Perfusion procedures
Preparation for Perfusion
The choice of equipment and its configuration depends on the nature of the planned surgical procedure as well as on the patient’s condition. Therefore, preparation for perfusion usually begins with a multidisciplinary discussion. It is necessary to review the patient’s medical history, paying particular attention to height and weight, history of previous surgeries, overall clinical status, neurological condition, carotid artery blood flow studies, hematologic disorders, pulmonary status, allergy history, and other factors that may influence the conduct of perfusion.
Among laboratory investigations, the most important parameters are hematocrit, platelet count, fibrinogen level, creatinine, total protein and serum electrolytes, as well as the presence of cold agglutinins. Deviations from normal values may necessitate changes in circuit configuration or in the composition of the priming solution, such as adding packed red blood cells or albumin, incorporating a hemofilter into the circuit, excluding routinely used drugs due to allergy, or accounting for specific anatomical features.
Preparation for Perfusion
Before initiating perfusion, the target pump flow rate and the doses of components required for priming the circuit are calculated. The calculated cannula size must be communicated to the surgeon. In some cases, due to surgical or anatomical considerations, a different type or a smaller cannula may be required—for example, when the patient’s heart is smaller than usual or when the ascending aorta is severely calcified.
Hematocrit Calculation
Prior to perfusion, the patient’s expected hematocrit must be calculated based on the baseline hematocrit and the priming volume. The calculation of circulating blood volume (CBV) is presented below. The “volume–concentration” formula is used:
V₁ × C₁ = V₂ × C₂
Example
Patient weight: 75 kg
Baseline hematocrit: 30%
Priming volume: 2200 ml
· V₁ = 75 × 70 ml = 5250 ml (CBV)
· V₂ = 5250 + 2200 = 7450 ml
· C₁ = 0.30
· C₂ = unknown
C₂ = V₁ × C₁ / V₂
C₂ = 5250 × 0.30 / 7450 = 0.211 (21.1%)
Thus, after the initiation of perfusion, the hematocrit will be 21.1%.
If a target hematocrit of, for example, 25% is required, the necessary volume of packed red blood cells can be calculated using the same formula.
Volume occupied by erythrocytes at baseline hematocrit:
5250 × 0.30 = 1575 ml
Volume occupied by erythrocytes at hematocrit 25%:
7450 × 0.25 = 1862.5 ml
Required additional erythrocyte volume:
1862.5 – 1575 = 287.5 ml
If the hematocrit of packed red blood cells is 70%, the required volume will be:
287.5 / 0.7 = 410.7 ml
Hematocrit can also be recalculated after adding crystalloid solutions. For example, if 500 ml of crystalloid is added:
· V₁ = 7450 ml, C₁ = 0.25
· V₂ = 7450 + 500 = 7950 ml
C₂ = V₁ × C₁ / V₂ = 7450 × 0.25 / 7950 = 0.23
If 350 ml of packed red blood cells with a hematocrit of 70% is added, the erythrocyte volume will be:
0.7 × 350 = 245 ml
Total erythrocyte volume:
1862.5 + 245 = 2107.5 ml
Resulting hematocrit:
2107.5 / (7950 + 350) ≈ 0.25
Readiness Check Prior to Perfusion
Before initiating perfusion, a checklist must be completed and documented:
· Patient data entered into the computer
· Oxygenator holder correctly and securely installed
· Tubing not kinked
· Luer connections tightened securely
· Gas lines connected
· Gas lines airtight, not kinked or compressed
· Gas blenders functioning properly
· Oxygenator gas outlet cap removed; shunt from the trap functioning
· Power cords properly connected and insulation intact
· Backup power supply available
· Manual drive prepared for use
· Backup light source available
· Water lines connected to the heat exchanger
· Heater–cooler unit functioning and connected to the control unit
· Oxygenator tested for integrity prior to priming
· Proper occlusion set (for roller pumps)
· Arterial filter (bubble trap) filled
· Cardioplegia delivery system primed and temperature checked
· Required drugs added to cardioplegia solution
· Correct rotation direction of suction pump motors
· Left ventricular vent valve oriented correctly
· Pressure transducer calibrated
· Stopcocks securely closed
· Required drugs added to the prime
· Level sensor functioning
· Bubble detector functioning
· Alarm reset function operational
· Temperature probes connected
· Gas analyzer calibrated
· Line-mounted sensors calibrated
· All necessary accessories and spare parts available
After completing all checks, the cardiopulmonary bypass (CPB) machine in the operating room is running, the perfusate is circulating through the circuit and being warmed. The system is checked once again for proper function and absence of air. Warming the perfusate is necessary to prevent cardiac fibrillation at the onset of perfusion.
Heparin Dosing
Heparin is administered by the anesthesiologist via a central venous catheter. Activated clotting time (ACT) is measured 3–5 minutes after administration. The optimal ACT is approximately 480 seconds. Patients with antithrombin III deficiency due to prolonged heparin therapy may require additional, sometimes high, doses of heparin. If additional heparin is ineffective, administration of fresh frozen plasma containing antithrombin III or a specific antithrombin preparation may be required.
Cannulation
The surgeon inserts the cannulas after placing purse-string sutures at the cannulation sites. After aortic cannulation, a test flow is initiated. If arterial line pressure rises significantly, the cannula tip may be abutting the aortic wall or, more critically, entering the media, which may lead to aortic dissection. The cannula for retrograde cardioplegia is usually placed prior to the initiation of perfusion.
Initiation of Perfusion
Perfusion is initiated upon the surgeon’s command. The perfusionist must loudly announce the initiation of perfusion to all personnel in the operating room. This mutual communication helps prevent errors and confirms readiness of the surgical team. At the onset of perfusion, the anesthesiologist discontinues mechanical ventilation.
Although techniques vary between institutions and perfusionists, general principles apply.
Oxygen is supplied to the oxygenator, the arterial line clamp is released, and the pump is started at low speed. Arterial line pressure is monitored to ensure unobstructed flow. A sudden rise in arterial line pressure requires immediate cessation of perfusion and investigation of the cause.
Causes of Increased Arterial Line Pressure
1. Kinking of the tubing or cannula
2. Improper cannulation
3. Aortic cross-clamp placed too close to the cannula
4. Cannula too small
5. Increased systemic arterial pressure
6. Aortic dissection
7. Obstruction of the arterial filter
After a short period, the venous line clamp is opened and venous return is assessed. Pump flow is then gradually increased to a cardiac index of 2.4–3.0 L/min/m². Adequate perfusion cannot be achieved if venous return is insufficient.
Causes of Poor Venous Return
1. Kinking of the venous tubing or cannula
2. Air in the cannula or tubing
3. Oxygenator positioned too high
4. Use of extracardiac suction instead of coronary suction
5. Rapid interstitial fluid accumulation due to low osmolarity
6. Improper venous cannula position with inadequate vena cava drainage
7. Blood loss through open cardioplegia lines or LV vent
8. Bleeding due to accidental injury to the posterior heart surface
9. Bleeding from another source (e.g., gastrointestinal ulcer)
Marked negative pressure in the venous line may cause characteristic noise. In such cases, the line should be partially clamped.
Monitoring During Perfusion
Immediately after achieving target pump flow, the following parameters must be checked:
1. Pump flow corresponds to calculated value
2. Arterial line pressure within 120–200 mmHg
3. Gas mixture delivered at correct flow and ratio
4. Arterial oxygen tension within 150–250 mmHg
5. Systemic arterial pressure 50–90 mmHg
6. Patient temperature appropriate for the surgical stage
7. Coagulation parameters within acceptable range
At least once, the presence and function of the following must be verified:
· Bubble detector enabled
· Level sensor enabled
· Proper positioning of all tubing
· All required medications administered
· Gas analyzer enabled
Monitor Surveillance
Continuous monitoring is the primary method of perfusion control. Some parameters, such as ECG, are displayed on a central monitor. ECG monitoring is especially important before aortic cross-clamping and cardioplegia administration, as well as after aortic unclamping and restoration of cardiac activity. Attention is paid to ST-segment changes, rhythm disturbances, and other abnormalities.
ECG interpretation may be difficult due to electrical interference, often caused by proximity of power cables to monitoring equipment. Additionally, tubing in operating pumps may become electrically charged, transmitting current to the patient. Interference can be reduced by preventing drying of ECG electrodes. All equipment, not only the CPB machine, must be checked for leakage current, which should not exceed 100 microamperes.
Another important parameter is diastolic pulmonary artery pressure, used to assess cardiac filling. Monitoring is performed via a Swan–Ganz catheter placed preoperatively through the internal jugular vein into the right atrium and pulmonary artery. Pulmonary artery pressure serves as a guide for terminating perfusion and assessing cardiac filling or overfilling. Normal pulmonary artery pressure is approximately 25/8 mmHg and typically increases after perfusion.
Low Systemic Arterial Pressure
Adequate arterial pressure is essential for organ perfusion. Although opinions vary, mean arterial pressure is generally maintained between 60 and 90 mmHg. Cerebral blood flow is autoregulated at pressures above 60 mmHg.
At the onset of perfusion, hemodilution reduces circulating catecholamine concentrations, potentially causing transient hypotension. Systemic vascular resistance is also decreased. Later during surgery, adrenal catecholamine release in response to stress may elevate blood pressure above normal, leading to tissue shunting and inadequate perfusion of vital organs and skeletal muscle.
Correction of transient hypotension must therefore be cautious. Pump flow adequacy, absence of shunting, correct dosing of vasodilators, and pressure transducer calibration must be confirmed.
If blood pressure does not normalize, vasopressors are administered. Typically, phenylephrine is given at a dose of 40–50 µg in adults, with adjustment as needed. If ineffective, more potent agents such as norepinephrine are used.
High Systemic Arterial Pressure
Hypertension is no less dangerous than hypotension. Excessively high blood pressure may cause bleeding from suture lines and the aortic cannulation site. During procedures involving opening the aorta, such as aortic valve replacement, hypertension may result in severe bleeding after unclamping.
Arterial pressure during perfusion should not exceed 90 mmHg. Often, pump flow must be reduced temporarily until antihypertensive agents take effect, while monitoring blood gases and increasing oxygen flow if needed.
Blood pressure reduction strategies include ensuring adequate anesthesia. Fentanyl is commonly used to block afferent CNS pathways, and appropriate dosing is often sufficient. Inhalational sevoflurane is also used. Sodium nitroprusside may be administered via the oxygenator as a potent vasodilator acting on venules and arterioles; the infusion rate should not exceed 10 µg/kg/min due to potential toxicity, and the solution must be protected from light.
Temperature Management
To prevent cardiac fibrillation at the onset of perfusion, the perfusate must be warmed. During perfusion, patients are usually cooled to 28–30°C, providing minimal protection in case of pump failure. A 7°C decrease in body temperature reduces oxygen consumption by approximately 50%.
Normothermic perfusion results in less platelet dysfunction but greater trauma to blood elements due to higher flow rates. Modern oxygenators allow adequate gas exchange during normothermic perfusion even in large patients.
During cooling, the temperature gradient between venous and arterial blood must not exceed 10°C to prevent microbubble formation. Temperature is monitored using probes placed in the nasopharynx, rectum, bladder, and tympanic membrane.
Oxygenation Issues
Reduced arterial oxygen saturation may result from inadequate skeletal muscle relaxation, requiring administration of muscle relaxants, or from insufficient pump flow, necessitating an increase to an index of 2.4 L/min/m² or higher. Since oxygen consumption decreases with hypothermia, cooling may be required if oxygenation cannot be normalized.
Adequate pump flow is the primary determinant of oxygen delivery to vital organs. In adults, cerebral blood flow averages 750 ml/min and coronary blood flow approximately 225 ml/min, with about 70% oxygen extraction in the coronary circulation.
Organ Blood Flow Distribution at Rest and During Perfusion
· Brain: 15%
· Heart: 4–5%
· Kidneys: 27%
· Liver: 29%
Specific oxygenator characteristics should always be consulted, and gas flow adjusted according to laboratory data.
Renal Function During Perfusion
Normal renal function is an indicator of adequate perfusion. Renal blood flow constitutes approximately 27% of systemic flow, while oxygen consumption is only about 7%. Adequate renal filtration requires continuous high blood flow; therefore, renal function is affected early during hypoperfusion. Short periods of anuria during perfusion are preferable to reduced cerebral or vital organ perfusion.
Although urine output during perfusion does not guarantee normal postoperative renal function, urine flow of 0.5–1.0 ml/kg/min (approximately 1 ml/min in adults) is desirable and indicates adequate systemic perfusion. Adequate urine output also prevents hyperkalemia and fluid overload. Urine output is assessed 15 minutes after perfusion onset. Absence of urine for 30 minutes requires intervention.
Common causes include catheter kinking, disconnection, leakage, or blockage by lubricating gel. Gentle bladder compression may resolve gel obstruction.
Anuria may also result from fluid extravasation or hypotension. Mannitol administration is often effective; if not, furosemide is given at 0.25 mg/kg.
Causes of Anuria and Corrective Measures
1. Kinked or disconnected catheter — straighten and reconnect
2. Gel obstruction — compress bladder
3. Low blood pressure — administer vasopressors
4. Low pump flow — increase flow
5. Tissue edema — administer mannitol
Aortic Cross-Clamping
The surgeon applies the aortic cross-clamp before the main surgical stage. Cooling may begin at this time if required. Pump flow is reduced during clamp application and then gradually increased to target levels under arterial line pressure control. Excessive pressure may occur if the clamp is placed too close to the cannula.
Cardioplegia Administration
The first dose of cardioplegia is usually delivered antegrade. After cardiac arrest, retrograde administration is used. Antegrade delivery allows assessment of aortic cross-clamp adequacy: if cardioplegia line pressure does not decrease during transient pump flow reduction, the clamp is complete.
Numerous cardioplegia formulations and delivery techniques exist, with or without hypothermia. All contain potassium ions to achieve electromechanical cardiac arrest.
During antegrade delivery, cardioplegia line pressure should be approximately 150 mmHg. Considering pressure drop across the cannula, this corresponds to about 50 mmHg in the aortic root. During retrograde delivery, pressure is measured in the coronary sinus and should not exceed 50 mmHg to avoid rupture.
The solution flows from the coronary sinus into coronary veins, capillaries, arteries, and finally into the aorta, from which it must be evacuated. During antegrade delivery, cardioplegia drains via the right atrium through the venous cannula.
Asystole is confirmed by a flat ECG line, although electrical interference may complicate interpretation. The usual dose is 10 ml/kg.
Additional doses are administered every 20 minutes for blood cardioplegia and every 60 minutes for Custodiol. Cardioplegia may also be delivered through venous grafts after distal anastomoses to assess graft patency and perfuse the supplied myocardium.
Myocardial temperature should not exceed 15°C. Prior to aortic unclamping, warm cardioplegia (36–38°C) may be administered to wash out metabolites and air and replenish ATP stores.
Rewarming is performed gradually. Circulating water temperature must not exceed 42°C. The temperature gradient between warming water and blood should not exceed 12°C in adults and 8°C in children to prevent hemolysis.
Left Ventricular Venting
The purpose of left ventricular venting is to remove air and blood from the left ventricle or aorta. Blood may enter the LV via pulmonary veins and pulmonary circulation even with effective venous drainage. In aortic insufficiency, cardioplegia may enter the LV. In congenital defects such as ASD or VSD, blood may also fill the LV. Excessive LV distension leads to myocardial injury.
One disadvantage of femoro-femoral CPB is the lack of cardiac decompression. Venting can be achieved by placing a cannula directly into the LV, using the aortic cardioplegia cannula connected via a Y-connector (not during antegrade delivery), via the right superior pulmonary vein through the mitral valve, or via the pulmonary artery. All vents should be equipped with valves to prevent excessive suction and air entry.
Fluid Balance
During perfusion, CBV increases due to priming solutions and intraoperative infusions. Hematocrit typically decreases to 22–29%, improving capillary perfusion compared to higher values. Mean arteriolar closing pressure is approximately 20 mmHg; reduced blood viscosity allows adequate flow at lower pressures. Flow becomes laminar in the oxygenator and tubing, and flow velocity is inversely proportional to viscosity.
Large volumes of crystalloid may reduce oncotic pressure and cause tissue edema. In such cases, 25% albumin should be added at a ratio of 25% per 100% crystalloid. Severe edema may prevent sternal closure.
Termination of Perfusion
Before terminating perfusion, patient readiness must be reassessed, including ECG, hematocrit, and potassium level (3.5–5.5 mEq/L). Hyperkalemia manifests as tall peaked T waves, QRS widening, loss of P waves, and sine-wave ECG. Hypokalemia may cause arrhythmias, ST shortening, and prominent U waves.
Before termination, ensure suction is discontinued and inform the surgeon. Perfusion is terminated by gradually clamping the venous line while reducing pump flow. Mechanical ventilation is resumed by the anesthesiologist.
CBV is assessed using diastolic pulmonary artery pressure, which should be approximately 16 mmHg. Adequate cardiac output is indicated by arterial pressure ≥90–100 mmHg. Under these conditions, the pump is stopped, the venous line clamped, followed by the arterial line. Pumps are then turned off and termination announced.
Hypotension after termination may require slow CBV replacement with monitoring of LV output. During assessment of LV function, perfusate infusion is discontinued. Normal adult cardiac output is 5–6 L/min at rest, with a cardiac index >2.2.
During protamine administration, all suction must be discontinued to prevent clotting within the circuit. The surgeon removes the aortic cannula after protamine due to thrombosis risk; venous cannulas are removed earlier. ACT is measured to assess reversal. If perfusion must be resumed, heparin is re-administered.
Use of Residual Perfusate
Various methods exist for managing residual perfusate remaining in the circuit and oxygenator. Cell saver systems may be used but remove plasma proteins and formed elements except erythrocytes. Ultrafiltration preserves plasma proteins and is preferable, though it increases procedural cost.
Because perfusion may need to be resumed at any time, for example due to a severe reaction to protamine, the CPB circuit should not be dismantled or emptied until the operation is fully completed.
The choice of equipment and its configuration depends on the nature of the planned surgical procedure as well as on the patient’s condition. Therefore, preparation for perfusion usually begins with a multidisciplinary discussion. It is necessary to review the patient’s medical history, paying particular attention to height and weight, history of previous surgeries, overall clinical status, neurological condition, carotid artery blood flow studies, hematologic disorders, pulmonary status, allergy history, and other factors that may influence the conduct of perfusion.
Among laboratory investigations, the most important parameters are hematocrit, platelet count, fibrinogen level, creatinine, total protein and serum electrolytes, as well as the presence of cold agglutinins. Deviations from normal values may necessitate changes in circuit configuration or in the composition of the priming solution, such as adding packed red blood cells or albumin, incorporating a hemofilter into the circuit, excluding routinely used drugs due to allergy, or accounting for specific anatomical features.
Preparation for Perfusion
Before initiating perfusion, the target pump flow rate and the doses of components required for priming the circuit are calculated. The calculated cannula size must be communicated to the surgeon. In some cases, due to surgical or anatomical considerations, a different type or a smaller cannula may be required—for example, when the patient’s heart is smaller than usual or when the ascending aorta is severely calcified.
Hematocrit Calculation
Prior to perfusion, the patient’s expected hematocrit must be calculated based on the baseline hematocrit and the priming volume. The calculation of circulating blood volume (CBV) is presented below. The “volume–concentration” formula is used:
V₁ × C₁ = V₂ × C₂
Example
Patient weight: 75 kg
Baseline hematocrit: 30%
Priming volume: 2200 ml
· V₁ = 75 × 70 ml = 5250 ml (CBV)
· V₂ = 5250 + 2200 = 7450 ml
· C₁ = 0.30
· C₂ = unknown
C₂ = V₁ × C₁ / V₂
C₂ = 5250 × 0.30 / 7450 = 0.211 (21.1%)
Thus, after the initiation of perfusion, the hematocrit will be 21.1%.
If a target hematocrit of, for example, 25% is required, the necessary volume of packed red blood cells can be calculated using the same formula.
Volume occupied by erythrocytes at baseline hematocrit:
5250 × 0.30 = 1575 ml
Volume occupied by erythrocytes at hematocrit 25%:
7450 × 0.25 = 1862.5 ml
Required additional erythrocyte volume:
1862.5 – 1575 = 287.5 ml
If the hematocrit of packed red blood cells is 70%, the required volume will be:
287.5 / 0.7 = 410.7 ml
Hematocrit can also be recalculated after adding crystalloid solutions. For example, if 500 ml of crystalloid is added:
· V₁ = 7450 ml, C₁ = 0.25
· V₂ = 7450 + 500 = 7950 ml
C₂ = V₁ × C₁ / V₂ = 7450 × 0.25 / 7950 = 0.23
If 350 ml of packed red blood cells with a hematocrit of 70% is added, the erythrocyte volume will be:
0.7 × 350 = 245 ml
Total erythrocyte volume:
1862.5 + 245 = 2107.5 ml
Resulting hematocrit:
2107.5 / (7950 + 350) ≈ 0.25
Readiness Check Prior to Perfusion
Before initiating perfusion, a checklist must be completed and documented:
· Patient data entered into the computer
· Oxygenator holder correctly and securely installed
· Tubing not kinked
· Luer connections tightened securely
· Gas lines connected
· Gas lines airtight, not kinked or compressed
· Gas blenders functioning properly
· Oxygenator gas outlet cap removed; shunt from the trap functioning
· Power cords properly connected and insulation intact
· Backup power supply available
· Manual drive prepared for use
· Backup light source available
· Water lines connected to the heat exchanger
· Heater–cooler unit functioning and connected to the control unit
· Oxygenator tested for integrity prior to priming
· Proper occlusion set (for roller pumps)
· Arterial filter (bubble trap) filled
· Cardioplegia delivery system primed and temperature checked
· Required drugs added to cardioplegia solution
· Correct rotation direction of suction pump motors
· Left ventricular vent valve oriented correctly
· Pressure transducer calibrated
· Stopcocks securely closed
· Required drugs added to the prime
· Level sensor functioning
· Bubble detector functioning
· Alarm reset function operational
· Temperature probes connected
· Gas analyzer calibrated
· Line-mounted sensors calibrated
· All necessary accessories and spare parts available
After completing all checks, the cardiopulmonary bypass (CPB) machine in the operating room is running, the perfusate is circulating through the circuit and being warmed. The system is checked once again for proper function and absence of air. Warming the perfusate is necessary to prevent cardiac fibrillation at the onset of perfusion.
Heparin Dosing
Heparin is administered by the anesthesiologist via a central venous catheter. Activated clotting time (ACT) is measured 3–5 minutes after administration. The optimal ACT is approximately 480 seconds. Patients with antithrombin III deficiency due to prolonged heparin therapy may require additional, sometimes high, doses of heparin. If additional heparin is ineffective, administration of fresh frozen plasma containing antithrombin III or a specific antithrombin preparation may be required.
Cannulation
The surgeon inserts the cannulas after placing purse-string sutures at the cannulation sites. After aortic cannulation, a test flow is initiated. If arterial line pressure rises significantly, the cannula tip may be abutting the aortic wall or, more critically, entering the media, which may lead to aortic dissection. The cannula for retrograde cardioplegia is usually placed prior to the initiation of perfusion.
Initiation of Perfusion
Perfusion is initiated upon the surgeon’s command. The perfusionist must loudly announce the initiation of perfusion to all personnel in the operating room. This mutual communication helps prevent errors and confirms readiness of the surgical team. At the onset of perfusion, the anesthesiologist discontinues mechanical ventilation.
Although techniques vary between institutions and perfusionists, general principles apply.
Oxygen is supplied to the oxygenator, the arterial line clamp is released, and the pump is started at low speed. Arterial line pressure is monitored to ensure unobstructed flow. A sudden rise in arterial line pressure requires immediate cessation of perfusion and investigation of the cause.
Causes of Increased Arterial Line Pressure
1. Kinking of the tubing or cannula
2. Improper cannulation
3. Aortic cross-clamp placed too close to the cannula
4. Cannula too small
5. Increased systemic arterial pressure
6. Aortic dissection
7. Obstruction of the arterial filter
After a short period, the venous line clamp is opened and venous return is assessed. Pump flow is then gradually increased to a cardiac index of 2.4–3.0 L/min/m². Adequate perfusion cannot be achieved if venous return is insufficient.
Causes of Poor Venous Return
1. Kinking of the venous tubing or cannula
2. Air in the cannula or tubing
3. Oxygenator positioned too high
4. Use of extracardiac suction instead of coronary suction
5. Rapid interstitial fluid accumulation due to low osmolarity
6. Improper venous cannula position with inadequate vena cava drainage
7. Blood loss through open cardioplegia lines or LV vent
8. Bleeding due to accidental injury to the posterior heart surface
9. Bleeding from another source (e.g., gastrointestinal ulcer)
Marked negative pressure in the venous line may cause characteristic noise. In such cases, the line should be partially clamped.
Monitoring During Perfusion
Immediately after achieving target pump flow, the following parameters must be checked:
1. Pump flow corresponds to calculated value
2. Arterial line pressure within 120–200 mmHg
3. Gas mixture delivered at correct flow and ratio
4. Arterial oxygen tension within 150–250 mmHg
5. Systemic arterial pressure 50–90 mmHg
6. Patient temperature appropriate for the surgical stage
7. Coagulation parameters within acceptable range
At least once, the presence and function of the following must be verified:
· Bubble detector enabled
· Level sensor enabled
· Proper positioning of all tubing
· All required medications administered
· Gas analyzer enabled
Monitor Surveillance
Continuous monitoring is the primary method of perfusion control. Some parameters, such as ECG, are displayed on a central monitor. ECG monitoring is especially important before aortic cross-clamping and cardioplegia administration, as well as after aortic unclamping and restoration of cardiac activity. Attention is paid to ST-segment changes, rhythm disturbances, and other abnormalities.
ECG interpretation may be difficult due to electrical interference, often caused by proximity of power cables to monitoring equipment. Additionally, tubing in operating pumps may become electrically charged, transmitting current to the patient. Interference can be reduced by preventing drying of ECG electrodes. All equipment, not only the CPB machine, must be checked for leakage current, which should not exceed 100 microamperes.
Another important parameter is diastolic pulmonary artery pressure, used to assess cardiac filling. Monitoring is performed via a Swan–Ganz catheter placed preoperatively through the internal jugular vein into the right atrium and pulmonary artery. Pulmonary artery pressure serves as a guide for terminating perfusion and assessing cardiac filling or overfilling. Normal pulmonary artery pressure is approximately 25/8 mmHg and typically increases after perfusion.
Low Systemic Arterial Pressure
Adequate arterial pressure is essential for organ perfusion. Although opinions vary, mean arterial pressure is generally maintained between 60 and 90 mmHg. Cerebral blood flow is autoregulated at pressures above 60 mmHg.
At the onset of perfusion, hemodilution reduces circulating catecholamine concentrations, potentially causing transient hypotension. Systemic vascular resistance is also decreased. Later during surgery, adrenal catecholamine release in response to stress may elevate blood pressure above normal, leading to tissue shunting and inadequate perfusion of vital organs and skeletal muscle.
Correction of transient hypotension must therefore be cautious. Pump flow adequacy, absence of shunting, correct dosing of vasodilators, and pressure transducer calibration must be confirmed.
If blood pressure does not normalize, vasopressors are administered. Typically, phenylephrine is given at a dose of 40–50 µg in adults, with adjustment as needed. If ineffective, more potent agents such as norepinephrine are used.
High Systemic Arterial Pressure
Hypertension is no less dangerous than hypotension. Excessively high blood pressure may cause bleeding from suture lines and the aortic cannulation site. During procedures involving opening the aorta, such as aortic valve replacement, hypertension may result in severe bleeding after unclamping.
Arterial pressure during perfusion should not exceed 90 mmHg. Often, pump flow must be reduced temporarily until antihypertensive agents take effect, while monitoring blood gases and increasing oxygen flow if needed.
Blood pressure reduction strategies include ensuring adequate anesthesia. Fentanyl is commonly used to block afferent CNS pathways, and appropriate dosing is often sufficient. Inhalational sevoflurane is also used. Sodium nitroprusside may be administered via the oxygenator as a potent vasodilator acting on venules and arterioles; the infusion rate should not exceed 10 µg/kg/min due to potential toxicity, and the solution must be protected from light.
Temperature Management
To prevent cardiac fibrillation at the onset of perfusion, the perfusate must be warmed. During perfusion, patients are usually cooled to 28–30°C, providing minimal protection in case of pump failure. A 7°C decrease in body temperature reduces oxygen consumption by approximately 50%.
Normothermic perfusion results in less platelet dysfunction but greater trauma to blood elements due to higher flow rates. Modern oxygenators allow adequate gas exchange during normothermic perfusion even in large patients.
During cooling, the temperature gradient between venous and arterial blood must not exceed 10°C to prevent microbubble formation. Temperature is monitored using probes placed in the nasopharynx, rectum, bladder, and tympanic membrane.
Oxygenation Issues
Reduced arterial oxygen saturation may result from inadequate skeletal muscle relaxation, requiring administration of muscle relaxants, or from insufficient pump flow, necessitating an increase to an index of 2.4 L/min/m² or higher. Since oxygen consumption decreases with hypothermia, cooling may be required if oxygenation cannot be normalized.
Adequate pump flow is the primary determinant of oxygen delivery to vital organs. In adults, cerebral blood flow averages 750 ml/min and coronary blood flow approximately 225 ml/min, with about 70% oxygen extraction in the coronary circulation.
Organ Blood Flow Distribution at Rest and During Perfusion
· Brain: 15%
· Heart: 4–5%
· Kidneys: 27%
· Liver: 29%
Temperature | Index | FiO₂ | Gas Flow / FiO₂ Ratio |
37°C | 2.4 | 0.80 | 1:1 |
34°C | 2.2 | 0.70 | 0.8:1 |
30°C | 2.0 | 0.65 | 0.7:1 |
28°C | 1.8 | 0.60 | 0.6:1 |
22°C | 1.6 | 0.50 | 0.5:1 |
Renal Function During Perfusion
Normal renal function is an indicator of adequate perfusion. Renal blood flow constitutes approximately 27% of systemic flow, while oxygen consumption is only about 7%. Adequate renal filtration requires continuous high blood flow; therefore, renal function is affected early during hypoperfusion. Short periods of anuria during perfusion are preferable to reduced cerebral or vital organ perfusion.
Although urine output during perfusion does not guarantee normal postoperative renal function, urine flow of 0.5–1.0 ml/kg/min (approximately 1 ml/min in adults) is desirable and indicates adequate systemic perfusion. Adequate urine output also prevents hyperkalemia and fluid overload. Urine output is assessed 15 minutes after perfusion onset. Absence of urine for 30 minutes requires intervention.
Common causes include catheter kinking, disconnection, leakage, or blockage by lubricating gel. Gentle bladder compression may resolve gel obstruction.
Anuria may also result from fluid extravasation or hypotension. Mannitol administration is often effective; if not, furosemide is given at 0.25 mg/kg.
Causes of Anuria and Corrective Measures
1. Kinked or disconnected catheter — straighten and reconnect
2. Gel obstruction — compress bladder
3. Low blood pressure — administer vasopressors
4. Low pump flow — increase flow
5. Tissue edema — administer mannitol
Aortic Cross-Clamping
The surgeon applies the aortic cross-clamp before the main surgical stage. Cooling may begin at this time if required. Pump flow is reduced during clamp application and then gradually increased to target levels under arterial line pressure control. Excessive pressure may occur if the clamp is placed too close to the cannula.
Cardioplegia Administration
The first dose of cardioplegia is usually delivered antegrade. After cardiac arrest, retrograde administration is used. Antegrade delivery allows assessment of aortic cross-clamp adequacy: if cardioplegia line pressure does not decrease during transient pump flow reduction, the clamp is complete.
Numerous cardioplegia formulations and delivery techniques exist, with or without hypothermia. All contain potassium ions to achieve electromechanical cardiac arrest.
During antegrade delivery, cardioplegia line pressure should be approximately 150 mmHg. Considering pressure drop across the cannula, this corresponds to about 50 mmHg in the aortic root. During retrograde delivery, pressure is measured in the coronary sinus and should not exceed 50 mmHg to avoid rupture.
The solution flows from the coronary sinus into coronary veins, capillaries, arteries, and finally into the aorta, from which it must be evacuated. During antegrade delivery, cardioplegia drains via the right atrium through the venous cannula.
Asystole is confirmed by a flat ECG line, although electrical interference may complicate interpretation. The usual dose is 10 ml/kg.
Additional doses are administered every 20 minutes for blood cardioplegia and every 60 minutes for Custodiol. Cardioplegia may also be delivered through venous grafts after distal anastomoses to assess graft patency and perfuse the supplied myocardium.
Myocardial temperature should not exceed 15°C. Prior to aortic unclamping, warm cardioplegia (36–38°C) may be administered to wash out metabolites and air and replenish ATP stores.
Rewarming is performed gradually. Circulating water temperature must not exceed 42°C. The temperature gradient between warming water and blood should not exceed 12°C in adults and 8°C in children to prevent hemolysis.
Left Ventricular Venting
The purpose of left ventricular venting is to remove air and blood from the left ventricle or aorta. Blood may enter the LV via pulmonary veins and pulmonary circulation even with effective venous drainage. In aortic insufficiency, cardioplegia may enter the LV. In congenital defects such as ASD or VSD, blood may also fill the LV. Excessive LV distension leads to myocardial injury.
One disadvantage of femoro-femoral CPB is the lack of cardiac decompression. Venting can be achieved by placing a cannula directly into the LV, using the aortic cardioplegia cannula connected via a Y-connector (not during antegrade delivery), via the right superior pulmonary vein through the mitral valve, or via the pulmonary artery. All vents should be equipped with valves to prevent excessive suction and air entry.
Fluid Balance
During perfusion, CBV increases due to priming solutions and intraoperative infusions. Hematocrit typically decreases to 22–29%, improving capillary perfusion compared to higher values. Mean arteriolar closing pressure is approximately 20 mmHg; reduced blood viscosity allows adequate flow at lower pressures. Flow becomes laminar in the oxygenator and tubing, and flow velocity is inversely proportional to viscosity.
Large volumes of crystalloid may reduce oncotic pressure and cause tissue edema. In such cases, 25% albumin should be added at a ratio of 25% per 100% crystalloid. Severe edema may prevent sternal closure.
Termination of Perfusion
Before terminating perfusion, patient readiness must be reassessed, including ECG, hematocrit, and potassium level (3.5–5.5 mEq/L). Hyperkalemia manifests as tall peaked T waves, QRS widening, loss of P waves, and sine-wave ECG. Hypokalemia may cause arrhythmias, ST shortening, and prominent U waves.
Before termination, ensure suction is discontinued and inform the surgeon. Perfusion is terminated by gradually clamping the venous line while reducing pump flow. Mechanical ventilation is resumed by the anesthesiologist.
CBV is assessed using diastolic pulmonary artery pressure, which should be approximately 16 mmHg. Adequate cardiac output is indicated by arterial pressure ≥90–100 mmHg. Under these conditions, the pump is stopped, the venous line clamped, followed by the arterial line. Pumps are then turned off and termination announced.
Hypotension after termination may require slow CBV replacement with monitoring of LV output. During assessment of LV function, perfusate infusion is discontinued. Normal adult cardiac output is 5–6 L/min at rest, with a cardiac index >2.2.
During protamine administration, all suction must be discontinued to prevent clotting within the circuit. The surgeon removes the aortic cannula after protamine due to thrombosis risk; venous cannulas are removed earlier. ACT is measured to assess reversal. If perfusion must be resumed, heparin is re-administered.
Use of Residual Perfusate
Various methods exist for managing residual perfusate remaining in the circuit and oxygenator. Cell saver systems may be used but remove plasma proteins and formed elements except erythrocytes. Ultrafiltration preserves plasma proteins and is preferable, though it increases procedural cost.
Because perfusion may need to be resumed at any time, for example due to a severe reaction to protamine, the CPB circuit should not be dismantled or emptied until the operation is fully completed.