Central venous and bladder pressure reflect transdiaphragmatic pressure during pressure support ventilation

Study objectives: To determine whether the change in bladder pressure (Pblad) and central venous pressure (Pcvp) may reflect the changes in esophageal pressure (Pes) and gastric pressure (Pgas) when inspiratory pressure support (IPS) is altered. Design: Prospective clinical study. Setting: The ICUs of a teaching hospital. Patients: Ten patients currently, receiving IPS ventilation via a tracheostomy or an endotracheal tube who, already had bladder and central venous catheters in situ. Measurements and, results: Airway pressure, Pes, Pgas, Pcvp, Pblad, and flow were measured at the original IPS setting. IPS then was reduced by 5-cm. H(2)O increments until IPS was zero or was at the minimum pressure that could be tolerated by each patient. At each level of IPS, pressures and flow were measured at steady-state breathing. The maximum pressure difference for each pressure during inspiration was calculated. We found that the DeltaPblad Correlated closely, with the DeltaPgas (r = 0.904) and that the DeltaPes correlated with the DeltaPcvp (r = 0.95 1). When the DeltaPcvp - DeltaPblad was compared with the transdiaphragmatic pressure for each patient as die IPS was altered, the correlation coefficients varied from 0.952 to 0.999. Conclusion: Although absolute values for the DeltaPcvp during mechanical ventilation do not always reflect the DeltaPes, useful information can be obtained from this route. In individual patients, the two sites of measurement followed each other when IPS was changed, enabling a bedside assessment of the response to reducing respiratory support.