Fluid Resuscitation & Hemodynamics

• Water loss by evaporation 40-800mL/day
• Open abdomen ~ 1L/h 70kg person
• GI losses (i. e. illness, bowel obstruction, fistula)
• Hemorrhage
• Endothelial Injury (sepsis, trauma, burns, inflammatory states)
• Iatrogenic

“Increase preload, aka the stressed venous volume, leading to an increased stroke volume and cardiac output”

• Only ~50% of hemodynamically unstable patients are fluid responsive
• Hemodynamic response to a fluid challenge is usually small & short lived without lasting effect on cardiac index/output, BP, UOP
• Over resuscitation is not benign

Fluid administration is not benign….

• Soft tissue edema
• Intestinal edema/ileus
• Pulmonary Edema
• Prolonged Ventilation
• ARDS
• Heart failure
• Damaged glycocalyx
• Abdominal Compartment
• End organ damage
• Reduced wound healing
• Mortality

• Reduced tissue perfusion
• End organ damage
• Mortality

• Fluid responsive = SV increases by >10% following a fluid challenge (really need invasive or non-invasive cardiac monitoring system to determine)
• Need 2 things to increase SV:

1) Bolus increases the stressed blood volume -> causing the mean systemic pressure to increase enough to increase the gradient for venous return 2) Both ventricles on the ascending limb of the Frank-Starling Curve

Unstressed blood volume (UBV): Blood volume in the venous system that doesn't create significant pressure; physiologically inert until recruited. Stressed blood volume (SBV): The volume beyond the UBV that causes distending pressure in the veins, determining mean systemic pressure (MSP) and venous return.

Bathtub Bucket Tub will drain to the level of the drainpipe but no farther. The remainder of the water in the system is considered the unstressed volume Fluid bolus augments venous return by , increasing both the total volume and stressed volume Alternatively vasopressors can augment venous return by compressing the walls of the tub (reducing compliance), increasing the stressed volume without increasing total volume

Examples

• HR (increased) –
• Reduced cap refill hypovolemia?
• Weak, rapid pulse
• BP (decreased, ideally w Cool, clammy skin increased HR) – compensation not
• Dry membranes enough to sustain
• Skin turgor perfusion
• RR (increased) – metabolic acidosis from hypoperfusion (resp comp)
• UOP (<1ml/kg/h) – hypovolemia, hypointravascular volume

• BUN/Cr (increased)
• Lactic acidosis
• Hct (low – hemorrhagic hypo, high – hemoconcentrated/hypo volemic)
• ABG
• Static Measures: CVP

• Fails to reliably predict CO response to a fluid bolus
• Testing CVP to guide fluid challenge in sepsis = CVP <8 mm Hg predics fluid responsiveness only 47%
• CVP ability to accurately predict CO response to a fluid bolus = AUC of

0.56 (like flipping a coin)

• Should not be used in isolation
• Trending can be of use – pattern overtime improves efficacy
• Can result in fluid overload
• Higher ≠ better

Elevated CVP’s – associated with increased risk organ failure/AKI

• Mechanically Ventilated: Δ in IVC diameter >15% between inspiration & expiration indicates preload responsiveness
• Measurements should be taken 1-2 cm distal to the hepatic veins
• Using cine-loop with manual measurement at a fixed anatomical point helps avoid errors
• Sensitivity ~ 75%, Specificity ~82%
• BUT: require specific conditions - ventilated in VC 8mL/kg IBW, sinus rhythm, no ventilator dyssynchrony, normal right ventricular function &

RV-to-LV coupling

• Pulse Pressure Variation (PPV): % of change between the highest PP & lowest PP over a respiratory cycle
• Stroke Volume Variation (SVV): % of change in stroke volume during a respiratory cycle
• >10-15% suggest fluid responsiveness
• Demonstrate accuracy in mechanically ventilated patients receiving controlled ventilation (PPV/SVV AUC ~ 0.87)
• BUT: require specific conditions - controlled mechanical ventilation with

TV ≥8 mL/kg, PEEP<10, sinus rhythm, absence of spontaneous breathing efforts, normal thoracic/abdominal compliance

• SVV requires min-invasive cardiac monitoring technology (Flotrac,

Vigileo)

(PLR)

• Awake or intubated
• Represents ~300ml bolus – venous blood from lower body to right heart (preload)
• >10% SV or >15% CI = possible fluid response (30-90s max effect)
• One of the most accurate methods for predicting fluid responsiveness, positive likelihood ratio of 11 and specificity of 92%
• Does NOT require controlled mechanical ventilation, though may be less reliable in patients with intra-abdominal hypertension
• Most broadly applicable test in patients with arrhythmias, spontaneous breathing, altered lung compliance, low TV ventilation
• Ideally need CO measurement, less accurate using blood pressure
• Requires moving patient & raising leg
• Represents about 300ml bolus – venous blood from lower body to right heart (preload)
• >10% SV or >15% CI fluid response
• 30-90s max effect

• Small bolus 100-250ml
• Rapidly infused over 1-5 minutes
• Responsive test = increased SV or CO 10%
• High predictive value of fluid responsiveness (AUC 0.9)
• Similar to PLR - applicable test in patients with arrhythmias, spontaneous breathing, altered lung compliance, low TV ventilation
• Requires continuous cardiac output monitoring (to get the accuracy stated above)

examples End-expiratory occlusion test (EEOT) - end expiratory pause (15-30s) – temporarily augments venous return – increases preload – on release of hold monitor for change in CO

• Responsive - >5% increase CO

Tidal Volume Challenge - Increase ventilator tidal volume from 6 mL/kg to 8 for 60s

• Responsive - Δ𝑃𝑃𝑉 of > 2%, or a final PPV>11% at the higher volume

Both need continuous cardiac monitoring There is no perfect test Dynamic test out perform static BUT typically require specific conditions to obtain reported accuracy Need to look at the big picture Clinical context Patient dynamics Risk v benefit Use your clinical tools as adjuncts – not the rule

Approach needs to be tailored to etiology & patient factors…

Hypovolemic (GI loss, dehydration, absolute fluid loss)

• Isotonic Crystalloid
• LR, plasmalyte
• NS (in specific situations) – hyperchloremic acidosis, possible higher AKI risk
• • Hypovolemic hemorrhagic
• 1:1:1 RBC: plasma: plt (+/- cryo, fibrinogen) and/or whole blood
• Calcium
• Vasopressor

• Septic Shock
• Typically distributive – vasodilation – increased vascular/venous compliance – reduced stressed volume - resulting in relative hypovolemia
• Can also have absolute hypovolemia (depending on etiology)
• Surviving sepsis guidelines:

• Surviving sepsis guidelines:
• 30 mL/kg crystalloid fluids recommended in 1 st 3h
• Albumin - no clear benefits over balanced crystalloids. Weak recommendation - after infusing “large volume crystalloid” to improve blood pressure
• Add vasopressors if initial fluid resuscitation not adequate
• Lactate does not need to normalize BUT levels approaching normal suggest successful resuscitation

• Need to fix the pump – inotropes & vasopressor
• Hypovolemic – may need fluid (typically isotonic crystalloid)
• Hypervolemic –diuresis