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A MODIFICATION OF EXTON’S METHOD FOR BLOOD OXYGEN CONTENT
Brit. J. Anasth. (1053). 25, 297
By E. A. PASK
Department of Anaesthesia, University of Durham
T
HE convenience and speed of the method for estimating the oxygen content of blood which was described by Exton et al. (1945) has been increased by modifications which permit the whole procedure to be carried out in a special syringe. The reagents used are identical with those required by Exton et al. and the original article should be consulted for their preparation. The special syringe comprises a 1 ml. tuberculin syringe fused on to a length of 0.3/0.5 capillary tube (fig. 1). A mark on the capillary tube is made such that the capillary will contain 0.1 ml. of blood between its entry and the mark. The plunger of the syringe should be controlled by a spring-clip.
O - l ML 1ML
FIG.
SYRINGE
1
Procedure. Fill the syringe and capillary with borax solution, expel all air bubbles and then expel the borax solution until the plunger of the syringe stands at the 0.2* ml. mark. Draw in a small amount of mercury (about 0.01-0.02 ml.). Draw up 0.1 ml. of ferrous sulphate solution, so that the outer edge of the mercury bead stands at the mark on the capillary. To prevent any entry of air, part of the first 297
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 11, 2015
A MODIFICATION OF EXTON'S METHOD FOR BLOOD OXYGEN CONTENT
298
British Journal of Anaesthesia
REFERENCE
Exton, W. G., Schotter, F., Korman, S., and Rose, A. R. (1945). /. Lab. din. Med., 30, 84.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 11, 2015
mercury bead can be ejected into the ferrous sulphate solution. Follow the ferrous sulphate with a second mercury bead. Draw in blood carefully so that the outer edge of the mercury bead stands exactly on the 0.1 ml. mark on the capillary. This is the only measurement which needs to be made with great precision. Immediately follow the blood by drawing in a mercury bead. If the blood sample is contained in a syringe, a short length of elastic tube can be used to unite the blood syringe and the capillary tube for filling in the usual way. Finally, draw up further borax solution until the plunger of the syringe stands at the 0.6 ml. mark. The mercury beads will now have found their way into the syringe and can be used for mixing its contents. Leave the syringe for two minutes. There is no need to cap the outer end of the capillary since the active reagents are protected from atmospheric air by several cms. of aerated borax solution. Place 2 ml. of sulphosalicylic acid in a tube calibrated to 10 ml. Draw some of this solution into a syringe and eject immediately into the same tube. Now repeatedly draw up distilled water into the syringe and eject into the 10 ml. tube until its mark is reached. In this way the syringe is rinsed and washed clean ready for the next estimation and the dilution is performed conveniently. The contents of the 10 ml. tube are then filtered as described in the original method and the clear filtrate estimated in the cuvette of a photocolorimeter. Blank estimations and calibrations are performed in the manner described in the original article.
By E. A. PASK
Department of Anaesthesia, University of Durham
T
HE convenience and speed of the method for estimating the oxygen content of blood which was described by Exton et al. (1945) has been increased by modifications which permit the whole procedure to be carried out in a special syringe. The reagents used are identical with those required by Exton et al. and the original article should be consulted for their preparation. The special syringe comprises a 1 ml. tuberculin syringe fused on to a length of 0.3/0.5 capillary tube (fig. 1). A mark on the capillary tube is made such that the capillary will contain 0.1 ml. of blood between its entry and the mark. The plunger of the syringe should be controlled by a spring-clip.
O - l ML 1ML
FIG.
SYRINGE
1
Procedure. Fill the syringe and capillary with borax solution, expel all air bubbles and then expel the borax solution until the plunger of the syringe stands at the 0.2* ml. mark. Draw in a small amount of mercury (about 0.01-0.02 ml.). Draw up 0.1 ml. of ferrous sulphate solution, so that the outer edge of the mercury bead stands at the mark on the capillary. To prevent any entry of air, part of the first 297
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 11, 2015
A MODIFICATION OF EXTON'S METHOD FOR BLOOD OXYGEN CONTENT
298
British Journal of Anaesthesia
REFERENCE
Exton, W. G., Schotter, F., Korman, S., and Rose, A. R. (1945). /. Lab. din. Med., 30, 84.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 11, 2015
mercury bead can be ejected into the ferrous sulphate solution. Follow the ferrous sulphate with a second mercury bead. Draw in blood carefully so that the outer edge of the mercury bead stands exactly on the 0.1 ml. mark on the capillary. This is the only measurement which needs to be made with great precision. Immediately follow the blood by drawing in a mercury bead. If the blood sample is contained in a syringe, a short length of elastic tube can be used to unite the blood syringe and the capillary tube for filling in the usual way. Finally, draw up further borax solution until the plunger of the syringe stands at the 0.6 ml. mark. The mercury beads will now have found their way into the syringe and can be used for mixing its contents. Leave the syringe for two minutes. There is no need to cap the outer end of the capillary since the active reagents are protected from atmospheric air by several cms. of aerated borax solution. Place 2 ml. of sulphosalicylic acid in a tube calibrated to 10 ml. Draw some of this solution into a syringe and eject immediately into the same tube. Now repeatedly draw up distilled water into the syringe and eject into the 10 ml. tube until its mark is reached. In this way the syringe is rinsed and washed clean ready for the next estimation and the dilution is performed conveniently. The contents of the 10 ml. tube are then filtered as described in the original method and the clear filtrate estimated in the cuvette of a photocolorimeter. Blank estimations and calibrations are performed in the manner described in the original article.