On-line Monitoring of Systolic Pressure Variation

Abstract

To the Editor: Recent studies indicate that intravascular blood volume status in mechanically ventilated patients is sensitively assessed by dynamic variables, i.e., respiratory systolic pressure variation (SPV) and its negative and positive components (dDown and dUp) using a reference systolic pressure at end-expiration or pulse pressure variation (dPP) (1). Moreover, these variables are considered to be superior to the such conventional variables as central venous pressure, pulmonary artery occlusion pressure, or even left ventricular end-diastolic area using echocardiography in predicting the responsiveness of fluid loading in intensive care units and operating theaters (2,3). Although SPV and dPP measurement is simple and requires no additional catheter except for a radial arterial catheter, the need for off-line quantification has been a problem for routine clinical application (3,4,5). We developed an on-line system to monitor SPV, dDown, dUp, and dPP minute by minute continuously. It consists of an IBM compatible personal computer equipped with a 16-bit analogue to digital interface board and custom-made software (written by one of the authors (Y.F.) with Visual C++ 6.0). Airway pressure and arterial pressure signals are simultaneously sampled at a rate of 1000 Hz and sent to the computer. The mapping of systolic arterial pressure synchronized with respiratory cycles shows the SPV curve on-line. Examples of the display are shown in Figure 1, A and B.Figure 1: Displays of the system when 1500 mL of blood was lost (A), and when 1200 mL of blood was transfused (B) in a patient undergoing Th8 laminectomy. Ordinate: pressure in mmHg and abscissa: time after the beginning of inspiration during one respiratory cycle. A shows dDown of 4.5 mm Hg and dPP of 23.8%, and B, dDown of 0.9 mm Hg and dPP of 7.4%.Since the system functions with the two input signals of airway and arterial pressures, it can be implemented for use with usual hemodynamic monitors equipped with two pressure-monitoring units. The on-line bedside monitoring of SPV is now feasible as a routine hemodynamic monitor in patients under mechanical ventilation. Yoshihisa Fujita Atsuo Sari Tokunori Yamamoto