Surg Today Jpn J Surg (1997) 27:220-225 ~ S U I ~ E R Y T O D A Y

© Springer-Verlag 1997

Relationship Between Respiratory Distress and Cytokine Response After Cardiopulmonary Bypass [-{IROSHI ITO, KIMIKAZU HAMANO, HIDENORI GOHRA, TOMOE KATOH, YOSHIHIKO FUJIMURA, HIDETOSHI TSUBOI, and KENSUKE ESATO

First Department of Surgery, Yamaguchi University School of Medicine, 1114 Kogushi, Ube, Yamaguchi 755, Japan

Abstract: The influence of cytokines on the inflammatory re- sponse in surgery has recently been the subject of investiga- tions. We measured tumor necrotic factor-~ (TNF-~), interleukin 1[~ (IL-I[~), interlenkin 6 (IL-6), interleukin 8 (IL- 8), and granulocyte elastase (GEL) in 26 patients undergoing elective cardiac operations using cardiopulmonary bypass (CPB), preoperatively, immediately after CPB, and on post- operative days (PODs) 1, 3, and 6. To evaluate the effect of these cytokines on pulmonary function, the patients were di- vided according to whether the oxygenation index (OI) on POD I was > 250 or < 250, into groups A and B, respectively. TNF-~ and IL-1 [~ were undetectable and there were no sig- nificant differences in the preoperative IL-6, IL-8, and GEL levels. However, immediately following CPB, the mean IL-6, IL-8 and GEL levels in both groups were significantly higher than the preoperative levels (P < 0.01). Moreover, all these levels were significantly higher in group B than in group A, at 162 -- 150pg/ml v s 64 -+ 53 pg/ml ( P < 0.05) for IL-6; 53 -+ pg/ ml v s 22 +_ 20 pg/ml (P < 0.01) for IL-8 ; and 2477 _+ 1642mg/ i vs 1397 - 774mg/1 (P < 0.01) for GEL. The IL-6 levels returned to the preoperative values in both groups on POD 1; however, the GEL levels remained significantly higher in group B than in group A postoperatively, at 616 _ 326mg/I v s

378 +_ 70mg/l on POD 1, and at 292 -+ 70mg/! v s 218 -+ 62mg/ I on POD 3 (P < 0.05). Thus high levels of cytokines such as IL-6, ILl8, and GEL may be detrimental to respiratory function.

Key Words: cytokine, respiratory function, cardiopulmonary bypass

recent investigations. The longer operative time and significant operative bleeding associated with such op- erations as esophageal cancer resections and pancre- atoduodenectomy increase the cytokine response, and therefore, cytokines increase in relation to the severity of injury. 3 In thoracic surgery, the influence of cytokines is even more significant than in abdominal surgery de- spite the shorter operative time and less bleeding, which is thought to be due to lung manipulation during the operative procedure? In cardiac surgery, there is the unique impact of cardiopulmonary bypass (CPB). With CPB, as the blood makes contact with the artificial de- vices, the complement cascade is activated. 4,5 Plasma osmolarity is decreased by the priming solutions, lead- ing to fluid retention in the extravascular space, e while hypothermia associated with CPB stimulates an adren- ergic response and catecholamine release. 7 Low blood flow disrupts the endocrine system leading to hyperglycemia and abnormal mineral homeostasis3 CPB creates an environment which is very different from that of general surgery, facilitating a particularly strong cytokine response. Recent studies have focused on the relationship between postpump inflammatory response and cytokines. 79 In this study, we evaluated the cytokine response following CPB and its role in respiratory function.

Materials and M e t h o d s

Introduct ion

The relationship between surgical procedures and cytokine response z,2 has been the subject of a number of

Reprint requests to: H. Ito (Received for publication on Aug. 23, 1995; accepted on July 4, 1996)

P a t i e n t s

A total of 26 patients ranging in age from 19 to 74 years, with a mean age of 55.5 _+ 13 years, who were scheduled to undergo open heart surgery were included in this study (Table 1). To evaluate the relationship between respiratory function following open heart surgery and plasma cytokines, the patients were divided into two groups according to the oxygenation index (OI), which

H. Ito et al.: Cytokine Response After Cardiopulmonary Bypass 221

Table 1. Perioperative variables in the two groups

Group A Group B

Age 53 -+ 15 60 ± 8 N.S. Sex (M:F) 10:5 7:4 N.S. Respiratory function FEV10 77.0 _+ 19.5 92.5 __+ 5.8 N.S. %VC 75.0 -+ 19.5 71.5 + 22.9 N.S. CPB time (min) 142 -+ 74 243 _+ 45 i ° < 0.05 Ao. clamp time (min) 81 -+ 50 98 + 30 N.S. Oxygenation index 389 -+ 92 162 ___ 52 P = 0.0001

FEV~.0, forced expiratory volume in ls; VC, vital capacity; CPB, cardiopulmonary bypass; Ao, aorta; N.S., not significant Values are expressed as the mean -+ SD

Table 2. Operative procedures in the two groups

Group A Group B (n = 16) (n = 10)

ASD closure 6 1 VSD closure 1 0 CABG 5 7 MVR 3 0 CABG + AVR 0 1 AVR + MVR 0 1 VSP 1 0

Total 16 10

ASD, atrial septal defect; VSD, ventricular septal defect; CABG, coronary artery bypass grafting; MVR, mitral valve replacement; AVR, aortic valve replacement; VSP, ventricular septal perforation

was defined as Pa%/FiO2. Group A was comprised of patients whose OI was more than 250 on POD 1, or those able to be weaned from the respirator prior to extubation on the day of surgery (n = 16). Group B was comprised of patients whose OI was less than 250 on POD 1 (n = 10). An OI of 250 or less was viewed as an indication that the patient could be successfully extubated. If the PaO2 was over 100 mmHg on 40% FiO2, patients could be extubated. In group A, 6 patients underwent atrial septal defect (ASD) closure, 1 underwent ventricular septal defect (VSD) clos- ure, 5 underwent coronary artery bypass grafting (CABG), 3 underwent mitral valve replacement (MVR), and 1 underwent ventricular septal perforation (VSP) closure. In group B, 1 patient underwent ASD closure, 7 underwent CABG, 1 underwent aortic valve replacement (AVR), 1 underwent MVR, and 1 underwent C A B G and A V R (Table 2). No patient was suspected of having an infectious disease. During surgery, anesthetic induction and mainten- ance were achieved with a high dosage of fentanyl. The extracorporeal circuit consisted of a biopump (Bio-Console, Bio-Medicus, Minneapolis, MI, USA), a cardiotomy reservoir, and a membrane oxygenator

(Capiox-E, Terumo, Tokyo, Japan). The circuit was primed with 1500-2000ml of Ringer's lactate. Heparin, 400 IU/kg body weight, was infused to main- tain an activated clotting time of more than 400 seconds during bypass, and betamethasone 4mg/kg was added to the priming to prevent blood cell injury. Flow rates of 2.41/m2/min were used. Intermittent crystalloid cardio- plegia was used for myocardial protection. At the end of CPB, heparin was neutralized with protamine sulfate and during CPB, the hematocrit value was maintained at 18%-22% in all patients. When hemolysis was evident in the urine during CPB, human haptoglobin was administerd.

Sample Collection

Serial blood samples were obtained from a radial artery catheter prior to surgery, at the end of CPB, 24 h follow- ing surgery, defined as postoperative day (POD) 1, on POD 3, and on POD 6. Blood samples were collected into vacuum tubes with ethylenediaminetetraacetic acid (EDTA) and immediately centrifuged at 600g for 10min at 4°C. Plasma was stored a t -7 0 ° C until the cytokines were assayed.

Cytokine Assay

The levels of plasma TNF-c~, IL-I[3, IL-2, IL-6, and IL- 8 were measured by enzyme-linked immunosorbent as- say (ELISA) kits (Toray-Fuji Bionics, Tokyo, Japan) and the levels of plasma G E L were measured by enzyme immunosorbent assay (ELA) kits (Merck, Darmstadt, Germany).

Statistics

Data are presented as the mean + the standard devia- tion (SD) and analyzed by Mann-Whitney U tests. A P-value of < 0.05 was considered significant.

222

Results

Patients ' s Background

There was no significant difference in age, sex, and preoperative respiratory function between the two groups. Group B had a significantly longer CPB time than group A (P < 0.05) (Table 1).

Correlation Between Cytokine and CPB Time

At the termination of CPB, correlations were observed between IL-6 and CPB time (R = 0.605, P < 0.005; Fig. la); IL-8 and CPB time (R = 0.636, P < 0.001; Fig. lb); and G E L and CPB time (R = 0.505, P < 0.05; Fig. lc). No correlation was observed between TNF-(~

H. Ito et al.: Cytokine Response After Cardiopulmonary Bypass

and CPB time, IL-I~ and CPB time, or IL-2 and CPB time.

Cytokine Responses of the Two Groups

There were no significant differences in the preoper- ative levels of IL-6, IL-8, and G E L between the two groups.

IL-6. At the termination of CPB, the mean IL-6 levels in both groups were significantly higher than the preoperative levels (P < 0.01). The IL-6 levels in group B, at 162 +_ 150pg/ml. were significantly higher than those in group A, 64 + 53 pg/ml (P < 0.05). Following POD 1, the IL-6 levels returned to the baseline

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Fig. 1. a Relationship between cardiopnlmonary bypass (CPB) time and interleukin-6 (IL-6) levels at the termination of CPB. There was a positive correlation, b Relationship between CPB time and interleukin-8 (IL-8) levels at the termination of CPB. There was a positive correlation, c Relationship between CPB time and granulocyte elastase (GEL) levels at the termination of CPB. There was a positive correlation

H. Ito et al.: Cytokine Response After Cardiopulmonary Bypass 223

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Fig. 2. a Changes in IL-6 levels. There was no significant difference preoperatively between the two groups. At the ter- mination of CPB, the IL-6 levels in group B were significantly higher than those in group A. After postoperative day (POD) 1, there was no significant difference between the two groups. b Changes in IL-8 levels. There was no significant difference preoperatively between the two groups. At the termination of CPB, and on POD 1 and POD 3, the IL-8 levels in group B

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were significantly higher than those in group A. On POD 6, there was no significant difference between the two groups, c Changes in GEL levels. There was no significant difference preoperatively between the two groups. At the termination of CPB, and on POD 1 and POD 3, the GEL levels in group B were significantly higher than those in group A. On POD 6, there was no significant difference between the two groups

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preoperat ive levels, with no significant differences be- tween the two groups (Fig. 2a).

IL-8. At the terminat ion of CPB, the mean IL-8 levels in both groups were significantly higher than the preoperat ive levels. The IL-8 levels in group B, at 53 ± 49pg/ml, were significantly higher than those in group A, at 22 ± 20pg/ml (P < 0.01). In group B, the IL-8 levels remained significantly higher than those in group A until P O D 3 (Fig. 2b).

GEL. At the termination of CPB, the mean G E L levels in both groups were significantly higher than the preoperat ive levels. The G E L levels in group B, at 2477 ± 1642mg/1, were significantly higher than those in group A, at 1397 ± 774mg/1 (P < 0.01). In group B, the G E L levels remained significantly higher than those in group A, at 616 ± 326mg/1 vs 378 ± 70mg/1 on P O D 1,

and 292 _+ 70 mg/1 vs 218 ± 62mg/1 on P O D 3. The G E L levels were not significantly different on P O D 6 be- tween the two groups (Figs. 2-3).

Discussion

Many recent studies have investigated the relationship between surgical invasion and cytokine response. How- ever, cytokine response following CPB is different f rom that seen in general surgery. 7-9 In general surgery, the surgical procedure leads to an acute-phase response, the main mediators of which are thought to be IL-1, IL-6, and TNF. 2 These acute-phase reactants also play an important role in cardiac surgery with CPB, but patients undergoing CPB are in a vastly different situation f rom those undergoing general surgery. With CPB, as the blood makes contact with the artificial devices, the

224 H. Ito et al.: Cytokine Response After Cardiopulmonary Bypass

complement cascade is activated; 4,5 hence, vascularity increases and intravascular fluid extravasates into the interstitial space. Plasma osmolarity is decreased by priming solutions leading to the retention of water in the extravascular space, 6 while hypothermia stimulates an adrenergic response and the release of catechola- mines. 7 Fur thermore, low blood flow disrupts the endo- crine system, leading to hyperglycemia and abnormal mineral homeostasis?

IL-6 is produced by monocytes, macrophages, endot- helial cells, and fibroblasts by the stimulation of TNF and IL-1.1° IL-6 induces B cell proliferation and the production of antibodies as an acute-phase immuno- logic reaction, and it also induces liver cells to produce acute-phase protein. At the end of CPB, IL-6 levels are maximal, but quickly return to normal by POD 1.

IL-8 is thought to be produced by the stimulation of TNF-~ and IL-l[3, and also as a result of hypoxia due to ischemia. 11-18 It is produced mainly by endothelial cells, macrophages, and monocytes as an acute-phase reac- tion, and induces neutrophil chemotaxis and degranula- tion. G E L attacks many organs to cause damage, and the results of our study clearly demonstra ted a positive correlation between IL-8 and GEL. TNF-c~ and IL- I~ could not be detected, and there was no correlation between these cytokines and IL-8; however, there was a positive correlation between IL-8 and CPB time and aortic clamp time. Therefore, IL-8 may be produced by ischemia or CPB. We also found that in patients with respiratory distress whose intraoperative Of was less than 250, G E L and IL-8 were significantly higher than in those without respiratory distress. While there was no significant difference in the preoperat ive respiratory function, age, sex, and aortic clamp time between these two groups of patients, the CPB time was significantly longer in the respiratory distress group, and the IL-6, IL-8, and G E L levels at the end of CPB in the patients with respiratory distress were significantly higher than in those without respiratory distress. These data suggest that in open heart surgery, CPB and reperfusion follow- ing declamping of the aorta could be the pr imary causes of IL-6, IL-8, and G E L release. The CPB time has a more profound effect on postoperat ive respiratory dis- tress through IL-6, IL-8, and G E L release than the aor- tic clamp time. Although reperfusion may be an important factor in producing these cytokines, CPB it- self must also play an important role in producing IL-6, IL-8, and GEL. The role of CPB on cytokine produc- tion may reflect the long period during which the blood is exposed to foreign materials of abnormal shear forces.

Respiratory distress frequently occurs following pro- longed cardiac operations. In this study, we investigated the levels of plasma cytokines following CPB as one of the mediators of pulmonary dysfunction and found that

the plasma IL-6, IL-8, and G E L levels were significantly higher in patients with respiratory distress than in pa- tients without respiratory distress following cardiac sur- gery. These results suggests that IL-8 induced by CPB causes the degranulation of adhesion neutrophils which attack the endothelium, causing injury and consequent capillary leakage. 13 With hypergranulocyte elastasemia, the degree of pulmonary vascular injury and pulmonary capillary leakage is severe. Moreover, systemic capillary leakage causes fluid extravasation into the extravascular space. These factors may cause respiratory distress fol- lowing cardiac surgery.

In conclusion, hypercytokinemia following CPB may play an important role in respiratory distress following cardiac surgery. The IL-6, IL-8, and G E L levels were observed to be significantly higher in patients with a poor OI (<250) than in those with an acceptable OI (>250), suggesting that anticytokine therapy may be effective in preventing pos tpump respiratory distress.

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