Fluid Responsiveness and Fluid Tolerance Testing - OnePager Summary Fluid resuscitation can be beneficial when required or harmful in excess. Methods to predict fluid responsiveness enable parsimonious administration of fluids, resulting in reduced fluid shorter duration pf vasopressors and lower risk of renal failure. Fluid responsive (FR) - a 10-15% increase in cardiac output (CO) when fluid administered; fluid responsiveness does not mean fluid is "needed" only the CO will increase with volume. Arterial Line: • Pulse Pressure Variation (PPV): Variation in pulse pressure (PPV) with the respiratory cycle suggests fluid responsiveness due to heart lung interactions. • Pulse Contour Cardiac Output: Analysis of the waveform can be used to estimate stroke volume variation (SW) or cardiac output (CO) using proprietary formulas. Central Venous Line: • Central Venous Pressure (CVP): Measures CVP as a surrogate for RV filling pressure. Pulmonary Artery Catheter: • Thermodilution CO/CI: Thermodilution measurement of CO via a PAC, which can be either continuous (via heating) or intermittent (via cold saline injection). • PAOP/PCWP: PAOP/PCWP approximates LAP. • Mixed Venous O2 Saturation (SvO2): An increase in SvO2 suggests improved CO, however high baseline Sv02 does not preclude FR. Point of Care Ultrasound: • IVC Size & Distensibility: IVC size reflects RA pressure, similar to CVP. Thus measuring the IVC size & phasic variation with respiration might predict FR. • LV End Diastolic Area (LVEDA): Measure the cross sectional area of the LV at the end of diastole (reflects adequate filling); "kissing papillary muscles" is the extreme • LVOT VTI: Measure outflow of blood from the LV. Variability in VTI is analogous to PPV, absolute values can be compared before/after a challenge maneuver. • Carotid VTI: Similar to L VOT VTI but easier to measure carotid facilitating repeat measurements. Minimally Invasive: • BIOREACTANCE/NICOM: Detection of blood flow in the chest by application of an external electric field. Averages blood flow over 8-30 seconds. Combine with a challenge (PLR, microbolus) to measure ΔSV. • END TIDAL CO2: An increase cardiac output causes increases delivery of CO2 to the lungs, increasing exhaled CO2. • PULSE OXIMETRY WAVEFORM ANALYSIS: Analysis of the plethysmographic waveform is analogous to PPV measurement using arterial line: a high degree of respiratory variation predicts FR. • PULMONARY A vs B-LINE PATTERN: Sonographic lung changes precede other signs of volume overload. An A-line predominant lung US pattern suggests fluid tolerance (FT). Challenges: • PASSIVE LEG RAISE (PLR): Positioning a patient flat (00), then raising legs to 450) quickly (30-90 sec) returns a reservoir of ~300 ml of venous blood to the central circulation. • MINI-BOLUS & MICRO BOLUS: Observing the hemodynamic response to the rapid infusion of a small volume 50-100m!) of fluid can predict the response to a larger bolus • HIGH PEEP CHALLENGE: For patients on MV increasing PEEP can identify FR by identifying a decrease in MAP. • END EXPIRATORY OCCLUSION (EEO): For MV patients, each breath increases intrathoracic pressure & impedes venous return. Interrupting MV at end expiration transiently increases preload. Decrease in CO during a 15 sec expiratorv hold maneuver predicts FR by Nick Mark MD @nickmmark #Fluid #Responsiveness #Tolerance #testing #diagnosis #criticalcare #comparison #challenges #management
