Optimizing Fluid Administration

Hypovolemia is common among patients scheduled for surgery. During anesthesia, goal-directed therapy or GDT (a technique were fluid and/or drugs are given to reach or maintain certain hemodynamic parameters within a certain range) has been proven to improve outcome in several different settings from orthopedic to abdominal surgery when performed using an FTc-based fluids algorithm protocol. Below is the algorithm developed by TJ Gans for fluid administration using corrected flow time (FTc) and stroke volume (SV). [1] FTC and SV can be measured continuously in less than 30 seconds after placing the sensors and inputting the height and weight. With the EC monitors conducting peri-operative GDT can be implemented with ease. The benefits of GDT include significant improvement in postoperative recovery and shortened hospital stay, reduction in incidence of gastrointestinal mucosal hypoperfusion and major complications such as gastrointestinal and renal dysfunction in patients who receive plasma volume optimization.

Figure 1. Fluid administration algorithm based on FTc monitoring (from Gan et al. [2]). FT: corrected flow; SV: stroke volume.

Potential Use: Identifying High-Risk Surgical Patients

Patients with poor ventricular function who are unable to increase cardiac output to meet the postsurgical demand have a significantly high mortality rate. Identification of these patients pre-operatively by formal dynamic testing of functional capacity is desirable. [3] Paul Older et al. have used have used cardiopulmonary exercise testing (CPX) for such preoperative risk stratification and has demonstrated that an anaerobic threshold >11 ml/min/kg predicts postoperative survival with high sensitivity and specificity. [4] This test is normally performed on a bicycle ergometer using respiratory gas analysis and electrocardiogram. Oxygen consumption and carbon dioxide production are measured during a ‘ramp’ exercise protocol. Under exercise conditions, oxygen consumption becomes a linear function of cardiac output. The measurement of aerobic capacity thus becomes a surrogate for the measurement of ventricular function. The EC monitors do not require a certified technician for operation like the equipment necessary for a normal CPX and has the ability to continuously measure both ventricular output and contractility of a patient throughout the cardiopulmonary performance test.

[1] (Gan, 2002)

[2] (Gan, 2002)

[3] (Lees, 2009)

[4] (Older, 2004)