Closed-Circuit Xenon Delivery Using a Standard Anesthesia Workstation

Abstract

Xenon (Xe) is an anesthetic with minimal side effects, now also showing promise as a neuroprotectant both in vitro and in vivo. Although scarce and expensive, Xe is insoluble and patient uptake is low, making closed circuits the optimum delivery method. Although the future of Xe anesthesia is uncertain, effective neuroprotection is highly desirable even if moderately expensive. A factor limiting Xe research in all these fields may be the perceived need to purchase special Xe anesthesia workstations that are expensive and difficult to service. We investigated the practicality of 1) true closed-circuit Xe delivery using an unmodified anesthesia workstation with gas monitoring/delivery attachments restricted to breathing hoses only, 2) a Xe delivery protocol designed to eliminate wastage, and 3) recovering Xe from exhaled gas. Sixteen ASA physical status I/II patients were recruited for surgery of > 2 h. Denitrogenation with 100% oxygen was started during induction and tracheal intubation under propofol/remifentanil anesthesia. This continued after operating room transfer for 30 min. All fresh gases were then temporarily stopped, metabolic oxygen consumption then being replaced with 250-mL Xe boluses until F(I)Xe = 50%. A basal oxygen fresh gas flow was thereafter restored with additional Xe given as required via the expiratory hose to maintain a F(I)Xe > or = 50%. At no time, apart from during circle flushes every 90 min, were the bellows allowed to completely fill and spill gas, ensuring the circle remained closed. On termination of anesthesia, the first 10 exhaled breaths were collected as was residual gas from the circle, allowing measurement of the Xe content of each. Total Xe consumption, including initial wash-in and circle flushes, was 12.62 (5.31) L or 4.95 (0.82) L/h, mean (sd). However, consumption during maintenance periods was lower: 3 L/h at 1 h and 2 L/h thereafter. Of the total Xe used, 8.98% (5.94%) could be recovered at the end of the procedure. We report that closed-circuit Xe delivery can be achieved with a modified standard anesthesia workstation with breathing hose alterations only and that the protocol was very gas efficient, especially during the normally wasteful Xe wash-in. A Xe mixture of > or = 50% was delivered for up to 341 min (5 h 41 min) and Xe consumption was 4.95 (0.82) L/h, maintenance being achieved with 2-3 L/h. With this degree of efficiency, Xe recovery/recycling at the end of anesthesia may be of little additional benefit.