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Complement (C3, C4) Consumption in Cardiopulmonary Bypass, Cardioplegia, and Protamine Administration
Complement (C3,C4) Consumption in Cardiopulmonary Bypass, Cardioplegia, and Pmtamine Administration Ray Chu-Jeng Chiu, M.D., Ph.D., and Roger Samson, C.P. ABSTRACT Anaphylatoxins produced by complement activation have been postulated to be responsible for postperfusion syndrome and protamine hypotension in patients undergoing cardiac surgical procedures. The consumption of serum complement components C3 and C4, which reflects the classic and alternate pathway activations of the complement system, was studied in 22 patients undergoing cardiac operations. Prior to the onset of cardiopulmonary bypass, the complement levels were within normal range. Rapid reduction in both C3 and C4 within minutes of cardiopulmonary bypass indicated rapid complement activation. Such a reduction in complement levels could not be accounted for by either hemodilution or transfusion of complement-poor blood. Aortic cross-clamping and cold potassium cardioplegia followed by myocardial reperfusion did not lead to further consumption of C3 and C4. Slow intravenous infusion of protamine sulfate after cardiopulmonary bypass did not change C3 and C4 levels significantly in our patients, although protamine and heparin-protamine complex have been shown to activate complement components in vitro. In another group of 9 similar cardiac surgical patients, 0and C4 were found to return to normal levels within 24 hours after operation. This study thus confirms the rapid activation of the complement system by cardiopulmonary bypass but fails to demonstrate further activation of the complement system by cardioplegia or protamine administration. The complement system plays an important role in immunological defenses as well as in tissue injuries. Rapid activation of the complement system is associated with the consumption of serum complement components and the liberation of complement split products. It has been reported that cardiopulmonary bypass with the pump oxygenator can activate the complement system and that this in turn may lead to the development of postperfusion syndrome in the lung [1J . The possible participation of the complement system in the ischemic damage of myocardium has recently been suggested [2, 31, but whether hypothermia and cold potassium cardioplegia, a currently popular technique for protection of the myocardium against such an injury, would have any effect From the Division of Cardiovascular and Thoracic Surgery, McCill University and The Montreal General Hospital, Montreal, PQ, Canada. Accepted for publication Mar 24, 1983 Address reprint requests to Dr. Chiu, The Montreal General Hospital, 1650 Cedar Ave, Montreal, PQ, Canada H3G 1A4.
229
on the complement system is not known. On the other hand, there have been a number of reports indicating that protamine and, in particular, heparin-protamine complex are strong activators of complement [4]. This has been postulated as the possible mechanism of the protamine-induced hypotension observed fairly often during cardiac procedures [5]. Although serum contains complement proteins (C1 to C9), enzymes, and other factors that constitute the complement system, determinations of two components, C3 and C4, can shed light on complement activation through two major pathways, namely, the classic and alternate pathways. As summarized in Figure 1, in the acute phase of classic activation both C3 and C4 are consumed, while the alternate properdin activation bypasses C4 and only C3 consumption occurs. In the following study, therefore, we serially determined C3 and C4 levels in patients undergoing cardiac procedures in order to observe the changes associated with cardiopulmonary bypass, cardioplegia, and protamine administration.
Material and Methods In the first group of 22 consecutive patients undergoing cardiac operations, there were 4 women and 18 men, ranging in age from 39 to 67 years. Fifteen patients underwent one to four aortocoronary bypass grafts, 5 had replacement of the aortic or mitral valve or both, 1 had an aortic valve replacement and an aortocoronary bypass graft, and 1 underwent left ventricular aneurysmectomy. All patients were given 300 units of heparin per kilogram of body weight prior to cardiopulmonary bypass. For the extracorporeal circuit, a Bentley BOS-10 oxygenator, Tygon and silicon tubings, a Shiley cardiotomy reservoir, and a Bentley P-F427 arterial fiiter were used. Two liters of Ringer's lactate solution containing 44 mEq of sodium bicarbonate and 12.5 gm of mannitol was used to prime the pump oxygenator. The potassium cardioplegic solution [6] at 4°C was injected initially to achieve cardiac standstill and adequate myocardial hypothermia, and Normosol solution without supplementary potassium was used for repeated (multidose) infusions to maintain myocardial cooling. In addition, topical cooling with cold Ringer's lactate solution and moderate systemic hypothermia of 27" to 30°C were employed. Blood samples were obtained serially prior to the start of cardiopulmonary bypass, after several minutes on cardiopulmonary bypass but prior to aortic crossclamping and the injection of cardioplegic solutions into the aortic root or into the coronary ostia, after the aortic cross-clamp had been removed and the patient had been
230 The Annals of Thoracic Surgery Vol 37 No 3 March 1984
Classic Activation
mg/dl
(0.9.Anligen.Anlibody Complex) I
Alternate Activation (a g Properdin)
Factor D.--
Fig I . Abbreviated scheme of complement activation pathways. Determinations of C3 and C4 reflect the activation of classic or alternate pathways or both.
taken off cardiopulmonary bypass but prior to the injection of protarnine, and ten minutes after completion of the intravenous injection of a neutralizing dose of protamine sulfate. The blood samples were sent to the immunology laboratory for determination of the levels of C3 and C4. The radioimmunodiffusion kits of Kallestad quantiplate and endoplate* were used for measuring C3 and C4, respectively. With the radioimmunodiffusion technique, the normal range in our laboratory for C3 is 100 to 250 mg/dl and for C4, 20 to 50 mg/dl. In the second group of 9 patients, who underwent one to four aortocoronary bypass graft operations, the blood samples were obtained 24 hours after operation and the C3 and C4 levels were determined as described previously. The procedures for cardiopulmonary bypass, cardioplegia, and protamine injection were similar to those used in the first group.
t
* * 0
Results There is a rapid activation of the complement system following the onset of cardiopulmonary bypass (Fig 2). Both C3 and C4 decreased significantly (p < 0.001) within minutes of cardiopulmonary bypass. As shown in Figure 3, rapid hernodilution took place, with a significant drop in hematocrit (p < 0.001) as 2 liters of Ringer's lactate solution was used to prime the extracorporeal circuits. To correct complement levels for the hemodilution that occurred, the following formula was used [l]:
Normal Range For C,
I
I
I
I
3 t 4 Cardloplegia Protamine
2 t
I t Cardiopulmonary Bypass
Fig 2 . Measured changes in C3 and C4 following onset of cardiopulmonary bypass. (* = p < 0.001 by Student t test; N = 22.)
TO
Hernatocrits
at
complement corrected = complement measured x (initial packed-red-cell volume/ packed-red-cell volume during bypass)
Figure 4 indicates that both C3 and C4, after being corrected for hemodilution, still showed significant reduction after the initiation of cardiopulmonary bypass (p < 0.01 and p C 0.05, respectively; paired t test). Our data also indicate that levels of C3 and C4, measured and corrected for hemodilution, did not change significantly as the result of aortic crossclamping, infusion of cardioplegia, and reperfusion. Hematocrits and complement levels remained stable during this period (p > 0.1 by Student t test and paired t test).
*Kallestad Laboratories, Inc., 2000 Austin National Bank Tower, Austin,
TX 78701.
't Cardiopulmonary
*t Cardioplagia
3t
4
Prolamine
Bypass
Fig 3. Changes in hematocrit as a result of hemodilution, during bypass, and during the course of cardiac surgety. (' = p < 0.001 by Student t test; N = 10.)
231 Chiu and Samson: Complement Consumption in CPB
rngfdl
200c
150 -
100
-
50- T
If
2f
3f
4
Cardiopulmonary Cardloplegla Prolamlne Bypasn
Fig 4 . Changes in C3 and C4 after being corrected for the 4fects of hemodilution. P = p < 0.001 by paired t test; t = p < 0.02 by paired t test; N = 10.)
Slow intravenous infusion of protamine sulfate sufficient to neutralize heparin, as practiced routinely in our cardiac procedures and guided by the accelerated clotting time, does not induce significant consumption of the complement components. Neither C3 nor C4, measured and corrected for hematocrit changes, was significantly affected by the protamine administration (p > 0.7) (see Figs 2, 4). In Group 2, C3 and C4 levels in 9 patients were determined 24 hours after cardiac surgical procedures. The C3 and C4 levels were 106.3 f 8.0 (mean f standard error of the mean) and 20.3 f 4.6 mg/dl, respectively. These were not significantly different from the prebypass levels observed in Group 1 (p > 0.7 for C3 and p > 0.2 for C4), suggesting the recovery of these two complement components within 24 hours after cardiac operation. Incidentally, these preoperative and postoperative values are within the normal ranges observed in our clinical immunology laboratory at the Montreal General Hospital. In both groups of patients, hemodynamic responses to protamine injection were minimal to mild and the serious protamine hypotension encountered at times in cardiac procedures did not occur.
Comment The complement system not only facilitates the ingestion of pathogens by phagocytes (opsonization) but also mediates many aspects of inflammation and tissue injury. The striking similaritiesbetween the known biological activities of the complement-derived anaphylatoxins
and many clinical manifestations of the so-called postperfusion syndrome led a number of investigators to study the possible activation of the complement system during the cardiopulmonary bypass procedure. Although there has been considerable progress in the safe utilization of cardiopulmonary bypass, the postperfusion syndrome still plays an important role in the morbidity and mortality of patients undergoing cardiac operations, particularly after prolonged extracorporeal bypass. Such sequelae may be manifested as increased capillary permeability with interstitial fluid pooling, coagulopathies, and varying degrees of organ dysfunction, particularly in the lung and the kidney. As noted by Chenoweth and associates [l], these clinical manifestations strongly suggest the participation of the complement system in their pathogenesis. In 1971, Parker and colleagues [ A studied changes in serum complements before and after cardiopulmonary bypass by determining 50% hemolytic complement (CH50). They reported significant depression of CH50 4 and 20 hours after cardiopulmonary bypass, but it returned to a normal level after 44 hours. They suggested that complement components bound to the tissue might contribute to the increased capillary permeability and that a decrease in serum complements may predispose patients to certain infections. That such consumption of complements during cardiopulmonary bypass may be rapid and transient was suggested by the studies of Genetet and co-workers [8],who found no significant depression of C3 and C4 levels one and seven days after cardiopulmonary bypass as compared to preoperative values. It is obvious that serial sampling at close intervals is needed to elucidate complement activation during cardiopulmonary bypass. Chenoweth and associates [l]studied the generation of two split products of complement, namely, C3a and C5a anaphylatoxins, in patients undergoing cardiopulmonary bypass by taking serial samples during the procedure. There was a significant and rapid increase in C3a concentration within ten minutes of onset of cardiopulmonary bypass, while C5a did not change sigruficantlyduring cardiopulmonary bypass. However, neutropenia during bypass and marked transpulmonary neutropenia suggested to these authors that pulmonary vascular sequestration of C5aactivated granulocytes was taking place. They also found that the incubation of blood with the nylon mesh liner of the bubble oxygenator, as well as vigorous oxygenation of whole blood, promoted complement activation. Our observation that C3 and C5 are consumed rapidly after the onset of cardiopulmonary bypass is consistent with their findings and indicates rapid activation of complements through the classic pathway, although the properdin pathway may also be activated. Such a decrease in the level of complements could not be attributed to hemodilution or to the infusion of stored blood deficient in complement because no blood transfusions took place during this period. Rapid recovery of C3 and C5 levels after operation, either by resynthesis or transfusion, is also confirmed in our Group 2 patients. There is experimental evidence that complements also
232 The Annals of Thoraac Surgery Vol 37 No 3 March 1984
may play a part in ischemic injury of myocardium in the baboon [2] as well as in postoperative myocardial infarctions in human beings [3]. Lack of complement activation after aortic cross-clamping thus could be a reflection of adequate myocardial protection with the cold potassium cardioplegia employed in this series, but at present this remains speculative. There has been a renewed interest in the pathogenesis of protamine-induced hypotension during cardiac operations. Such hypotension is generally associated with marked peripheral vasodilatation, but whether protamine has direct negative inotropic effects on the myocardium remains controversial. Sethna and colleagues [9] reported that heparin and protamine did not produce adverse alterations in the global myocardial metabolic state. Although protamine had been reported to reduce contractility in a canine isometric heart model [lo], recent clinical studies indicate that many patients can increase cardiac output to compensate for peripheral vasodilatation and hypotension produced by protamine [111* Nevertheless, catastrophic cardiovascular collapse can occur occasionally following the administration of protamine after cardiopulmonary bypass [12]. Such collapse may be associated with massive noncardiogenic pulmonary edema. Various hypotheses to explain this protamine hypotension include anaphylaxis [13, 141, histamine release from the lung tissue [15], and lowering of plasma-ionized calcium [161. Complement activation was postulated as an important mechanism following the discovery in 1975 by Rent and co-workers [4] that protamine, and particularly the heparin-protamine complex, can cause massive activation of the complement system. In the in vitro system, such a complex can induce virtually complete depletion of total hemolytic complement activity. This depletion is dependent on time, temperature, pH, divalent cations, and serum concentrations. Siegel and associates [17] further showed that protamine may interact with C-reactive protein and induce complement consumption. The split products of complement activation, such as C3a and C5a, have been postulated to have a role in protamine-induced hypotension [5]. In spite of these well-documented studies, our patients failed to show significant changes in C3 and C4 following the administration of protamine. We administered protamine slowly into the vein since our clinical experience suggests that rapid injection of protamine is more likely to produce serious hypotension. Whether the speed of protamine administration affects the magnitude of complement activation is not known. Although Kirklin [18] recently reported a rapid increase in complement split products after protamine injection, at present the role of the complement system in protamineinduced hypotension remains hypothetical. Further investigation is required to eluadate the mechanism of protamine-induced hypotension, which is still a potentially dangerous complication of cardiac surgical procedures.
This work was partly supported by a Quebec Heart Foundation grant. We wish to thank Marlene Elliott, R.N., and Mrs. Emma Lisi for their assistance.
References 1. Chenoweth DE, Cooper SW, Hugh TE, et al: Complement
activation during cardiopulmonary bypass: evidence for generation of C3a and C5a anaphylatoxins. N Engl J Med 304:497, 1981 2. Crawford MH, Grover FL, ORourke RA, et al: Preservation
of jeopardized myocardium by C3 depletion in the baboon. Am Fed Clin Res 27160A, 1979
3. Lyakhov NT, Zhivoderov VM, Belobrzhek LM. Immunological changes in postoperative myocardial infarction. Khirurgiia (Mosk) 1:21, 1979 4. Rent R, Ertel N, Eisenstein R, et al: Complement activation by interaction of polyanions and polycations: I. Heparinprotamine induced consumption of complement. J Immunol 114120, 1975 5. White JV:Complement activation during cardiopulmonary bypass (letter). N Engl J Med 305:51, 1981 Cain S The importance 6. Chiu RCJ,Blundell PE, Scott HJ, of monitoring intramyocardial temperature during hypothermic myocardial protection. Ann Thorac Surg 28317, 1979 7. Parker DJ, CantreU JW, Karp RB, et al: Changes in serum complement and immunoglobulins following cardiopulmonary bypass. Surgery 71:824, 1971 8. Genetet N, Sapene M, Genetet 8, et al: Modifications immunitaires apr& chirurgie cardiaque faite sous circulation extra-corporelle. Nouv F’resse Med 11:433, 1982 9. Sethna DH, Moffitt E, Gray RJ, et al: Effects of protamine sulfate on myocardial oxygen supply and demand in patients following cardiopulmonary bypass. Anesth Analg (Cleve) 61247, 1982 10. Gourin A, Streisand RL, Stuckey JH. Total cardiopulmonary bypass, myocardial contractility, and the administration of protamine sulfate. J Thorac Cardiovasc Surg 61:160, 1971 11. Shapira N, Schaff HV, Piehler JM, et ak Cardiovascular effects of protamine sulfate in man. J Thorac Cardiovasc Surg W.505,1982 12. OGger GN, Becker RM,Bonchek LI: Noncardiogenic pulmonary edema and peripheral vascular collapse following cardiopulmonary bypass: rare protamine reaction? Ann Thorac Surg 2920, 1980 13. Knape JTA, Schuller JL, DeHaan P, et al: An anaphylactic reaction to protamine in a patient allergic to fish. Anesthesiology 55:324, 1981 14. Moorthy SS, Pond W, Rowland RG: Severe drmlatory shodc following protamine (an anaphylactic reaction). Anesth Analg (Cleve) 5977,1980 15. Frater R W M : Discussion of (11) 16. Jones RM, Hill AB, Nahrwold ML, et ak Effect of protamine on plasma ionized calcium in the dog. Can Anaesth Soc J 2965, 1982 17. Siegel J, Rent R, Gewurz H. Interaction of C-reactive pmtein with the complement system. I. Protamine-induced consumption of complement in acute phase sera. J Exp Med 140631, 1974 18. Kirklin J: Discussion of [ l l ]
229
on the complement system is not known. On the other hand, there have been a number of reports indicating that protamine and, in particular, heparin-protamine complex are strong activators of complement [4]. This has been postulated as the possible mechanism of the protamine-induced hypotension observed fairly often during cardiac procedures [5]. Although serum contains complement proteins (C1 to C9), enzymes, and other factors that constitute the complement system, determinations of two components, C3 and C4, can shed light on complement activation through two major pathways, namely, the classic and alternate pathways. As summarized in Figure 1, in the acute phase of classic activation both C3 and C4 are consumed, while the alternate properdin activation bypasses C4 and only C3 consumption occurs. In the following study, therefore, we serially determined C3 and C4 levels in patients undergoing cardiac procedures in order to observe the changes associated with cardiopulmonary bypass, cardioplegia, and protamine administration.
Material and Methods In the first group of 22 consecutive patients undergoing cardiac operations, there were 4 women and 18 men, ranging in age from 39 to 67 years. Fifteen patients underwent one to four aortocoronary bypass grafts, 5 had replacement of the aortic or mitral valve or both, 1 had an aortic valve replacement and an aortocoronary bypass graft, and 1 underwent left ventricular aneurysmectomy. All patients were given 300 units of heparin per kilogram of body weight prior to cardiopulmonary bypass. For the extracorporeal circuit, a Bentley BOS-10 oxygenator, Tygon and silicon tubings, a Shiley cardiotomy reservoir, and a Bentley P-F427 arterial fiiter were used. Two liters of Ringer's lactate solution containing 44 mEq of sodium bicarbonate and 12.5 gm of mannitol was used to prime the pump oxygenator. The potassium cardioplegic solution [6] at 4°C was injected initially to achieve cardiac standstill and adequate myocardial hypothermia, and Normosol solution without supplementary potassium was used for repeated (multidose) infusions to maintain myocardial cooling. In addition, topical cooling with cold Ringer's lactate solution and moderate systemic hypothermia of 27" to 30°C were employed. Blood samples were obtained serially prior to the start of cardiopulmonary bypass, after several minutes on cardiopulmonary bypass but prior to aortic crossclamping and the injection of cardioplegic solutions into the aortic root or into the coronary ostia, after the aortic cross-clamp had been removed and the patient had been
230 The Annals of Thoracic Surgery Vol 37 No 3 March 1984
Classic Activation
mg/dl
(0.9.Anligen.Anlibody Complex) I
Alternate Activation (a g Properdin)
Factor D.--
Fig I . Abbreviated scheme of complement activation pathways. Determinations of C3 and C4 reflect the activation of classic or alternate pathways or both.
taken off cardiopulmonary bypass but prior to the injection of protarnine, and ten minutes after completion of the intravenous injection of a neutralizing dose of protamine sulfate. The blood samples were sent to the immunology laboratory for determination of the levels of C3 and C4. The radioimmunodiffusion kits of Kallestad quantiplate and endoplate* were used for measuring C3 and C4, respectively. With the radioimmunodiffusion technique, the normal range in our laboratory for C3 is 100 to 250 mg/dl and for C4, 20 to 50 mg/dl. In the second group of 9 patients, who underwent one to four aortocoronary bypass graft operations, the blood samples were obtained 24 hours after operation and the C3 and C4 levels were determined as described previously. The procedures for cardiopulmonary bypass, cardioplegia, and protamine injection were similar to those used in the first group.
t
* * 0
Results There is a rapid activation of the complement system following the onset of cardiopulmonary bypass (Fig 2). Both C3 and C4 decreased significantly (p < 0.001) within minutes of cardiopulmonary bypass. As shown in Figure 3, rapid hernodilution took place, with a significant drop in hematocrit (p < 0.001) as 2 liters of Ringer's lactate solution was used to prime the extracorporeal circuits. To correct complement levels for the hemodilution that occurred, the following formula was used [l]:
Normal Range For C,
I
I
I
I
3 t 4 Cardloplegia Protamine
2 t
I t Cardiopulmonary Bypass
Fig 2 . Measured changes in C3 and C4 following onset of cardiopulmonary bypass. (* = p < 0.001 by Student t test; N = 22.)
TO
Hernatocrits
at
complement corrected = complement measured x (initial packed-red-cell volume/ packed-red-cell volume during bypass)
Figure 4 indicates that both C3 and C4, after being corrected for hemodilution, still showed significant reduction after the initiation of cardiopulmonary bypass (p < 0.01 and p C 0.05, respectively; paired t test). Our data also indicate that levels of C3 and C4, measured and corrected for hemodilution, did not change significantly as the result of aortic crossclamping, infusion of cardioplegia, and reperfusion. Hematocrits and complement levels remained stable during this period (p > 0.1 by Student t test and paired t test).
*Kallestad Laboratories, Inc., 2000 Austin National Bank Tower, Austin,
TX 78701.
't Cardiopulmonary
*t Cardioplagia
3t
4
Prolamine
Bypass
Fig 3. Changes in hematocrit as a result of hemodilution, during bypass, and during the course of cardiac surgety. (' = p < 0.001 by Student t test; N = 10.)
231 Chiu and Samson: Complement Consumption in CPB
rngfdl
200c
150 -
100
-
50- T
If
2f
3f
4
Cardiopulmonary Cardloplegla Prolamlne Bypasn
Fig 4 . Changes in C3 and C4 after being corrected for the 4fects of hemodilution. P = p < 0.001 by paired t test; t = p < 0.02 by paired t test; N = 10.)
Slow intravenous infusion of protamine sulfate sufficient to neutralize heparin, as practiced routinely in our cardiac procedures and guided by the accelerated clotting time, does not induce significant consumption of the complement components. Neither C3 nor C4, measured and corrected for hematocrit changes, was significantly affected by the protamine administration (p > 0.7) (see Figs 2, 4). In Group 2, C3 and C4 levels in 9 patients were determined 24 hours after cardiac surgical procedures. The C3 and C4 levels were 106.3 f 8.0 (mean f standard error of the mean) and 20.3 f 4.6 mg/dl, respectively. These were not significantly different from the prebypass levels observed in Group 1 (p > 0.7 for C3 and p > 0.2 for C4), suggesting the recovery of these two complement components within 24 hours after cardiac operation. Incidentally, these preoperative and postoperative values are within the normal ranges observed in our clinical immunology laboratory at the Montreal General Hospital. In both groups of patients, hemodynamic responses to protamine injection were minimal to mild and the serious protamine hypotension encountered at times in cardiac procedures did not occur.
Comment The complement system not only facilitates the ingestion of pathogens by phagocytes (opsonization) but also mediates many aspects of inflammation and tissue injury. The striking similaritiesbetween the known biological activities of the complement-derived anaphylatoxins
and many clinical manifestations of the so-called postperfusion syndrome led a number of investigators to study the possible activation of the complement system during the cardiopulmonary bypass procedure. Although there has been considerable progress in the safe utilization of cardiopulmonary bypass, the postperfusion syndrome still plays an important role in the morbidity and mortality of patients undergoing cardiac operations, particularly after prolonged extracorporeal bypass. Such sequelae may be manifested as increased capillary permeability with interstitial fluid pooling, coagulopathies, and varying degrees of organ dysfunction, particularly in the lung and the kidney. As noted by Chenoweth and associates [l], these clinical manifestations strongly suggest the participation of the complement system in their pathogenesis. In 1971, Parker and colleagues [ A studied changes in serum complements before and after cardiopulmonary bypass by determining 50% hemolytic complement (CH50). They reported significant depression of CH50 4 and 20 hours after cardiopulmonary bypass, but it returned to a normal level after 44 hours. They suggested that complement components bound to the tissue might contribute to the increased capillary permeability and that a decrease in serum complements may predispose patients to certain infections. That such consumption of complements during cardiopulmonary bypass may be rapid and transient was suggested by the studies of Genetet and co-workers [8],who found no significant depression of C3 and C4 levels one and seven days after cardiopulmonary bypass as compared to preoperative values. It is obvious that serial sampling at close intervals is needed to elucidate complement activation during cardiopulmonary bypass. Chenoweth and associates [l]studied the generation of two split products of complement, namely, C3a and C5a anaphylatoxins, in patients undergoing cardiopulmonary bypass by taking serial samples during the procedure. There was a significant and rapid increase in C3a concentration within ten minutes of onset of cardiopulmonary bypass, while C5a did not change sigruficantlyduring cardiopulmonary bypass. However, neutropenia during bypass and marked transpulmonary neutropenia suggested to these authors that pulmonary vascular sequestration of C5aactivated granulocytes was taking place. They also found that the incubation of blood with the nylon mesh liner of the bubble oxygenator, as well as vigorous oxygenation of whole blood, promoted complement activation. Our observation that C3 and C5 are consumed rapidly after the onset of cardiopulmonary bypass is consistent with their findings and indicates rapid activation of complements through the classic pathway, although the properdin pathway may also be activated. Such a decrease in the level of complements could not be attributed to hemodilution or to the infusion of stored blood deficient in complement because no blood transfusions took place during this period. Rapid recovery of C3 and C5 levels after operation, either by resynthesis or transfusion, is also confirmed in our Group 2 patients. There is experimental evidence that complements also
232 The Annals of Thoraac Surgery Vol 37 No 3 March 1984
may play a part in ischemic injury of myocardium in the baboon [2] as well as in postoperative myocardial infarctions in human beings [3]. Lack of complement activation after aortic cross-clamping thus could be a reflection of adequate myocardial protection with the cold potassium cardioplegia employed in this series, but at present this remains speculative. There has been a renewed interest in the pathogenesis of protamine-induced hypotension during cardiac operations. Such hypotension is generally associated with marked peripheral vasodilatation, but whether protamine has direct negative inotropic effects on the myocardium remains controversial. Sethna and colleagues [9] reported that heparin and protamine did not produce adverse alterations in the global myocardial metabolic state. Although protamine had been reported to reduce contractility in a canine isometric heart model [lo], recent clinical studies indicate that many patients can increase cardiac output to compensate for peripheral vasodilatation and hypotension produced by protamine [111* Nevertheless, catastrophic cardiovascular collapse can occur occasionally following the administration of protamine after cardiopulmonary bypass [12]. Such collapse may be associated with massive noncardiogenic pulmonary edema. Various hypotheses to explain this protamine hypotension include anaphylaxis [13, 141, histamine release from the lung tissue [15], and lowering of plasma-ionized calcium [161. Complement activation was postulated as an important mechanism following the discovery in 1975 by Rent and co-workers [4] that protamine, and particularly the heparin-protamine complex, can cause massive activation of the complement system. In the in vitro system, such a complex can induce virtually complete depletion of total hemolytic complement activity. This depletion is dependent on time, temperature, pH, divalent cations, and serum concentrations. Siegel and associates [17] further showed that protamine may interact with C-reactive protein and induce complement consumption. The split products of complement activation, such as C3a and C5a, have been postulated to have a role in protamine-induced hypotension [5]. In spite of these well-documented studies, our patients failed to show significant changes in C3 and C4 following the administration of protamine. We administered protamine slowly into the vein since our clinical experience suggests that rapid injection of protamine is more likely to produce serious hypotension. Whether the speed of protamine administration affects the magnitude of complement activation is not known. Although Kirklin [18] recently reported a rapid increase in complement split products after protamine injection, at present the role of the complement system in protamineinduced hypotension remains hypothetical. Further investigation is required to eluadate the mechanism of protamine-induced hypotension, which is still a potentially dangerous complication of cardiac surgical procedures.
This work was partly supported by a Quebec Heart Foundation grant. We wish to thank Marlene Elliott, R.N., and Mrs. Emma Lisi for their assistance.
References 1. Chenoweth DE, Cooper SW, Hugh TE, et al: Complement
activation during cardiopulmonary bypass: evidence for generation of C3a and C5a anaphylatoxins. N Engl J Med 304:497, 1981 2. Crawford MH, Grover FL, ORourke RA, et al: Preservation
of jeopardized myocardium by C3 depletion in the baboon. Am Fed Clin Res 27160A, 1979
3. Lyakhov NT, Zhivoderov VM, Belobrzhek LM. Immunological changes in postoperative myocardial infarction. Khirurgiia (Mosk) 1:21, 1979 4. Rent R, Ertel N, Eisenstein R, et al: Complement activation by interaction of polyanions and polycations: I. Heparinprotamine induced consumption of complement. J Immunol 114120, 1975 5. White JV:Complement activation during cardiopulmonary bypass (letter). N Engl J Med 305:51, 1981 Cain S The importance 6. Chiu RCJ,Blundell PE, Scott HJ, of monitoring intramyocardial temperature during hypothermic myocardial protection. Ann Thorac Surg 28317, 1979 7. Parker DJ, CantreU JW, Karp RB, et al: Changes in serum complement and immunoglobulins following cardiopulmonary bypass. Surgery 71:824, 1971 8. Genetet N, Sapene M, Genetet 8, et al: Modifications immunitaires apr& chirurgie cardiaque faite sous circulation extra-corporelle. Nouv F’resse Med 11:433, 1982 9. Sethna DH, Moffitt E, Gray RJ, et al: Effects of protamine sulfate on myocardial oxygen supply and demand in patients following cardiopulmonary bypass. Anesth Analg (Cleve) 61247, 1982 10. Gourin A, Streisand RL, Stuckey JH. Total cardiopulmonary bypass, myocardial contractility, and the administration of protamine sulfate. J Thorac Cardiovasc Surg 61:160, 1971 11. Shapira N, Schaff HV, Piehler JM, et ak Cardiovascular effects of protamine sulfate in man. J Thorac Cardiovasc Surg W.505,1982 12. OGger GN, Becker RM,Bonchek LI: Noncardiogenic pulmonary edema and peripheral vascular collapse following cardiopulmonary bypass: rare protamine reaction? Ann Thorac Surg 2920, 1980 13. Knape JTA, Schuller JL, DeHaan P, et al: An anaphylactic reaction to protamine in a patient allergic to fish. Anesthesiology 55:324, 1981 14. Moorthy SS, Pond W, Rowland RG: Severe drmlatory shodc following protamine (an anaphylactic reaction). Anesth Analg (Cleve) 5977,1980 15. Frater R W M : Discussion of (11) 16. Jones RM, Hill AB, Nahrwold ML, et ak Effect of protamine on plasma ionized calcium in the dog. Can Anaesth Soc J 2965, 1982 17. Siegel J, Rent R, Gewurz H. Interaction of C-reactive pmtein with the complement system. I. Protamine-induced consumption of complement in acute phase sera. J Exp Med 140631, 1974 18. Kirklin J: Discussion of [ l l ]