Wash-in and wash-out curves of sevoflurane and isoflurane in morbidly obese patients

Background. The aim of this prospective, randomized study is to compare sevoflurane and isoflurane pharmacokinetics in morbidly obese patients. Methods. With Ethical Committee approval and written informed consent, 14 obese patients (BMI >35 kg/m2), ASA physical status II, undergoing laparoscopic, silicone-adjustable gastric banding were randomly allocated to receive either sevoflurane (n=7) or isoflurane (n=7) as main anesthetic agents. General anesthesia was induced with 1 μg-kg-1 fentanyl, 6 mg-kg- 1 sodium thiopental, and 1 mg-kg-1 succinylcholine followed by 0.4 mg kg-1-h1 atracurium bromide (doses were referred to ideal body weight). Intermittent positive pressure ventilation (IPPV) was applied using a Servo-900C ventilator with a nonrebreathing circuit and a 15 l-min-1 fresh gas flow (tidal volume: of 10 ml-kg- 1; respiratory rate: 12 breaths/min; inspiratory to expiratory time ratio of 1:2) using an oxygen/air mixture (FiO2=50%), while supplemental boluses of thiopental or fentanyl were given as indicated in order to maintain blood pressure and heart rate values within ±20% from baseline. After adequate placement of tracheal tube and stabilization of the ventilation parameters, 2% sevoflurane or 1.2% isoflurane was given for 30 min via a nonrebreathing circuit. End-tidal samples were collected at 1, 5, 10, 15, 20, 25 and 30 min, and measured using a calibrated infrared gas analyzer. General anesthesia was then maintained with the same inhalational agents, while supplemental fentanyl was given as indicated. After the last skin suture the inhalational agents were suspended, and the end tidal samples were collected at 0.5, 1, 1.5, 2, 2.5, 3, 3-5, 4, 4.5, and 5 min. Then the lungs were manually ventilated until extubatioin. Results. No differences in age, gender and body mass index were reported between the two groups. Surgical procedure required 91±13 in the sevoflurane group and 83±32 min in the isoflurane group. The FA/FI ratio was higher in the sevoflurane group from the 5th to the 30th min. Also the washout curve was faster hi the sevoflurane group during the observation period; however, the observed differences were statistically significant only 30 and 60 sec after discontinuation of the inhalational agents. Conclusions. The results of this prospective, randomized study confirmed that sevoflurane provides more rapid wash-in and -wash-out curves than isoflurane also in the morbid obese patient.