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 ΔPblad correlated closely with the ΔPgas ( r = 0.904) and that theΔ Pes correlated with the ΔPcvp ( r = 0.951). When the ΔPcvp − ΔPblad was compared with the transdiaphragmatic pressure for each patient as the IPS was altered, the correlation coefficients varied from 0.952 to 0.999. Conclusion Although absolute values for the ΔPcvp during mechanical ventilation do not always reflect the ΔPes, 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.