/ femoral artery

Total CPB

When all venous blood draining toward the heart is

diverted into the pump oxygenator.

Partial CPB

When only a portion of systemic venous blood drains

to the pump oxygenator while passes through the

right heart and lungs and ejected by the left ventricle.

Anesthesiologist Pre Bypass Check List

Anticoagulation

Generally adequate heparinisation requires a activated coagulation

time > 480 seconds.

ACT accurately measured within two minutes of heparin administration.

Anesthesia

Concentration of drugs in the blood diluted by the prime

Supplemental medication necessary

Neuromuscular blockers

Anesthesia,Analgesics and Amnesics

Cannulations

Aortic cannula

Position within the lumen of the aorta should be checked

Aortic pressure should be pulsatile and correlate with radial artery pressure

Check Carotid pulsation

Drips IV lines closed on heparinisation to prevent further hemodilution.

Monitoring

Check the zero and calibration of the arterial pressure

transducer.

Insert nasopharyngeal temp. probe prior to heparinisation

Foley’s catheter to check urine output.

Maintenance Of Bypass Anticoagulation

ACT > 480 seconds

ACT checked every 30-60 mins

Perfusion pressure on CPB Lower flow and pressure during CPB may optimise revascularisation

while higher flow and pressure may minimise patient complication.

Cerebral Autoregulation: Mean ABP of 50-150mm Hg.

Higher perfusion pressure needed in severe atheromatous

states,advanced age, systemic hypertension and diabetes

Pump flow on CPB

Careful balance between surgical visualization and adequate oxygen

delivery must be maintained

1-2 L/min/m2 perfuses most of the microcirculation when Hct is 22%

and hypothermic CPB is used.

Mixed Venous saturation is 70%

Blood gas and acid base status

Should be checked soon after intitiation of CPB

Every 30-60 min

Arterial oxygenation maintained at 100 - 300mm Hg

Alpha Stat Vs. pH Stat

Alpha Stat

Uncorrected (37°C) pH is kept at 7.40 with

PCO2 at 40 mm Hg creating a relative alkalosis

at the patient arterial body temperature.

pH Stat

Maintains a pH of 7.40 and PCO2 of 40 mm

Hg when corrected for body temperature,

typically requiring the addition of CO2 during

hypothermic CPB.

Potent vasodilatory effect increased

cerebral blood flow.

May be advantageous in paediatric patients

Anesthetic Depth

Should be sufficient to

Suppress hypertensive or tachycardic responses to surgical

stimuli

Prevent awareness

Prevent unconsciousness movement and respiration

because hypothermia reduces the anesthetic requirement

they are most commonly used during the rewarming

periods.

Ventilation Should cease during total CPB

During partial Bypass occasional ventilation wth 100% O2 may

be needed.

Urine production Sign of renal perfusion

As a guide for fluid management

>1ml/kg/hr should be maintained

Fluid management

Hemodilution

Lowers the blood viscosity counteracting the deleterious viscosity

changes caused by hypothermia

Organ blood flow improved

Optimal hematocrit > 20

Usually a clear priming(non-blood containing) solution is

utilised.

Fluid replacement during CPB

Based on Hb, < 5g/dl – Blood, otherwise usually colloids used

Ultrafiltration

If adequate diuresis cannot be produced an

ultrafiltration device added to CPB circuit t remove

excess water.

Heparin may be removed during ultrafiltration, so

anticoagulation must be monitored frequently.

Weaning from CPB

Temperature Systemic hypothermia is widely used during CPB,therefore patient must be

rewarmed

Core temp (nasopharnygeal / tympanic/bladder)

> 36°C prior to terminating CPB.

Order of rewarming: Vessel Rich> Muscle> Fat

Excessive perfusate heating not advisable Denaturation of plasma proteins

Cerebral hyperthermia

Air embolism

Rewarming may be enhanced By increasing blood flow

Use of arterial vasodilators(SNP)

Analysis and correlation of electrolyte , Acid base balance and

Oxygen transport status

Acid base status must be optimised

Acidosis

Myocardial depressant

Increased Pulmonary hypertension

Metabolic acidosis due to inadequate tissue perfusion

Inadequate perfusion flow

A low hemoglobin level

Inadequate oxygenation of blood

Other causes

DKA

Renal Failure

NaHCO3 can be used to treat the primary cause

Serum K+ >4.0 meq/l to reduce the incidence f arrhythmia

Ca2+ - to treat hypocalcemia and hyperkalemia

Dose- 5-15 ml/kg,

can cause coronary spasm, augmentation of

reperfusion injury

Hematocrit

Must be adequate to provide oxyge carrying capacity

HCt > 20% or greater is appropriate for termination of bypass.

Coagulation

Additional heparin may be needed because rewarming accelerates heparin a

metabolism

Blood products should be readily available to use if needed(Platelets /FFP /

fibrinogen)

Blood products can be used after termination of CPB

Re-establish adequate ventilation

Once ventricular ejection(pulsatile arterial waveform) is

seen, ventilation is started (4 - 6 breaths/min)

Also help to eliminate air from the pulmonary veins

Adequate oxygenation and ventilation amust be

nesured while pt is on CPB.

Lungs should be re-expanded with 2-3 sustained

breaths(15-20 seconds) with visualisation of bilateral

lung expansion and resolution of atelectasis

tracheal suction done

Prevent LIMA graft damage caused by lung

overdistension.

Inspired oxygen fraction should be 1.0

Predictors

Preoperative EF>40%

Ongoing ischemia/Infarct in the pre-CPB period

Prolonged CPB duration

Inadequate Surgical Repair

Incomplete coronary revascularisation

Residual valvular regurgitation.

Incomplete Myocardial Preservation

Incomplete diastolic arrest

Incomplete Cardioplegia

Other Drugs / Infusions

Volume expanders

Vasopressors and inotropes

Vasodilators

Anesthetic State

Because of the potential for hemodynamic instability during and shortly after

weaning from CPB, it is better to avoid additional anesthetic adminstration.

Supplemental medications are best given during rewarming

Post ACC removal

Atleast 10-15 min should elapse after the removal of the ACC before

attempting sepertion from CPB.

Myocardial injury and edema are reduced by avoiding myoacrdial

perfusion pressures in excess of 60 mm Hg in the first 10-15 mins after

reperfusion.

Thereafter sustaining coronary perfusion pressure above above 70

mmHG for the last 5-10 min of CPB improves outcome.

Final Checklist for Terminating CPB

Confirm Ventilation – lungs ventilated with 100% oxygen.

The patient is sufficiently rewarmed.

Complete de-airing done from heart/ grafts/ great

vessels.

Optimal metabolic condition.

All equipment and drugs are ready.

Sequence Of events

Step1: Retarding the venous return to the pump

Slowly the venous line is partially occluded

Blood flow through RV increased - the Heart begins to

eject

Preload- the amount of venous line occlusion is adjusted

carefully and maintain a certain optimal pre-

load(adequate cardiac output).

Step 2: Lowering pump flow into aorta

Attaining partial bypass

The rise in preload causes the heart to begin to contribute to the cardiac output.

Reduced Pump outflow requirement

The amount of arterial blood returned from the pump to the patient can be reduced

Cardiac function And hemodynamics carefully monitored

Readjusting venous line resistance

To maintain the constant filling resistance.

Step 3: Terminating Bypass

If the heart is generating adequate systolic pressure (90-

100 mm Hg) at an acceptable preload with a pump flow of

1L/min or less the patient is ready for termination of CPB.

The pump is stopped and both pump cannulas are

clamped fully

Immediately After Terminating CPB

Preload

Infusing blood from the pump In adult patients, volume is infused at 50-100ml

increments from the venous pump reservoir to the patient through aortic cannula

Should be watched for air bubbles in aortic cannula W/F blood pressure/ filling pressures/ heart

Measuring cardiac function

Cardiac Index > 2.0 L/min/M2

Measuring patient perfusion

Adequate tissue perfusion –ABG/ pH after 5 min after CPB

U/O – normally rise after CPB.

Removing the venous cannulae

Removing the aortic cannula