British Journal of Anaesthesia, 2002, Vol. 89, No. 6 814-819
© 2002 The Board of Management and Trustees of the British Journal of Anaesthesia
Clinical Investigations |
Phase behaviour of premixed 0.25% isoflurane in 50% nitrous oxide and 50% oxygen
Department of Environmental and Occupational Medicine, University of Aberdeen, University Medical School, Foresterhill, Aberdeen AB25 2ZD, UK j.a.ross@abdn.ac.uk
Declaration of interest. Patented by Aberdeen University. If commercial production were to occur, the university and the authors would benefit.
Background. Isoflurane (0.25%) in premixed nitrous oxide and oxygen 50/50, v/v, (IN2O), has been suggested for pain relief in labour.
Methods. Possible phase separation of this mixture was studied by analysis of samples from pre-filled cylinders as they were cooled.
Results. Condensation of isoflurane was found at 3.1°C in a cylinder, which held 8.7 MPa at 15°C. In a cylinder holding 13.8 MPa, which is the standard filling pressure stipulated by the National Health Service, the condensation temperature was 2.3°C. At the highest cylinder filling pressure investigated (14.15 MPa) the separation temperature was even less, 3.0°C. After exposure of cylinders to 40°C and complete phase separation of the mixture, complete mixing was achieved by 24 h storage in the horizontal position at room temperature and, either three complete inversions of the cylinder or mechanical rolling at 30 r.p.m.
Conclusions. These findings should assist the use and storage of IN2O.
Br J Anaesth 2002; 89: 81419
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J. A. Ross and M. E. Tunstall Simulated use of premixed 0.25% isoflurane in 50% nitrous oxide and 50% oxygen{dagger} Br. J. Anaesth., December 1, 2002; 89(6): 820 - 824. [Abstract] [Full Text] [PDF] |
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