General Protocol and Patients
This prospective, randomized, controlled study was performed at Yokohama City University Hospital. The data were collected from October 2008 to September 2009, with approval from the institutional review board (Date of IRB approval: 08-01-2007; approval number: 07-021), and written informed consent was obtained from all the patients preoperatively.
Patients aged between 20 and 85 years, undergoing hepatectomy, were considered eligible for enrolment in this study. Patients with an American Society of Anesthesiologists' physical status (ASA-PS) value of 3 and above, pre-existing lung disease, tumor in the portal vein or inferior vena cava, requirement of bile duct or gastrointestinal tract repair, or requirement of additional surgical procedures other than hepatectomy were excluded.
Patients were randomly assigned to those ventilated with a VT of 12 mL per predicted body weight (kg) (TV12) or with a VT of 6 mL per predicted body weight (TV6). The assignment was performed using a random number table by an investigator who was not involved in data collection and was notified to anesthesiologists who were not involved in the study using an envelope method. The investigators who collected the data and samples were blinded to the ventilation settings at any time of the experiment. Mechanical ventilation was performed in a volume-controlled mode, with the ratio of the duration of inspiration to the duration of expiration (I/E) of 1:2 and an end-inspiratory pause time of 10 %, using an anesthesia machine (Drager Fabius GS, Drager Medical, Telford, PA, USA). The patients did not receive premedication. Propofol 2 mg·kg−1, vecuronium 0.1 mg·kg−1, and fentanyl 100 μg was administered to facilitate orotracheal intubation with a cuffed tube. General anesthesia was maintained with sevoflurane 0.6–1.5 % and was supplemented by epidural anesthesia with mepivacaine.
The target arterial partial oxygen pressure (PaO2) of approximately 150 mmHg was attained by adjusting the inspired oxygen fraction (FIO2) and the arterial partial carbon dioxide pressure (PaCO2) was maintained between 35 and 45 mmHg by changing the ventilation frequency referring to the previous blood gas analysis and end-tidal carbon dioxide pressure. PEEP was applied at 3 cm H2O in both the groups. Ephedrine was administered when the systolic blood pressure dropped below 80 mmHg. Methylprednisolone (8 mg·kg−1) was administered intravenously prior to the Pringle maneuver (obstruction of both branches of the hepatic artery and portal vein). Muscle relaxation was reversed with neostigmine and atropine when surgery was completed. Lungs were recruited manually with approximately 20 cmH2O for 15 to 20 s prior to extubation in both groups.
Blood Sampling and Blood Gas Analysis
Arterial blood was drawn just prior to bronchoscopic microsampling (BMS), and blood gas analysis (BGA) was performed (model 860, Chiron Diagnostics, Emeryville CA, USA) every 3 h thereafter. Whole blood was centrifuged at 4 °C at 3000 RPM, and the plasma was aliquoted and stored at −80 °C until use. When the patient arrived in the post-anesthetic care unit (PACU), BGA was repeated.
Bronchoscopic Microsampling Method
Epithelial Lining Fluid Sampling. Epithelial lining fluid (ELF) was collected with BMS probes using a previously reported method. Briefly, a BMS probe was inserted into the channel of a fibreoptic bronchoscope that was inserted into the tracheal tube. The tip of the BMS probe was attached to a segmental bronchus of the right middle lobe under optical guidance of a bronchoscope for 20 s. The BMS probe was then withdrawn from the bronchoscope. These procedures were repeated 3 times using 3 different BMS probes. The tips of the BMS probes, made of cotton, were inserted into pre-weighed test tubes. The tubes were sealed, weighed again with the probe tips, and stored at −80 °C. The collections were performed immediately after intubation and after 3 and 6 h.
Determination of the Sample Weight and ELF Extraction. One milliliter of distilled water was added to each test tube containing BMS probes. The tubes were centrifuged at 4 °C for 10 min, and the supernatant was collected and aliquoted. The BMS probes were dried on a bench top at room temperature for 3 days and weighed. The weight of the collected sample was calculated using the following formula:
S = (T + P1) – T – P2, where S is the sample weight, T is the weight of the tube, (T + P1) is the weight of the tube and the BMS probes after sampling, and P2 is the weight of the dried probes after extraction. A sample dilution factor (DF) in distilled water was then calculated as follows:
Measurements of Mediator Concentrations in the Blood and ELF
Cytokines and adhesion molecules were measured using an enzyme-linked immunosorbent assay (ELISA). Tumor necrosis factor (TNF)-α (Quantikine® Human TNF-α/TNFSF1A, R&D Systems, Minneapolis, MN, USA), interleukin (IL)-8 (EH2IL8, Thermo Scientific, Rockford, IL, USA), and intercellular adhesion molecule (ICAM)-1 (EH5400, Thermo Scientific) levels were measured according to the manufacturer's instructions.
Clinical Data Collection
Preoperative data were collected from routine clinical documentation that was stored in the institutional medical record system. Intraoperative physiological and ventilatory data were recorded in a data sheet.
All data were statistically analyzed using Statcel 2nd edition (OMS Publishing, Tokorozawa, Japan). The student t-test and Mann–Whitney U test were used to assess quantitative variables. Variables measured only once were compared using an unpaired t-test. Variables that were measured repeatedly were compared using two-way repeated measures analysis of variance (ANOVA) followed by Bonferroni post hoc. Results were expressed as mean ± standard deviation; p < 0.05 was considered significant.
BMC Anesthesiol. 2016;16(47) © 2016 BioMed Central, Ltd.