Invasive blood pressure monitoring systems in the ICU: influence of the blood-conserving device on the dynamic response characteristics and agreement with noninvasive measurements.

OBJECTIVES

Invasive blood pressure monitoring is the most reliable method in critically ill patients. Noninvasive oscillometric pressure monitoring is also widely used in the ICU, and discrepancies between the methods are common. Inclusion of a blood-conserving device may influence the fidelity of the system and reliability of the invasive pressure values. We examined the dynamic response characteristics of the monitoring systems with and without the blood-conserving device, and assessed agreement between invasive and noninvasive blood pressures.

MATERIALS AND METHODS

Fifty-three invasive arterial blood pressure monitoring systems were evaluated over an 8-week period. A standard fast flush test was performed. The natural frequency (Fn) and the amplitude ratio of the invasive monitoring systems were calculated. Simultaneous invasive and noninvasive blood pressures were recorded, and the agreement between two methods was evaluated.

RESULTS

The Fn was significantly higher (15.7 ± 5.1 Hz) in the systems without the blood-conserving device than in the systems containing the device (9.1 ± 2.6 Hz). There was no significant difference in the amplitude ratio. Significant differences were observed between invasive and noninvasive pressures, with systolic pressure showing more variability than the mean arterial pressure.

CONCLUSION

Inclusion of a blood-conserving device in the existing monitoring circuit may affect its dynamic response characteristics. Discrepancies between invasive and noninvasive pressures are common, with systolic pressure showing more variability than the mean arterial pressure. The low Fn of the invasive monitoring system could be a contributing factor to the discrepancy between two methods.