Gastric PCO(2) monitoring during canine hemorrhagic shock encountered occasional baseline drift to higher direction when conventional PCO(2) sensor was used. As a result of chemical analysis of gastric juice of dogs and human, hydrogen sulfide and acetic acid were identified as causative compounds. It was speculated that these weak acid molecules would permeate gas-permeable silicone membrane to be accumulated in the inner solution of Severinghaus-type PCO(2) sensors. In order to prevent this phenomenon, double-membrane type PCO(2) sensor was constructed. In this sensor, acid-neutralizing solution was installed between the inner and the outer membranes in order to dissociate weak acid molecules into corresponding ions, which can not diffuse into the inner silicone membrane. In addition, Cu2O particles were mixed in the inner silicone membrane to trap hydrogen sulfide in this membrane. It was confirmed by experiments in vitro that the readings of improved gastric PCO(2) sensors were not affected by acetic acid or hydrogen sulfide. As a result of a preliminary clinical evaluation, continuous monitoring of gastric PCO(2) was carried out for 72 h without detectable baseline drift or the change of sensitivity.
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