Fig. 5. Comparison of the mass of tracheal aspirate obtained at two levels of suctioning pressure (−200 vs. −400 cm H2O) using closed-circuit endotracheal suctioning. Data expressed as mean ± SD are represented on the left , whereas individual values are represented on the right . The mass of tracheal aspirate is significantly greater with a suctioning pressure of −400 cm H2O than with a suctioning pressure of −200 cm H2O.