Anaesthetic management:

One hour before thoracic surgery, the patient-subjects received diazepam 0.15 mg kg-1 as premedication. After arriving at the operating theatre, standard monitoring system practices was applied, including heart rate (HR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), and pulse oximetry (SpO2). Moreover, an intra-vein cannula was placed, and the infusion of multi-electrolytic fluid 5-10 ml kg-1 h-1 was started. After pre-oxygenation, atropine 0.5 mg and fentanyl 3 µg kg-1 were given, and the induction of anaesthesia with thiopentone 5-7 mg kg-1 was started. Suxamethonium was administered for neuromuscular blockade, and bronchial intubation with a Robertshow double lumen tube was performed. The left bronchus was intubated for right lung surgery, and the right bronchus was intubated for left lung surgery. Tube placement was checked via auscultation and fiberscope. Anaesthesia was maintained with sevoflurane, additional fentanyl doses were used if needed, and neuromuscular blockade was obtained with vecuronium 0.1 mg kg-1. Additionally, 0.1 mg kg-1 dose of morphine was given subcutaneously for postoperative pain control. Patients were also ventilated with O2 (oxygen) and AIR (air) mixture, using the following settings: volume control intermittent positive pressure ventilation, FiO2 (oxygen fraction) 0.4, Vt (tidal volume) 6-10 ml/kg, and f (frequency) 12-15 /min. Furthermore, end tidal CO2 (carbon dioxide) was monitored due to normocapnia maintenance (4.0-5.3 kPa). At the end of surgery, intercostal blockade was brought about with 0.5% bupivacaine, with 5 ml for each nerve. Finally, the neuromuscular blockade was reversed with neostigmine 0.04 mg kg-1 and with atropine 0.01 mg kg-1.

After anaesthesia stabilisation, the unique control system was used, called the 'tidal volume divider'. This device was placed between the anaesthetic machine and the double lumen tube of the patient. This control system enables conventional ventilation (without any intervention from the control system, as the settings are defined on the ventilator), as well as independent ventilation with division of the tidal volume between the lungs in proportions of 1:1, 2:1, 3:1, and 5:1. It also enables PEEP (selective positive end-expiratory pressure) application to each lung. With independent ventilation, settings such as frequency, tidal volume and inspiration time are defined by ventilator, and this system only controls the direction of tidal volume to each lung (as the control system is a flow divider) by using a differential pneumatic resistor. It also enables dependent and non-dependent lung ventilation in the lateral decubitus positions. Furthermore, the system monitors the expired volume, airway pressure and dynamic compliance of each lung. This device was described and tested on mechanical lung models with a variety of lung model mechanics (compliance, resistance) and ventilation parameters (frequency, tidal volume). It was also tested clinically for its safety during our previous study. The system was invented, developed and patented by a group of Polish engineers from the Nałęcz Institute of Biocybernetics and Biomedical Engineering, the Polish Academy of Sciences, Poland.