The stop-flow arm equilibrium pressure in preoperative patients: Stressed volume and correlations with echocardiography.

Abstract

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. 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. 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 (R²  = 0.29, P = 0.01). Preoperative measurements of P_arm increased following acute expansion of the intravascular volume. Echocardiography demonstrated poor correlation with P_arm .