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From: Contemporary Cardiology: Cardiopulmonary Resuscitation Edited by: J. P. Ornato and M. A. Peberdy © Humana Press Inc., Totowa, NJ
16 Percutaneous Cardiopulmonary Bypass As an Adjunctive
Strategy for Resucitation
The State of the Art
Catherine Cooper,
MDand Bruce D. Spiess,
MD,
FAHACONTENTS
INTRODUCTION
PERCUTANEOUS CARDIOPULMONARY BYPASS
INDICATIONS AND CONTRAINDICTIONS FOR PCPB PCPB TECHNIQUE
COMPLICATIONS OF PCPB OUTCOME WITH USE OF PCPB CONCLUSION
REFERENCES
INTRODUCTION
Cardiopulmonary bypass (CPB) is now 50 years old. Although developed originally to allow correction of congenital and valvular heart disease, CPB has affected all of medicine profoundly. As an artificial circulatory support for systemic and pulmonary functions, CPB has allowed for the development of cardiovascular surgery. Today, coro- nary artery bypass grafting is the most commonly performed cardiac surgery. The current trend is to perform a larger number of more complicated coronary revascularization surgeries “off pump.” However, CPB supported work still accounts for the vast majority of surgeries. The CPB technology has evolved from one with large oxygenators, blood prime, and complex heating and cooling to today’s smaller and less complex technologies.
CPB supports systemic blood flow, blood pressure, and tissue oxygenation when the heart and lungs are either being operated on or are unable to maintain these functions.
In patients with coronary artery disease (CAD), limited flow past either a fixed obstruct- ing lesion or an acute platelet thrombus creates a volume of myocardial tissue that is forced to switch from aerobic to anaerobic metabolism. If present for a long enough period of time, the tissue is at risk for infarction. The CPB machine physiologically
improves the supply and demand ratios of at risk myocardium physiologically. CPB decreases demand by eliminating myocardial work, as the CPB machine takes over systemic cardiac output. Supply increases by a number of mechanisms. First, most CPB flow is nonpulsatile and with the myocardium no longer doing mechanical work and not creating left ventricular (LV) wall tension, blood flows to the left ventricle throughout the entire heart cycle. Second, the CPB machine supplies a mean blood pressure that is elevated above diastolic pressure, perfusing myocardium continuously at a higher pres- sure. Therefore, a luxury of perfusion occurs in a state in which metabolic oxygen demand is decreased. Cardiac surgeons realize this advantage and use the CPB machine as their “bail out” when presented with an acute ischemic emergency. It makes wonder- ful physiological sense to export this technology from the operating room to other hospital and potentially nonhospital environments in which CPB technology could save lives.
PERCUTANEOUS CARDIOPULMONARY BYPASS
Percutaneous cardiopulmonary bypass (PCPB) was first used in 1983 for patients with cardiac arrest (CA) and cardiogenic shock (CS [1]). The primary indication for emergent PCPB is the presence of a surgically correctible anatomic lesion causing the CA or shock state, with the highest survival rates reported in this group of patients.
PCPB is used currently in patients who fail traditional resuscitation therapies and is considered a temporary support until more definitive treatment is available. For condi- tions amenable to surgical intervention (e.g., coronary disease or pulmonary embolism), this temporary support may provide time for diagnostic angiography followed by emer- gency surgery. For conditions not readily treatable with surgery (e.g., heart failure from cardiomyopathy), PCBP is a bridge to long-term circulatory support in the form of extracorporeal membrane oxygenation (ECMO) or the implantation of a ventricular assist device (VAD).
CPB technology has evolved from bulky machines requiring complicated set up and surgical insertion of cannulae in the operating room to small, portable machines with disposable, pre-assembled circuits and percutaneously introduced cannulae. The latter allow very rapid institution of CBP throughout the hospital. PCPB systems have been studied as elective adjuncts to support high-risk cardiology interventions, particularly angioplasty and valvuloplasty. Experience with the technique used electively in the cardiac catheterization laboratory led to its use in emergency situations, including coro- nary dissection, ventricular failure, and ventricular rupture. The PCPB technique has been extended to other emergency cases of CA and CS unresponsive to traditional mea- sures including acute myocardial infarction (AMI), PE, ventricular rupture, trauma, and hypothermia.
The systems utilized by centers employing PCPB are portable, fitting onto one small cart. They most often employ a centrifugal pump—often a Biomedicus (Medtronic Per- fusion Systems, Anaheim, CA) system. These pumps can be run from a battery pack for transport through hospital corridors allowing movement of patients to the operating room for definitive treatment. Hollow fiber, membrane oxygenators that are heparin-bonded have been used widely in these systems. In many of the recently published series, either critical care nurses or others present in the hospital 24 hours a day were trained and primed the PCPB systems with crystalloid. Some series have utilized systemic heparinization with target activated clotting time (ACT) of 400 seconds. Often a quick 20,000 IU bolus
is given to the patient and time is not taken for dosage personalization to achieve a 400 to 500 second ACT. The key difference between PCPB systems and those utilized in the operating rooms is size and portability.
For elective cardiac surgery in the operating room, arterial and venous cannulae are placed in the ascending aorta and the right atrium. Often, variations are made depend- ing on the patient’s physiology and planned operation. For PCPB, most series report the use of femoral arterial and venous cannulations. The femoral vein cannulation usually uses a long fenestrated cannula that is passed up the vena cava. Its tip is lodged in the right atrium and the fenestrations allow for drainage of blood from throughout the vena cava.
Often, the PCPB systems can be placed by a resident or attending cardiologist or surgeon. Nurses can prime the PCPB machine with crystalloid quickly. In a cardiac catheterization laboratory, vessels are already cannulated and wires are often in place, saving precious minutes. In an unwitnessed arrest or one that occurs on a hospital ward, the individual would have to undergo CPR for some time as he or she is moved to a place in which cannulation can be performed. PCPB requires a large commitment by a medical center to make teams available 24 hours a day.
INDICATIONS AND CONTRAINDICATIONS FOR PCPB
Current contraindications and indications for PCPB are based on survival data, with unwitnessed CA being a very poor prognostic indicator and probably an absolute con- traindication to PCPB, except in cases of profound hypothermia. Aortic dissection and aortic regurgitation also preclude effective use of PCPB. Other relative contraindications include CA longer than 30 minutes (only rare survivors), no correctable anatomic defect, and terminal illness. Recent stroke, diabetes, and peripheral vascular disease also com- plicate initiation and successful weaning from PCPB (2).
CA is one the most common indications for initiation of PCPB. A National Cardiop- ulmonary Support Registry from 17 institutions collected data on the use of PCPB and reported initial findings in 1992 (3). Although published in 1992, it is still the largest series published to date on PCPB, including 187 patients from 17 major institutions. The largest number of patients had undergone CA, but significant numbers of victims had CS or hypothermia. The largest number of survivors were those who had CS but who had not gone on to CA yet. Table 1 shows the data from this study and differentiates individuals who survived less than or more than 30 days. Patients who did undergo CA were far more likely to survive if the time from witnessed arrest to institution of PCPB was short. Some patients were started on PCPB in less than 15 minutes. More than 50% of these patients survived.
No patients with unwitnessed arrest survived.
Most cases of PCPB were for patients who experienced CA and on whom traditional cardiopulmonary resuscitation (CPR) had failed. AMI was the most common precipitat- ing event. Other causes included post-pericardiotomy arrest, refractory arrhythmias, PE, rupture of aneurysm or cardiac graft, pericardial tamponade, and aortic valve lesions. CS was the second most common indication, most often as a result of AMI, myocarditis, and rupture of ventricular free wall or septum (4). One series of six severe trauma patients younger than age 55 who were felt to have recoverable injuries instituted PCPB for poor oxygenation, hypothermia, hypovolemia, and coagulopathy (5). Patients with pulmonary insufficiency, smoke inhalation, and status asthmaticus have also been treated with PCPB in a few cases.
Table 1
Survival After Percutaneous Cardiopulmonary Bypass
Died Alive Alive Unknown
Cause on bypass <30 days >30 days outcome
Cardiac arrest 88 6 15 2
CA after cardiotomy 12 0 2 0
Cardiogenic shock 21 0 15 2
CS after cardiotomy 4 0 2 0
Hypothermia 4 0 3 0
Pulmonary insufficiency 5 1 3 0
Other 1 1 0 0
Total (N = 187) 135 (72.2%) 8 (4.3%) 40 (21.4%) 4 (2.1%) CA, cardiac arrest; CS, cardiogenic shock. (Adapted from ref. 3.)
PCPB TECHNIQUE
The technique of implementing PCPB is similar to routine CPB, but employs a port- able cart containing prepackaged circuits ready for priming; a battery-powered centrifu- gal pump, which actively aspirates venous blood; a membrane oxygenator with oxygen source; and percutaneously placed long, thin-walled venous and arterial cannulae. Full systemic heparinization is required with frequent monitoring of the ACT. Heparin-coated systems are being developed that may allow considerably lower levels of anticoagula- tion. Surgeons, cardiologists, or emergency physicians can insert PCPB cannulae with the PCPB set-up by perfusionists or ECMO-trained intensive care nurses. The time to initiation of emergency PCPB depends on the team’s familiarity and experience with the procedure. Faster initiation of bypass and improved results are noted as an institution performs PCPB regularly.
COMPLICATIONS OF PCPB
Complications of PCPB are relatively rare. Bleeding at the cannulation sites is the complication reported most often. Perfusion problems include arterial or venous injury, air embolus, tubing disconnections, and embolization of arterial plaque. Ischemia of the brain, myocardium, and kidney usually result from the original CA and delay before institution of PCPB. However, femoral arterial perfusion is likely to be inadequate for adequate cerebral perfusion if used for more than 4 to 6 hours and strong consideration should be given to converting to an aortic cannula if continuing bypass support is needed.
Ischemic limb complications have been reported, sometimes requiring embolectomy or amputation. Hemolysis and coagulopathy are rarely clinically significant with PCPB times of less than 6 hours. A small-sized cannula presents significant risk factor for hemolysis.
OUTCOME WITH USE OF PCPB
In 2002, Kurusz tabulated results from all case reports of PCPB use over a 10-year period in the 1990s. Long-term (>30-day) survival was better in patients with CS (40.1%
of 335 survived) vs those with CA (21.6% of 335). Other uses of PCBP were more infrequent, but had comparable survival rates to that seen in patients with CS; 5 of 12 (41.7%) patients with pulmonary causes survived, 5 of 9 (55.6%) patients with trauma survived, and 5 of 13 (38.5%) patients with hypothermia survived (1). For patients with fulminant myocarditis, survival rates were as high as 70 to 100%. Patients with cardio- genic shock had the greatest benefit from PCPB, suggesting that PCPB is best applied before CA occurs and hypoxic injury begins. However, there were survivors among patients in CA who could not be resuscitated otherwise, a group with a 100% predicted mortality.
There were no survivors of PCPB in patients with unwitnessed CA, except in profound hypothermia. The duration of CPR prior to PCBP was predictive of survival, with only 5 to 14% of patients surviving who received greater than 30 minutes of CPR. In contrast, 25 to 50% of patients with less than 30 minutes of CPR survived. In one group of three pediatric patients (6), two survived CPR for longer than 30 minutes, suggesting that children may tolerate CPR better than adults. Immediate application of PCPB significantly improves cardiac output, helping preserve myocardial and neurological function.
Survival is more likely in patients with correctable anatomic defects. Examples of primary correctable lesions include CAD, ventricular rupture, and PE. In patients treated with PCPB, survival was 15 to 40%, compared with 0 to 13% in patients without such an intervention.
Several authors report comparable increased survival rates in patients undergoing cardiac surgery soon after initiation of PCPB to correct anatomic defects. In 1991, Money and colleagues reported a series of 11 patients who required CPB for CA (7). All of the five patients who had complications in the cardiac catheterization lab and went to the operating room survived. Of six patients on PCPB initiated outside the catheterization lab, three had lesions amenable to surgery and two of the three survived. The nonsurvivor was judged to be at a very high risk for surgery with marginally correctable anatomy. This patient required biventricular assist devices and died 4 days later. Of the three patients without surgically correctable problems, none survived. All patients were resuscitated successfully, and all seven of the patients with clearly correctable lesions survived. The authors concluded that rapid initiation of PCPB by an experienced team and rapid trans- port to the operating room for definitive correction allows excellent survival in desperately ill patients who would otherwise not survive.
Wittenmyer reported that 104 patients from 1987 to 1992 who received interventional therapy soon after PCBP had better survival to hospital discharge than patients who could not be so treated (8). Of 74 patients receiving interventional therapy, survival was 26%
for those treated in the cardiovascular lab (thrombolytics, angioplasty, and valvulo- plasty) and 44% for those treated operatively (coronary bypass grafting, valve replace- ment, pulmonary embolectomy, ventricular septal defect repair, and cardiac perforation/
rupture). Higher survival (52%) was noted in patients treated for CS than for those in CA (24%). No patient with unwitnessed CA survived. None of the three patients transferred from another hospital after PCPB initiation survived.
A more recent review of 43 patients treated with PCPB from 1992 to 1998 by Mitsui et al. examined eight patients who had cardiac surgery (9). Only two of the patients survived to be discharged from the hospital, although six were weaned from CPB suc- cessfully. Three patients had coronary bypass surgery, but LV function did not recover in two of those patients. The three patients with ventricular septal defects (VSD), LV rupture, and both LV rupture and VSD, were weaned successfully but all had deteriora-
tion of LV function. Two patients had aortic valve replacement (one with a Maze proce- dure as well), both were weaned but both experienced postoperative ventricular arrhythmias (VAs). One survived and one died from refractory VA.
In 1999, von Segesser reviewed cardiopulmonary support (PCPB) and ECMO, high- lighting both the usefulness and difficulties associated with PCPB (10). PCBP is portable and rapidly available, with less technological demands for initiation. However, because of the small-bore cannulae, PCPB is a temporary measure, best used to support the circulation until a definitive anatomic repair can be performed or a more permanent circulatory support system (VAD) can be implanted. PCBP is most useful in patients with CS who have not progressed to CA.
CONCLUSION
PCPB is best used in patients with cardiogenic shock (before cardiac arrest occurs) who have anatomically correctable lesions amenable to surgical intervention. Patients with unwitnessed arrest and those with greater than 30 minutes of CPR prior to PCBP are unlikely to survive despite aggressive management of their underlying disease.
PCBP is a temporary measure designed to support the circulation until definitive diagnosis and treatment can be accomplished. In particular, cardiac deterioration as a result of CAD, ventricular rupture, ventricular septal defect, aortic stenosis, and PE has been successfully treated with PCPB. In these patients who were previously considered to have near 100% mortality, rapid initiation of PCPB, and definitive surgical correction may provide up to 35% survival to hospital discharge.
Much of the work on this technique was done in the late 1980s and early 1990s. Today, as hospital budgets get ever more trimmed it the maintenance of teams for PCPB repre- sent a very large outlay of personnel. Technology will be ever improving for CPB and, with smaller machines, better anticoagulation and improved systems, it may be possible for survival statistics to improve further.
REFERENCES
1. Phillips SJ, Ballentine B, Slonine D, et al. Percutaneous initiation of cardiopulmonary bypass. Ann Thorac Surg 1983; 36:223–225.
2. Kurusz M, Zwischenberger. Percutaneous cardiopulmonary bypass for cardiac emergencies. Perfusion 2002; 17:269–277.
3. JG, Bruhn PS, Cohen SE et al. Emergent applications of cardiopulmonary support: A multiinstitutional experience. Ann Thorac Surg 1992; 54:699–704.
4. Willms DC,Atkins PJ, Dembitsky WP, et al. Analysis of clinical trends in a program of emergent ECLS for cardiovascular collapse. ASAIO J 1997; 43:65–68.
5. Perchinsky MJ, Long WB, Hill JG, et al. Extracorporeal cardiopulmonary life support with heparin-bonded circuitry in the resuscitation of massively injured trauma patients. Am J Surg 1995; 169:488–491.
6. CochraneJB, Tecklenburg FW, LauYR, et al. Emergency cardiopulmonary bypass for cardiac arrest refractory to pediatric advanced life support, Pediatr Emerg Care 1999; 15:30-32.
7. Mooney MR, Arom KV, Joyce LD, et al. Emergency cardiopulmonary bypass support in patients with cardiac arrest. J Thorac Cardiovasc Surg 1991; 101:450-454.
8. Wittenmyer BL, Pomerants BJ, Duff SB, et al. Single hospital experience with emergency cardiopul- monary bypass using the portable CPS (Bard) System. J Extra-Corpor Technol 1997; 29:73–77.
9. Mitsui N, Koyama T, Marui A, et al. Experience with emergency cardiac surgery following institution of percutaneous cardiopulmonary support. Artif Organs 1999; 23:496–499.
10. Von Segesser. Cardiopulmonary support and extracorporeal membrane oxygenation for cardiac assist.
Ann Thorac Surg 1999; 68:672–677.
