Methyldopa in Treatment of Severe Toxaemia of Pregnancy.

It is known that 50% N20 and 50% 02 mixture is a safe and efficient analgesic for parturient women. The British Oxygen Company have produced single cylinders of premixed gases containing a 50/50 gas and oxygen mixture, which would be ideal for use in midwifery if they could be relied upon to dispense a constant 50/50 mixture. Composition changes in premixed gas and oxygen mixtures have been reported at low temperatures ; for this reason an experimental investigation has been conducted into the effects of cooling upon premixed cylinders of the recommended 50°% N20 and 50% 02 mixture. Under certain conditions of use partially filled cylinders of 50/50 N20 and 02 exposed to temperatures of -80 C. or below undergo partial stratification of the constituent gases. The result of this could be that the last fraction of gas obtained from the cylinder contains as little as 2% 02. The conditions leading to this state of affairs are discussed and are thought to be unlikely to arise in practice (P=0.0001). The nature of the dispensing apparatus is such as to minimize the danger. The precautions necessary to prevent stratification appear to be so elementary as to fail to constitute a barrier to the domiciliary use of 50/50 N20 and 02 and trouble can be completely avoided by protecting the cylinders from very low temperatures.