CP10 CPB Adults
Cardiopulmonary bypass CPB is used to support the patient’s circulation during the period of surgical intervention. This can be achieved with various pump oxygenator combinations, and the system used in this hospital will be described in detail. Attempts will be made to evaluate and update the system whenever new and improved equipment is available.
Cardiopulmonary bypass is indicated for patients who undergo heart or major vessel surgery and require that the blood flow to these organs be diverted to the heart-lung machine for artificial oxygenation and circulation and to provide a safe and effective exposure during surgical repair. Hypothermia and hemodilution provide safe periods of low flow and/or circulatory arrest when necessary. This is determined by the attending surgeon, depending on the complexity of the operation.
Blood flow is determined by the patient’s body surface area (BSA). A calculated blood flow at and index of 2.4L/min/m2 is used to determine the size of the circuit.
Available in a sterile component that contains the adult tubing pack, the oxygenator, and an integrated cardiotomy reservoir. The arterial line is 3/8” and the venous line is ½”. An adult arterial line filter with a 3/8” bridge may be included. The configurations of these disposable products are reviewed and changes are made to improve as necessary. The arterial limb of the circuit also consists of 3/8” tubing, and it is connected to the outlet of the arterial centrifugal pump with a one-way duckbill valve to help protect the oxygenator, from negative pressure. Output from this pump is directed to and adult membrane oxygenator and then to an arterial filter, before being returned to the patient. The venous reservoir is protected against excessive suction with a positive and negative pressure relief valve.
Circuit Design and Safety Consideration
The perfusion circuit has been designed to maintain adequate blood flow with minimal hemolysis and avoid accidental air embolism. The latter is achieved with the combination of a centrifugal pump, a vented arterial filter, and an inline air bubble detector. Various devices to reduce the risk of accidental air and offer a greater margin of safety are utilized. These include level detection with pump stop, positive and negative pressure monitoring of arterial line pressure, cardiotomy/venous reservoir pressure, and cardioplegia delivery pressure. In addition, one-way vacuum relief valves are used on the suction lines to guard against reverse pump direction and to reduce hemolysis.
All equipment, and periodic monthly inspections by the Bioengineering Department are completed before expiration to insure electrical safety.
Priming the Circuit
After setting up the circuit and flushing with 100% CO2 through a sterile gas filter, priming of the circuit can begin. 1000 ml Normosol is used as the priming solution, and the circuit is debubbled and recirculated before use. The oxygenator is ventilated with 100% O2 to reduce the CO2 level before the final priming. A predicted postdilutional pump hematocrit of <20% may require that packed red cells be added to the perfusion circuit. This decision is surgeon directed and is usually based on the complexity of the surgical procedure and preoperative condition of the patient.
Packed cells should be refrigerated in the blood refrigerator after being chcked by the prefusionist and another qualified professional. Porper identification of the blood with the patient’s name, birth date, hospital number, blood type donor number, and expiration date is mandatory before addition to the pump. This must be witnessed by another member of the open heart team, and both signatures must be recorded on the transfusion form.
Additional prime constituents include 10,000U Heparin, 50 mEq sodium bicarbonate, and 12.5g Mannitol. If blood is added to the prime, then the prebypass filter must be either removed from the circuit, or recirculation can be only through the AV bridge. Crystolloid priming volume should be reduced by the additional blood volume. Hemoconcentration is available during bypass to increase the hematocrit when excess circulation blood volume is present.
Documentation of the Perfusion Procedure
At the beginning of each procedure, the following forms are necessary:
- Perfusion record
- Pharmacy record
- PRP record
- Charge record
- Perfusion Checklist
After calculating the patient’s BSA, flow rate, heparin dose, and postdilutional hematocrit, the rest of the preoperative data and history should be recorded on the appropriate forms. Serial numbers for disposables and equipment should be noted, and the prebypass checklist completed. During bypass, documentation of the blood flow rate, arterial blood temperature, esophageal temperature, acillary or rectal temperature, mean arterial blood pressure, and central venous pressure must be made on the perfusion record at least every 15 minutes. Additional information is recorded in the comments section.
In addition to continuous monitoring of the venous oxygen saturation by the perfusionist, blood gases and electrolytes should be monitored at least once during hypothermia, and once during rewarming. Blood gas and electrolyte values are obtained by use of the iSTAT handheld blood gas analyzer. Blood gases and electrolytes should be adjusted by the perfusionist to maintain normal levels. For longer bypass procedures, these studies should be done at least once an hour and recorded on the perfusion record.