Pulmonary artery pressure measurement in patients with elevated pressures: effect of backrest elevation and method of measurement.

OBJECTIVE

To determine whether pulmonary artery pressure measurement is accurate if the head of the bed is elevated; to compare the end-expiratory graphic recording and digital monitor methods for pulmonary artery pressure measurement; to determine whether either mean arterial pressure or mixed venous oxygen saturation changes during backrest elevation.

DESIGN

Nonrandomized clinical trial.

SETTING

A six-bed cardiac surgical intensive care unit of a 540-bed federal facility.

POPULATION

Twenty-five postoperative cardiac surgical patients with elevated pulmonary artery pressures (systolic higher than 35 mm Hg).

INTERVENTIONS

In supine patients pulmonary artery pressures were measured at each of the following backrest elevations: 0, 20, 30, 45 and again at 0 degrees. Measurements were obtained once during mechanical ventilation and once during normal breathing after extubation.

MAIN OUTCOME MEASURES

End-expiratory graphic recording of pulmonary artery pressures; digital monitor values of pulmonary artery pressures; mean arterial pressure; and mixed venous oxygen saturation.

RESULTS

No statistical difference was found in pulmonary artery pressures measured at each of the backrest elevations during mechanical ventilation or normal breathing after extubation. Pulmonary artery diastolic and pulmonary capillary wedge pressures obtained with the digital monitor method were significantly lower than the end expiratory graphic recording method during normal breathing after extubation but not during mechanical ventilation. No changes in mean arterial pressure or mixed venous oxygen saturation occurred during backrest elevation.

CONCLUSIONS

These results show that pulmonary artery pressures can be measured accurately with the head of the bed in an elevated position. The data indicate that obtaining pulmonary artery pressure measurements from the digital display of the bedside monitor is accurate when respiratory wave form fluctuations are minimal but may lead to inaccurate values with prominent respiratory fluctuations. Further research is needed to validate this finding in different patient populations and with other models of monitoring equipment.