Mediastinal, left, and right atrial pressure variations with different modes of mechanical and spontaneous ventilation.

Variations in mediastinal, left, and right atrial pressures (MedP, LAP, RAP, respectively) were measured by means of catheters and tubes positioned in ten patients with nonvalvular cardiac surgery. For each pressure, a maximum, minimum, and mean value was determined in relation to its oscillations during the respiratory cycle. Thus, we compared the variations in MedP, LAP, and RAP in controlled mechanical ventilation (CMV), CMV with 5 cm H2O PEEP, synchronous intermittent mandatory ventilation (SIMV), SIMV with 5 cm H2O PEEP, continuous positive airway pressure (CPAP), and spontaneous respiration (SR). We built an experimental model to compare the measurements obtained by air-filled tubes inserted at surgery with those obtained by esophageal balloons filled with water. The maximum MedP did not vary significantly in these patients except when SIMV and SR were compared; however, the minimum MedP diminished significantly (p less than .001) in SIMV, SIMV-PEEP, CPAP, and SR, with negative inspiratory values reaching significant proportions. The mean values of MedP, LAP, and RAP showed a similar tendency although to a lesser degree. The experimental model revealed a strong linear relation between the values obtained with air-filled tubes and those obtained with water-filled esophageal balloons (r = .99, p less than .001). These results suggest that the mean values of MedP, LAP, and RAP do not reflect the dynamic variations in ventricular filling pressure accurately, nor the important negative inspiratory peaks that appear in different types of ventilation using spontaneous cycles with and without PEEP. These inspiratory peaks can overload the left ventricle by hydrostatic gradients, and lead to pulmonary edema in susceptible patients.(ABSTRACT TRUNCATED AT 250 WORDS)