[Blood gas levels using spontaneous breathing and the Bain circuit. Our experience during head surgery (author's transl)].

The authors use the Bain Circuit with spontaneous breathing during head surgery (neurosurgery and ophthalmological procedures). Suitable for both adult and pediatric use, it seems to be, due to its unique characteristics, the choice circuit for all anaesthesia procedures in which the physician does not have direct control over the patient's head. Comparative analysis of blood gas levels is effected, on the one hand in children connected to a Digby-Leigh system and Bain Circuit, and on the other hand in adults, some of whom are connected to a two-way system and the other under a filter circuit; all of the patients are then connected to the Bain Circuit. In children the analysis of results shows that for an identical protocol of anaesthesia the quality of spontaneous breathing obtained using the Bain Circuit is the same as that obtained using the Digby-Leigh. In adults anaesthetized using fluothane and with spontaneous breathing, the average level of hypercapnia under filter circuit and Bain Circuit is identical. Also, the same level of alveolar hypoventilation is obtained under spontaneous breathing with the two-way and Bain Circuit systems when there are properly provisioned. Thus this work confirms other studies by showing that the Bain Circuit is particularly well adapted to head surgery because of its low weight and easy manageability. On the other hand, when using spontaneous breathing the level of alveolar hypoventilation, and thus the degree of hypercapnia, is directly related to the level of anaesthesia and independent of the circuit chosen. Only the setting up of controlled breathing would allow the physician to work under the desired level of normo or hypocapnia.