• Nitric oxide (NO) is a free radical in gas state which plays an important role in a variety of processes relevant to respiratory physiology. It represents a means of detecting airway hyperresponsiveness and appears to have a strong correlation with the eosinophilic infiltration of the airway. Patients who suffered bronchospasm or laryngospasm intraoperatively or postoperatively showed higher levels of exhaled NO.
• Propofol modifies NO production by stimulating the constitutive synthesis of NO and by inhibiting the inducible production of NO. It seems to exert protective effects on acute lung injury (ALI) in experimental models and it can possibly reduce exhaled NO. There is also evidence that some intravenous anesthetic agents can influence chemotaxis of eosinophils in vitro.
• Variation of exhaled NO and eosinophils in surgical patients undergoing anesthesia has not been studied before. Therefore, the aim of this study will be to investigate the differential impact of maintenance of general anesthesia with propofol versus maintenance with sevoflurane on exhaled NO and eosinophil blood count.

• Nitric oxide (NO) is a free radical in gas state which plays an important role in a variety of processes relevant to respiratory physiology. NO is produced by several cellular types (epithelial, endothelial, neuronic, inflammatory cells) (Gaston B, et al, 1994), it represents a means of detecting airway hyperresponsiveness and appears to have a strong correlation with the eosinophilic infiltration of the airway (Warke TJ, et al, 2002). Patients who suffered bronchospasm or laryngospasm intraoperatively or postoperatively showed higher levels of exhaled NO (Saraiva-Romanholo BM, et al, 2009).
• Propofol modifies NO production by stimulating the constitutive synthesis of NO and by inhibiting the inducible production of NO (González-Correa JA, et al, 2008). It seems to exert protective effects on acute lung injury in experimental models (Chu CH, et al, 2007; Chen HJ, et al, 2008) and possibly reduces exhaled NO (Fijałkowska A, et al, 2012). There is also evidence that some intravenous anesthetic agents can influence chemotaxis of eosinophils in vitro (Krumholz W, et al, 1999)
• Variation of exhaled NO and eosinophils in surgical patients undergoing anesthesia has not been studied before. Therefore, the aim of this study will be to investigate the differential impact of maintenance of general anesthesia with propofol versus maintenance with sevoflurane on exhaled NO and eosinophil blood count.
• Patients with ASA score I-III who undergo thyroidectomy under general anaesthesia will participate in this study. Thyroidectomy has been chosen for the following reasons: a) there will be consistency in both the surgeon and the type of surgery and as a result manipulations and surgical stress will be similar for all patients and b) abdominal walls are not manipulated at all during thyroidectomy and therefore postoperative measurement of exhaled NO will be easier and painless for patients.
• Patients will be randomized to one of two groups: one group with general anesthesia maintenance based on an intravenous agent (propofol) and a second group with general anesthesia maintenance based on an inhalational agent (sevoflurane).
• When patients arrive in the operating room, standard monitoring will be applied and exhaled NO will be measured immediately before induction with the NObreath® device ( Antus B, et al, 2010, Pisi R, et al, 2010) and a blood sample will be taken for eosinophil count measurement.
• During the patients' stay in the PACU and when Aldrete score is ≥8, exhaled NO will be measured again and a second blood sample will be taken. Exhaled NO will be measured again 24 hours postoperatively.
• The clinical implications of this study lie in the fact that it may provide further information on the effects of anesthetics (intravenous and inhalational) on the physiology and pathophysiology of the respiratory system. In addition, new evidence may come to light about the relationship between intravenous and inhalational agents and NO production.

Inclusion Criteria:

• adult patients, American Society of Anesthesiologists (ASA) distribution I-III, scheduled for thyroidectomy

Exclusion Criteria:

• patients with history of airway hyperreactivity (asthma, bronchitis)
• patients with history of allergy