The stop-flow arm equilibrium pressure in preoperative patients: Stressed volume and correlations with echocardiography
Résumé
Background The distending intravascular pressure at no flow conditions reflects the stressed volume. While this haemodynamic variable is recognised as clinically important, there is a paucity of reports of its range and responsiveness to volume expansion in patients without cardiovascular disease and no reports of correlations to echocardiographic assessments of left ventricular filling. Methods Twenty-seven awake (13 male), spontaneously breathing patients without any history of cardiopulmonary, vascular or renal disease were studied prior to induction of anaesthesia. The no-flow equilibrium pressure in the arm following rapid circulatory occlusion (P-arm) was measured via a radial arterial catheter. Transthoracic echocardiography was used to measure left ventricular end diastolic area and volume as well as the diameter of the inferior vena cava. The P-arm and echocardiographic variables were measured before and after administration of 500 mL 0.9% NaCl over 10 minutes. Changes were analysed by paired t test, Pearson's correlation and multiple linear regression. Results P-arm increased overall from 22 +/- 5 mm Hg to 25 +/- 6 mm Hg (mean difference 3.0 +/- 4.5 mm Hg, P = 0.002) following the fluid bolus with corresponding increases in arterial pressure and echocardiographic variables. Variability in the direction of the P-arm response reflected concomitant changes in vascular compliance. Only weak correlations were observed between changes in P-arm and inferior vena cava diameter indexed to body surface area (R-2 = 0.29, P = 0.01). Conclusion Preoperative measurements of P-arm increased following acute expansion of the intravascular volume. Echocardiography demonstrated poor correlation with P-arm.