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Anesthetic potency of sevoflurane with and without nitrous oxide in mechanically ventilated Dumeril monitors

Mads F. Bertelsen DVM, DVSc1,2,3, Craig A. E. Mosley DVM, MSc, DACVA4,5, Graham J. Crawshaw BVM, MS, DACZM6, Doris H. Dyson DVM, DVSc, DACVA7, and Dale A. Smith DVM, DVSc8
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  • 1 Toronto Zoo, 361A Old Finch Ave, Scarborough, ON M1B 5K7, Canada.
  • | 2 Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 3 Present address is Center for Zoo and Wild Animal Health, Copenhagen Zoo, Søndre Fasanvej 79, DK-2000 Frederiksberg, Denmark.
  • | 4 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 5 Present address is Veterinary Teaching Hospital, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.
  • | 6 Toronto Zoo, 361A Old Finch Ave, Scarborough, ON M1B 5K7, Canada.
  • | 7 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 8 Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

Abstract

Objective—To determine the minimum alveolar concentration (MAC) of sevoflurane and assess the sevoflurane-sparing effect of coadministration of nitrous oxide in mechanically ventilated Dumeril monitors (Varanus dumerili).

Design—Prospective crossover study.

Animals—10 healthy adult Dumeril monitors.

Procedure—Anesthesia was induced with sevoflurane in 100% oxygen or sevoflurane in 66% nitrous oxide (N2O) with 34% oxygen, delivered through a face mask. Monitors were endotracheally intubated, and end-tidal and inspired isoflurane concentrations were measured continuously; MAC was determined by use of a standard bracketing technique. An electrical stimulus (50 Hz, 50 V) was delivered to the ventral aspect of the tail as the supramaximal stimulus. A blood sample for blood gas analyses was collected from the ventral coccygeal vessels at the beginning and end of the anesthetic period. An interval of at least 7 days was allowed to elapse between treatments.

Results—The MAC ± SDs of sevoflurane in oxygen and with N2O were 2.51 ± 0.46% and 1.83 ± 0.33%, respectively. There was a significant difference between the 2 treatments, and the mean MAC-reducing effect of N2O was 26.4 ± 11.4%. Assuming simple linear additivity of sevoflurane and N2O, the MAC for N2O was estimated to be 244%. No significant differences in blood gas values—with the predictable exception of oxygen pressure—were detected between the 2 groups.

Conclusions and Clinical Relevance—The MAC of sevoflurane in Dumeril monitors is similar to that reported for other species. The addition of N2O significantly decreased the MAC of sevoflurane in this species. (J Am Vet Med Assoc 2005;227:575–578)

Abstract

Objective—To determine the minimum alveolar concentration (MAC) of sevoflurane and assess the sevoflurane-sparing effect of coadministration of nitrous oxide in mechanically ventilated Dumeril monitors (Varanus dumerili).

Design—Prospective crossover study.

Animals—10 healthy adult Dumeril monitors.

Procedure—Anesthesia was induced with sevoflurane in 100% oxygen or sevoflurane in 66% nitrous oxide (N2O) with 34% oxygen, delivered through a face mask. Monitors were endotracheally intubated, and end-tidal and inspired isoflurane concentrations were measured continuously; MAC was determined by use of a standard bracketing technique. An electrical stimulus (50 Hz, 50 V) was delivered to the ventral aspect of the tail as the supramaximal stimulus. A blood sample for blood gas analyses was collected from the ventral coccygeal vessels at the beginning and end of the anesthetic period. An interval of at least 7 days was allowed to elapse between treatments.

Results—The MAC ± SDs of sevoflurane in oxygen and with N2O were 2.51 ± 0.46% and 1.83 ± 0.33%, respectively. There was a significant difference between the 2 treatments, and the mean MAC-reducing effect of N2O was 26.4 ± 11.4%. Assuming simple linear additivity of sevoflurane and N2O, the MAC for N2O was estimated to be 244%. No significant differences in blood gas values—with the predictable exception of oxygen pressure—were detected between the 2 groups.

Conclusions and Clinical Relevance—The MAC of sevoflurane in Dumeril monitors is similar to that reported for other species. The addition of N2O significantly decreased the MAC of sevoflurane in this species. (J Am Vet Med Assoc 2005;227:575–578)