INCREASED PULMONARY VASCULAR RESISTANCE FOLLOWING PROLONGED PUMP OXYGENATION

INCREASED P U L M O N A R Y VASCULAR RESISTANCE FOLLOWING PROLONGED PUMP O X Y G E N A T I O N N. K. Yong, M.D., F.R.C.S. (Eng. and Ed.),* B. Eiseman. F. C. Spencer, M.D., and N. Rossi, M.D., Lexington,

M.D.,

Ky.

R

ESPIRATORY insufficiency following prolonged cardiopulmonary bypass oc­ casionally is a puzzling complication of open-heart surgery. 3 ' *•13 The pathologic changes1' *'12'13'16 and alterations in pulmonary function tests 9,16 have been fully described, and numerous suggestions made 1 0 , 1 5 ' 1 S as to its pathogenesis. Such a complication of perfusion is particularly critical when the underlying cardiopulmonary defect may elevate the pulmonary vascular re­ sistance. This study was designed to determine whether circulation of blood through a pump oxygenator for 2 hours resulted in the liberation or formation of vasoactive material that would appreciably alter pulmonary vascular resistance (PVR) and pulmonary compliance. An ex vivo canine lung, isolated in a per­ fusion chamber, was utilized as an indicator to quantitate such changes. Con­ centrations of both histamine and serotonin were correlated with observed changes in PVR in this test preparation. METHODS

Preparation of Isolated Ex Vivo Lung.—Adult (15 to 20 kilograms) mon­ grel dogs were anesthetized with 25 mg. per kilogram of body weight of sodium pentobarbital, and artificially respired via a cuffed endotracheal tube. Thoracotomy was performed through a median sternotomy, and the pericardium was opened widely. The azygos vein was ligated and divided prior to isolating and encircling with umbilical tapes the trachea, the ascending aorta, and the pul­ monary artery. Following heparinization (3 mg./Kg. body weight), a plastic cannula was introduced into the pulmonary artery through a right ventriculotomy, and tied in place. The heart and lungs were rapidly removed from the animal by transecting the trachea above a non-crushing clamp, and severing Department of Surgery, University of Kentucky Medical School, Lexington, Ky. Supported by grants from the U. S. Public Health Service, the Fred Rankin Fund, and the Kentucky Division of the American Cancer Society. Received for publication Aug. 25, 1964. *Research Fellow China Medical Board. Present Address: Department of Surgery, Faculty of Medicine, University of Singapore, Sepoy Lines, Singapore 3, Malaya. 580

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7XCREASEI) PULMONARY VASCULAR RESISTANCE

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OU

the aortic arch, and the venae cavae. The left ventricle was opened widely to allow free drainage of pulmonary venous blood. The lungs with the plastic catheter within the pulmonary artery were trans­ ferred to a sterile perfusion chamber. The trachea was tied over a cannula fitted into the lid of the chamber, and the lungs were insufflated ten times per minute with 500 to 600 ml. of room air, via a Harvard animal respirator. A side-arm from the insufflation cannula led to an electronic recorder for measurement of endotracheal insufflation pressure. Perfusates.—In order to determine the effect of 2 hours of bubble oxygenation on PVR, a pool of 3,500 ml. of freshly drawn sterile heparinized dog blood was divided into two equal portions. Pool A, the fresh blood, was perfused through the isolated lung without further treatment. Pool B was recirculated through a disposable bubble oxygenator for 2 hours (2 L./min., 95 per cent oxygen, 5 per cent carbon dioxide) following which it was used as the perfusate through the same isolated lung. The experimental design is illustrated in Fig. 1. Perfusion pressures (7 experiments) or flow (3 experiments) were kept constant so that the pulmonary vascular resistance could be monitored con­ stantly. Flow rates through the lung varied in individual experiments between 500 and 1,000 ml. per minute: pressures between 16 and 40 mm. Hg. The p H was maintained at 7.4. Histamine and Serotonin.—Whole blood histamine (14) and serotonin (18) concentrations were measured prior to and at the end of each perfusion. Controls.—1. Stability of the system was proved in two experiments by perfusion of a single lot of fresh blood for 2 hours through the lung without alteration in PVR. Tn two additional experiments, rather than add a second

Pooled Blood

Pool B

Pool A

2 H r e . Bubble Oxygenation

30 Min. P e r f u s i o n I s o l a t e d Lung Fig. 1.—Experimental design.

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J. Thoracic and Cardiovas. Surg.

charge of blood that had been through the oxygenator, fresh blood was added to the system. There was no change in PVR. 2. Effect of hemolysis: Blood from Pool B that had been bubble oxygenated for 2 hours was appreciably hemolyzed. (Range, 792 mg. per cent to 3,120 mg. per cent: mean, 1,377 mg. per cent.) This was more than ten times the degree of hemolysis of Pool A (mean, 73 mg. per cent). In order to eliminate hemolysis alone as the cause of alteration in PVR, a level of plasma-free hemoglobin, equivalent to that in Pool B following 2 hours of oxygenation, was attained by the addition of sterile distilled water to 250 ml. of blood which caused its total hemolysis. This produced a plasmafree hemoglobin of 15.25 mg. per milliliter. Such addition of hemolyzed blood to the lung perfusate did not significantly alter either PVR or tracheal resistance. The significant data are shown in Table I. TABLE I.

EFFECT

OF HEMOLYZED BLOOD

ON PULMONARY

VASCULAR

RESISTANCE

6 0 M I N . AFTER HEMOLYZED BLOOD LOAD

PRELOADING

%

CHANGE

EXPER. N O .

PL.-FREE HOB. (MG./ML.)

PVR*

PL.-FREE HGB. (MG./ML.)

PVR*

PVR

1 2 3 6

3.30 4.74 6.4 3.48

0.0187 0.015 0.0127 0.0166

20.02 23.2 21.0 25.28

0.0187 0.015 0.0158 0.0166

0 0 +24 0

*PVR — — Pressure (mm. Hg) Flow (ml./min.) RESULTS

Pulmonary Vascular Resistance.—The results on both blood flow and endotracheal pressure during the ten technically satisfactory perfusions are shown in Table II, which also summarizes the percentage elevation of PVR and tra­ cheal resistance. In eight of the ten experiments there was an immediate and marked rise in PVR when blood that had been oxygenated for 2 hours was used as the perfusate. In five experiments, this was indicated by a fall in pulmonary blood flow with a constant perfusion pressure, while in three others an increased pressure was required to maintain a constant flow. The change in PVR varied from 0 to 162 per cent, with mean increase of 74 per cent if judged from the end of perfusion A to the beginning of perfusion with oxygenated blood, or 54 per cent if compared from the end of both com­ parable periods of perfusion. In two of the ten perfusions (experiments 2 and 6), there was no altera­ tion in PVR following switching of perfusates. There is no explanation for this discrepancy. These changes are significant at a 5 per cent level of ex­ pectancy (p < 0.01). The slight change of PVR from the beginning to the end of perfusion with oxygenated blood is not significant (p > 0.05). Tracheobronchial Resistance.—There was no significant change in the re-

INCREASED PULMONARY VASCULAR RESISTANCE

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583

TABLE I I . E F F E C T OF BUBBLE OXYGENATION ON PULMONARY VASCULAR AND TRACHEOBRONCHIAL RESISTANCE

POOL A (FRESH BLOOD) EXPER. NO.

1

PVR*

5 30 5 30 5 30 5 30 5 30 5 30 5 30 5 30 5 30 5 30

2 3 4 5 6 7 8 9 10

0.05 0.047 0.04 0.04 0.066 0.066 0.057 0.053 0.083 0.073 0.047 0.043 0.033 0.036 0.02 0.024 0.048 0.05 0.08 0.076

POOL B (BUBBLE OXYGENATED BLOOD) TBR (M.M. HG)

TBRt (M.M. HO)

16 16 15 15 11 12.5 17 21 14 12 15 15

Not

measured Not measured 17 20 20 21

0.07 0.07 0.044 0.04 0.17 0.10 0.10 0.09 0.111 0.092 0.043 0.04 0.082 0.057 0.036 0.036 0.117 0.131 0.153 0.131

16 16 15 15 17 17 18 21 13 15 15 15 Not measured Not measured 20 21 22 23

%

CHANGE PVR

END A / BEG. B

END A / END B

+49

+49

0

0

+157

+51

+88

+69

+52

+25

0

0

+127

+58

+50

+50

+114

+162

+100 Mean+74

+72 +54

Pressure (mm. H g ) Flow (ml./min.) tTBR = Tracheobronchial resistance. •PVR

corded endotracheal pressures between perfusion with fresh versus previously bubble-oxygenated blood. It is evident that 2 hours of bubble oxygenation of the perfusate did not alter tracheobronchial airway resistance at a time when it was effecting a change in pulmonary vascular resistance. Serotonin.—Table I I I summarizes changes in the concentrations occurring during bubble oxygenation as well as during lung perfusion. The data demon­ strate that in vitro bubble oxygenation for 2 hours does not release serotonin. There was indeed a mean drop of 66 per cent in 5-hydroxytryptamine (5-HT) concentration during mechanical oxygenation. Due to the wide deviation, this change was not statistically valid. I t is unlikely therefore that serotonin ac­ counts for the increased PVR that follows mechanical bubble oxygenation. The diminution in the blood levels of 5-HT during perfusion through the lung (mean of 63 per cent of base line) is in keeping with the proved metabolic degradation of serotonin to 5-hydroxyindolacetic acid by the perfused lung. 6 Following bubble oxygenation, serotonin levels were too low to provide a sig­ nificant base line for subsequent changes. Histamine.—In Table IV are summarized the significant whole blood con­ centrations of histamine following bubble oxygenation or during perfusion through the isolated lung. Histamine blood levels decrease rather than rise fol­ lowing mechanical oxygenation. This excludes the vasoactivity of histamine as

YONG ET AL.

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J. Thoracic and Cardiovas. Surg.

accounting for any alteration in PVR following bubble oxygenation. The sta­ tistically insignificant (p > 0.2) changes in histamine during perfusion of bub­ ble-oxygenated blood through the lung are in keeping with our earlier studies,6 demonstrating no appreciable metabolism of histamine by the lung. TABLE I I I .

SEROTONIN

F R E S H BLOOD (POOL A ) EXPER. NO.

CONTROL

FOLLOWING LUNG PERFUSION

%

CHANGE

1.275 1.030 Avg. 1.153

0.55

0.28 0.24 Avg. 0.26

Not sampled

1.194 1.66 Avg. 1.43

0.764

-47

0.730

-13

0.610

-37

0.720 0.963

-52

Avg. 0.84 10

1.010 0.944 Avg. 0.97

Mean

-37

TABLE IV.

HISTAMINE

F R E S H BLOOD (POOL A ) EXPER. N O .

CONTROL

0.707 0.026

FOLLOWING LUNG PERFUSION

0.018

%

CHANGE

-60

Avg. 0.048 0.059 0.061

Not sampled

Avg. 0.060 0.042 0.069 Avg. 0.055 0.058 0.064

0.025

-54

0.031

-50

0.027

-62

Avg. 0.060 10

0.094 0.048 Avg. 0.072

Mean

-56

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INCREASED PULMONARY VASCULAR RESISTANCE

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Previous studies have been in conflict concerning the identification of a humoral factor responsible for increased PVR following mechanical pump oxygenation. In 1957, Woods and associates18 noted that low flow perfusion re­ sulted in elevation of circulating catecholamines. Replogle and co-workers15 con(IN

MlCROGRAMS) BUBBLE-OXYGENATED BLOOD (POOL

B)

FOLLOWING P U M P OX.

% CHANGE P U M P OX.

FOLLOWING LUNG P E R F U S I O N

% CHANGE LUNG P E R F U S I O N

0.078

-93

0.060

-23

0.40

-85

0.635 0.605

+55

% CHANGE PVR END A / B E G . B

+127

Avg. 0.62 0.722

-50

0.509

-40

0.800

+57

+114

0.363

-63

0.807

+122

+100

+50

Sample contaminated

+53

-66

(IN

MlCROGRAMS) BUBBLE-OXYGENATED BLOOD (POOL B ) FOLLOWING LUNG P E R F U S I O N

% LUNG

CHANGE PERFUSION

% CHANGE PVR END A / B E G . B

FOLLOWING P U M P OX.

% CHANGE P U M P OX.

0.060

+25

0.041

-32

0.031

-48

0.150 0.114 Avg. 0.132

+326

+127

0.033

-40

0.041

+24

+50

0.047

-22

0.080

+70

+114

0.032

-56

0.050

+56

+100

-28

+89

YONG ET AL.

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J. Thoracic and Cardiovas. Surg.

firmed this fact and also noted elevation of serotonin. The latter finding was confirmed by Frick. T Hollenberg and his associates8 indirectly implicated both histamine and serotonin as the vasoactive agents responsible for elevation of PVR following pump oxygenation but did not specifically identify either sub­ stance by chemical means. Cooper and colleagues2 found elevations in histamine blood concentrations following pumping but could not correlate such changes with clinical altera­ tions in pulmonary vascular or airway resistance. In previous studies we have demonstrated that histamine Mill produce an elevation both in PVR and tracheobronehial resistance 11 in the isolated dog lung. However, since neither histamine nor serotonin concentrations rose ap­ preciably following bubble oxygenation, in the current studies these two vaso­ active agents are not apparently responsible for changes in either the vascular or tracheobronehial resistance. Mechanical alteration of blood elements or some other pharmacologic agent must be responsible for the undeniable change that was shown to accompany bubble oxygenation. 10 DISCUSSION

These experiments demonstrate that the isolated ex vivo perfused lung is a convenient laboratory tool for quantitating the alteration in PVR that occurs following 2 hours of bubble oxygenation of blood. A perfusate that pre­ viously had been oxygenated results in an immediate increase in PVR of the isolated lung. The various controls, as well as similar studies by Donald, 5 demon­ strate that such changes are not due merely to prolonged perfusion of the lung. I t is clear, therefore, that some sort of damage to the blood or its formed elements during oxygenation is the cause of the characteristic increased PVR observed following prolonged pump oxygenation. Hemolysis accompanies prolonged bubble oxygenation and raises the pos­ sibility that erythrocyte destruction or release of some intracellular element might produce an increased PVR. Schramel and co-workers16 found no correla­ tion between the degree of hemolysis and pulmonary damage. In the current studies, hemolysis per se can be absolved, since the addition of separately hemolyzed erythrocytes did not produce a significant elevation in PVR. SUMMARY AND

CONCLUSIONS

1. The effect of prolonged bubble oxygenation of blood on pulmonary vas­ cular resistance has been quantitated by utilizing an excised ex vivo dog lunginsufflated with air and perfused via the pulmonary artery. 2. Comparison of the vasoactive effect of fresh blood perfusate with blood that has been bubble oxygenated for 2 hours demonstrates marked elevation in pulmonary vascular resistance immediately following perfusion with the blood that had previously undergone 2 hours of bubble oxygenation. 3. Although increased erythrocyte destruction accompanied bubble oxy­ genation, the vasoactive effect was not caused by free hemoglobin. 4. Both histamine and serotonin were elevated in the blood that produced

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587 °° '

an increase PVR. This suggests, but does not prove, a causative relationship between these vasoactive substances and pulmonary vasoconstrietion. 5. The isolated perfused dog lung has proved to be a simple biologic prepa­ ration for the investigation and identification of the agents responsible for producing pulmonary hypertension following prolonged pump oxygenation. REFERENCES

1. Baer, D. M., and Osborn, J . J . : The Post-Perfusion Pulmonary Congestion Syndrome, Am. J . Clin. Path. 34: 442, 1960. 2. Cooper, T., Jellinick, M., Willman, V., Schweiss, J . F., and Hanlon, C. R.: Plasma Histamine During Cardiopulmonary Bypass in Man, Arch. Surg. 86: 138, 1962. 3. Dammann, J . F., J r . , Thung, N., Christlieb, I., Littlefield, J . B., and Muller, W. H., J r . : The Management of the Severely 111 Patient After Open-Heart Surgery, J . THORACIC & CARDIOVAS. SURG. 4 5 : 80, 1963.

4. Dodrill, F . D . : The Effects of Total Body Perfusion Upon the Lungs in Extracorporeal Circulation, Springfield, 111., 1958, Charles C Thomas, Publisher, p . 327. 5. Donald, D. E . : A Method for Perf usion of Isolated Dog Lungs, J . Appl. Physiol. 14: 1053, 1959. 6. Eiseman, B., Bryant, L., and Waltuch, T . : Metabolism of Vasomotor Agents b y t h e Isolated Perfused Lung, J . THORACIC & CARDIOVAS. SURG. 4 8 : 798, 1964.

7. Frick, J . H . : Influence of 5-Hydroxytryptamine on Renal Function in Extracorporeal Circulation, Nature 187: 609, 1960. 8. Hollenberg, M., Pruett, R., and Thai, A . : Vasoactive Substances Liberated by Prolonged Bubble Oxygenation, J . THORACIC & CARDIOVAS. SURG. 4 5 : 402, 1963.

9. Howatt, W. F . , Talner, N. S., Sloan, H., and DeMuth, G. R.: Pulmonary Function Changes Following Repair of Heart Lesions With the Aid of Extracorporeal Circu­ lation, J . THORACIC & CARDIOVAS. SURG. 4 3 : 649, 1962.

10. Lee, W. H., Jr., Krumliaar, D., Fonkalsrud, E . W., Schjeide, O. A., and Maloney, J . R., J r . : Denaturation of Plasma Proteins as a Cause of Morbidity and Death After Intracardiac Operations, Surgery 50: 39, 1961. 11. Moore, T. C , Normel, L., and Eiseman, B . : Effect of Histamine on Blood Flow and Tracheal Resistance in Isolated Perfused Lungs, Surgery ( I n press.) 12. Neville, W. E., Kontaxis, A., Gavin, T., and Clowes, G. H. A., J r . : Post-perfusion Pul­ monary Vasculitis. I t s Relationship to Blood Trauma, Arch. Surg. 86: 126, 1963. 13. Osborn, J . J., Popper, R. W., Kerth, W. J., and Gerbode, F . : Respiratory Insufficiency Following Open-Heart Surgery, Ann. Surg. 156: 638, 1962. 14. Shore, P . A., Burkhalter, A., and Cohn, V. H., J r . : A Method for the Fluorometric Assay of Histamine in Tissues, J . Pharmacol. & Exper. Therap. 127: 182, 1959. 15. Replogle, R., Levy, M., DeWall, R. A., and Lillehei, R. C.: Catecholamine and Serotonin Response to Cardiopulmonary Bypass, J . THORACIC & CARDIOVAS. SURG. 44: 638, 1962.

16. Schramel, R., Schmidt, F., Davis, F., Palmisano, D., and Creech, O., J r . : Pulmonary Lesions Produced by Prolonged Partial Perfusion, Surgery 54: 224, 1963. 17. Waalkes, T. P . : The Determination of Serotonin (5-Hydroxytryptamine) in Human Blood, J . Lab. & Clin. Med. 54: 824, 1959. 18. Woods, E. F., Richardson, J . A., Lee, W. H., J r . , Asmore, J . D., and Parker, E. F . : Plasma Concentrations of Epinephrine and Arterenol During Cardiopulmonary Bypass, Cir­ culation 16: 955, 1957.