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Correspondence |
Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Canada, E-mail: rene.martin{at}USherbrooke.ca
To the Editor:
We read with interest the article by Yogendran et al.1 comparing patient controlled inhalation induction (PCI) with the most commonly used vital capacity induction (VCI). The authors concluded that "PCI was comparable to VCI in sevoflurane induction with respect to the speed of induction, side effects during induction and patient satisfaction".
We partially disagree with this conclusion because we believe that there was a problem with the VCI in the study. Considering that the volume of gas inhaled in a vital capacity inspiration is 70 mL·kg–1 (5.6 L for an 80-kg patient) and requires a very high peak flow that current vaporizers cannot accommodate, and considering that the authors used a circle breathing system connected to a Datex-Ohmeda® AS/3 unit with a canister volume of 900 mL and a 2-L reservoir (information obtained from authors), and assuming the average patient’s weight is 80 kg, the primed circuit afforded half of the volume needed for a VCI induction. Consequently, patients in the VCI group didn’t breath sevoflurane 6 to 8%, but instead received diluted sevoflurane 3 to 4% during the first minute of induction. This might explain the 1.5-min necessary to achieve loss of eyelash reflex in the VCI group in the present study, in contrast to the induction times (32 to 54 sec) generally reported by other authors,2–4 even without 5 Five-litre reservoir bags should be used, and fresh gas flow can be reduced to 2 L·min–1 after loss of conciousness to diminish sevoflurane consumption in VCI.
References
1 Yogendran S, Prabhu A, Henly A, et al. Vital capacity and patient controlled sevoflurane inhalation result in similar induction characteristics. Can J Anesth 2005; 52: 45–9.
2 Yurino M, Kimura H. A comparison of vital capacity breath and tidal breathing techniques for induction of anaesthesia with high sevoflurane concentrations in nitrous oxide and oxygen. Anaesthesia 1995; 50: 308–11.[Medline]
3 Yurino M, Kimura H. Induction of anesthesia with sevoflurane, nitrous oxide, and oxygen: a comparison of spontaneous ventilation and vital capacity rapid inhalation induction (VCRII) techniques. Anesth Analg 1993; 76: 598–601.
4 Colas MJ, Tétrault JP, Dumais L, Truong P, Claprood Y, Martin R. The SiBI connector: a new medical device to facilitate preoxygenation and reduce waste anesthetic gases during inhaled induction with sevoflurane. Anesth Analg 2000; 91: 1555–9.
5 Yurino M, Kimura H. Comparaison of induction time and characteristics between sevoflurane and sevoflurane/nitrous oxide. Acta Anaesthesiol Scand 1995; 39: 356–8[Medline]
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