Influence of negative expiratory pressure ventilation on hemodynamic variables during severe hemorrhagic shock

Objective. Outcome after trauma with severe hemorrhagic shock is still dismal. Since the majority of blood is present in the venous vessels, it might be beneficial to perform venous recruiting via the airway during severe hemorrhagic shock. Therefore, the purpose of our study was to evaluate the effects of negative expiratory pressure ventilation on mean arterial blood pressure, cardiac output, and short-term survival during severe hemorrhagic shock. Design: Prospective study in 21 laboratory animals. Setting. University hospital research laboratory. Subjects: Tyrolean domestic pigs. Interventions. After induction of controlled hemorrhagic shock (blood loss similar to 45 mL/kg), 21 pigs were randomly ventilated with either zero end-expiratory pressure (0 PEEP; n = 7), 5 cm H2O positive end-expiratory pressure (5 PEEP; n = 7), or negative expiratory pressure ventilation (up to -30 cm H2O at the endotracheal tube during expiration; n = 7). Measurements and Main Results: Mean (+/-SD) arterial blood pressure was significantly higher in the negative expiratory pressure ventilation swine when compared with the 0 PEEP (38 +/- 5 vs. 27 +/- 3 mm Hg; p =.001) and the 5 PEEP animals (38 +/- 5 vs. 20 +/- 6 mm Hg; p <.001) after 5 mins of the experiment. Cardiac output was significantly higher in the negative expiratory pressure ventilation swine when compared with the 0 PEEP (3.1 +/-.4 vs. 1.9 +/-.9 L/min; p =.001) and 5 PEEP animals (3.1 +/-.4 vs. 1.2 +/-.8 L/min; p <.001) after 5 mins of the experiment. All seven negative expiratory pressure ventilation animals, but only three of seven 0 PEEP animals (p =.022), survived the 120-min study period, whereas all seven of seven 5 PEEP animals were dead within 35 mins (p <.001). Limitations include that blood loss was controlled and that the small sample size limits the evaluation of survival outcome. Conclusions: When compared with pigs ventilated with either 0 PEEP or 5 PEEP, negative expiratory pressure ventilation during severe hemorrhagic shock improved mean arterial blood pressure and cardiac output.