MINIMAL INVASIVE MONITORING OF VOLUME STATUS IN PATIENTS AFTER MAJOR ABDOMINAL SURGERY.

Determining volume status is important in critically-ill patients. Currently no gold-standard is available to accurately assess a patient’s volume status and physicians use clinical signs and hemodynamic parameters (like cardiac output) to estimate volume status.
Currently, the Pulmonary Artery Catheter (PAC) is one of the standards to monitor major abdominal surgery patients. Its use, however, is related to complications upsetting its value in other subpopulations like septic patients. The primary aim of this study is to evaluate the use of less invasive techniques to determine cardiac output (with pulse contour) compared to thermodilution cardiac output measurement with a pulmonary artery catheter. If proven accurate less invasive techniques could replace the PAC in the perioperative monitoring of major abdominal surgery patients.

A second aim of this study is to develop novel techniques to determine mean systemic filling pressure. Mean systemic filling pressure (Pmsf) is the equilibrium pressure in the systemic circulation when there is no flow. Mean systemic filling pressure is thus a measure of volume of the systemic circulation (and thus volume status)[1]. In the operating room and intensive care unit it is not possible to achieve a situation when there is no systemic flow. However, two novel methods can be used to accurately determine Pmsf [2] in heart-beating patients; 1: by arm occlusion or 2: through a ventilator hold maneuver. We hypothesize that a third model can be used; mean systemic filling pressure can be calculated beat-to-beat using cardiac output (CO), stroke volume (SV), central venous pressure (CVP) and mean arterial pressure (MAP) measured during normal ventilation, a single expiratory hold and a single inspiratory hold of 12 seconds. The former two models have been validated in patients after coronary artery by-pass grafting surgery. The two methods to estimate Pmsf have not yet been used in other populations.

Another important issue regarding estimation of volume status is the use of sedative drugs in the ICU and OR and their effects on hemodynamic parameters and their influence on the quality of the measurement of these parameters. In this study we will evaluate the effect of different levels of propofol sedation on Pmsf, venous and arterial resistance and the accuracy of CO measurement with different techniques (for instance pulse contour analysis).

Propofol does not change accuracy of pulse contour cardiac output measurements

11 min after TCI of propofol has achieved a predicted blood concentration of 6 µg•mL-1, again 11 minutes after the propofol target concentration is lowered to achieve a blood concentration of 4 µg•mL-1 using TCI. These steps are repeated at target propofol concentrations of 2 and 1 µg•mL-1. Subsequently measurements are repeated prior to, 30 seconds after start and 2 minutes after returning to baseline conditions for 30° passive leg raising, PEEP +5 cmH2O and PEEP +10cmH2O. Finally, 500 mL of Voluven is administered in 50 mL bolus with intermediate measurements.

Propofol administration at different plasma concentrations.