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Eur J Cardiothorac Surg 2005;27:379-383
© 2005 Elsevier Science NL
a University of Athens Medical School, First Propaedeutic Surgical Department, Athens, Greece
b First Thoracic Surgical Department, SOTIRIA General Hospital for Chest Diseases, 7 P. Dimitrakopoulou Street, 11141 Athens, Greece
Received 5 September 2004; received in revised form 13 December 2004; accepted 17 December 2004.
* Corresponding author. Tel./fax: +30 210 252 9048. (E-mail: pamnisthos{at}yahoo.gr).
| Abstract |
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Key Words: Oxidative stress Lung reexpansion Lung reperfusion
| 1. Introduction |
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During one lung ventilation the operated lung remains completely atelectatic for a period of time. It is well known that non-ventilated lung is also hypoperfused due to hypoxic vasoconstriction [5]. Besides, the postresectional remaining pulmonary tissue has been subjected to considerable manipulation during the conducted lobectomy or segmentectomy. When bronchial block is ended the following immediate lung reexpansion along with tissue reperfusion might generate oxygen free radicals through a fairly well described mechanism [69]. Although lung is a resistant tissue to hypoxia because of its dual blood flow and the use of oxygen reserves in alveolar spaces reexpansion injury detected after pneumothorax management and reperfusion injury after lung transplantation are two examples for possible oxidative damage [10,11].
The authors conducted a prospective analysis in order to investigate the generation of oxygen free radicals through lipid peroxidation metabolites after one-lung ventilation (OLV) pulmonary resections.
| 2. Material and methods |
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Group B included patients with documented NSCLC who were subjected to pneumonectomy with one lung ventilation. The aim of this group was to record malondialdehyde (MDA) plasma levels in cases of OLV but with the affected lung removed from the body so as to estimate the systematic effect of oxygen free radicals generated by other systems to serum MDA levels.
The next three groups were the actual study groups and included patients who were subjected to OLV lobectomy. These patients were grouped according to the duration of OLV. Group C included patients subjected to 60min OLV. Group D included patients subjected to 90min OLV. Group E included patients subjected to 120min OLV.
Chemotherapy, radiation, mechanical ventilation and infection are widely considered as free oxygen radicals generators [1214]. Twelve patients that needed mechanical ventilation or were septic within the first 48h postoperatively were excluded from the study.
Finally patients, who were treated for minor chest trauma as outpatients participated in this study as baseline group after their rehabilitation (group F). All were ex-smokers, without COPD.
Serum MDA was measured. Plasma MDA levels were recorded in every patient following a fixed blood sampling protocol. Peripheral venous blood was aspirated to a amount of 5cm3 each time. The timing of blood sampling was the following: (a) 1 sample 24h preoperatively, (b) 1 sample 30min after the onset of operation for the control groups or 30min after the OLV onset for the study groups, and (c) 1 sample 5min after lung reoxygenation (groups CE), after pneumonectomy completed (group B) and, after non-OLV lobectomy performed (group A), (d) 1 sample at 1, 6, 12, 24 and, 48h postoperatively for all patients.
Plasma MDA levels as an index of lipid peroxidation due to oxygen free radicals, were measured using high-performance liquid chromatography. A sensitive and easily reproduced method was used that was developed by Fukunaga and colleagues [15].
Statistical analysis was performed using Student's t-test (otherwise the Wilcoxon rank-sum test) and
2 (Fisher's Exact test when needed) test where appropriate.
| 3. Results |
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When OLV was used the oxidative stress proved to be the most severe. Groups CE disclosed the same tendency. At the beginning of the operation all three groups showed a mild elevation of MDA levels like the first two groups. Comparison between A2E2 did not revealed significant differences. But 5min after the end of OLV a notable increase of MDA levels was measured which overdoubled the figures. In group C raised from 6.44±3.6nmol/ml during OLV to 14.48±5.8nmol/ml (P<0.001) after reventilation. In groups D and E from 6.44±3.2 and 6.35±0.4nmol/ml raised to 15.71±4.0 (P<0.001) and 18.31±3.9nmol/ml (P<0.001), respectively, in minutes after the end of OLV. This increase was significantly more intense than the respective one in groups A and B (A3 and B3 vs. C3E3, all P<0.001). Characteristically the raise of MDA serum levels was relevant to the duration of lung atelectasis. E3 was significantly higher than D3 (P<0.001) and D3 than C3 (P<0.001). The more prolonged OLV the more strengthful oxidative stress was developed. These high values were noted up to 1h postoperatively. After that a gradual decrease was detected (Table 2) to lower than preoperative levels (C1 vs. C8, D1 vs. D8 and E1 vs. E8 were all statistically significant, P<0.001).
In all groups, the oxidative stress gradually subsided after the first 6 postoperative hours. This was more pronounced after pneumonectomy (B4 vs C4E4, P<0.001, respectively).
Besides, the malignancy itself produced increased lipid peroxidation compared to group F. Tumor removal led in a short time (48h) to decreased levels of MDA in comparison to preoperative measurements (A1E1 vs. A8-E8, P<0.001). This was independent to the use or not of OLV (Table 2).
| 4. Comment |
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Severe oxidative stress is developed when one-lung ventilation is used, which is supported biochemically and pathophysiologically by the reexpansion/reperfusion syndrome. Comparative study of all groups reveals that after subtracting all the free radicals generating factors mentioned above, OLV produces severe oxidative burden to the organism a few minutes after reventilation of the atelectatic lung. The degree of the amount of generated oxygen free radicals was associated to the duration of OLV. The longer the atelectasis the more powerful the subsequent oxidative stress. A common pathway was observed in groups CE: a steep rise of MDA serum levels immediately after reventilation which gradually returned to near preoperative levels in almost 12-h period. The significantly higher levels of MDA between group A and groups CE at 6h postoperatively suggests that the reventilated remaining lobe has been suffered a much more severe oxidative stress than the manipulated non-atelectatic remaining lobe in group A. Furthermore the gradual decrease of MDA levels postoperatively suggests a common internal antioxidative mechanism of oxygen free radicals clearance and a constant counteraction by the endogenous antioxidant systems (glutathione, superoxide dismutase, etc).
Pneumonectomy group B represents a model of OLV without subsequent reperfusion/reoxygenation, in which the affected lung is removed. The lowest long-term postoperative MDA levels (B8) were observed. It is suggested that although OLV ischemia and surgical stress were responsible for a certain amount of oxidative stress, the lack of reexpansion/reperfusion effect led to the lowest MDA levels postoperatively. Consequently, lung reexpansion could be considered as the main contributor of free radicals generation, since it was the only factor altered in the comparison between groups AE. Besides, the removal of the non-ventilated lung led to the greatest and fastest decrease of MDA levels postoperatively compared to groups A, CE. This should not be attributed to the reversal of surgical stress or to tumor removal, but rather to the resection of the manipulated lung tissue. In that context is difficult to attribute postpneumonectomy pulmonary edema to the action of the generated oxygen free radicals.
Although oxidative stress after OLV was documented, the clinical implications remain still obscure. This intensifies the need for more studies in order to define the possible deleterious effects of oxidative stress to postoperative function of the lung and other organs. Also, different groups of patients should be studied such as with COPD, ischemic heart disease, in sepsis or long-term mechanically ventilated. In this future context we might have much more informations concerning the use of exogenous antioxidant factors in several situations such as lung transplantation, ARDS, radiation pneumonitis and even during lung resections.
From the comparative study of groups AF one can conclude that: (1) Patients with NSCLC have a higher production level of oxygen free radicals than normal population. (2) Mechanical ventilation and surgical trauma are weak free radical generators. (3) Manipulated lung tissue is also a source of oxygen free radicals, not only intraoperatively but also for several hours later. (4) Tumor resection removes a large oxidative burden from the organism (5) Lung reexpansion provoked severe oxidative stress. (6) The degree of the amount of generated oxygen free radicals was associated to the duration of OLV.
| Appendix A. Conference discussion |
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Dr Misthos: We have used only double-lumen endotracheal tubes. Since the main mechanism for one lung ventilation is common, one should not wait for different results.
Dr D. Van Raemdonck (Leuven, Belgium): I think it's a very interesting study, and I think it has a very important messagethat we should avoid one-lung ventilation as often as possible. You stated that the lung was ischemic, but there is still bronchial circulation, so how can you say that the lung is ischemic?
Dr Misthos: Well, you mean reperfusion during one-lung ventilation. Actually, this is a relative matter. During lung preservation, as a graft, we can have a better model for that event. But at the clinical setting, I think we can assume that it is a reasonable factor. We know that atelectasis leads to pulmonary vasoconstriction. So there is a relative hypoxia. But I think that the main mechanism is alvelar hypoxic conditions followed by reoxygenation after reexpansion.
Dr S. Mattioli (Bologna, Italy): If I understood, you suggest that there are two sources of free radicals: the tumor itself and the excluded lung. In light of your results, would you suggest to inflate the excluded lung for short periods during the operation in order to reduce the pulmonary oxidative stress?
Dr Misthos: That reminds me of preconditioning of the lung tissue. Well, we have to study and measure our results to propose something like that. We wanted to see for the first time in a clinical setting whether oxidative stress happens or not after lung resection. Repeted atelectasis-reexpansion would increase the generated oxidation stress.
Dr P. van Schil (Edegem, Belgium): I think our anesthesiologists will be very pleased with your conclusions. They completely agree. Sometimes they put a low flow of oxygen on the collapsed lung by way of a catheter through the double lumen tube. Do you think this is a good idea, or do you have any other methods to propose to reduce the oxidative stress?
Dr Misthos: A continuous flow of oxygen to the lung tissue might protect to some extent. Maybe I'm being repetitive, but I think we should measure all these. I can't say it is better or worse. There are no clues. It is a quite new field. There is a lot of work to be done.
| Footnotes |
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| References |
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