Reply to Birdas

We appreciate the comments of Dr Birdas. One-lung ventilation (OLV) is widely used in thoracic surgery. In our initial report the generation of oxidative stress after OLV was demonstrated [1]. Due to complete lack of previous solid evidence the aim of our next study was to study whether there is any association between postresectional oxidative stress and postoperative complications [2]. This was a preliminary work.

Some degree of free radicals are generated in almost every physiologic and pathophysiologic pathway. However, their actual impact on clinical situations is still under investigation. Thus, any possible perioperative parameter, situation, complication or drug may affect the level of free radicals and consequently should be entered into multivariate analysis. This would lead to extreme complexity of the study plan with variables that have not thoroughly checked for their role, if any, on the generation of oxidative stress. In order to bypass this fundamental obstacle to our study methodology, we decided to use the most common variables that have already been proved to be independent risk factors for postoperative complication after lung resection surgery and compare them with oxidative stress per se: cases with hemoglobin ≪9 mg/l, albumin ≪2.5 mg/dl, diabetes mellitus, serum creatinine >1.5 mg/l, preoperative FEV1 ≪2 l, PaO₂ ≪70 mmHg, preoperative PaCO₂ >45 mmHg, history of coronary artery disease, concurrent thoracic wall excision, intraoperative blood loss >300 ml, duration from entrance into the pleura space until lobectomy completion >1 h and need for intensive care unit postoperatively were recorded. These factors along with other clinical characteristics such as age >65 years, gender, side of the lesion and pathologic staging were subjected to multivariate analysis with independent variables set by the results of the univariate analysis about the most common complications in OLV groups in order to evaluate the role of oxidative stress as an independent risk factor.

The authors want to state that it is our routine policy not to give prophylactic antiarrhythmic medication. Cardiac arrhythmias are usually detected on the second or third postoperative day. This might be explained by long-acting biochemical pathways that may be triggered by the short-lived (12 h) oxidative response. There are some indications on subcellular level for long-acting effects after experimental lung oxidative stress [3].

This is actually a work in progress. Our paper [2] was the first one that studied the relation between the systematic generation of free radicals and adverse effects after lung resection surgery. We fully agree to the recommendation for further studies to evaluate in more detail the role of intraoperative oxidative stress on postoperative complications. Dr Birdas’ remarks will help us with our future projects on this subject.

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