A surgeon's view of extracorporeal circulation

Leucocytes and cardiopulmonary bypass: in vitro production of oxygen free radicals and trapping in the reperfused myocardium

The production of oxygen free radicals (OFR) by leucocytes was evaluated ex vivo by chemiluminescence (CL) before, during and after routine coronary artery bypass surgery (group A, n=11). The possibility of leucocyte trapping in the coronary circulation during the early reperfusion period was also investigated (group B, n=9). In group A, arterial blood samples were taken immediately before the start of surgery during anaesthesia, five minutes before and five and 30 minutes after the start of cardiopulmonary bypass (CPB), five minutes before and five and 30 minutes after the start of reperfusion of the heart, and then four and 24 hours after the end of CPB. In group B, arterial and coronary sinus blood samples were simultaneously drawn five and 30 minutes after the release of the aortic crossclamp. All blood samples were corrected for haemodilution. In group A, both CL and the level of circulating leucocytes declined during CPB. The lowest value of CL was measured 30 minutes after the start of CPB (69± 2% of baseline values) (mean±SEM). The lowest level of leucocytes was found after 30 minutes of CPB: 2.6±0.4 (109/l) vs 4.2±0.5 before surgery. Twenty-four hours after CPB, CL was increased to 170±49% and a leucocytosis was present (12.2±1.1). In group B, after five minutes of reperfusion the number of circulating leucocytes in arterial blood was 3.8±0.9 x 10 9/l as compared to 2.2±0.5 x 109/l in the coronary sinus (p<0.0017). However, no such difference was found after 30 minutes of reperfusion. The decreased CL during CPB was probably due to in vivo activation and exhaustion of leucocytes. The postischaemic trapping of these cells may play a pathogenetic role in reperfusion injury.

Impact of residency status on perfusion times and outcomes for coronary artery bypass graft surgery

BACKGROUND

A price of training residents in cardiothoracic surgery is often perceived to be a loss in intraoperative efficiencies, leading to prolonged cardiopulmonary bypass and perfusion time. Because these indicators are also thought to adversely affect operative outcome, we investigated the association between residency training status, perfusion times, and outcomes.

METHODS

Using the Society of Thoracic Surgeons (STS) National Cardiac Database, we studied 369,906 CABG patients undergoing isolated coronary artery bypass graft (CABG) procedures during January 2002 through June 2005. Participating institutions were stratified by residency versus nonresidency status and by perfusion time categories and analyzed for association with clinical outcomes.

RESULTS

Overall, 57 (10%) of 594 STS participants had a residency training program. Residency programs had longer mean cross-clamp and perfusion times than nonresidency programs, 73.10 versus 67.44 minutes and 104.75 versus 98.00 minutes, respectively (p < 0.0001 for both. Longer perfusion time was significantly associated with higher operative mortality at the patient level. Unadjusted mortality rates were, however, similar for patients at residency and nonresidency programs (2.30% versus 2.27%), with an adjusted odds ratio of 0.96 (95% confidence interval, 0.84 to 1.09). Although perfusion times have not changed significantly over time between residency and nonresidency programs, mortality rates have significantly improved over time at each.

CONCLUSIONS

Residency programs have longer CABG perfusion times than nonresidency cardiothoracic surgery programs, but these differences are minor. Adjusted procedural outcomes at residency training programs are similar to those at nonresidency centers; thus, patients do not appear to be adversely impacted by the time costs of surgical training.

Early techniques of extracorporeal circulation

While the techniques and equipment used 50 years ago may seem primitive by today's standards, they did permit cardiac surgery to rapidly develop. As early as 1951, Karlson would write: 'Recent advances in surgery have made operations upon the heart much more than surgical stunts, and have opened a hitherto relatively untouched field of surgical endeavor. A few years later, Mustard would defend his abysmal series of repairs of congenital cardiac defects by saying, 'Our techniques of perfusion and operation have proved feasible in three human cases, but the results are not adequate to operate freely on good-risk patients at the present time. It is hoped that improvements in techniques will soon make this possible'. By the end of the decade of the 1950s. Gross would express the following: In the support of human patients on pump oxygenators, the intricacies of technic are many, and the extent of problems is broad, but much clarity of thought is now evident. We can set forth certain statements considered to represent truths or valuable viewpoints, since in most cases they have derived from scores of laboratory experiences during which some 800 dogs have been used by us, or else they have been crystallized from bitter experience at the operating table, or shattering disappointments in postoperative failures. Fortunately, many of the conclusions have sprung from happy and rewarding results exhibited by patients who have weathered corrective surgery in a very satisfactory manner. In closing, after reviewing the early perfusion literature, it is evident that many techniques used in the 1930s, 1940s, and 1950s persist to the present. Some techniques fell out of favor, such as elective hyperkalemic arrest, only to be re-established decades later. Simplicity is the hallmark of the most enduring techniques, a thought expressed by Lillehei in 1955. Somewhat amazingly, full automation of the extracorporeal circuit existed on some of the very early machines, but perhaps because of the explosive growth of cardiac surgery and the need for disposable circuits that could be rapidly assembled, the safety aspects of heart-lung machines were neglected for many decades. Some would argue it still has not realized its potential for elimination of error in the conduct of cardiopulmonary bypass. However, cardiac surgery would not wait, and in 1956, Osborn would boldly state: 'Extracorporeal circulation for surgery of the heart has now come of age.

Alterations in hemostasis associated with hyperthermia in a canine model

Use of hyperthermia in the treatment of cancer and viral infection has received renewed interest. However, the in vivo relationship between hyperthermia and direct versus indirect effects upon hemostasis are incompletely defined, although we do know that disseminated intravascular coagulation (DIC) is a common sequel to heat stroke. The purpose of the present study was to more precisely define the relationship between hyperthermia and derangements of hemostasis, thereby providing a guideline for the development of safe hyperthermia treatment regimens. The present investigation examined the in vivo effects of high-grade whole-body hyperthermia (WBH) (42.5 degrees C, 90 min) on hemostasis in a canine model. Induction of hyperthermia via extracorporeal circulation of heated blood (ECC-WBH) caused thrombocytopenia, increased plasma fibrin degradation products (FDPs), prolonged clotting times, increased serum liver enzymes, and evidence of spontaneous bleeding. However, when WBH was induced by peritoneal lavage (PL-WBH), transient thrombocytopenia was the only significant alteration. Temporal correlation between hemostatic alterations and elevations in serum alanine aminotransferase (ALT) levels in the ECC-WBH treatment group suggested that liver injury is responsible, at least in part, for the coagulopathy associated with high-grade hyperthermia and that in the absence of liver injury, identical degrees of hyperthermia cause only incidental decreases in platelet numbers.

Whole body hyperthermia: effects upon canine immune and hemostatic functions

In this study, the effects of induced whole body hyperthermia (WBH; 42.3 degrees C for 90 min) on peripheral blood mononuclear cell (PBMC) phenotype distribution, in vitro blastogenic responsiveness and selected parameters of hemostasis were determined in dogs. Hyperthermia was induced by heating venous blood during extracorporeal circulation (EC); induction of WBH by peritoneal lavage (PL) and perfusion without heating (i.e. euthermic EC and euthermic PL) were used as controls. Whole body hyperthermia was associated with lymphopenia and thrombocytopenia that persisted throughout the eight-day post-treatment observation interval. The lymphopenia was selective in that CD5-positive T lymphocytes were more sensitive than were sIg-positive B cells and, within the T-cell compartment, suppressor (CD8-positive) cells were more sensitive to hyperthermic stress than helper (CD4 positive) lymphocytes. Lymphopenia was also observed in EC and PL euthermic controls, although that lymphopenia was transient and nonselective. Persistent suppression of T-cell phytomitogen-induced blastogenesis was induced by WBH in contrast to transient suppression in euthermic controls. For all treatment groups, lymphopenia and suppressed blastogenesis were correlated to elevated plasma cortisol levels. Induction of WBH by EC resulted in coagulopathy characterized by thrombocytopenia, increased plasma fibrin degradation products, prolonged clotting times, and evidence of spontaneous bleeding. These hemostatic alterations were correlated temporally to increased serum levels of liver enzymes. However, there was no evidence of hepatic injury when WBH was induced by PL, where transient thrombocytopenia was the only significant hemostatic alteration. These results indicate that 42.3 degrees C whole body hyperthermia can be well-tolerated and, although associated with suppression of general indexes of immunocompetence, is not associated with opportunistic infections.