Volatile gas consumption after introduction of the Dräger Zeus® anesthesia machine.

Abstract

To the Editor, Markham Stouffville Hospital, a community hospital in Ontario, Canada, recently became the first hospital in North America to acquire the Drager Zeus anesthesia machine (Drager Medical Canada, Richmond Hill, ON, Canada). The Zeus offers an automatic mode which enables the machine to control fresh gas flows. It compares inspiratory and expiratory volatile gas concentrations, and once steady state is approached, fresh gas flows are reduced to as low as 200 mL min. As part of a planned replacement of anesthesia machines, we compared volatile gas consumption of the Drager Julien machine, which allows only manual control of fresh gas flow rates, with that of the new Drager Zeus machine, which features both manual and automatic modes. Previous investigators have documented reduced volatile gas consumption where flow rates are reduced according to an algorithm and the effect of a similar type of technology change in a tertiary care centre. The goal of our study was to compare the volatile agent consumption and cost differences between the two machines in a community hospital setting. This observational study, approved by our hospital’s research ethics board, was conducted over a two-year period. In the first year, the older Julien machines were utilized, and in the second year, the new Zeus machines were used. Cesarean deliveries and hip and knee arthroplasties were excluded from the study as the majority of these were performed under regional anesthesia. Operating room (OR) utilization data were used to track case volumes, and average case length was obtained from a chart review. Volatile gas consumption (numbers of bottles) was tracked from pharmacy data. Steady state average flow rates for the Julien machine were calculated after being obtained from a chart review. Flow rates for the Zeus machine, obtained from the machine’s readout, were recorded both as a steady state snapshot during cases in the automatic mode and as an overall average for the case duration. The results are presented in the Table. The average cost of volatile agent decreased from $9.77 to $8.77CAD per case. After adjusting for a slight difference in case volumes between the two years of the study, the resulting savings was $7,000 in five ORs or $1,400 per machine. While a savings of $1,400 per machine over one year is significant, the decision to replace traditional machines with those that feature this latest type of technology should be carefully considered given that differences in acquisition costs can be as much as $30,000 per machine. The savings were less than expected given the low flow rates that the Zeus machine is capable of achieving. Although a snapshot of observed flows with the Zeus in the automatic mode averaged 269.9 mL min, adjusting volatile gas concentrations during a case causes a transient increase in fresh gas flows. In addition, the machine intermittently flushes the circuit during cases using flows as high as 18 L min. These two factors contribute to higher average flow rates during cases (approximately 1,130 mL min). In addition, while the automatic mode is available, the Zeus machine can be used in the manual mode. Possible reasons to use the manual mode include the minimum recommended flow rate for sevoflurane in Canada (i.e., 2 L min), A. Lokoff (&) Royal College of Surgeons in Ireland, Dublin, Ireland e-mail: alokoff@gmail.com