Higher fraction of inspired oxygen in anesthesia induction does not affect functional residual capacity reduction after intubation: a comparative study of higher and lower oxygen concentration

Abstract

Low fraction of inspired oxygen (FIO2) reduces the atelectasis area during anesthesia induction. However, atelectasis may occur during laryngoscopy and endotracheal intubation because lungs can collapse within a fraction of a second. We assessed the effects of ventilation with 100 and 40% oxygen on functional residual capacity (FRC) in patients undergoing general anesthesia. Twenty patients scheduled for elective open abdominal surgery were randomized into 40% oxygen (GI, n=10) and 100% oxygen (GII, n=10) groups and FRC was measured. Preoxygenation and mask ventilation with 40 and 100% oxygen were used in GI and GII, respectively. In both groups, 40% oxygen was used for anesthesia maintenance after intubation. Bilateral lung ventilation was performed with volume guarantee and low tidal volume (7ml/kg predicted body weight) using bilevel airway pressure. We measured FRC and blood gas in all patients during preoxygenation, after intubation, and during surgery. FRC decreased from during preoxygenation (GI 2380ml, GII 2313ml) to after intubation (GI 1569ml, GII 1586ml) and significantly decreased during surgery (GI 1338ml, GII 1417ml) (P<0.05). PaO2/FIO2 decreased from during preoxygenation (GI 419mmHg, GII 427mmHg) to after intubation (GI 381mmHg, GII 351mmHg) and significantly decreased during surgery (GI 333mmHg, GII 291mmHg) (P<0.05). No significant differences were found between the groups in both parameters. FRC significantly decreased from the awake state to surgery in both groups. FRC was not influenced by FIO2 elevation at anesthesia induction.