High frequency jet ventilation: use of the Bain system for entrainment

The use of a Bain system to convey anaesthetic gases for entrainment during high frequency jet ventilation (HFJV) was evaluated by examining the effect of varying the fresh gas flow (Vf) on the end-tidal carbon dioxide (PECO2) in 46 ASA physical status I and II patients undergoing extracorporeal shock-wave lithotripsy (ESWL). Anaesthesia was induced with methohexitone (1-2 mg.kg-1), fentanyl (1-1.5 micrograms.kg-1) and vecuronium (0.1 mg.kg-1). After endotracheal intubation with a Mallinckrodt Hi-Lo Jet cuffed endotracheal tube, the patient was immersed in a water bath and HFJV at 150 breaths per minute was instituted with an Acutronic AMS 1000 jet ventilator attached to the side channel of the Hi-Lo tube. A Bain system was attached to the proximal end of the endotracheal tube to provide gases for entrainment. Anaesthesia was maintained with an intravenous infusion of methohexitone (5 mg.kg-1.h-1) and 50% nitrous oxide in oxygen for both the jetted and entrained gases. PECO2 was determined at 5-min intervals by a single-breath technique using a calibrated Engstrom Eliza capnograph. Thirty patients were randomly allocated to receive Vf's of 50 (Group 1), 75 (Group 2) and 100 (Group 3) ml.kg-1.min-1, respectively. A further eight patients (Group 4) received a Vf of 100 ml.kg-1.min-1 for 15 min, 75 ml.kg-1.min-1 for the next 15 min and 50 ml.kg-1.min-1 thereafter. In a further group of eight patients (Group 5), Vf was initially 25 ml.kg-1.min-1 for 10 min and was then switched off for the remainder of the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)