The purpose of this study was to examine possible peripheral mechanisms for the reduction of propofol injection pain by the addition of ketamine. We hypothesised that pH changes associated with the addition of ketamine to propofol decrease propofol-induced pain on injection. We compared the efficacy of intravenous ketamine pretreatment under tourniquet with ketamine added to the propofol. In the pre-treatment group, patients received ketamine 10 mg in a total volume of 1.0 ml with 0.9% saline (n=94; Group P) under tourniquet for 30 seconds before administration of propofol after release of the tourniquet. In the mixture group, propofol 9 ml was mixed with ketamine 10 mg in 0.9% NaCl 1.0 ml (n=94, Group M). Pain was assessed with a four-point scale: 0=no pain, 1=mild pain, 2=moderate pain, 3=severe pain at the time of propofol injection. The pH of propofol, ketamine and a range of propofol-ketamine mixtures were also measured. Forty-eight patients (51%) in Group P complained of pain on injection compared with 28 patients (30%) in Group M (P=0.005). The pH of the 1% propofol-ketamine mixture was 5.84 while 1% propofol had a pH of 7.86. Our results support pH changes as a more important cause for the decrease in propofol injection pain with the addition of ketamine to propofol than a peripheral effect of ketamine.

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By the techniques of far-infrared optically detected cyclotron resonance and magnetophotoconductivity, we have performed cyclotron-resonance measurements on relaxed In Ga& As epitaxial layers with a wide range of composition. The measured electron effective mass as a function of indium composition has been analyzed with the five-band k p calculation. It is found that the effect of disorder-induced conductionvalence-band mixing must be included in order to resolve the discrepancy between the results of the k p theory and experiments. The linewidths of cyclotron resonance and photoluminescence as a function of alloy composition have also been studied. Comparing with the measurement of doublecrystal x-ray diffraction, we point out that the cyclotron-resonance and photoluminescence signals in In"oa& As alloys are dominated by the dislocation scattering. In addition, we show that the quality of a ternary epilayer is not only influenced by the lattice mismatch; the surface migration lengths of the cation atoms in the initial growth stage also play a very important role.

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