Where is end expiration? Measuring PAWP when the patient is on pressure support ventilation

The hemodynamic information obtained from the pulmonary artery catheter provides physiologic rationale for a selected therapy and allows rapid determination of patients' response to the therapy. A wide range of pressure support levels have been used in pressure support ventilation (PSV), and patients' breathing patterns change from a spontaneous breathing pattern with low levels of PSV to a pressure control pattern with high levels of PSV. Different levels of pressure support have different effects on intrathoracic pressure. Changes in intrathoracic pressure may change the respiratory pattern and affect the timing for measuring the pulmonary artery wedge pressure.

The purpose of this study was to identify the pressure support level at which a patient's breathing pattern switches from a pressure control pattern to a spontaneous breathing pattern.

Fourteen patients admitted to the cardiovascular surgery ICU between January 2001 and December 2001 agreed to participate in the study. Four patients' data were not useable. Ten patients' data were analyzed. In this group, nine patients were male and one female. Patients'ages ranged, from 45 to 87-years-old with a mean age of 66.7 years. One patient had a left ventricular aneurysm repair, four patients had aortic valve repair and five patients had aortic coronary bypass performed.

This study was an exploratory descriptive study. Simultaneous pressure tracings of the pulmonary artery wedge pressure (PAWP) and proximal airway pressure were recorded during the weaning of pressure support at 2 cm H2O intervals from 18 cm H2O to below 10 cm H2O. End expiration was identified by using the proximal airway pressure when measuring the PAWP. Simultaneous pressure tracings of the PAWP and proximal airway pressure were used to analyze changes in respiratory patterns at different pressure levels during weaning of PSV.

One patient's breathing pattern switched into the spontaneous pattern at PSV 16 cm H2O, one at 14 cm H2O, and the rest of the patients at 12 cm H2O.

Different levels of pressure support have various impacts on the intrathoracic pressure and alter the respiratory pattern. Using the proximal airway pressure, nurses can identify the location of end-expiration and measure the PAWP accurately.