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 H2O 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