Isoflurane consumption and cost when closed circuit or semi-closed circuit is used in cardiac anaesthesia

Aim of the Study: In this observational study; we aimed to determine the comsumptions and costs of isoflurane (I), oxygen (O2) and air (A) when closed circuit (CC) or semi-closed circuit (SCC) is used in adult patients undergoing open heart surgery (OHS). Materials and Methods: After obtaining ethics committee approval and patient consent, sixty OHS patients randomized into either closed circuit group (CCG, n:30) or semi-closed circuit group (SCCG, n:30). Anesthesia was induced (100% O2 6 L/min) with pentothal-fentanyl(F)/or morphine(M), and maintained with I-F(or M) except the cardiopulmonary bypass(CPB) period. In the CPB period midazolam-F(or M) was used for maintenance. SCC anesthesia (50% O2/50% A/I, 4 L/min flow) was applied at the first 5 min of maintenance in the CCG and the whole maintenance time in SCCG. In CCG, after 5 min of maintenance, CC anesthesia (self-control, 50% O2/50% A/I) was applied. All patients were ventilated using volume control AutoFlow ventilation mode (VT:5-8 L/kg, RR:10±2 fr/min). During CPB, VT and RR were decreased 50% and O2 was increased 100%. During aortic-cross-clamping period, O2 insufflation (0,5 L/min) was applied. Three min after weaning CPB, 50% O2/50% A/I were applied. In the last ~5 min of surgery, SCC anesthesia (100% O2, 4L/min.) was applied for patients. Fischer's exact, Independent Samples T and Mann Whitney U tests were used. Values were given as mean.±SD or number(%). P<0,05 was considered significant. Results: There was no difference (p>0,05) between groups in demographics, preoperative evaluation, surgical and anesthetic properties. Hourly consumption of I, O2 and air; in CCG (3.19±1.28 mL/min, 67.10±20.95 L/min, 27.55±17.05 L/min, respectively) were lower than SCCG (6.59±1.26 mL/min, 112.58±19.90 L/min, 79.64±23.53 L/min, respectively), (p=0.00, p=0.00, p=0.00, respectively). Also hourly cost of I and O2 in CCG (1.71±0.68 TL/min, 24.69±7.71 TL/min, respectively) were lower than SCCG (3.55±0.68 TL/min, 41.43±7.32 TL/min, respectively). Cost of air was ignored. Conclusion: This is the first observational study which compaires I/O2/A consumption and their costs in OHS during CC anesthesia or SCC anesthesia. I, O2 and A consumptions and I, O2 costs markedly decrease when CC anesthesia is used. Key words: Open heart surgery, closed circuit, semi-closed circuit, isoflurane, oxygen, air, consumption, cost.