Tetramethylammonium ion causes respiratory failure related mortality in a rat model

Aim of the study: Tetramethylammonium ion (TMA) is an emerging industrial chemical and has caused mortalities in humans. The present study was conducted to evaluate the effects of subcutaneously injected TMA on heart rate (HR), mean arterial blood pressure (MAP) and arterial blood gases (ABG) and to determine whether pretreatment using mechanical ventilation (MV) or atropine could prevent the mortality caused by TMA. Methods: Male Wistar rats were anesthetized and catheterized in the femoral arterials for monitoring. We injected 25, 50, 100, and 200μmol/kg of TMA s.c. in four groups of rats respectively and compared them to a control group. The effects of MV and atropine (1mg/kg, s.c.) pretreatment were evaluated by comparing the treatment groups with the 200μmol/kg group. The primary outcome was survival curve, and the secondary endpoints included the changes of HR, MAP, and ABG, such as arterial pH, PaO ₂, PaCO ₂ and calculated HCO ₃ ^-. Results: TMA decreased HR, MAP, pH, and PaO ₂, increased PaCO ₂ and calculated HCO ₃ ^- and resulted in death of all animals in the 200μmol/kg group by 15min. All animals pretreated with MV survived. Although all animals receiving atropine died, the mean survival time increased by 37min. Both MV and atropinization improved HR, MAP, and ABG. Conclusion: This rat model suggests that acute respiratory failure is responsible for the mortality caused by TMA, and therefore first aid should emphasize respiratory support. Atropinization prolonged survival time in the present study that possibly bought time for further management.