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